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Zhang Y, Jen FEC, Fox KL, Edwards JL, Jennings MP. The biosynthesis and role of phosphorylcholine in pathogenic and nonpathogenic bacteria. Trends Microbiol 2023; 31:692-706. [PMID: 36863982 PMCID: PMC10272106 DOI: 10.1016/j.tim.2023.01.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2021] [Revised: 01/18/2023] [Accepted: 01/23/2023] [Indexed: 03/03/2023]
Abstract
Phosphorylcholine (ChoP) can be found in all life forms. Although this molecule was first thought to be uncommon in bacteria, it is now appreciated that many bacteria express ChoP on their surface. ChoP is usually attached to a glycan structure, but in some cases, it is added as a post-translational modification to proteins. Recent findings have demonstrated the role of ChoP modification and phase variation (ON/OFF switching) in bacterial pathogenesis. However, the mechanisms of ChoP synthesis are still unclear in some bacteria. Here, we review the literature and examine the recent developments in ChoP-modified proteins and glycolipids and of ChoP biosynthetic pathways. We discuss how the well-studied Lic1 pathway exclusively mediates ChoP attachment to glycans but not to proteins. Finally, we provide a review of the role of ChoP in bacterial pathobiology and the role of ChoP in modulating the immune response.
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Affiliation(s)
- Yuan Zhang
- Institute for Glycomics, Griffith University, Gold Coast Campus, Southport, QLD 4222, Australia
| | - Freda E-C Jen
- Institute for Glycomics, Griffith University, Gold Coast Campus, Southport, QLD 4222, Australia
| | - Kate L Fox
- School of Chemistry and Molecular Biosciences, The University of Queensland, St Lucia, Brisbane, Queensland 4072, Australia
| | - Jennifer L Edwards
- Center for Microbial Pathogenesis, Abigail Wexner Research Institute at Nationwide Children's Hospital, Columbus, OH 43205, USA; Department of Pediatrics, The Ohio State University, Columbus, OH 43210, USA
| | - Michael P Jennings
- Institute for Glycomics, Griffith University, Gold Coast Campus, Southport, QLD 4222, Australia.
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Iuchi H, Ohori J, Kyutoku T, Ito K, Kawabata M. Inhibitory effects of 2-methacryloyloxyethyl phosphorylcholine polymer on the adherence of bacteria causing upper respiratory tract infection. J Oral Microbiol 2020; 12:1808425. [PMID: 33062198 PMCID: PMC7531866 DOI: 10.1080/20002297.2020.1808425] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Objective We aimed to investigate the inhibitory effect of 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer on the adherence of Streptococcus pneumoniae (Spn) and nontypeable Haemophilus influenzae (NTHi) in vitro and in vivo. Materials and Methods Phosphorylcholine (PC) expression of 21 strains each of Spn and NTHi was evaluated using fluorescence-activated cell sorting; the adherence of bacteria to Detroit 562 cells and to the nasal mucosa of BALB/c mice was determined. MPC polymer-mediated inhibitory effects were compared with PC-keyhole limpet hemocyanin (PC-KLH)-mediated inhibitory effects. Results In vitro experiments showed that pretreatment with MPC polymer markedly inhibited the adherence of Spn and NTHi in a concentration dose–dependent manner independently of PC expression. No correlation was observed between PC expression and MPC polymer-mediated inhibitory effects. Contrarily, there was a significant negative correlation between PC-KLH-mediated inhibitory effects and PC expression in Spn and NTHi. The same results were obtained via in vivo experiments. The MPC polymer did not affect the histology of the nasal mucosa. Conclusions MPC polymer might be effective to reduce the occurrence of upper respiratory tract infection caused by Spn and NTHi and could be applied for the development of local treatments, such as topical gargles and nebulizer medications.
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Affiliation(s)
- Hiroyuki Iuchi
- Department of Otolaryngology, Head and Neck Surgery, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan
| | - Junichiro Ohori
- Department of Otolaryngology, Head and Neck Surgery, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan
| | - Takayuki Kyutoku
- Department of Otolaryngology, Head and Neck Surgery, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan
| | - Kotoko Ito
- Department of Otolaryngology, Head and Neck Surgery, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan
| | - Masaki Kawabata
- Department of Otolaryngology, Head and Neck Surgery, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan
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Phase variation with altering phosphorylcholine expression of nontypeable Haemophilus influenzae affects bacteria clearance and mucosal immune response in the middle ear and nasopharynx. Auris Nasus Larynx 2020; 48:57-64. [PMID: 32684402 DOI: 10.1016/j.anl.2020.07.001] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2020] [Revised: 06/24/2020] [Accepted: 07/02/2020] [Indexed: 11/24/2022]
Abstract
OBJECTIVES Nontypeable Haemophilus influenzae (NTHi) is a chief pathogen in both acute otitis media and otitis media with effusion. Phosphorylcholine (ChoP) is expressed on lipooligosaccharides, and ChoP has phase variation, which is related to its adhesion to and invasion of epithelial cells in the upper airway. However, little is known about the role of ChoP expression. We examined the kinetics of the mucosal clearance of NTHi from the nose and middle ear and the mucosal immune response to NTHi infection by comparing ChoP(+) and ChoP(-) strains in a mouse model of middle ear and nasal challenge. METHODS Six-week-old male BALB/c mice were subjected to bacterial challenge in the middle ear and nasopharynx. Mice were inoculated with a suspension of a ChoP(+) strain or ChoP(-) strain of NTHi. On days 1, 3, and 7 after inoculation, the middle ear wash (MEW) and nasal wash (NW) were harvested from each group. The samples were used for bacterial counts and the supernatant was used to measure the level of cytokines and C-reactive protein (CRP). RESULTS MEWs in the ChoP(+) strain group had significantly higher bacterial counts than those in the ChoP(-) strain group on day 1. However, bacteria were eradicated in the ChoP(+) strain group on day 7. NWs in the ChoP(+) strain group had higher bacterial counts than those in the ChoP(-) strain group during the experiment, however, there was no significant difference between the two strains. The levels of cytokines were significantly higher in the ChoP(-) strain group than in the ChoP(+) strain group in MEWs, but these cytokine levels were low in NWs. The CRP concentration in the ChoP(-) group was high on day 7 in the MEWs. In NWs, the CRP concentration was low in all groups during the experiment. CONCLUSION ChoP expression of NTHi changes the organism susceptible to killing by CRP, and the ChoP(+) strain might be gradually eradicated from the middle ear via the CRP-complement cascade, but not from nasopharynx. Based on our findings, phase variation by altering Phosphorylcholine expression of nontypeable Haemophilus influenzae affects bacteria clearance and mucosal immune response in the middle ear and nasopharynx.
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Nontypeable Haemophilus influenzae Invasive Blood Isolates Are Mainly Phosphorylcholine Negative and Show Decreased Complement-Mediated Killing That Is Associated with Lower Binding of IgM and CRP in Comparison to Colonizing Isolates from the Oropharynx. Infect Immun 2019; 87:IAI.00604-18. [PMID: 30455196 DOI: 10.1128/iai.00604-18] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2018] [Accepted: 11/09/2018] [Indexed: 11/20/2022] Open
Abstract
Nontypeable Haemophilus influenzae (NTHi) bacteria express various molecules that contribute to their virulence. The presence of phosphocholine (PCho) on NTHi lipooligosaccharide increases adhesion to epithelial cells and is an advantage for the bacterium, enabling nasopharyngeal colonization, as measured in humans and animal models. However, when PCho is expressed on the lipooligosaccharide, it is also recognized by the acute-phase protein C-reactive protein (CRP) and PCho-specific antibodies, both of which are potent initiators of the classical pathway of complement activation. In this study, we show that blood isolates, which are exposed to CRP and PCho-specific antibodies in the bloodstream, have a higher survival in serum than oropharyngeal isolates, which was associated with a decreased presence of PCho. PCholow strains showed decreased IgM, CRP, and complement C3 deposition, which was associated with increased survival in human serum. Consistent with the case for the PCholow strains, removal of PCho expression by licA gene deletion decreased IgM, CRP, and complement C3 deposition, which increased survival in human serum. Complement-mediated killing of PChohigh strains was mainly dependent on binding of IgM to the bacterial surface. These data support the hypothesis that a PCholow phenotype was selected in blood during invasive disease, which increased resistance to serum killing, mainly due to lowered IgM and CRP binding to the bacterial surface.
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Iuchi H, Ohori J, Kyutoku T, Ito K, Kurono Y. Role of phosphorylcholine in Streptococcus pneumoniae and nontypeable Haemophilus influenzae adherence to epithelial cells. Auris Nasus Larynx 2018; 46:513-519. [PMID: 30503566 DOI: 10.1016/j.anl.2018.11.003] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2018] [Revised: 09/26/2018] [Accepted: 11/14/2018] [Indexed: 10/27/2022]
Abstract
OBJECTIVE Phosphorylcholine (PC) is a structural component of Streptococcus pneumoniae (Spn) and nontypeable Haemophilus influenzae (NTHi), and is known to be associated with adherence through the platelet activating factor receptor (PAF-R). Furthermore, high PC expression is considered to be involved in Spn and NTHi virulence. In this study, we examined the influence of PC expression on the adherence of Spn and NTHi to epithelial cells in order to clarify the potential effectiveness of a vaccine targeting PC. METHODS Twenty-seven strains of Spn and twenty-two strains of NTHi were used, cultured overnight, and PC expression was evaluated by fluorescence activated cell sorting; the strains were divided into two groups: PC low expression (PC-low) and PC high expression (PC-high) groups. Bacterial adherence was then examined using Detroit 562 cells and BALB/c mice. Bacterial invasion was then examined in Detroit 562 cells. RESULTS The adherence of Spn and NTHi and invasion of NTHi in the PC-high group was significantly reduced by pretreatment with a monoclonal anti-PC antibody (TEPC-15), PAF-R antagonist (ABT-491), and PC-keyhole limpet hemocyanin (PC-KLH). However, such findings were not observed in the PC-low group. CONCLUSION The present study suggests that PC is involved in the mucosal adhesion of Spn and NTHi, and the mucosal invasion of NTHi with PC-high strains, but not PC-low strains. These results suggest that a PC-targeting mucosal vaccine only affects PC-high Spn and NTHi strains and does not disturb commensal bacterial flora in the upper respiratory tract, which comprises nonpathogenic PC-low bacteria.
