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Cheng KKW, Fingerhut L, Duncan S, Prajna NV, Rossi AG, Mills B. In vitro and ex vivo models of microbial keratitis: Present and future. Prog Retin Eye Res 2024; 102:101287. [PMID: 39004166 DOI: 10.1016/j.preteyeres.2024.101287] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2024] [Revised: 07/09/2024] [Accepted: 07/10/2024] [Indexed: 07/16/2024]
Abstract
Microbial keratitis (MK) is an infection of the cornea, caused by bacteria, fungi, parasites, or viruses. MK leads to significant morbidity, being the fifth leading cause of blindness worldwide. There is an urgent requirement to better understand pathogenesis in order to develop novel diagnostic and therapeutic approaches to improve patient outcomes. Many in vitro, ex vivo and in vivo MK models have been developed and implemented to meet this aim. Here, we present current in vitro and ex vivo MK model systems, examining their varied design, outputs, reporting standards, and strengths and limitations. Major limitations include their relative simplicity and the perceived inability to study the immune response in these MK models, an aspect widely accepted to play a significant role in MK pathogenesis. Consequently, there remains a dependence on in vivo models to study this aspect of MK. However, looking to the future, we draw from the broader field of corneal disease modelling, which utilises, for example, three-dimensional co-culture models and dynamic environments observed in bioreactors and organ-on-a-chip scenarios. These remain unexplored in MK research, but incorporation of these approaches will offer further advances in the field of MK corneal modelling, in particular with the focus of incorporation of immune components which we anticipate will better recapitulate pathogenesis and yield novel findings, therefore contributing to the enhancement of MK outcomes.
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Affiliation(s)
- Kelvin Kah Wai Cheng
- Centre for Inflammation Research, Institute of Regeneration and Repair, University of Edinburgh, United Kingdom
| | - Leonie Fingerhut
- Centre for Inflammation Research, Institute of Regeneration and Repair, University of Edinburgh, United Kingdom
| | - Sheelagh Duncan
- Centre for Inflammation Research, Institute of Regeneration and Repair, University of Edinburgh, United Kingdom
| | - N Venkatesh Prajna
- Department of Cornea and Refractive Surgery Services, Aravind Eye Hospital and Postgraduate Institute of Ophthalmology, Madurai, Tamil Nadu, India
| | - Adriano G Rossi
- Centre for Inflammation Research, Institute of Regeneration and Repair, University of Edinburgh, United Kingdom
| | - Bethany Mills
- Centre for Inflammation Research, Institute of Regeneration and Repair, University of Edinburgh, United Kingdom.
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2
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Resko ZJ, Suhi RF, Thota AV, Kroken AR. Evidence for intracellular Pseudomonas aeruginosa. J Bacteriol 2024; 206:e0010924. [PMID: 38597609 PMCID: PMC11112991 DOI: 10.1128/jb.00109-24] [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] [Indexed: 04/11/2024] Open
Abstract
Pseudomonas aeruginosa is a significant cause of global morbidity and mortality. Although it is often regarded as an extracellular pathogen toward human cells, numerous investigations report its ability to survive and replicate within host cells, and additional studies demonstrate specific mechanisms enabling it to adopt an intracellular lifestyle. This ability of P. aeruginosa remains less well-investigated than that of other intracellular bacteria, although it is currently gaining attention. If intracellular bacteria are not killed after entering host cells, they may instead receive protection from immune recognition and experience reduced exposure to antibiotic therapy, among additional potential advantages shared with other facultative intracellular pathogens. For this review, we compiled studies that observe intracellular P. aeruginosa across strains, cell types, and experimental systems in vitro, as well as contextualize these findings with the few studies that report similar observations in vivo. We also seek to address key findings that drove the perception that P. aeruginosa remains extracellular in order to reconcile what is currently understood about intracellular pathogenesis and highlight open questions regarding its contribution to disease.
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Affiliation(s)
- Zachary J. Resko
- Department of Microbiology and Immunology, Loyola University Chicago, Maywood, Illinois, USA
| | - Rachel F. Suhi
- Department of Microbiology and Immunology, Loyola University Chicago, Maywood, Illinois, USA
| | - Adam V. Thota
- Department of Microbiology and Immunology, Loyola University Chicago, Maywood, Illinois, USA
| | - Abby R. Kroken
- Department of Microbiology and Immunology, Loyola University Chicago, Maywood, Illinois, USA
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Verma N, Sharma T, Bhardwaj A, Vemuluri VR. Comparative genomics and characterization of a multidrug-resistant Acinetobacter baumannii VRL-M19 isolated from a crowded setting in India. INFECTION, GENETICS AND EVOLUTION : JOURNAL OF MOLECULAR EPIDEMIOLOGY AND EVOLUTIONARY GENETICS IN INFECTIOUS DISEASES 2024; 118:105549. [PMID: 38181886 DOI: 10.1016/j.meegid.2023.105549] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/31/2023] [Revised: 12/17/2023] [Accepted: 12/31/2023] [Indexed: 01/07/2024]
Abstract
A crowded vegetable market serves as a mass gathering, posing a potential risk for infection transmission. In this study, we isolated a multidrug-resistant Acinetobacter baumannii strain, VRL-M19, from the air of such a market and conducted comparative genomics and phenotypic characterization. Antimicrobial susceptibility testing, genome sequencing using Illumina HiSeq X10, and pan-genome analysis with 788 clinical isolates identified core, accessory, and unique drug-resistant determinants. Mutational analysis of drug-resistance genes, virulence factor annotation, in vitro pathogenicity assessment, subsystem analysis, Multilocus sequence typing, and whole genome phylogenetic analysis were performed. VRL-M19 exhibited multidrug resistance with 69 determinants, and analysis across 788 clinical isolates and 350 Indian isolates revealed more accessory genes (52 out of 69) in the Indian isolates. Multiple mutations were observed in drug target modification genes, and the strain was identified as a moderate biofilm-former with 55 virulence factors. Whole genome phylogenetics indicated a close relationship between VRL-M19 and clinical A. baumannii strains. In conclusion, our comprehensive study suggests that VRL-M19 is a multidrug-resistant, potential pathogen with biofilm-forming capabilities, closely associated with clinical A. baumannii strains.