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Affiliation(s)
- Hiroyuki Iuchi
- Department of Otolaryngology, Head and Neck Surgery, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan.
| | - Junichiro Ohori
- Department of Otolaryngology, Head and Neck Surgery, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan
| | - Takayuki Kyutoku
- Department of Otolaryngology, Head and Neck Surgery, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan
| | - Kotoko Ito
- Department of Otolaryngology, Head and Neck Surgery, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan
| | - Yuichi Kurono
- Department of Otolaryngology, Head and Neck Surgery, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan
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Mucosal and systemic immune response to sublingual or intranasal immunization with phosphorylcholine. Auris Nasus Larynx 2018; 45:273-280. [DOI: 10.1016/j.anl.2017.04.009] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2016] [Revised: 12/25/2016] [Accepted: 04/12/2017] [Indexed: 11/21/2022]
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Lichtenegger S, Bina I, Durakovic S, Glaser P, Tutz S, Schild S, Reidl J. Serum resistance and phase variation of a nasopharyngeal non-typeable Haemophilus influenzae isolate. Int J Med Microbiol 2017; 307:139-146. [PMID: 28179078 DOI: 10.1016/j.ijmm.2017.01.005] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2016] [Revised: 01/24/2017] [Accepted: 01/24/2017] [Indexed: 11/28/2022] Open
Abstract
Haemophilus influenzae harbours a complex array of factors to resist human complement attack. As non-typeable H. influenzae (NTHi) strains do not possess a capsule, their serum resistance mainly depends on other mechanisms including LOS decoration. In this report, we describe the identification of a highly serum resistant, nasopharyngeal isolate (NTHi23) by screening a collection of 77 clinical isolates. For NTHi23, we defined the MLST sequence type 1133, which matches the profile of a previously published invasive NTHi isolate. A detailed genetic analysis revealed that NTHi23 shares several complement evading mechanisms with invasive disease isolates. These mechanisms include the functional expression of a retrograde phospholipid trafficking system and the presumable decoration of the LOS structure with sialic acid. By screening the NTHi23 population for spontaneous decreased serum resistance, we identified a clone, which was about 103-fold more sensitive to complement-mediated killing. Genome-wide analysis of this isolate revealed a phase variation in the N'-terminal region of lpsA, leading to a truncated version of the glycosyltransferase (LpsA). We further showed that a NTHi23 lpsA mutant exhibits a decreased invasion rate into human alveolar basal epithelial cells. Since only a small proportion of the NTHi23 population expressed the serum sensitive phenotype, resulting from lpsA phase-off, we conclude that the nasopharyngeal environment selected for a population expressing the intact and functional glycosyltransferase.
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Affiliation(s)
- Sabine Lichtenegger
- Institute of Molecular Biosciences, University of Graz, Humboldtstr. 50, 8010 Graz, Austria; Institute of Hygiene, Microbiology and Environmental Medicine, Medical University of Graz, Neue Stiftingtalstraße 2, 8010 Graz, Austria.
| | - Isabelle Bina
- Institute of Molecular Biosciences, University of Graz, Humboldtstr. 50, 8010 Graz, Austria
| | - Sanel Durakovic
- Institute of Molecular Biosciences, University of Graz, Humboldtstr. 50, 8010 Graz, Austria
| | - Philippe Glaser
- Insitut Pasteur, 25-28 rue du docteur Roux, 75015 Paris, France
| | - Sarah Tutz
- Institute of Molecular Biosciences, University of Graz, Humboldtstr. 50, 8010 Graz, Austria
| | - Stefan Schild
- Institute of Molecular Biosciences, University of Graz, Humboldtstr. 50, 8010 Graz, Austria; BioTechMed-Graz, Austria
| | - Joachim Reidl
- Institute of Molecular Biosciences, University of Graz, Humboldtstr. 50, 8010 Graz, Austria; BioTechMed-Graz, Austria.
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Bluestone CD, Hebda PA, Alper CM, Sando I, Buchman CA, Stangerup SE, Felding JU, Swarts JD, Ghadiali SN, Takahashi H. 2. Eustachian Tube, Middle Ear, and Mastoid Anatomy; Physiology, Pathophysiology, and Pathogenesis. Ann Otol Rhinol Laryngol 2016; 194:16-30. [PMID: 15700932 DOI: 10.1177/00034894051140s105] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Affiliation(s)
- Charles D Bluestone
- Department of Otolaryngology, University of Pittsburgh School of Medicine, Children's Hospital of Pittsburgh, Pennsylvania, USA
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Khan MN, Ren D, Kaur R, Basha S, Zagursky R, Pichichero ME. Developing a vaccine to prevent otitis media caused by nontypeable Haemophilus influenzae. Expert Rev Vaccines 2016; 15:863-78. [PMID: 26894630 DOI: 10.1586/14760584.2016.1156539] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Nontypeable Haemophilus influenzae (NTHi) is a predominant organism of the upper respiratory nasopharyngeal microbiota. Its disease spectrum includes otitis media, sinusitis, non-bacteremic pneumonia and invasive infections. Protein-based vaccines to prevent NTHi infections are needed to alleviate these infections in children and vulnerable populations such as the elderly and those with chronic obstructive pulmonary disease (COPD). One NTHi protein is included in a pneumococcal conjugate vaccine and has been shown to provide efficacy. Our lab has been interested in understanding the immunogenicity of NTHi vaccine candidates P6, protein D and OMP26 for preventing acute otitis media in young children. We expect that continued investigation and progress in the development of an efficacious protein based vaccine against NTHi infections is achievable in the near future.
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Affiliation(s)
- M Nadeem Khan
- a Center for Infectious Disease and Immunology , Rochester General Hospital Research Institute , Rochester , NY , USA
| | - Dabin Ren
- a Center for Infectious Disease and Immunology , Rochester General Hospital Research Institute , Rochester , NY , USA
| | - Ravinder Kaur
- a Center for Infectious Disease and Immunology , Rochester General Hospital Research Institute , Rochester , NY , USA
| | - Saleem Basha
- a Center for Infectious Disease and Immunology , Rochester General Hospital Research Institute , Rochester , NY , USA
| | - Robert Zagursky
- a Center for Infectious Disease and Immunology , Rochester General Hospital Research Institute , Rochester , NY , USA
| | - Michael E Pichichero
- a Center for Infectious Disease and Immunology , Rochester General Hospital Research Institute , Rochester , NY , USA
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10
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Puig C, Marti S, Hermans PWM, de Jonge MI, Ardanuy C, Liñares J, Langereis JD. Incorporation of phosphorylcholine into the lipooligosaccharide of nontypeable Haemophilus influenzae does not correlate with the level of biofilm formation in vitro. Infect Immun 2014; 82:1591-9. [PMID: 24452688 PMCID: PMC3993405 DOI: 10.1128/iai.01445-13] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2013] [Accepted: 01/20/2014] [Indexed: 12/20/2022] Open
Abstract
Nontypeable Haemophilus influenzae (NTHi) is an opportunistic pathogen that causes otitis media in children and community-acquired pneumonia or exacerbations of chronic obstructive pulmonary disease in adults. A large variety of studies suggest that biofilm formation by NTHi may be an important step in the pathogenesis of this bacterium. The objective of this report was to determine the relationship between the presence of phosphorylcholine in the lipooligosaccharide of NTHi and the level of biofilm formation. The study was performed on 111 NTHi clinical isolates collected from oropharyngeal samples of healthy children, middle ear fluid of children with otitis media, and sputum samples of patients with chronic obstructive pulmonary disease or community-acquired pneumonia. NTHi clinical isolates presented a large variation in the level of biofilm formation in a static assay and phosphorylcholine content. Isolates collected from the oropharynx and middle ear fluid of children tended to have more phosphorylcholine and made denser biofilms than isolates collected from sputum samples of patients with chronic obstructive pulmonary disease or community-acquired pneumonia. No correlation was observed between biofilm formation and the presence of phosphorylcholine in the lipooligosaccharide for either planktonic or biofilm growth. This lack of correlation was confirmed by abrogating phosphorylcholine incorporation into lipooligosaccharide through licA gene deletion, which had strain-specific effects on biofilm formation. Altogether, we present strong evidence to conclude that there is no correlation between biofilm formation in a static assay and the presence of phosphorylcholine in lipooligosaccharide in a large collection of clinical NTHi isolates collected from different groups of patients.
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Affiliation(s)
- Carmen Puig
- Microbiology Department, Hospital Universitari de Bellvitge-Universitat de Barcelona, IDIBELL, Barcelona, Spain
- Laboratory of Pediatric Infectious Diseases, Department of Pediatrics, Radboud University Medical Center, Nijmegen, The Netherlands
- CIBER de Enfermedades Respiratorias, ISCIII, Madrid, Spain
| | - Sara Marti
- Microbiology Department, Hospital Universitari de Bellvitge-Universitat de Barcelona, IDIBELL, Barcelona, Spain
- Laboratory of Pediatric Infectious Diseases, Department of Pediatrics, Radboud University Medical Center, Nijmegen, The Netherlands
- CIBER de Enfermedades Respiratorias, ISCIII, Madrid, Spain
| | - Peter W. M. Hermans
- Laboratory of Pediatric Infectious Diseases, Department of Pediatrics, Radboud University Medical Center, Nijmegen, The Netherlands
| | - Marien I. de Jonge
- Laboratory of Pediatric Infectious Diseases, Department of Pediatrics, Radboud University Medical Center, Nijmegen, The Netherlands
| | - Carmen Ardanuy
- Microbiology Department, Hospital Universitari de Bellvitge-Universitat de Barcelona, IDIBELL, Barcelona, Spain
- CIBER de Enfermedades Respiratorias, ISCIII, Madrid, Spain
| | - Josefina Liñares
- Microbiology Department, Hospital Universitari de Bellvitge-Universitat de Barcelona, IDIBELL, Barcelona, Spain
- CIBER de Enfermedades Respiratorias, ISCIII, Madrid, Spain
| | - Jeroen D. Langereis
- Laboratory of Pediatric Infectious Diseases, Department of Pediatrics, Radboud University Medical Center, Nijmegen, The Netherlands
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Fox KL, Atack JM, Srikhanta YN, Eckert A, Novotny LA, Bakaletz LO, Jennings MP. Selection for phase variation of LOS biosynthetic genes frequently occurs in progression of non-typeable Haemophilus influenzae infection from the nasopharynx to the middle ear of human patients. PLoS One 2014; 9:e90505. [PMID: 24587383 PMCID: PMC3938747 DOI: 10.1371/journal.pone.0090505] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2013] [Accepted: 02/03/2014] [Indexed: 11/18/2022] Open
Abstract
Surface structures in Haemophilus influenzae are subject to rapid ON/OFF switching of expression, a process termed phase variation. We analyse tetranucleotide repeats controlling phase variation in lipo-oligosaccharide (LOS) genes of H. influenzae in paired isolates from both the nasopharynx and middle ears of paediatric patients with chronic or recurrent otitis media. A change in expression of at least one of the seven phase variable LOS biosynthesis genes was seen in 12 of the 21 strain pairs. Several strains showed switching of expression in multiple LOS genes, consistent with a key role for phase variable LOS biosynthetic genes in human infection.
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Affiliation(s)
- Kate L Fox
- School of Molecular and Microbial Sciences, University of Queensland, St. Lucia, Brisbane, Queensland, Australia
| | - John M Atack
- Institute for Glycomics, Griffith University, Gold Coast, Queensland, Australia
| | - Yogitha N Srikhanta
- Institute for Glycomics, Griffith University, Gold Coast, Queensland, Australia
| | - Anja Eckert
- School of Molecular and Microbial Sciences, University of Queensland, St. Lucia, Brisbane, Queensland, Australia
| | - Laura A Novotny
- Centre for Microbial Pathogenesis, The Research Institute at Nationwide Children's Hospital, Columbus, Ohio, United States of America
| | - Lauren O Bakaletz
- Centre for Microbial Pathogenesis, The Research Institute at Nationwide Children's Hospital, Columbus, Ohio, United States of America
| | - Michael P Jennings
- Institute for Glycomics, Griffith University, Gold Coast, Queensland, Australia
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12
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Poole J, Foster E, Chaloner K, Hunt J, Jennings MP, Bair T, Knudtson K, Christensen E, Munson RS, Winokur PL, Apicella MA. Analysis of nontypeable haemophilus influenzae phase-variable genes during experimental human nasopharyngeal colonization. J Infect Dis 2013; 208:720-7. [PMID: 23715658 DOI: 10.1093/infdis/jit240] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
BACKGROUND Studies of nontypeable Haemophilus influenzae (NTHi) have demonstrated that a number of genes associated with infectivity have long repeat regions associated with phase variation in expression of the respective gene. The purpose of this study was to determine the genes that underwent phase variation during a 6-day period of experimental human nasopharyngeal colonization. METHODS Strain NTHi 2019Str(R)1 was used to colonize the nasopharynx of human subjects in a study of experimental colonization. Thirteen phase-variable genes were analyzed in NTHi 2019Str(R)1. Samples of NTHi 2019Str(R)1 were cultured from subjects during the 6-day colonization period. We used capillary electrophoresis and Roche 454 pyrosequencing to determine the number of repeats in each gene from each sample. RESULTS A significant number of samples switched licA and igaB from phase off in the inoculated strain to phase on during the 4-day period of observation. lex2A also showed variability as compared to baseline, but the differences were not significant. The remaining genes showed no evidence of phase variation. CONCLUSIONS Our studies suggest that the phase-on genotypes of licA and igaB are important for early human nasopharynx colonization. lex2A showed a trend from phase off to phase on, suggesting a potentially important role in the colonization process.
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Affiliation(s)
- Jessica Poole
- Department of Microbiology, University of Iowa, Iowa City, IA 52242, USA
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13
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Inzana TJ. Identification of phase-variable genes that may contribute to nontypeable haemophilus influenzae nasopharyngeal colonization in humans contributes to our understanding of specific host-pathogen interactions. J Infect Dis 2013; 208:713-6. [PMID: 23715662 DOI: 10.1093/infdis/jit243] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
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14
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Clark SE, Eichelberger KR, Weiser JN. Evasion of killing by human antibody and complement through multiple variations in the surface oligosaccharide of Haemophilus influenzae. Mol Microbiol 2013; 88:603-18. [PMID: 23577840 DOI: 10.1111/mmi.12214] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/20/2013] [Indexed: 11/29/2022]
Abstract
The lipopolysaccharide (LPS) of H. influenzae is highly variable. Much of the structural diversity is derived from phase variation, or high frequency on-off switching, of molecules attached during LPS biosynthesis. In this study, we examined the dynamics of LPS phase variation following exposure to human serum as a source of antibody and complement in multiple H. influenzae isolates. We show that lic2A, lgtC and lex2A switch from phase-off to phase-on following serial passage in human serum. These genes, which control attachment of a galα1-4gal di-galactoside structure (lic2A and lgtC phase-on) or an alternative glucose extension (lex2A phase-on) from the same hexose moiety, reduce binding of bactericidal antibody to conserved inner core LPS structures. The effects of the di-galactoside and alternative glucose extension were also examined in the context of the additional LPS phase variable structures phosphorylcholine (ChoP) and sialic acid. We found that di-galactoside, the alternative glucose extension, ChoP, and sialic acid each contribute independently to bacterial survival in the presence of human complement, and have an additive effect in combination. We propose that LPS phase variable extensions serve to shield conserved inner core structures from recognition by host immune components encountered during infection.
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Affiliation(s)
- Sarah E Clark
- Department of Microbiology, University of Pennsylvania, Philadelphia, PA, USA
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Boase S, Jervis-Bardy J, Cleland E, Pant H, Tan L, Wormald PJ. Bacterial-induced epithelial damage promotes fungal biofilm formation in a sheep model of sinusitis. Int Forum Allergy Rhinol 2013; 3:341-8. [PMID: 23307805 DOI: 10.1002/alr.21138] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2012] [Revised: 10/29/2012] [Accepted: 11/17/2012] [Indexed: 11/12/2022]
Abstract
BACKGROUND Fungal biofilms have been discovered in chronic rhinosinusitis (CRS) patients, but factors contributing to their establishment are obscure. A recent animal study showed bacterial co-inoculation was required. We examine the role of 4 bacterial species and a cilia toxin on fungal biofilm formation in a sheep sinusitis model. The importance of epithelial integrity on fungal biofilm formation is also examined. METHODS Forty-eight frontal sinuses were inoculated with Aspergillus fumigatus alone, with 1 of 4 bacteria, or a cilia toxin. Bacterial and fungal biofilm was determined using confocal scanning laser microscopy. Inflammation and cilia integrity were assessed using light microscopy and transmission electron microscopy, respectively. RESULTS No fungal biofilm formed when inoculated alone. Florid fungal biofilm developed in more than 75% of sinuses associated with bacterial biofilm of all species, except Haemophilus influenzae, which failed to establish bacterial biofilm. Fungal biofilm also established in association with cilia toxin. Significant cilial damage was incited by all bacterial biofilms and cilia toxin, and was associated with fungal proliferation. Fungal biofilm formation did not significantly increase mucosal inflammation or epithelial damage over that caused by the bacteria or cilia toxin alone. CONCLUSION Bacterial biofilms cause sinonasal mucosal inflammation and epithelial injury, which provides conditions appropriate for fungal biofilm proliferation. The role of cilia in sinonasal mucosal defense against fungal organisms has been demonstrated. Without such an insult, fungal biofilms fail to proliferate in occluded sinuses. Improving cilial recovery postoperatively and treating bacterial biofilms may be key factors in reducing recalcitrance in allergic fungal rhinosinusitis patients.
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Affiliation(s)
- Sam Boase
- Department of Surgery-Otorhinolaryngology, Head and Neck Surgery, University of Adelaide, Adelaide, Australia
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16
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Microbial modulation of host immunity with the small molecule phosphorylcholine. Infect Immun 2012; 81:392-401. [PMID: 23230294 DOI: 10.1128/iai.01168-12] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
All microorganisms dependent on persistence in a host for survival rely on either hiding from or modulating host responses to infection. The small molecule phosphorylcholine, or choline phosphate (ChoP), is used for both of these purposes by a wide array of bacterial and parasitic microbes. While the mechanisms underlying ChoP acquisition and expression are diverse, a unifying theme is the use of ChoP to reduce the immune response to infection, creating an advantage for ChoP-expressing microorganisms. In this minireview, we discuss several benefits of ChoP expression during infection as well as how the immune system fights back against ChoP-expressing pathogens.
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Haemophilus parainfluenzae has a limited core lipopolysaccharide repertoire with no phase variation. Glycoconj J 2012; 30:561-76. [PMID: 23093380 DOI: 10.1007/s10719-012-9455-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2012] [Revised: 10/14/2012] [Accepted: 10/15/2012] [Indexed: 10/27/2022]
Abstract
Cell surface lipopolysaccharide (LPS) is a well characterized virulence determinant for the human pathogen Haemophilus influenzae, so an investigation of LPS in the less pathogenic Haemophilus parainfluenzae could yield important insights. Using a panel of 18 commensal H. parainfluenzae isolates we demonstrate that the set of genes for inner core LPS biosynthesis largely resembles that of H. influenzae, with an additional heptosyltransferase I gene similar to waaC from Pasteurella multocida. Inner core LPS structure is therefore likely to be largely conserved across the two Haemophilus species. Outer core LPS biosynthetic genes are much less prevalent in H. parainfluenzae, although homologues of the H. influenzae LPS genes lpsB, non-phase variable lic2A and lgtC, and losA1, losB1 and lic2C are found in certain isolates. Immunoblotting using antibodies directed against selected LPS epitopes was consistent with these data. We found no evidence for tetranucleotide repeat-mediated phase variation in H. parainfluenzae. Phosphocholine, a phase variable H. influenzae LPS epitope that has been implicated in disease, was absent in H. parainfluenzae LPS as were the respective (lic1) biosynthetic genes. The introduction of the lic1 genes into H. parainfluenzae led to the phase variable incorporation of phosphocholine into its LPS. Differences in LPS structure between Haemophilus species could affect interactions at the bacterial-host interface and therefore the pathogenic potential of these bacteria.
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Hellenbrand KM, Forsythe KM, Rivera-Rivas JJ, Czuprynski CJ, Aulik NA. Histophilus somni causes extracellular trap formation by bovine neutrophils and macrophages. Microb Pathog 2012; 54:67-75. [PMID: 23022668 PMCID: PMC7125803 DOI: 10.1016/j.micpath.2012.09.007] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2012] [Revised: 09/17/2012] [Accepted: 09/19/2012] [Indexed: 12/17/2022]
Abstract
Histophilus somni (formerly Haemophilus somnus) is a Gram-negative pleomorphic coccobacillus that causes respiratory, reproductive, cardiac and neuronal diseases in cattle. H. somni is a member of the bovine respiratory disease complex that causes severe bronchopneumonia in cattle. Previously, it has been reported that bovine neutrophils and macrophages have limited ability to phagocytose and kill H. somni. Recently, it was discovered that bovine neutrophils and macrophages produce extracellular traps in response to Mannheimia haemolytica, another member of the bovine respiratory disease complex. In this study, we demonstrate that H. somni also causes extracellular trap production by bovine neutrophils in a dose- and time-dependent manner, which did not coincide with the release of lactate dehydrogenase, a marker for necrosis. Neutrophil extracellular traps were produced in response to outer membrane vesicles, but not lipooligosacchride alone. Using scanning electron microscopy and confocal microscopy, we observed H. somni cells trapped within a web-like structure. Further analyses demonstrated that bovine neutrophils trapped and killed H. somni in a DNA-dependent manner. Treatment of DNA extracellular traps with DNase I freed H. somni cells and diminished bacterial death. Treatment of bovine monocyte-derived macrophages with H. somni cells also caused macrophage extracellular trap formation. These findings suggest that extracellular traps may play a role in the host response to H. somni infection in cattle.