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Affiliation(s)
- Neha Verma
- Microbial Type Culture Collection and Gene Bank (MTCC), CSIR-Institute of Microbial Technology, Chandigarh 160036, India; Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India
| | - Tina Sharma
- Bioinformatics Centre, CSIR-Institute of Microbial Technology, Chandigarh 160036, India; Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India
| | - Anshu Bhardwaj
- Bioinformatics Centre, CSIR-Institute of Microbial Technology, Chandigarh 160036, India; Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India.
| | - Venkata Ramana Vemuluri
- Microbial Type Culture Collection and Gene Bank (MTCC), CSIR-Institute of Microbial Technology, Chandigarh 160036, India; Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India.
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4
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Andriyanov PA, Kashina DD, Menshikova AN. Genomic analysis of multidrug-resistant Delftia tsuruhatensis isolated from raw bovine milk. Front Microbiol 2024; 14:1321122. [PMID: 38239723 PMCID: PMC10794605 DOI: 10.3389/fmicb.2023.1321122] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2023] [Accepted: 12/06/2023] [Indexed: 01/22/2024] Open
Abstract
Delftia tsuruhatensis is a gram-negative, aerobic bacterium mostly known as an organic pollutant degrading and growth-promoting microorganism. However, it recently emerged as an opportunistic human pathogen. To date, the source of D. tsuruhatensis infection is not clear. The majority of studies of D. tsuruhatensis have focused on environmental or clinical strains, while investigations of D. tsuruhatensis strains isolated from food sources are limited. In the present study, we report the case of D. tsuruhatensis isolation from raw bovine milk. Classical bacteriology approaches, as well as next-generation sequencing and comparative genomics, were used to characterize the features of the D. tsuruhatensis MR-6/3H strain. The MR-6/3H strain was resistant to 19 antimicrobials among 23 tested, including all aminoglycosides, phenicol, trimethoprim-sulfamethoxazole, and almost all β-lactams. Phylogenetically, the MR-6/3H was close to clinical origin strains, including those previously isolated in Russia. Comparative genomics revealed the presence of putative antimicrobial resistance genes in the MR-6/3H isolate, mostly associated with efflux systems. Notably, genus-specific OXA-926-like β-lactamase was also detected. In all, 27 putative virulence factors were predicted, the majority of which were associated with motility, adherence, stress survival, siderophore synthesis, and immunomodulation. In the MR-6/3H genome, the five prophage regions were identified, including two with intact levels. Integrons and CRISPR-Cas systems were not detected in the MR-6/3H isolate. Thus, our findings suggest that raw milk can be the potential source of and transmission route for the dissemination of multidrug-resistant D. tsuruhatensis.
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Affiliation(s)
- Pavel A. Andriyanov
- Federal Research Center for Virology and Microbiology, Branch in Nizhny Novgorod, Nizhny Novgorod, Russia
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Di Pilato V, Willison E, Marchese A. The microbiology and pathogenesis of nonfermenting Gram-negative infections. Curr Opin Infect Dis 2023; 36:537-544. [PMID: 37732777 PMCID: PMC10624403 DOI: 10.1097/qco.0000000000000969] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/22/2023]
Abstract
PURPOSE OF REVIEW This review provides an overview of most recent evidence about pathogenesis traits and virulence factors contributing to successful colonization or infection by P. aeruginosa , A. baumannii , S. maltophilia and B. cepacia complex, among the most clinically relevant nonfermenting Gram-negative bacteria (NFGNB). RECENT FINDINGS The growing clinical importance of NFGNB as important opportunistic pathogens causing difficult-to-treat infections in a fragile patients' population in stressed by numerous studies. Identification of novel virulence factors and deciphering of their mechanisms of action have greatly furthered our understanding of NFGNB pathogenesis, revealing that each pathogen-specific armamentarium of virulence factors (adhesins, motility, capsule, biofilm, lipopolysaccharide, exotoxins, exoenzymes, secretion systems, siderophores) can be likely responsible for the difference in the pathophysiology even in the context of a similar infection site. Emerging evidence of the immunomodulatory effect of some virulence factors is also acknowledged. SUMMARY NFGNB continue to be a serious global problem as cause of life-threatening opportunistic infections, owing to a highly heterogeneous content of virulence factors and their extensive number of intrinsic resistance mechanisms. Further efforts in development of novel effective antimicrobials and of alternative strategies targeting key virulence factors are warranted.