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Affiliation(s)
- Katrina M. Hellenbrand
- Department of Pathobiological Sciences, University of Wisconsin – Madison, Madison, WI 53706, USA
| | | | - Jose J. Rivera-Rivas
- Department of Pathobiological Sciences, University of Wisconsin – Madison, Madison, WI 53706, USA
| | - Charles J. Czuprynski
- Department of Pathobiological Sciences, University of Wisconsin – Madison, Madison, WI 53706, USA
- Food Research Institute, University of Wisconsin – Madison, Madison, WI 53706, USA
- Corresponding author. Department of Pathobiological Sciences, 2015, Linden Drive, West, Madison, WI 53706, USA. Tel./fax: +1 608 262 8102.
| | - Nicole A. Aulik
- Department of Pathobiological Sciences, University of Wisconsin – Madison, Madison, WI 53706, USA
- Biology Department, Winona State University, Winona, MN 55987, USA
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Intranasal immunization with nontypeable Haemophilus influenzae outer membrane vesicles induces cross-protective immunity in mice. PLoS One 2012; 7:e42664. [PMID: 22880074 PMCID: PMC3411803 DOI: 10.1371/journal.pone.0042664] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2012] [Accepted: 07/10/2012] [Indexed: 01/29/2023] Open
Abstract
Haemophilus influenzae is a Gram-negative human-restricted bacterium that can act as a commensal and a pathogen of the respiratory tract. Especially nontypeable H. influenzae (NTHi) is a major threat to public health and is responsible for several infectious diseases in humans, such as pneumonia, sinusitis, and otitis media. Additionally, NTHi strains are highly associated with exacerbations in patients suffering from chronic obstructive pulmonary disease. Currently, there is no licensed vaccine against NTHi commercially available. Thus, this study investigated the utilization of outer membrane vesicles (OMVs) as a potential vaccine candidate against NTHi infections. We analyzed the immunogenic and protective properties of OMVs derived from various NTHi strains by means of nasopharyngeal immunization and colonization studies with BALB/c mice. The results presented herein demonstrate that an intranasal immunization with NTHi OMVs results in a robust and complex humoral and mucosal immune response. Immunoprecipitation revealed the most important immunogenic proteins, such as the heme utilization protein, protective surface antigen D15, heme binding protein A, and the outer membrane proteins P1, P2, P5 and P6. The induced immune response conferred not only protection against colonization with a homologous NTHi strain, which served as an OMV donor for the immunization mixtures, but also against a heterologous NTHi strain, whose OMVs were not part of the immunization mixtures. These findings indicate that OMVs derived from NTHi strains have a high potential to act as a vaccine against NTHi infections.
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20
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Elswaifi SF, Scarratt WK, Inzana TJ. The role of lipooligosaccharide phosphorylcholine in colonization and pathogenesis of Histophilus somni in cattle. Vet Res 2012; 43:49. [PMID: 22676226 PMCID: PMC3406970 DOI: 10.1186/1297-9716-43-49] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2012] [Accepted: 06/07/2012] [Indexed: 11/17/2022] Open
Abstract
Histophilus somni is a Gram-negative bacterium and member of the Pasteurellaceae that is responsible for respiratory disease and other systemic infections in cattle. One of the bacterium’s virulence factors is antigenic phase variation of its lipooligosaccharide (LOS). LOS antigenic variation may occur through variation in composition or structure of glycoses or their substitutions, such as phosphorylcholine (ChoP). However, the role of ChoP in the pathogenesis of H. somni disease has not been established. In Haemophilus influenzae ChoP on the LOS binds to platelet activating factor on epithelial cells, promoting bacterial colonization of the host upper respiratory tract. However, ChoP is not expressed in the blood as it also binds C-reactive protein, resulting in complement activation and killing of the bacteria. In order to simulate the susceptibility of calves with suppressed immunity due to stress or previous infection, calves were challenged with bovine herpes virus-1 or dexamethazone 3 days prior to challenge with H. somni. Following challenge, expression of ChoP on the LOS of 2 different H. somni strains was associated with colonization of the upper respiratory tract. In contrast, lack of ChoP expression was associated with bacteria recovered from systemic sites. Histopathology of cardiac tissue from myocarditis revealed lesions containing bacterial clusters that appeared similar to a biofilm. Furthermore, some respiratory cultures contained substantial numbers of Pasteurella multocida, which were not present on preculture screens. Subsequent biofilm experiments have shown that H. somni and P. multocida grow equally well together in a biofilm, suggesting a commensal relationship may exist between the two species. Our results also showed that ChoP contributed to, but was not required for, adhesion to respiratory epithelial cells. In conclusion, expression of ChoP on H. somni LOS contributed to colonization of the bacteria to the host upper respiratory tract, but phase variable loss of ChoP expression may help the bacteria survive systemically.
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Affiliation(s)
- Shaadi F Elswaifi
- Center for Molecular Medicine and Infectious Diseases, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Tech, Blacksburg, VA 24061, USA.
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Phosphorylcholine allows for evasion of bactericidal antibody by Haemophilus influenzae. PLoS Pathog 2012; 8:e1002521. [PMID: 22396641 PMCID: PMC3291618 DOI: 10.1371/journal.ppat.1002521] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2011] [Accepted: 12/20/2011] [Indexed: 11/19/2022] Open
Abstract
The human pathogen Haemophilus influenzae has the ability to quickly adapt to different host environments through phase variation of multiple structures on its lipooligosaccharide (LPS), including phosphorylcholine (ChoP). During colonization with H. influenzae, there is a selection for ChoP+ phase variants. In a murine model of nasopharyngeal colonization, this selection is lost in the absence of adaptive immunity. Based on previous data highlighting the importance of natural antibody in limiting H. influenzae colonization, the effect of ChoP expression on antibody binding and its bactericidal activity was investigated. Flow cytometric analysis revealed that ChoP+ phase variants had decreased binding of antibody to LPS epitopes compared to ChoP- phase variants. This difference in antibody binding correlated with increased survival of ChoP+ phase variants in the presence of antibody-dependent, complement-mediated killing. ChoP+ phase variants were also more resistant to trypsin digestion, suggesting a general effect on the physical properties of the outer membrane. Moreover, ChoP-mediated protection against antibody binding correlated with increased resilience of outer membrane integrity. Collectively, these data suggest that ChoP expression provides a selective advantage during colonization through ChoP-mediated effects on the accessibility of bactericidal antibody to the cell surface.
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Inactivation of Haemophilus influenzae lipopolysaccharide biosynthesis genes interferes with outer membrane localization of the hap autotransporter. J Bacteriol 2012; 194:1815-22. [PMID: 22287523 DOI: 10.1128/jb.06316-11] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Nontypeable Haemophilus influenzae is a major cause of localized respiratory tract disease and initiates infection by colonizing the nasopharynx. Colonization requires adherence to host epithelial cells, which is mediated by surface proteins such as the Hap adhesin. In this study, we identified a relationship between Hap levels in the outer membrane and lipopolysaccharide (LPS) biosynthesis enzymes. We found that mutation of the rfaF, pgmB, lgtC, kfiC, orfE, rfbP, lsgB, or lsgD genes, which are involved in the synthesis of the LPS oligosaccharide core in H. influenzae strain Rd/HapS243A, resulted in loss of Hap in the bacterial outer membrane and a decrease in hap transcript levels. In contrast, the same mutations had no effect on outer membrane localization of H. influenzae P5 or IgA1 protease or levels of p5 or iga1 transcripts, suggesting a Hap-specific effect. Elimination of the HtrA periplasmic protease resulted in a return of Hap to the outer membrane and restoration of hap transcript levels. Consistently, in lgtC phase-off bacteria, Hap was absent from the outer membrane, and hap transcript levels were reduced. Hap localization and hap transcript levels were not related to LPS size but to the functions of the LPS biosynthesis enzymes themselves. We speculate that the lack of certain LPS biosynthesis enzymes causes Hap to mislocalize and accumulate in the periplasm, where it is degraded by HtrA. This degradation then leads to a decrease in hap transcript levels. Together, these data highlight a novel interplay between Hap and LPS biosynthesis that can influence H. influenzae interactions with the host.
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Trappetti C, Ogunniyi AD, Oggioni MR, Paton JC. Extracellular matrix formation enhances the ability of Streptococcus pneumoniae to cause invasive disease. PLoS One 2011; 6:e19844. [PMID: 21611130 PMCID: PMC3097209 DOI: 10.1371/journal.pone.0019844] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2011] [Accepted: 04/04/2011] [Indexed: 11/22/2022] Open
Abstract
During infection, pneumococci exist mainly in sessile biofilms rather than in planktonic form, except during sepsis. However, relatively little is known about how biofilms contribute to pneumococcal pathogenesis. Here, we carried out a biofilm assay on opaque and transparent variants of a clinical serotype 19F strain WCH159. After 4 days incubation, scanning electron microscopy revealed that opaque biofilm bacteria produced an extracellular matrix, whereas the transparent variant did not. The opaque biofilm-derived bacteria translocated from the nasopharynx to the lungs and brain of mice, and showed 100-fold greater in vitro adherence to A549 cells than transparent bacteria. Microarray analysis of planktonic and sessile bacteria from transparent and opaque variants showed differential gene expression in two operons: the lic operon, which is involved in choline uptake, and in the two-component system, ciaRH. Mutants of these genes did not form an extracellular matrix, could not translocate from the nasopharynx to the lungs or the brain, and adhered poorly to A549 cells. We conclude that only the opaque phenotype is able to form extracellular matrix, and that the lic operon and ciaRH contribute to this process. We propose that during infection, extracellular matrix formation enhances the ability of pneumococci to cause invasive disease.
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Affiliation(s)
- Claudia Trappetti
- Research Centre for Infectious Diseases, School of Molecular and Biomedical Science, The University of Adelaide, Adelaide, South Australia, Australia
| | - Abiodun D. Ogunniyi
- Research Centre for Infectious Diseases, School of Molecular and Biomedical Science, The University of Adelaide, Adelaide, South Australia, Australia
- * E-mail:
| | - Marco R. Oggioni
- Laboratorio di Microbiologia Molecolare e Biotecnologia, Dipartimento di Biologia Molecolare, Università di Siena, Siena, Italy
| | - James C. Paton
- Research Centre for Infectious Diseases, School of Molecular and Biomedical Science, The University of Adelaide, Adelaide, South Australia, Australia
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McCrea KW, Xie J, Marrs CF, Gilsdorf JR. Prevalence of genetic differences in phosphorylcholine expression between nontypeable Haemophilus influenzae and Haemophilus haemolyticus. BMC Microbiol 2010; 10:286. [PMID: 21073698 PMCID: PMC2992063 DOI: 10.1186/1471-2180-10-286] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2010] [Accepted: 11/12/2010] [Indexed: 11/17/2022] Open
Abstract
BACKGROUND Although non-typeable (NT) Haemophilus influenzae and Haemophilus haemolyticus are closely related human commensals, H. haemolyticus is non-pathogenic while NT H. influenzae is an important cause of respiratory tract infections. Phase-variable phosphorylcholine (ChoP) modification of lipooligosaccharide (LOS) is a NT H. influenzae virulence factor that, paradoxically, may also promote complement activation by binding C-reactive protein (CRP). CRP is known to bind more to ChoP positioned distally than proximally in LOS, and the position of ChoP within LOS is dictated by specific licD alleles (designated here as licDI, licDIII, and licDIV) that are present in a lic1 locus. The lic1 locus contains the licA-licD genes, and ChoP-host interactions may also be influenced by a second lic1 locus that allows for dual ChoP substitutions in the same strain, or by the number of licA gene tetranucleotide repeats (5'-CAAT-3') that reflect phase-variation mutation rates. RESULTS Using dot-blot hybridization, 92% of 88 NT H. influenzae and 42.6% of 109 H. haemolyticus strains possessed a lic1 locus. Eight percent of NT H. influenzae and none of the H. haemolyticus strains possessed dual copies of lic1. The licDIII and licDIV gene alleles were distributed similarly (18-22%) among the NT H. influenzae and H. haemolyticus strains while licDI alleles were present in 45.5% of NT H. influenzae but in less than 1% of H. haemolyticus strains (P < .0001). NT H. influenzae had an average of 26.8 tetranucleotide repeats in licA compared to 14.8 repeats in H. haemolyticus (P < .05). In addition, NT H. influenzae strains that possessed a licDIII allele had increased numbers of repeats compared to NT H. influenzae with other licD alleles (P < .05). CONCLUSIONS These data demonstrate that genetic similarities and differences of ChoP expression exist between NT H. influenzae and H. haemolyticus and strengthen the hypothesis that, at the population level, these differences may, in part, provide an advantage in the virulence of NT H. influenzae.
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Affiliation(s)
- Kirk W McCrea
- Department of Pediatrics and Communicable Diseases, University of Michigan, Ann Arbor, MI 48109, USA
| | - Jingping Xie
- Department of Epidemiology, University of Michigan, Ann Arbor, MI 48109-0244, USA
- Beacon Analytical Systems Inc., Saco, ME 04072, USA
| | - Carl F Marrs
- Department of Epidemiology, University of Michigan, Ann Arbor, MI 48109-0244, USA
| | - Janet R Gilsdorf
- Department of Pediatrics and Communicable Diseases, University of Michigan, Ann Arbor, MI 48109, USA
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Elswaifi SF, St Michael F, Sreenivas A, Cox A, Carman GM, Inzana TJ. Molecular characterization of phosphorylcholine expression on the lipooligosaccharide of Histophilus somni. Microb Pathog 2009; 47:223-30. [PMID: 19682567 DOI: 10.1016/j.micpath.2009.08.001] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2008] [Revised: 08/03/2009] [Accepted: 08/06/2009] [Indexed: 11/28/2022]
Abstract
Histophilus somni (Haemophilus somnus) is an important pathogen of cattle that is responsible for respiratory disease, septicemia, and systemic diseases such as thrombotic meningoencephalitis, myocarditis, and abortion. A variety of virulence factors have been identified in H. somni, including compositional and antigenic variation of the lipooligosaccharide (LOS). Phosphorylcholine (ChoP) has been identified as one of the components of H. somni LOS that undergoes antigenic variation. In this study, five genes (lic1ABCD(Hs) and glpQ) with homology to genes responsible for ChoP expression in Haemophilus influenzae LOS were identified in the H. somni genome. An H. somni open reading frame (ORF) with homology to H. influenzae lic1A (lic1A(Hi)) contained a variable number of tandem repeats (VNTR). However, whereas the tetranucleotide repeat 5'-CAAT-3' is present in lic1A(Hi), the VNTR in H. somni lic1A (lic1A(Hs)) consisted of 5'-AACC-3'. Due to the propensity of VNTR to vary during replication and cause the ORF to shift in and out of frame with the upstream start codon, the VNTR were deleted from lic1A(Hs) to maintain the gene constitutively on. This construct was cloned into Escherichia coli, and functional enzyme assays confirmed that lic1A(Hs) encoded a choline kinase, and that the VNTR were not required for expression of a functional gene product. Variation in the number of VNTR in lic1A(Hs) correlated with antigenic variation of ChoP expression in H. somni strain 124P. However, antigenic variation of ChoP expression in strain 738 predominately occurred through variable extension/truncation of the LOS outer core. These results indicated that the lic1(Hs) genes controlled expression of ChoP on the LOS, but that in H. somni there are two potential mechanisms that account for antigenic variation of ChoP.
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Affiliation(s)
- Shaadi F Elswaifi
- Center for Molecular Medicine and Infectious Diseases, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA
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Fujita K, Hirano T, Kodama S, Suzuki M. Prognostic impact of phosphorylcholine expression in nontypeable Haemophilus influenzae in otitis media with effusion. Acta Otolaryngol 2009; 129:832-8. [PMID: 18932100 DOI: 10.1080/00016480802468195] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
CONCLUSIONS The expression of phosphorylcholine (ChoP) in the surface of nontypeable Haemophilus influenzae (NTHi) is an important factor in the pathogenesis of persistent otitis media with effusion (OME) in humans. OBJECTIVES Lipooligosaccharide (LOS) in NTHi undergoes phase variation in expression of the ChoP epitope. In this study, we examined the phase variation of NTHi isolated from the nasopharynx of children who suffer from OME, and investigated the relationship between the phase variation and the pathogenesis of OME. SUBJECTS AND METHODS Forty NTHi strains were isolated from the nasopharynx of children with OME, and the ChoP expression of NTHi was examined by colony immunoblot analysis. The NTHi strains were classified into three groups according to the level of ChoP expression, i.e. strong, moderate, and weak expression groups. An adherence assay was also performed. RESULTS The NTHi strains expressing ChoP(+) LOS glycoforms accounted for 63% of all NTHi tested. Clinically, the strong expression group of ChoP were related to prolongation of the duration of OME. The adherence assay with the CCL 20.2 cell line revealed that the strong expression group attached more easily to the cell surface than the weak expression group.
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LuxS promotes biofilm maturation and persistence of nontypeable haemophilus influenzae in vivo via modulation of lipooligosaccharides on the bacterial surface. Infect Immun 2009; 77:4081-91. [PMID: 19564381 DOI: 10.1128/iai.00320-09] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Nontypeable Haemophilus influenzae (NTHI) is an extremely common airway commensal which can cause opportunistic infections that are usually localized to airway mucosal surfaces. During many of these infections, NTHI forms biofilm communities that promote persistence in vivo. For many bacterial species, density-dependent quorum-signaling networks can affect biofilm formation and/or maturation. Mutation of luxS, a determinant of the autoinducer 2 (AI-2) quorum signal pathway, increases NTHI virulence in the chinchilla model for otitis media infections. For example, bacterial counts in middle-ear fluids and the severity of the host inflammatory response were increased in luxS mutants compared with parental strains. As these phenotypes are consistent with those that we have observed for biofilm-defective NTHI mutants, we hypothesized that luxS may affect NTHI biofilms. A luxS mutant was generated using the well-characterized NTHI 86-028NP strain and tested to determine the effects of the mutation on biofilm phenotypes in vitro and bacterial persistence and disease severity during experimental otitis media. Quantitation of the biofilm structure by confocal microscopy and COMSTAT analysis revealed significantly reduced biomass for NTHI 86-028NP luxS biofilms, which was restored by a soluble mediator in NTHI 86-028NP supernatants. Analysis of lipooligosaccharide moieties using an enzyme-linked immunosorbent assay and immunoblotting showed decreased levels of biofilm-associated glycoforms in the NTHI 86-028NP luxS strain. Infection studies showed that NTHI 86-028NP luxS had a significant persistence defect in vivo during chronic otitis media infection. Based on these data, we concluded that a luxS-dependent soluble mediator modulates the composition of the NTHI lipooligosaccharides, resulting in effects on biofilm maturation and bacterial persistence in vivo.
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Pneumococcal Haemophilus influenzae protein D conjugate vaccine induces antibodies that inhibit glycerophosphodiester phosphodiesterase activity of protein D. Infect Immun 2008; 76:4546-53. [PMID: 18644877 DOI: 10.1128/iai.00418-08] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Haemophilus influenzae outer membrane protein D (PD) is a glycerophosphodiester phosphodiesterase (GlpQ) activity-possessing virulence factor and a promising vaccine antigen, providing 35.3% efficacy against acute otitis media caused by nontypeable H. influenzae (NTHI) when it was used as a carrier protein in a novel pneumococcal PD conjugate (Pnc-PD) vaccine. To study if PD-induced protection against NTHI could be due to antibodies that inhibit or neutralize its enzymatic activity, a GlpQ enzyme inhibition assay was developed, and serum samples collected from Finnish infants before and after Pnc-PD vaccination were analyzed for enzyme inhibition and anti-PD immunoglobulin G (IgG) antibody concentration. Before vaccination at age 2 months, the majority (84%) of infants (n = 69) had no detectable anti-PD IgG antibodies, and all were enzyme inhibition assay negative (inhibition index, <20). At age 13 to 16 months, all infants receiving three or four doses of Pnc-PD had detectable anti-PD IgG antibodies and 36% (8/22 infants) of the infants receiving three doses and 26% (6/23 infants) of the infants receiving four doses of Pnc-PD were inhibition assay positive (inhibition index, >/=20). No significant rise in anti-PD IgG antibodies or enzyme inhibition among control vaccinees (n = 24) receiving three doses of hepatitis B vaccine was detected. A modest correlation (r(s), approximately 0.66) between anti-PD IgG concentration and enzyme inhibition was detected; however, their kinetics were clearly different. These data suggest that measurement of antibody responses that inhibit PD's enzymatic activity could be a useful tool for assessing Pnc-PD vaccine-induced protective immunity against NTHI.
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Lee HY, Takeshita T, Shimada J, Akopyan A, Woo JI, Pan H, Moon SK, Andalibi A, Park RK, Kang SH, Kang SS, Gellibolian R, Lim DJ. Induction of beta defensin 2 by NTHi requires TLR2 mediated MyD88 and IRAK-TRAF6-p38MAPK signaling pathway in human middle ear epithelial cells. BMC Infect Dis 2008; 8:87. [PMID: 18578886 PMCID: PMC2447838 DOI: 10.1186/1471-2334-8-87] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2008] [Accepted: 06/25/2008] [Indexed: 01/22/2023] Open
Abstract
Background All mucosal epithelia, including those of the tubotympanium, are secreting a variety of antimicrobial innate immune molecules (AIIMs). In our previous study, we showed the bactericidal/bacteriostatic functions of AIIMs against various otitis media pathogens. Among the AIIMs, human β-defensin 2 is the most potent molecule and is inducible by exposure to inflammatory stimuli such as bacterial components or proinflammatory cytokines. Even though the β-defensin 2 is an important AIIM, the induction mechanism of this molecule has not been clearly established. We believe that this report is the first attempt to elucidate NTHi induced β-defensin expression in airway mucosa, which includes the middle ear. Methods Monoclonal antibody blocking method was employed in monitoring the TLR-dependent NTHi response. Two gene knock down methods – dominant negative (DN) plasmid and small interfering RNA (siRNA) – were employed to detect and confirm the involvement of several key genes in the signaling cascade resulting from the NTHi stimulated β-defensin 2 expression in human middle ear epithelial cell (HMEEC-1). The student's t-test was used for the statistical analysis of the data. Results The experimental results showed that the major NTHi-specific receptor in HMEEC-1 is the Toll-like receptor 2 (TLR2). Furthermore, recognition of NTHi component(s)/ligand(s) by TLR2, activated the Toll/IL-1 receptor (TIR)-MyD88-IRAK1-TRAF6-MKK3/6-p38 MAPK signal transduction pathway, ultimately leading to the induction of β-defensin 2. Conclusion This study found that the induction of β-defensin 2 is highest in whole cell lysate (WCL) preparations of NTHi, suggesting that the ligand(s) responsible for this up-regulation may be soluble macromolecule(s). We also found that this induction takes place through the TLR2 dependent MyD88-IRAK1-TRAF6-p38 MAPK pathway, with the primary response occurring within the first hour of stimulation. In combination with our previous studies showing that IL-1α-induced β-defensin 2 expression takes place through a MyD88-independent Raf-MEK1/2-ERK MAPK pathway, we found that both signaling cascades act synergistically to up-regulate β-defensin 2 levels. We propose that this confers an essential evolutionary advantage to the cells in coping with infections and may serve to amplify the innate immune response through paracrine signaling.