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Affiliation(s)
- Vincenzo Di Pilato
- Department of Surgical Sciences and Integrated Diagnostics (DISC), University of Genoa
| | - Edward Willison
- Microbiology Unit, IRCCS Ospedale Policlinico San Martino, Genoa, Italy
| | - Anna Marchese
- Department of Surgical Sciences and Integrated Diagnostics (DISC), University of Genoa
- Microbiology Unit, IRCCS Ospedale Policlinico San Martino, Genoa, Italy
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Hoque MN, Jahan MI, Hossain MA, Sultana M. Genomic diversity and molecular epidemiology of a multidrug-resistant Pseudomonas aeruginosa DMC30b isolated from a hospitalized burn patient in Bangladesh. J Glob Antimicrob Resist 2022; 31:110-118. [PMID: 36058512 DOI: 10.1016/j.jgar.2022.08.023] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2022] [Revised: 08/02/2022] [Accepted: 08/29/2022] [Indexed: 12/30/2022] Open
Abstract
OBJECTIVES Pseudomonas aeruginosa is a key opportunistic pathogen causing a wide range of community- and hospital-acquired infections in immunocompromised or catheterized patients. Here, we report the complete genome sequence of a multidrug-resistant (MDR) P. aeruginosa DMC30b to elucidate the genetic diversity, molecular epidemiology, and underlying mechanisms for antimicrobial resistance and virulence. METHODS P. aeruginosa DMC30b was isolated from septic wound swab of a severe burn patient. Whole-genome sequencing was performed under Ion Torrent platform. The genome was assembled using the SPAdes v. 3.12.01 in an integrated Genome Analysis Platform for Ion Torrent sequence data. The genome was annotated using the National Center for Biotechnology Information (NCBI) Prokaryotic Genome Annotation Pipeline. In-silico predictions of antimicrobial resistance genes, virulence factor genes, and metabolic functional potentials were performed using different curated bioinformatics tools. RESULTS P. aeruginosa DMC30b was found as a MDR strain and belonged to sequence type 244 (ST244). The complete genome size is 6 994 756 bp with a coverage of 76.76x, guanine-cytosine content of 65.7% and a Benchmarking Universal Single-Copy Orthologs score of 100. The genome of P. aeruginosa DMC30b harboured two predicted plasmid replicons (e,g. IncP-6; 78 007 bp and ColRNAI; 9359 bp), 35 resistomes (antimicrobial resistance genes) conferring resistance to 18 different antibiotics (including four beta-lactam classes), and 214 virulence factor genes. It was identified as the 167th ST244 strain among ∼ 5800 whole-genome sequences of P. aeruginosa available in the NCBI database. CONCLUSION The MDR P. aeruginosa DMC30b was identified as the 167th ST244 complete genome to be submitted to the NCBI, and the first ST244 isolate sequenced from Bangladesh. The complete genome data with high genetic diversity and underlying mechanisms for antimicrobial resistance and virulence of P. aeruginosa DMC30b will aid in understanding the evolution and phylogeny of such high-risk clones and provide a solid basis for further research on MDR or extensively drug resistant strains.
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Affiliation(s)
- M Nazmul Hoque
- Department of Gynaecology, Obstetrics and Reproductive Health, Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur, Bangladesh
| | - M Ishrat Jahan
- Department of Microbiology, University of Dhaka, Dhaka, Bangladesh
| | - M Anwar Hossain
- Department of Microbiology, University of Dhaka, Dhaka, Bangladesh
| | - Munawar Sultana
- Department of Microbiology, University of Dhaka, Dhaka, Bangladesh.
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Ma X, Liu Q, Song F, Huang Y. Differentially Expressed Genes of Pseudomonas aeruginosa Isolates from Eyes with Keratitis and Healthy Conjunctival Sacs. Infect Drug Resist 2022; 15:4495-4506. [PMID: 35983295 PMCID: PMC9380828 DOI: 10.2147/idr.s374335] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2022] [Accepted: 08/06/2022] [Indexed: 11/23/2022] Open
Abstract
Background Pseudomonas aeruginosa (P. aeruginosa) is the second-most common commensal bacterium in healthy conjunctival sacs. When the corneal epithelial barrier is damaged, P. aeruginosa in a healthy conjunctival sac can cause infectious keratitis, which can result in the loss of vision. This study was designed to investigate the differentially expressed genes (DEGs) of P. aeruginosa isolates from eyes with keratitis and from healthy conjunctival sacs to predict their functions and pathways through Illumina high-throughput RNA sequencing (RNA-seq). Methods P. aeruginosa isolates from keratitis and healthy conjunctival sacs were obtained. The transcriptome profile of P. aeruginosa was characterized by a high throughput RNA-seq strategy using the Illumina HiSeq 2500 platform. The DEGs were analyzed with DESeq and validated through quantitative real-time polymerase chain reaction (PCR) and with experimental mice. GO enrichment and the KEGG pathway were also analyzed. Results In genome-wide transcriptional analysis, 557 genes (332 upregulated and 225 downregulated) were found to be differentially expressed (fold change ≥ 2, p ≤ 0.05) in the strains from keratitis. GO enrichment analysis suggested that DEGs tended to be associated with cellular and metabolic processes. KEGG pathway analysis revealed the DEGs were typically associated with the pathways of the bacterial secretion system and pyoverdine metabolism. Eleven DEGs were validated using quantitative reverse-transcription PCR and verified with experimental mice. The results were consistent with those obtained in RNA-seq. Conclusion The DEGs related to pilin, T2SS, T3SS, and pyoverdine metabolisms were significantly altered in the strains from keratitis. The findings may be helpful for further investigations on genes or pathways related to the pathogenesis of and therapeutic targets for P. aeruginosa keratitis.
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Affiliation(s)
- Xiubin Ma
- Department of Ophthalmology, Eye Institute of Shandong First Medical University, Qingdao Eye Hospital of Shandong First Medical University, Qingdao, People's Republic of China.,State Key Laboratory Cultivation Base, Shandong Provincial Key Laboratory of Ophthalmology, Shandong Eye Institute, Qingdao, People's Republic of China.,Department of Ophthalmology, School of Ophthalmology, Shandong First Medical University, Qingdao, People's Republic of China
| | - Qing Liu
- Department of Ophthalmology, Eye Institute of Shandong First Medical University, Qingdao Eye Hospital of Shandong First Medical University, Qingdao, People's Republic of China.,State Key Laboratory Cultivation Base, Shandong Provincial Key Laboratory of Ophthalmology, Shandong Eye Institute, Qingdao, People's Republic of China.,Department of Ophthalmology, School of Ophthalmology, Shandong First Medical University, Qingdao, People's Republic of China
| | - Fangying Song
- Department of Ophthalmology, Eye Institute of Shandong First Medical University, Qingdao Eye Hospital of Shandong First Medical University, Qingdao, People's Republic of China.,State Key Laboratory Cultivation Base, Shandong Provincial Key Laboratory of Ophthalmology, Shandong Eye Institute, Qingdao, People's Republic of China.,Department of Ophthalmology, School of Ophthalmology, Shandong First Medical University, Qingdao, People's Republic of China
| | - Yusen Huang
- Department of Ophthalmology, Eye Institute of Shandong First Medical University, Qingdao Eye Hospital of Shandong First Medical University, Qingdao, People's Republic of China.,State Key Laboratory Cultivation Base, Shandong Provincial Key Laboratory of Ophthalmology, Shandong Eye Institute, Qingdao, People's Republic of China.,Department of Ophthalmology, School of Ophthalmology, Shandong First Medical University, Qingdao, People's Republic of China
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8
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Chang YF, Cheng YH, Ko YC, Chiou SH, Jui-Ling Liu C. Development of topical chitosan/ β-glycerophosphate-based hydrogel loaded with levofloxacin in the treatment of keratitis: An ex-vivo study. Heliyon 2022; 8:e08697. [PMID: 35028471 PMCID: PMC8741500 DOI: 10.1016/j.heliyon.2021.e08697] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2021] [Revised: 10/18/2021] [Accepted: 12/27/2021] [Indexed: 12/03/2022] Open
Abstract
Staphylococcus species are responsible for most cases of post-operative endophthalmitis. Topical ocular drug was applied for post-operative infection prevention, but the way of delivery encounters many challenges in terms of patient's compliance, drug efficacy, and drug penetration. We used the levofloxacin-loaded chitosan/gelatin/β-glycerophosphate hydrogel sustained releasing system with good in vitro anti-bacterial efficacy and biocompatibility, which we had previously designed, for ex vivo keratitis model to test the preclinical drug efficacy and to determine drug level in the anterior chamber of the eye. The result showed that the ex-vivo corneal keratitis model with S. aureus infection revealed mild opacity over the central cornea with stromal infiltrate, but without obvious stromal infiltration post levofloxacin-loaded hydrogel treatment after 24 h of infection. Quantification of viable bacteria showed a significant anti-bacterial activity. The histological evidence also showed no visible S. aureus after levofloxacin-loaded hydrogel treatment, with a significant anti-inflammatory effect. We also examined the drug concentration in the aqueous humor 24 h after instilling one drop of the levofloxacin-loaded hydrogel. The concentration achieved to a desired drug level. These results suggested that by the ex-vivo model, levofloxacin-loaded hydrogel can be applied for treatment in post-operative endophthalmitis or keratitis after the ophthalmic surgery.
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Affiliation(s)
- Yu-Fan Chang
- Institute of Clinical Medicine, National Yang-Ming University, Taipei 112, Taiwan
- Institute of Clinical Medicine, National Yang Ming Chiao Tung University, Taipei 112, Taiwan
- National Yang Ming Chiao Tung University School of Medicine, Taipei, Taiwan
- Department of Ophthalmology, Taipei Veterans General Hospital, Taipei, Taiwan
| | - Yung-Hsin Cheng
- Department of Materials Science and Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan
| | - Yu-Chieh Ko
- National Yang Ming Chiao Tung University School of Medicine, Taipei, Taiwan
- Department of Ophthalmology, Taipei Veterans General Hospital, Taipei, Taiwan
| | - Shih-Hwa Chiou
- Institute of Clinical Medicine, National Yang-Ming University, Taipei 112, Taiwan
- Institute of Clinical Medicine, National Yang Ming Chiao Tung University, Taipei 112, Taiwan
- National Yang Ming Chiao Tung University School of Medicine, Taipei, Taiwan
- Department of Ophthalmology, Taipei Veterans General Hospital, Taipei, Taiwan
| | - Catherine Jui-Ling Liu
- National Yang Ming Chiao Tung University School of Medicine, Taipei, Taiwan
- Department of Ophthalmology, Taipei Veterans General Hospital, Taipei, Taiwan
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Morin CD, Déziel E, Gauthier J, Levesque RC, Lau GW. An Organ System-Based Synopsis of Pseudomonas aeruginosa Virulence. Virulence 2021; 12:1469-1507. [PMID: 34180343 PMCID: PMC8237970 DOI: 10.1080/21505594.2021.1926408] [Citation(s) in RCA: 33] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Driven in part by its metabolic versatility, high intrinsic antibiotic resistance, and a large repertoire of virulence factors, Pseudomonas aeruginosa is expertly adapted to thrive in a wide variety of environments, and in the process, making it a notorious opportunistic pathogen. Apart from the extensively studied chronic infection in the lungs of people with cystic fibrosis (CF), P. aeruginosa also causes multiple serious infections encompassing essentially all organs of the human body, among others, lung infection in patients with chronic obstructive pulmonary disease, primary ciliary dyskinesia and ventilator-associated pneumonia; bacteremia and sepsis; soft tissue infection in burns, open wounds and postsurgery patients; urinary tract infection; diabetic foot ulcers; chronic suppurative otitis media and otitis externa; and keratitis associated with extended contact lens use. Although well characterized in the context of CF, pathogenic processes mediated by various P. aeruginosa virulence factors in other organ systems remain poorly understood. In this review, we use an organ system-based approach to provide a synopsis of disease mechanisms exerted by P. aeruginosa virulence determinants that contribute to its success as a versatile pathogen.
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Affiliation(s)
- Charles D Morin
- Centre Armand-Frappier Santé Biotechnologie, Institut National De La Recherche Scientifique (INRS), Laval, Quebec, Canada
| | - Eric Déziel
- Centre Armand-Frappier Santé Biotechnologie, Institut National De La Recherche Scientifique (INRS), Laval, Quebec, Canada
| | - Jeff Gauthier
- Département De Microbiologie-infectiologie Et Immunologie, Institut De Biologie Intégrative Et Des Systèmes (IBIS), Université Laval, Québec City, Quebec, Canada
| | - Roger C Levesque
- Département De Microbiologie-infectiologie Et Immunologie, Institut De Biologie Intégrative Et Des Systèmes (IBIS), Université Laval, Québec City, Quebec, Canada
| | - Gee W Lau
- Department of Pathobiology, University of Illinois at Urbana-Champaign, Urbana, IL, US
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Yaeger LN, Coles VE, Chan DCK, Burrows LL. How to kill Pseudomonas-emerging therapies for a challenging pathogen. Ann N Y Acad Sci 2021; 1496:59-81. [PMID: 33830543 DOI: 10.1111/nyas.14596] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2020] [Revised: 03/08/2021] [Accepted: 03/11/2021] [Indexed: 12/16/2022]
Abstract
As the number of effective antibiotics dwindled, antibiotic resistance (AR) became a pressing concern. Some Pseudomonas aeruginosa isolates are resistant to all available antibiotics. In this review, we identify the mechanisms that P. aeruginosa uses to evade antibiotics, including intrinsic, acquired, and adaptive resistance. Our review summarizes many different approaches to overcome resistance. Antimicrobial peptides have potential as therapeutics with low levels of resistance evolution. Rationally designed bacteriophage therapy can circumvent and direct evolution of AR and virulence. Vaccines and monoclonal antibodies are highlighted as immune-based treatments targeting specific P. aeruginosa antigens. This review also identifies promising drug combinations, antivirulence therapies, and considerations for new antipseudomonal discovery. Finally, we provide an update on the clinical pipeline for antipseudomonal therapies and recommend future avenues for research.