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Affiliation(s)
- Haa-Yung Lee
- The Gonda Department of Cell and Molecular Biology, House Ear Institute, Los Angeles, CA, USA.
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Pang B, Winn D, Johnson R, Hong W, West-Barnette S, Kock N, Swords WE. Lipooligosaccharides containing phosphorylcholine delay pulmonary clearance of nontypeable Haemophilus influenzae. Infect Immun 2008; 76:2037-43. [PMID: 18347044 PMCID: PMC2346676 DOI: 10.1128/iai.01716-07] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2007] [Revised: 01/25/2008] [Accepted: 03/06/2008] [Indexed: 11/20/2022] Open
Abstract
Nontypeable Haemophilus influenzae (NTHi) causes pulmonary infections in patients with chronic obstructive pulmonary disease and other mucociliary clearance defects. Like many bacteria inhabiting mucosal surfaces, NTHi produces lipooligosaccharide (LOS) endotoxins that lack the O side chain. Persistent NTHi populations express a discrete subset of LOS glycoforms, including those containing phosphorylcholine (PCho). In this study, we compared two NTHi strains with isogenic mutants lacking PCho for clearance from mice following pulmonary infection. Consistent with data from other model systems, populations of the strains NTHi 2019 and NTHi 86-028NP recovered from mouse lung contained an increased proportion of PCho+ variants compared to that in the inocula. PCho- mutants were more rapidly cleared. Serial passage of NTHi increased both PCho content and bacterial resistance to clearance, and no such increases were observed for PCho- mutants. Increased PCho content was also observed in NTHi populations within non-endotoxin-responsive C3H/HeJ and Toll-like receptor 4 null (TLR4-/-) mice, albeit at later times postinfection. Changes in bacterial subpopulations and clearance were unaffected in TLR2-/- mice compared to the subpopulations in and clearance from mice of the parental strain. The clearance of PCho- mutants occurred at earlier time points in both strain backgrounds and in all types of mice. Comparison of bacterial populations in lung tissue cryosections by immunofluorescent staining showed sparse bacteria within the air spaces of C57BL/6 mice and large bacterial aggregates within the lungs of MyD88-/- mice. These results indicate that PCho promotes bacterial resistance to pulmonary clearance early in infection in a manner that is at least partially independent of the TLR4 pathway.
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Affiliation(s)
- Bing Pang
- Department of Microbiology, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27157, USA
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Relationships of nontypeable Haemophilus influenzae strains to hemolytic and nonhemolytic Haemophilus haemolyticus strains. J Clin Microbiol 2007; 46:406-16. [PMID: 18039799 DOI: 10.1128/jcm.01832-07] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Haemophilus influenzae is both a human respiratory pathogen and pharyngeal commensal, while H. haemolyticus, the closest phylogenetic relative of H. influenzae, is arguably a strict pharyngeal commensal. A hemolytic phenotype has historically differentiated H. haemolyticus from H. influenzae, but the recent recognition of significant nonhemolytic H. haemolyticus colonization has decreased this trait's resolvability. Given this and the potential of recombination between the species, we examined the distribution of microbiologic and molecular traits between collections of H. influenzae and H. haemolyticus strains separated within a dendrogram obtained by multilocus sequence analysis (MLSA). All strains hybridizing with a probe to iga, a gene encoding an immunoglobulin A protease of H. influenzae, clustered apart from strains that did not hybridize with the probe. Other traits also segregated significantly along this division, suggesting a separation of the species. Of note, the LOS genes licA, lic2A, and lgtC of H. influenzae were approximately 2, 6, and 54 times, respectively, more prevalent in H. influenzae than in H. haemolyticus. In contrast to species separation, interspecies recombination was evidenced by the inability of single gene sequences to phylogenetically separate the species and by the "fuzzy" distribution of some species-specific traits across the species dividing line. Together, these data support the historically accurate and pragmatic division of these species while recognizing their potential for recombination. Future comparative genomic studies identifying common and distinctive genes could be useful in evaluating their role in the commensal or virulent growth, respectively, of H. influenzae.
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Tanaka N, Fukuyama S, Fukuiwa T, Kawabata M, Sagara Y, Ito HO, Miwa Y, Nagatake T, Kiyono H, Kurono Y. Intranasal immunization with phosphorylcholine induces antigen specific mucosal and systemic immune responses in mice. Vaccine 2007; 25:2680-7. [PMID: 17270319 DOI: 10.1016/j.vaccine.2006.10.014] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2006] [Revised: 10/06/2006] [Accepted: 10/10/2006] [Indexed: 11/26/2022]
Abstract
Phosphorylcholine (PC) is a structural component of a wide variety of pathogens including Streptococcus pneumoniae and Haemophilus influenzae, and anti-PC immune responses are known to protect mice against invasive bacterial diseases. The present study tested the capability of PC as an intranasal plurispecific vaccine against upper airway infections. BALB/c mice immunized with intranasal PC-keyhole limpet hemocyanin (KLH) plus cholera toxin (CT) as a mucosal adjuvant showed increased PC-specific IgM in serum, IgA in nasal wash and saliva, and numbers of PC-specific nasal and splenic antibody producing cells. Enhanced production of IL-4 and IFN-gamma by CD4+ T cells indicated the participation of Th2- and Th1-type cells. Salivary IgA antibodies produced by intranasal immunization with PC-KLH plus CT reacted to most strains of S. pneumoniae and H. influenzae. Further we demonstrated that the clearance of S. pneumoniae and H. influenzae from the nasal tract was significantly enhanced by nasal immunization with PC-KLH and CT. Thus, intranasal vaccination to induce PC-specific immune responses might help to prevent upper airway infections caused by S. pneumoniae and H. influenzae.
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Affiliation(s)
- Norimitsu Tanaka
- Department of Otolaryngology, Head and Neck Surgery, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan.
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Hong W, Mason K, Jurcisek J, Novotny L, Bakaletz LO, Swords WE. Phosphorylcholine decreases early inflammation and promotes the establishment of stable biofilm communities of nontypeable Haemophilus influenzae strain 86-028NP in a chinchilla model of otitis media. Infect Immun 2006; 75:958-65. [PMID: 17130253 PMCID: PMC1828519 DOI: 10.1128/iai.01691-06] [Citation(s) in RCA: 111] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Nontypeable Haemophilus influenzae (NTHi) is a leading causative agent of otitis media. Much of the inflammation occurring during NTHi disease is initiated by lipooligosaccharides (LOS) on the bacterial surface. Phosphorylcholine (PCho) is added to some LOS forms in a phase-variable manner, and these PCho(+) variants predominate in vivo. Thus, we asked whether this modification confers some advantage during infection. Virulence of an otitis media isolate (NTHi strain 86-028NP) was compared with that of an isogenic PCho transferase (licD) mutant using a chinchilla (Chinchilla lanigera) model of otitis media. Animals infected with NTHi 86-028NP licD demonstrated increased early inflammation and a delayed increase in bacterial counts compared to animals infected with NTHi 86-028NP. LOS purified from chinchilla-passed NTHi 86-028NP had increased PCho content compared to LOS purified from the inoculum. Both strains were recovered from middle ear fluids as long as 14 days postinfection. Biofilms were macroscopically visible in the middle ears of euthanized animals infected with NTHi 86-028NP 7 days and 14 days postchallenge. Conversely, less dense biofilms were observed in animals infected with NTHi 86-028NP licD 7 days postinfection, and none of the animals infected with NTHi 86-028NP licD had a visible biofilm by 14 days. Fluorescent antibody staining revealed PCho(+) variants within biofilms, similar to our prior results with tissue culture cells in vitro (S. L. West-Barnette, A. Rockel, and W. E. Swords, Infect. Immun. 74:1828-1836, 2006). Animals coinfected with equal proportions of both strains had equal persistence of each strain and somewhat greater severity of disease. We thus conclude that PCho promotes NTHi infection and persistence by reducing the host inflammatory response and by promoting formation of stable biofilm communities.
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Affiliation(s)
- Wenzhou Hong
- Department of Microbiology and Immunology, Wake Forest University Health Sciences, Winston-Salem, NC 27157, USA
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MacArthur CJ, Hefeneider SH, Kempton JB, Parrish SK, McCoy SL, Trune DR. Evaluation of the mouse model for acute otitis media. Hear Res 2006; 219:12-23. [PMID: 16887307 DOI: 10.1016/j.heares.2006.05.012] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/02/2006] [Revised: 04/12/2006] [Accepted: 05/10/2006] [Indexed: 11/15/2022]
Abstract
Various animal models have been employed for otitis media research. The mouse has been studied less, in spite of its many advantages. To better understand the suitability of the mouse for studies of otitis media, an evaluation was made of its middle ear inflammatory processes following inoculation with heat-killed Streptococcus pneumoniae (strain 6A), one of the three most common bacteria to cause otitis media in the human. A total of 94 BALB/c mice were injected transtympanically with three concentrations of heat-killed bacteria (10(4), 10(6), and 10(9) organisms per ml) and inflammation evaluated with both histologic examination and auditory brainstem response audiometry. Dose-related measures of the time course of inflammation showed it was maximal at 3 days. PBS-injected control mice also demonstrated some degree of middle ear inflammation. Therefore, inflammation measures from PBS injected mice were used as the threshold above which histologic inflammatory changes would be considered a response to bacteria. These quantitative comparisons of bacterial and PBS inoculations revealed the most significant middle ear measures of inflammation were amount of fluid in the middle ear, tympanic membrane thickness, and number of inflammatory cells. The induction of middle ear inflammation in the mouse demonstrated the applicability of this model for investigations of otitis media.
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Affiliation(s)
- Carol J MacArthur
- Department of Otolaryngology and Oregon Hearing Research Center, Oregon Health & Science University, 3181 SW Sam Jackson Park Road, PV-01, Portland, OR 97239-3098, USA.
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West-Barnette S, Rockel A, Swords WE. Biofilm growth increases phosphorylcholine content and decreases potency of nontypeable Haemophilus influenzae endotoxins. Infect Immun 2006; 74:1828-36. [PMID: 16495557 PMCID: PMC1418622 DOI: 10.1128/iai.74.3.1828-1836.2006] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Nontypeable Haemophilus influenzae (NTHI) is a common respiratory commensal and opportunistic pathogen. NTHI is normally contained within the airways by host innate defenses that include recognition of bacterial endotoxins by Toll-like receptor 4 (TLR4). NTHI produces lipooligosaccharide (LOS) endotoxins which lack polymeric O side chains and which may contain host glycolipids. We recently showed that NTHI biofilms contain variants with sialylated LOS glycoforms that are essential to biofilm formation. In this study, we show that NTHI forms biofilms on epithelial cell layers. Confocal analysis revealed that sialylated variants were distributed throughout the biofilm, while variants expressing phosphorylcholine (PCho) were found within the biofilm. Consistent with this observation, PCho content of LOS purified from NTHI biofilms was increased compared to LOS from planktonic cultures. Hypothesizing that the observed changes in endotoxin composition could affect bioactivity, we compared inflammatory responses to NTHI LOS purified from biofilm and planktonic cultures. Our results show that endotoxins from biofilms induced weaker host innate responses. While we observed a minimal effect of sialylation on LOS bioactivity, there was a significant decrease in bioactivity associated with PCho substitutions. We thus conclude that biofilm growth increases the proportion of PCho+ variants in an NTHI population, resulting in a net decrease in LOS bioactivity. Thus, in addition to their well-documented resistance phenotypes, our data show that biofilm communities of NTHI bacteria contain variants that evoke less potent host responses.