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Affiliation(s)
- Luke N Yaeger
- Department of Biochemistry and Biomedical Sciences and M.G. DeGroote Institute for Infectious Disease Research, McMaster University, Hamilton, Ontario, Canada
| | - Victoria E Coles
- Department of Biochemistry and Biomedical Sciences and M.G. DeGroote Institute for Infectious Disease Research, McMaster University, Hamilton, Ontario, Canada
| | - Derek C K Chan
- Department of Biochemistry and Biomedical Sciences and M.G. DeGroote Institute for Infectious Disease Research, McMaster University, Hamilton, Ontario, Canada
| | - Lori L Burrows
- Department of Biochemistry and Biomedical Sciences and M.G. DeGroote Institute for Infectious Disease Research, McMaster University, Hamilton, Ontario, Canada
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Szczotka-Flynn LB, Shovlin JP, Schnider CM, Caffery BE, Alfonso EC, Carnt NA, Chalmers RL, Collier S, Jacobs DS, Joslin CE, Kroken AR, Lakkis C, Pearlman E, Schein OD, Stapleton F, Tu E, Willcox MDP. American Academy of Optometry Microbial Keratitis Think Tank. Optom Vis Sci 2021; 98:182-198. [PMID: 33771951 PMCID: PMC8075116 DOI: 10.1097/opx.0000000000001664] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
SIGNIFICANCE Think Tank 2019 affirmed that the rate of infection associated with contact lenses has not changed in several decades. Also, there is a trend toward more serious infections associated with Acanthamoeba and fungi. The growing use of contact lenses in children demands our attention with surveillance and case-control studies. PURPOSE The American Academy of Optometry (AAO) gathered researchers and key opinion leaders from around the world to discuss contact lens-associated microbial keratitis at the 2019 AAO Annual Meeting. METHODS Experts presented within four sessions. Session 1 covered the epidemiology of microbial keratitis, pathogenesis of Pseudomonas aeruginosa, and the role of lens care systems and storage cases in corneal disease. Session 2 covered nonbacterial forms of keratitis in contact lens wearers. Session 3 covered future needs, challenges, and research questions in relation to microbial keratitis in youth and myopia control, microbiome, antimicrobial surfaces, and genetic susceptibility. Session 4 covered compliance and communication imperatives. RESULTS The absolute rate of microbial keratitis has remained very consistent for three decades despite new technologies, and extended wear significantly increases the risk. Improved oxygen delivery afforded by silicone hydrogel lenses has not impacted the rates, and although the introduction of daily disposable lenses has minimized the risk of severe disease, there is no consistent evidence that they have altered the overall rate of microbial keratitis. Overnight orthokeratology lenses may increase the risk of microbial keratitis, especially secondary to Acanthamoeba, in children. Compliance remains a concern and a significant risk factor for disease. New insights into host microbiome and genetic susceptibility may uncover new theories. More studies such as case-control designs suited for rare diseases and registries are needed. CONCLUSIONS The first annual AAO Think Tank acknowledged that the risk of microbial keratitis has not decreased over decades, despite innovation. Important questions and research directions remain.
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Affiliation(s)
| | | | | | | | - Eduardo C Alfonso
- Bascom Palmer Eye Institute, University of Miami Miller School of Medicine, Miami, Florida
| | - Nicole A Carnt
- School of Optometry and Vision Science, University of New South Wales, Sydney, New South Wales, Australia
| | | | - Sarah Collier
- U.S. Centers for Disease Control and Prevention, Atlanta, Georgia
| | - Deborah S Jacobs
- Massachusetts Eye and Ear, Cornea Service, Harvard Medical School, Boston, Massachusetts
| | - Charlotte E Joslin
- Department of Ophthalmology and Visual Science, College of Medicine, Division of Epidemiology and Biostatistics, School of Public Health, University of Illinois at Chicago, Chicago, Illinois
| | - Abby R Kroken
- School of Optometry, University of California, Berkeley, Berkeley, California
| | | | - Eric Pearlman
- Departments of Ophthalmology, and Physiology and Biophysics, University of California, Irvine, Irvine, California
| | - Oliver D Schein
- Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland
| | - Fiona Stapleton
- School of Optometry and Vision Science, University of New South Wales, Sydney, New South Wales, Australia
| | - Elmer Tu
- University of Illinois Eye and Ear Infirmary, Chicago, Illinois
| | - Mark D P Willcox
- School of Optometry and Vision Science, University of New South Wales, Sydney, New South Wales, Australia
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Muhammad MH, Idris AL, Fan X, Guo Y, Yu Y, Jin X, Qiu J, Guan X, Huang T. Beyond Risk: Bacterial Biofilms and Their Regulating Approaches. Front Microbiol 2020; 11:928. [PMID: 32508772 PMCID: PMC7253578 DOI: 10.3389/fmicb.2020.00928] [Citation(s) in RCA: 288] [Impact Index Per Article: 72.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2020] [Accepted: 04/20/2020] [Indexed: 12/24/2022] Open
Abstract
Bacterial biofilms are complex surface attached communities of bacteria held together by self-produced polymer matrixs mainly composed of polysaccharides, secreted proteins, and extracellular DNAs. Bacterial biofilm formation is a complex process and can be described in five main phases: (i) reversible attachment phase, where bacteria non-specifically attach to surfaces; (ii) irreversible attachment phase, which involves interaction between bacterial cells and a surface using bacterial adhesins such as fimbriae and lipopolysaccharide (LPS); (iii) production of extracellular polymeric substances (EPS) by the resident bacterial cells; (iv) biofilm maturation phase, in which bacterial cells synthesize and release signaling molecules to sense the presence of each other, conducing to the formation of microcolony and maturation of biofilms; and (v) dispersal/detachment phase, where the bacterial cells depart biofilms and comeback to independent planktonic lifestyle. Biofilm formation is detrimental in healthcare, drinking water distribution systems, food, and marine industries, etc. As a result, current studies have been focused toward control and prevention of biofilms. In an effort to get rid of harmful biofilms, various techniques and approaches have been employed that interfere with bacterial attachment, bacterial communication systems (quorum sensing, QS), and biofilm matrixs. Biofilms, however, also offer beneficial roles in a variety of fields including applications in plant protection, bioremediation, wastewater treatment, and corrosion inhibition amongst others. Development of beneficial biofilms can be promoted through manipulation of adhesion surfaces, QS and environmental conditions. This review describes the events involved in bacterial biofilm formation, lists the negative and positive aspects associated with bacterial biofilms, elaborates the main strategies currently used to regulate establishment of harmful bacterial biofilms as well as certain strategies employed to encourage formation of beneficial bacterial biofilms, and highlights the future perspectives of bacterial biofilms.