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Affiliation(s)
- Shayla West-Barnette
- Department of Microbiology and Immunology, Wake Forest University Health Sciences, 5101A Gray Building, Medical Center Blvd., Winston-Salem, NC 27157, USA
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Blumer JL. Evolution of a new drug formulation: the rationale for high-dose, short-course therapy with azithromycin. Int J Antimicrob Agents 2006; 26 Suppl 3:S143-7. [PMID: 16543075 DOI: 10.1016/s0924-8579(05)80320-6] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The rationale for the use of high-dose, short-course azithromycin treatment regimens is based on the pharmacokinetic properties of azithromycin. Its long elimination half-life (approximately 60 h) and antibacterial potency make short-course (1-day) regimens feasible. Azithromycin is concentrated within phagocytic cells, which deliver it in a targeted manner to sites of infection. In vitro and in vivo models demonstrate that azithromycin is taken up, transported and released at the sites of infection by polymorphonuclear neutrophils and macrophages. Uptake is not saturable, so delivery of the total azithromycin therapeutic regimen as a single dose of azithromycin microspheres should lead to increased uptake and delivery of the drug to sites of infection. By achieving higher drug concentrations at the site of infection, a single, high dose of azithromycin microspheres should maximize efficacy. The new microsphere formulation allows for 'front loading' of the dose to achieve the highest drug levels early in the course of infection while maintaining favorable tolerability.
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Affiliation(s)
- Jeffrey L Blumer
- Department of Pediatrics and Pharmacology, Case Western Reserve University, Cleveland, OH, USA.
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King SJ, Whatmore AM, Dowson CG. NanA, a neuraminidase from Streptococcus pneumoniae, shows high levels of sequence diversity, at least in part through recombination with Streptococcus oralis. J Bacteriol 2005; 187:5376-86. [PMID: 16030232 PMCID: PMC1196044 DOI: 10.1128/jb.187.15.5376-5386.2005] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Streptococcus pneumoniae, an important human pathogen, contains at least two genes, nanA and nanB, that express sialidase activity. NanA is a virulence determinant of pneumococci which is important in animal models of colonization and middle ear infections. The gene encoding NanA was detected in all 106 pneumococcal strains screened that represented 59 restriction profiles. Sequencing confirmed a high level of diversity, up to 17.2% at the nucleotide level and 14.8% at the amino acid level. NanA diversity is due to a number of mechanisms including insertions, point mutations, and recombination generating mosaic genes. The level of nucleotide divergence for each recombinant block is greater than 30% and much higher than the 20% identified within mosaic pbp genes, suggesting that a high selective pressure exists for these alterations. These data indicate that at least one of the four recombinant blocks identified originated from a Streptococcus oralis isolate, demonstrating for the first time that protein virulence determinants of pneumococci have, as identified previously for genes encoding penicillin binding proteins, evolved by recombination with oral streptococci. No amino acid alterations were identified within the aspartic boxes or predicted active site, suggesting that sequence variation may be important in evading the adaptive immune response. Furthermore, this suggests that nanA is an important target of the immune system in the interaction between the pneumococcus and host.
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Affiliation(s)
- Samantha J King
- 401A Johnson Pavilion, Department of Microbiology, University of Pennsylvania, Philadelphia, PA 19104-6076, USA.
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Lim DJ, Hermansson A, HellstrÖ SO, Hussl B, Alper CM, Uno Y, Andalibi A, Jung TTK, Bakaletz LO, Kawauchi H, Buchman CA, Kerschner J, Cayé-Thomasen P, Lin J, Chole RA, Merchant SN, Herman P, Lee HY, Kang SH, Paparella MM. 3. Animal Models; Anatomy and Pathology; Pathogenesis; Cell Biology and Genetics. Ann Otol Rhinol Laryngol 2005. [DOI: 10.1177/000348940511401s01] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
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Branger J, Wieland CW, Florquin S, Maris NA, Pater JM, Speelman P, Shimizu T, Ishii S, van der Poll T. PLATELET-ACTIVATING FACTOR RECEPTOR-DEFICIENT MICE SHOW AN UNALTERED CLEARANCE OF NONTYPEABLE HAEMOPHILUS INFLUENZAE FROM THEIR RESPIRATORY TRACT. Shock 2004; 22:543-7. [PMID: 15545826 DOI: 10.1097/01.shk.0000142818.91693.73] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Platelet-activating factor (PAF), a glycerophospholipid with proinflammatory properties, exerts its biological effects by interacting with the PAF receptor (PAFR) expressed on many different cell types. The PAFR specifically binds phosphorylcholine, the biologically active component of PAF. However, phosphorylcholine is also a component of the cell wall of nontypeable Haemophilus influenzae (NTHi). In recently published in vitro experiments, the invasion of respiratory epithelial cells by NTHi was mediated by the PAFR. To determine the role of the PAFR in host defense against pneumonia induced by NTHi, PAFR-deficient (PAFR-/-) and normal wild-type mice were intranasally inoculated with NTHi. The absence of a functional PAFR was associated with a normal innate immune response as indicated by similar bacterial counts, myeloperoxidase activity, and inflammation within the pulmonary compartment of PAFR-/- and wild-type mice. These data indicate that the PAFR does not interfere with the clearance of NTHi from the respiratory tract.
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Affiliation(s)
- Judith Branger
- Department of Experimental Internal Medicine, Academic Medical Center, University of Amsterdam, The Netherlands.
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Fan X, Pericone CD, Lysenko E, Goldfine H, Weiser JN. Multiple mechanisms for choline transport and utilization in Haemophilus influenzae. Mol Microbiol 2004; 50:537-48. [PMID: 14617177 DOI: 10.1046/j.1365-2958.2003.03703.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Haemophilus influenzae obtains choline from either its growth medium or host cell membrane lipids and expresses it on its lipopolysaccharide (LPS) in the form of phosphorylcholine (ChoP), which contributes to its pathogenesis by mimicry of host cell molecules. Two genes (licB and betT) revealed by whole genomic analysis as encoding potential choline transporters were tested for their role in LPS-ChoP synthesis. The betT gene in H. influenzae is similar to betT in Escherichia coli, which functions in choline transport for the generation of betaine in osmoprotection. The licB gene has homology to bacterial permeases including betT and is encoded in the lic1 locus, which is essential for the expression of LPS-ChoP. In the presence of high concentrations of choline, neither licB nor betT were necessary for expression of LPS-ChoP raising the possibility that other unidentified choline uptake mechanisms may exist in this species. However, under choline limiting conditions, including growth in human nasal airway surface fluid, the licB, but not betT, gene was required for choline transport and synthesis of LPS-ChoP suggesting that LicB functions as a high affinity choline permease. The betT, but not licB, gene was shown to function in osmoprotection in H. influenzae, similar to the role of betT in E. coli. Further analysis demonstrated growth condition dependent differences in the regulation of transcription of the licB and betT genes. We conclude that H. influenzae may have multiple mechanisms for choline uptake and distinct pathways for choline utilization in LPS-ChoP biosynthesis and osmoregulation.
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Affiliation(s)
- Xin Fan
- University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA
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Swords WE, Moore ML, Godzicki L, Bukofzer G, Mitten MJ, VonCannon J. Sialylation of lipooligosaccharides promotes biofilm formation by nontypeable Haemophilus influenzae. Infect Immun 2004; 72:106-13. [PMID: 14688087 PMCID: PMC343998 DOI: 10.1128/iai.72.1.106-113.2004] [Citation(s) in RCA: 111] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Nontypeable Haemophilus influenzae (NTHi) is a major cause of opportunistic respiratory tract infections, including otitis media and bronchitis. The persistence of NTHi in vivo is thought to involve bacterial persistence in a biofilm community. Therefore, there is a need for further definition of bacterial factors contributing to biofilm formation by NTHi. Like other bacteria inhabiting host mucosal surfaces, NTHi has on its surface a diverse array of lipooligosaccharides (LOS) that influence host-bacterial interactions. In this study, we show that LOS containing sialic (N-acetyl-neuraminic) acid promotes biofilm formation by NTHi in vitro and bacterial persistence within the middle ear or lung in vivo. LOS from NTHi in biofilms was sialylated, as determined by comparison of electrophoretic mobilities and immunochemical reactivities before and after neuraminidase treatment. Biofilm formation was significantly reduced in media lacking sialic acid, and a siaB (CMP-sialic acid synthetase) mutant was deficient in biofilm formation in three different in vitro model systems. The persistence of an asialylated siaB mutant was attenuated in a gerbil middle ear infection model system, as well as in a rat pulmonary challenge model system. These data show that sialylated LOS glycoforms promote biofilm formation by NTHi and persistence in vivo.
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Affiliation(s)
- W Edward Swords
- Department of Microbiology and Immunology, Wake Forest University Health Sciences, Winston-Salem, North Carolina, USA.
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Abstract
The rationale for the use of single dose and shorter course azithromycin treatment regimens is based on the pharmacokinetic properties of azithromycin. The drug has a long elimination half-life (>50 h), which enables short course 1- or 3-day dose regimens to be clinically effective. Azithromycin is concentrated within phagocytic cells and tissues and it achieves targeted delivery by these cells to sites of infection. In vitro and in vivo models have demonstrated that azithromycin is taken up, transported and released at the sites of infection by phagocytic cells such as polymorphonuclear neutrophils and macrophages. Uptake is not saturable; therefore delivery of the total dose of azithromycin as a 1- or 3-day regimen should lead to increased uptake and delivery of the drug to sites of infection.
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Affiliation(s)
- Emma M Gordon
- Department of Pediatrics, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA
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Warren MJ, Jennings MP. Identification and characterization of pptA: a gene involved in the phase-variable expression of phosphorylcholine on pili of Neisseria meningitidis. Infect Immun 2004; 71:6892-8. [PMID: 14638777 PMCID: PMC308910 DOI: 10.1128/iai.71.12.6892-6898.2003] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Pili of pathogenic Neisseria are major virulence factors associated with adhesion, cytotoxicity, twitching motility, autoaggregation, and DNA transformation. Pili are modified posttranslationally by the addition of phosphorylcholine. However, no genes involved in either the biosynthesis or the transfer of phosphorylcholine in Neisseria meningitidis have been identified. In this study, we identified five candidate open reading frames (ORFs) potentially involved in the biosynthesis or transfer of phosphorylcholine to pilin in N. meningitidis. Insertional mutants were constructed for each ORF in N. meningitidis strain C311#3 to determine their effect on phosphorylcholine expression. The effect of the mutant ORFs on the modification by phosphorylcholine was analyzed by Western analysis with phosphorylcholine-specific monoclonal antibody TEPC-15. Analysis of the mutants showed that ORF NMB0415, now defined as pptA (pilin phosphorylcholine transferase A), is involved in the addition of phosphorylcholine to pilin in N. meningitidis. Additionally, the phase variation (high frequency on-off switching of expression) of phosphorylcholine on pilin is due to changes in a homopolymeric guanosine tract in pptA.