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Affiliation(s)
| | | | | | | | | | | | | | | | - Tianpei Huang
- State Key Laboratory of Ecological Pest Control for Fujian and Taiwan Crops & Key Laboratory of Biopesticide and Chemical Biology of Ministry of Education, College of Life Sciences & College of Plant Protection & International College, Fujian Agriculture and Forestry University, Fuzhou, China
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Ayoub Moubareck C, Hammoudi Halat D. Insights into Acinetobacter baumannii: A Review of Microbiological, Virulence, and Resistance Traits in a Threatening Nosocomial Pathogen. Antibiotics (Basel) 2020; 9:antibiotics9030119. [PMID: 32178356 PMCID: PMC7148516 DOI: 10.3390/antibiotics9030119] [Citation(s) in RCA: 212] [Impact Index Per Article: 53.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2020] [Revised: 03/01/2020] [Accepted: 03/02/2020] [Indexed: 12/12/2022] Open
Abstract
Being a multidrug-resistant and an invasive pathogen, Acinetobacter baumannii is one of the major causes of nosocomial infections in the current healthcare system. It has been recognized as an agent of pneumonia, septicemia, meningitis, urinary tract and wound infections, and is associated with high mortality. Pathogenesis in A. baumannii infections is an outcome of multiple virulence factors, including porins, capsules, and cell wall lipopolysaccharide, enzymes, biofilm production, motility, and iron-acquisition systems, among others. Such virulence factors help the organism to resist stressful environmental conditions and enable development of severe infections. Parallel to increased prevalence of infections caused by A. baumannii, challenging and diverse resistance mechanisms in this pathogen are well recognized, with major classes of antibiotics becoming minimally effective. Through a wide array of antibiotic-hydrolyzing enzymes, efflux pump changes, impermeability, and antibiotic target mutations, A. baumannii models a unique ability to maintain a multidrug-resistant phenotype, further complicating treatment. Understanding mechanisms behind diseases, virulence, and resistance acquisition are central to infectious disease knowledge about A. baumannii. The aims of this review are to highlight infections and disease-producing factors in A. baumannii and to touch base on mechanisms of resistance to various antibiotic classes.
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Affiliation(s)
- Carole Ayoub Moubareck
- College of Natural and Health Sciences, Zayed University, Dubai P.O. Box 144534, UAE
- Correspondence: ; Tel.: +971-4-402-1745
| | - Dalal Hammoudi Halat
- Department of Pharmaceutical Sciences, School of Pharmacy, Lebanese International University, Beirut, Bekaa Campuses 1103, Lebanon;
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Fleiszig SMJ, Kroken AR, Nieto V, Grosser MR, Wan SJ, Metruccio MME, Evans DJ. Contact lens-related corneal infection: Intrinsic resistance and its compromise. Prog Retin Eye Res 2019; 76:100804. [PMID: 31756497 DOI: 10.1016/j.preteyeres.2019.100804] [Citation(s) in RCA: 66] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2019] [Revised: 11/05/2019] [Accepted: 11/12/2019] [Indexed: 12/20/2022]
Abstract
Contact lenses represent a widely utilized form of vision correction with more than 140 million wearers worldwide. Although generally well-tolerated, contact lenses can cause corneal infection (microbial keratitis), with an approximate annualized incidence ranging from ~2 to ~20 cases per 10,000 wearers, and sometimes resulting in permanent vision loss. Research suggests that the pathogenesis of contact lens-associated microbial keratitis is complex and multifactorial, likely requiring multiple conspiring factors that compromise the intrinsic resistance of a healthy cornea to infection. Here, we outline our perspective of the mechanisms by which contact lens wear sometimes renders the cornea susceptible to infection, focusing primarily on our own research efforts during the past three decades. This has included studies of host factors underlying the constitutive barrier function of the healthy cornea, its response to bacterial challenge when intrinsic resistance is not compromised, pathogen virulence mechanisms, and the effects of contact lens wear that alter the outcome of host-microbe interactions. For almost all of this work, we have utilized the bacterium Pseudomonas aeruginosa because it is the leading cause of lens-related microbial keratitis. While not yet common among corneal isolates, clinical isolates of P. aeruginosa have emerged that are resistant to virtually all currently available antibiotics, leading the United States CDC (Centers for Disease Control) to add P. aeruginosa to its list of most serious threats. Compounding this concern, the development of advanced contact lenses for biosensing and augmented reality, together with the escalating incidence of myopia, could portent an epidemic of vision-threatening corneal infections in the future. Thankfully, technological advances in genomics, proteomics, metabolomics and imaging combined with emerging models of contact lens-associated P. aeruginosa infection hold promise for solving the problem - and possibly life-threatening infections impacting other tissues.
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Affiliation(s)
- Suzanne M J Fleiszig
- School of Optometry, University of California, Berkeley, CA, USA; Graduate Group in Vision Science, University of California, Berkeley, CA, USA; Graduate Groups in Microbiology and Infectious Diseases & Immunity, University of California, Berkeley, CA, USA.
| | - Abby R Kroken
- School of Optometry, University of California, Berkeley, CA, USA
| | - Vincent Nieto
- School of Optometry, University of California, Berkeley, CA, USA
| | | | - Stephanie J Wan
- Graduate Group in Vision Science, University of California, Berkeley, CA, USA
| | | | - David J Evans
- School of Optometry, University of California, Berkeley, CA, USA; College of Pharmacy, Touro University California, Vallejo, CA, USA
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DMBT1 inhibition of Pseudomonas aeruginosa twitching motility involves its N-glycosylation and cannot be conferred by the Scavenger Receptor Cysteine-Rich bacteria-binding peptide domain. Sci Rep 2019; 9:13146. [PMID: 31511582 PMCID: PMC6739395 DOI: 10.1038/s41598-019-49543-w] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2019] [Accepted: 08/22/2019] [Indexed: 01/18/2023] Open
Abstract
The scavenging capacity of glycoprotein DMBT1 helps defend mucosal epithelia against microbes. DMBT1 binding to multiple bacterial species involves its conserved Scavenger Receptor Cysteine-Rich (SRCR) domains, localized to a 16-mer consensus sequence peptide, SRCRP2. Previously, we showed that DMBT1 bound Pseudomonas aeruginosa pili, and inhibited twitching motility, a pilus-mediated movement important for virulence. Here, we determined molecular characteristics required for twitching motility inhibition. Heat-denatured DMBT1 lost capacity to inhibit twitching motility and showed reduced pili binding (~40%). Size-exclusion chromatography of Lys-C-digested native DMBT1 showed that only high-Mw fractions retained activity, suggesting involvement of the N-terminal containing repeated SRCR domains with glycosylated SRCR-Interspersed Domains (SIDs). However, individual or pooled consensus sequence peptides (SRCRPs 1 to 7) showed no activity and did not bind P. aeruginosa pili; nor did recombinant DMBT1 (aa 1–220) or another SRCR-rich glycoprotein, CD163. Enzymatic de-N-glycosylation of DMBT1, but not de-O-glycosylation, reduced its capacity to inhibit twitching motility (~57%), without reducing pili binding. Therefore, DMBT1 inhibition of P. aeruginosa twitching motility involves its N-glycosylation, its pili-binding capacity is insufficient, and it cannot be conferred by the SRCR bacteria-binding peptide domain, either alone or mixed with other unlinked SRCRPs, suggesting an additional mechanism for DMBT1-mediated mucosal defense.
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Geisinger E, Huo W, Hernandez-Bird J, Isberg RR. Acinetobacter baumannii: Envelope Determinants That Control Drug Resistance, Virulence, and Surface Variability. Annu Rev Microbiol 2019; 73:481-506. [DOI: 10.1146/annurev-micro-020518-115714] [Citation(s) in RCA: 53] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Acinetobacter baumannii has emerged as an important nosocomial pathogen, particularly for patients in intensive care units and with invasive indwelling devices. The most recent clinical isolates are resistant to several classes of clinically important antibiotics, greatly restricting the ability to effectively treat critically ill patients. The bacterial envelope is an important driver of A. baumannii disease, both at the level of battling against antibiotic therapy and at the level of protecting from host innate immune function. This review provides a comprehensive overview of key features of the envelope that interface with both the host and antimicrobial therapies. Carbohydrate structures that contribute to protecting from the host are detailed, and mutations that alter these structures, resulting in increased antimicrobial resistance, are explored. In addition, protein complexes involved in both intermicrobial and host-microbe interactions are described. Finally we discuss regulatory mechanisms that control the nature of the cell envelope and its impact on host innate immune function.
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Affiliation(s)
- Edward Geisinger
- Department of Biology, Northeastern University, Boston, Massachusetts 02115, USA
| | - Wenwen Huo
- Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, Massachusetts 02111, USA
| | - Juan Hernandez-Bird
- Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, Massachusetts 02111, USA
| | - Ralph R. Isberg
- Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, Massachusetts 02111, USA
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Nieto V, Kroken AR, Grosser MR, Smith BE, Metruccio MME, Hagan P, Hallsten ME, Evans DJ, Fleiszig SMJ. Type IV Pili Can Mediate Bacterial Motility within Epithelial Cells. mBio 2019; 10:e02880-18. [PMID: 31431558 PMCID: PMC6703432 DOI: 10.1128/mbio.02880-18] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2018] [Accepted: 07/31/2019] [Indexed: 02/07/2023] Open
Abstract
Pseudomonas aeruginosa is among bacterial pathogens capable of twitching motility, a form of surface-associated movement dependent on type IV pili (T4P). Previously, we showed that T4P and twitching were required for P. aeruginosa to cause disease in a murine model of corneal infection, to traverse human corneal epithelial multilayers, and to efficiently exit invaded epithelial cells. Here, we used live wide-field fluorescent imaging combined with quantitative image analysis to explore how twitching contributes to epithelial cell egress. Results using time-lapse imaging of cells infected with wild-type PAO1 showed that cytoplasmic bacteria slowly disseminated throughout the cytosol at a median speed of >0.05 μm s-1 while dividing intracellularly. Similar results were obtained with flagellin (fliC) and flagellum assembly (flhA) mutants, thereby excluding swimming, swarming, and sliding as mechanisms. In contrast, pilA mutants (lacking T4P) and pilT mutants (twitching motility defective) appeared stationary and accumulated in expanding aggregates during intracellular division. Transmission electron microscopy confirmed that these mutants were not trapped within membrane-bound cytosolic compartments. For the wild type, dissemination in the cytosol was not prevented by the depolymerization of actin filaments using latrunculin A and/or the disruption of microtubules using nocodazole. Together, these findings illustrate a novel form of intracellular bacterial motility differing from previously described mechanisms in being directly driven by bacterial motility appendages (T4P) and not depending on polymerized host actin or microtubules.IMPORTANCE Host cell invasion can contribute to disease pathogenesis by the opportunistic pathogen Pseudomonas aeruginosa Previously, we showed that the type III secretion system (T3SS) of invasive P. aeruginosa strains modulates cell entry and subsequent escape from vacuolar trafficking to host lysosomes. However, we also showed that mutants lacking either type IV pili (T4P) or T4P-dependent twitching motility (i) were defective in traversing cell multilayers, (ii) caused less pathology in vivo, and (iii) had a reduced capacity to exit invaded cells. Here, we report that after vacuolar escape, intracellular P. aeruginosa can use T4P-dependent twitching motility to disseminate throughout the host cell cytoplasm. We further show that this strategy for intracellular dissemination does not depend on flagellin and resists both host actin and host microtubule disruption. This differs from mechanisms used by previously studied pathogens that utilize either host actin or microtubules for intracellular dissemination independently of microbe motility appendages.