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Affiliation(s)
- Matthew J Warren
- Department of Microbiology and Parasitology, School of Molecular and Microbial Sciences, University of Queensland, Brisbane, Australia
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Mason KM, Munson RS, Bakaletz LO. Nontypeable Haemophilus influenzae gene expression induced in vivo in a chinchilla model of otitis media. Infect Immun 2003; 71:3454-62. [PMID: 12761130 PMCID: PMC155704 DOI: 10.1128/iai.71.6.3454-3462.2003] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The gram-negative bacterium nontypeable Haemophilus influenzae (NTHI) is the predominant pathogen in chronic otitis media with effusion and, with Streptococcus pneumoniae and Moraxella catarrhalis, is a causative agent of acute otitis media. To identify potential virulence determinants, bacterial gene expression was monitored by differential fluorescence induction during early disease progression in one specific anatomical niche of a chinchilla model of NTHI-induced otitis media. Genomic DNA fragments from NTHI strain 86-028NP were cloned upstream of the promoterless gfpmut3 gene. NTHI strain 86-028NP served as the host for the promoter trap library. Pools of 2,000 transformants were inoculated into the left and right middle ear cavities of chinchillas. Middle ear effusions were recovered by epitympanic tap at 24 and 48 h, and clones containing promoter elements that were induced in vivo and producing green fluorescent protein were isolated by two-color fluorescence-activated cell sorting. Insert DNA was sequenced and compared to the complete genome sequence of H. influenzae strain Rd. In a screen of 16,000 clones, we have isolated 44 clones that contain unique gene fragments encoding biosynthetic enzymes, metabolic and regulatory proteins, and hypothetical proteins of unknown function. An additional eight clones contain gene fragments unique to our NTHI isolate. Using quantitative reverse transcription-PCR, we have confirmed that 26 clones demonstrated increased gene expression in vivo relative to expression in vitro. These data provide insight into the response of NTHI bacteria as they sense and respond to the middle ear microenvironment during early events of otitis media.
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Affiliation(s)
- Kevin M Mason
- Columbus Children's Research Institute, Department of Pediatrics, The Ohio State University College of Medicine and Public Health, Columbus 43205, USA
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Cody AJ, Field D, Feil EJ, Stringer S, Deadman ME, Tsolaki AG, Gratz B, Bouchet V, Goldstein R, Hood DW, Moxon ER. High rates of recombination in otitis media isolates of non-typeable Haemophilus influenzae. INFECTION, GENETICS AND EVOLUTION : JOURNAL OF MOLECULAR EPIDEMIOLOGY AND EVOLUTIONARY GENETICS IN INFECTIOUS DISEASES 2003; 3:57-66. [PMID: 12797973 PMCID: PMC2728426 DOI: 10.1016/s1567-1348(02)00152-1] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Non-typeable (NT) or capsule-deficient, Haemophilus influenzae (Hi) is a common commensal of the upper respiratory tract of humans and can be pathogenic resulting in diseases such as otitis media, sinusitis and pneumonia. The lipopolysaccharide (LPS) of NTHi is a major virulence factor that displays substantial intra-strain and inter-strain variation of its oligosaccharide structures. To investigate the genetic basis of LPS variation we sequenced internal regions of each of seven genes required for the biosynthesis of either the inner or the outer core oligosaccharide structures. These sequences were obtained from 25 representative NTHi isolates from episodes of otitis media. We found abundant evidence of recombination among LPS genes of NTHi, a finding in marked contrast to previous analyses of biosynthetic genes for capsular polysaccharide, a well-documented virulence factor of Hi. We found mosaic sequences, linkage equilibrium between loci and a lack of congruence between gene trees. These high rates were not confined to LPS genes since evidence for similar amounts of recombination was also found in eight housekeeping genes in a subset of the same 25 isolates. These findings provide a population based foundation for a better understanding of the role of NTHi LPS as a virulence factor and its potential as a candidate vaccine.
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Affiliation(s)
- Alison J Cody
- Molecular Infectious Diseases Group, Department of Paediatrics, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford OX3 9DS, UK.
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Starner TD, Swords WE, Apicella MA, McCray PB. Susceptibility of nontypeable Haemophilus influenzae to human beta-defensins is influenced by lipooligosaccharide acylation. Infect Immun 2002; 70:5287-9. [PMID: 12183584 PMCID: PMC128250 DOI: 10.1128/iai.70.9.5287-5289.2002] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Nontypeable Haemophilus influenzae (NTHI) lipooligosaccharide htrB mutants exhibited greater than 45-fold-increased sensitivity to human beta-defensin 2 (HBD-2) compared to the wild type. Complementation by htrB in trans to acylation competence reversed this increased sensitivity. In contrast, NTHI was more susceptible to HBD-3 and showed no changes in sensitivity as a result of lipooligosaccharide mutations in oligosaccharide and lipid A biosynthesis genes.
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Affiliation(s)
- Timothy D Starner
- Department of Pediatrics, The University of Iowa, Iowa City, Iowa 52242, USA
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Swords WE, Chance DL, Cohn LA, Shao J, Apicella MA, Smith AL. Acylation of the lipooligosaccharide of Haemophilus influenzae and colonization: an htrB mutation diminishes the colonization of human airway epithelial cells. Infect Immun 2002; 70:4661-8. [PMID: 12117980 PMCID: PMC128210 DOI: 10.1128/iai.70.8.4661-4668.2002] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Haemophilus influenzae is a commensal and opportunistic pathogen of the human airways. A number of surface molecules contribute to colonization of the airways by H. influenzae, such as adhesins, including structures found in the lipooligosaccharide (LOS). A human bronchiolar xenograft model was employed to investigate the host-bacterial interactions involved in the colonization of the airway by H. influenzae. Differential display was used to identify H. influenzae mRNA that reflect genes which were preferentially expressed in the xenograft compared to growth. Eleven mRNA fragments had consistent increased expression when the bacteria grew in xenografts. On sequencing these fragments, eight open reading frames were identified. Three of these had no match in the NCBI or the TIGR database, while an additional three were homologous to genes involved in heme or iron acquisition and utilization: two of the mRNAs encoded proteins homologous to enzymes involved in LOS biosynthesis: a heptosyl transferase (rfaF) involved in the synthesis of the LOS core and a ketodeoxyoctonate phosphate-dependent acyltransferase (htrB) that performs one of the late acylation reactions in lipid A synthesis. Inoculation of human bronchiolar xenografts revealed a significant reduction in colonization capacity by htrB mutants. In vitro, htrB mutants elicited lesser degrees of cytoskeletal rearrangement and less stimulation of host cell signaling with 16HBE14o(-) cells and decreased intracellular survival. These results implicate acylation of H. influenzae lipid A as playing a key role in the organisms' colonization of the normal airway.
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Affiliation(s)
- W Edward Swords
- Department of Microbiology, University of Iowa, Iowa City, USA
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Pettigrew MM, Foxman B, Marrs CF, Gilsdorf JR. Identification of the lipooligosaccharide biosynthesis gene lic2B as a putative virulence factor in strains of nontypeable Haemophilus influenzae that cause otitis media. Infect Immun 2002; 70:3551-6. [PMID: 12065495 PMCID: PMC128108 DOI: 10.1128/iai.70.7.3551-3556.2002] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Nontypeable (NT) strains of Haemophilus influenzae are an important cause of acute otitis media (OM). The pathogenic process by which NT H. influenzae strains cause OM is poorly understood. In order to identify specific virulence factors important for OM pathogenesis, genomic subtraction of the NT H. influenzae middle ear isolate G622 against H. influenzae strain Rd was conducted and the resulting subtraction products were used to screen a panel of H. influenzae isolates. Subtraction identified 36 PCR fragments unique to strain G622, which were used in a preliminary screen of 48 middle ear isolates and 46 nasopharyngeal and throat isolates to identify genes found more frequently among middle ear isolates. These experiments identified a PCR fragment with high homology to the lipooligosaccharide biosynthesis gene lic2B (originally identified in an H. influenzae type b strain) among 52% of the middle ear isolates and 9% of nasopharyngeal and throat isolates. The lic2B gene cloned from NT H. influenzae strain G622 was 99% identical at the amino acid level to that of the H. influenzae type b strain RM7004. The lic2B gene was used to screen a larger panel of H. influenzae isolates including the original 48 middle ear isolates, 40 invasive type b isolates, 90 NT H. influenzae throat isolates from children attending day care, and 32 NT H. influenzae nasopharyngeal clinical isolates. The lic2B gene was found 3.7 times more frequently among middle ear isolates than in throat isolates from children attending day care. These data suggest that a specific NT H. influenzae gene is associated with OM.
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Affiliation(s)
- M M Pettigrew
- Department of Epidemiology, University of Michigan, Ann Arbor, Michigan 48109-2029, USA
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Bayliss CD, van de Ven T, Moxon ER. Mutations in polI but not mutSLH destabilize Haemophilus influenzae tetranucleotide repeats. EMBO J 2002; 21:1465-76. [PMID: 11889052 PMCID: PMC125930 DOI: 10.1093/emboj/21.6.1465] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Haemophilus influenzae (Hi), an obligate upper respiratory tract commensal/pathogen, uses phase variation (PV) to adapt to host environment changes. Switching occurs by slippage of nucleotide repeats (microsatellites) within genes coding for virulence molecules. Most such microsatellites in Hi are tetranucleotide repeats, but an exception is the dinucleotide repeats in the pilin locus. To investigate the effects on PV rates of mutations in genes for mismatch repair (MMR), insertion/deletion mutations of mutS, mutL, mutH, dam, polI, uvrD, mfd and recA were constructed in Hi strain Rd. Only inactivation of polI destabilized tetranucleotide (5'AGTC) repeat tracts of chromosomally located reporter constructs, whereas inactivation of mutS, but not polI, destabilized dinucleotide (5'AT) repeats. Deletions of repeats were predominant in polI mutants, which we propose are due to end-joining occurring without DNA polymerization during polI-deficient Okazaki fragment processing. The high prevalence of tetranucleotides mediating PV is an exceptional feature of the Hi genome. The refractoriness to MMR of hypermutation in Hi tetranucleotides facilitates adaptive switching without the deleterious increase in global mutation rates that accompanies a mutator genotype.
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Affiliation(s)
- Christopher D Bayliss
- Molecular Infectious Diseases Group, Department of Paediatrics, Weatherall Institute for Molecular Medicine, John Radcliffe Hospital, Headington, Oxford OX3 9DU, UK.
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