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Affiliation(s)
- Vincent Nieto
- School of Optometry, University of California, Berkeley, California, USA
| | - Abby R Kroken
- School of Optometry, University of California, Berkeley, California, USA
| | - Melinda R Grosser
- School of Optometry, University of California, Berkeley, California, USA
| | - Benjamin E Smith
- Vision Science Program, University of California, Berkeley, California, USA
| | | | - Patrick Hagan
- Undergraduate Research Apprentice Program, University of California, Berkeley, California, USA
| | - Mary E Hallsten
- Undergraduate Research Apprentice Program, University of California, Berkeley, California, USA
| | - David J Evans
- School of Optometry, University of California, Berkeley, California, USA
- College of Pharmacy, Touro University California, Vallejo, California, USA
| | - Suzanne M J Fleiszig
- School of Optometry, University of California, Berkeley, California, USA
- Vision Science Program, University of California, Berkeley, California, USA
- Graduate Group in Microbiology, University of California, Berkeley, California, USA
- Graduate Group in Infectious Diseases and Immunity, University of California, Berkeley, California, USA
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Dolzani L, Milan A, Scocchi M, Lagatolla C, Bressan R, Benincasa M. Sub-MIC effects of a proline-rich antibacterial peptide on clinical isolates of Acinetobacter baumannii. J Med Microbiol 2019; 68:1253-1265. [PMID: 31215857 DOI: 10.1099/jmm.0.001028] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
INTRODUCTION Acinetobacter baumannii is one of the most important nosocomial pathogens, mainly due to its ability to accumulate antibiotic-resistances and to persist in the hospital environment - characteristics related to biofilm production. It is well-known that A. baumannii is inhibited by the proline-rich peptide Bac7(1-35), but its putative effects at sub-MICs were never considered. AIMS We examined the sub-MIC effect of Bac7(1-35) on the growth rate, resistance induction and some A. baumannii features linked to virulence. METHODOLOGY Growth kinetics in the presence of sub-MICs of Bac7(1-35) were evaluated spectrophotometrically. Peptide uptake was quantified by cytometric analysis. The ability of Bac7(1-35) to interfere with biofilm production was investigated by the crystal violet method and confocal microscopy. Bacterial motility was observed at the interphase between a layer of a semi-solid medium and the polystyrene bottom of a Petri dish. The induction of resistance was evaluated after serial passages with sub-MICs of the peptide. RESULTS Although the MIC of Bac7(1-35) was between 2-4 µM for all tested strains, its effect on the growth rate at sub-MICs was strain-dependent and correlated with the amount of peptide internalized by each strain. Sub-MICs of Bac7(1-35) induced a strongly strain-dependent effect on biofilm formation and reduced motility in almost all strains, but interestingly the peptide did not induce resistance. CONCLUSION Bac7(1-35) is internalized into A. baumannii and is able to inhibit biofilm formation and bacterial motility, without inducing resistance. This study stresses the importance of considering possible effects that antimicrobials could have at sub-MICs, mimicking a common condition during antibiotic treatment.
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Affiliation(s)
- Lucilla Dolzani
- Department of Life Sciences, University of Trieste, Trieste, Italy
| | - Annalisa Milan
- Department of Life Sciences, University of Trieste, Trieste, Italy
| | - Marco Scocchi
- Department of Life Sciences, University of Trieste, Trieste, Italy
| | | | - Raffaela Bressan
- Department of Life Sciences, University of Trieste, Trieste, Italy
| | - Monica Benincasa
- Department of Life Sciences, University of Trieste, Trieste, Italy
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Glycoprotein 340 in mucosal immunity and ocular surface. Ocul Surf 2018; 16:282-288. [DOI: 10.1016/j.jtos.2018.04.006] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2018] [Revised: 04/18/2018] [Accepted: 04/24/2018] [Indexed: 12/16/2022]
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Smith B, Li J, Metruccio M, Wan S, Evans D, Fleiszig S. Quantification of Bacterial Twitching Motility in Dense Colonies Using Transmitted Light Microscopy and Computational Image Analysis. Bio Protoc 2018; 8:e2804. [DOI: 10.21769/bioprotoc.2804] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022] Open
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Callegan MC, Parkunan SM, Randall CB, Coburn PS, Miller FC, LaGrow AL, Astley RA, Land C, Oh SY, Schneewind O. The role of pili in Bacillus cereus intraocular infection. Exp Eye Res 2017; 159:69-76. [PMID: 28336259 PMCID: PMC5492386 DOI: 10.1016/j.exer.2017.03.007] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2016] [Revised: 03/09/2017] [Accepted: 03/16/2017] [Indexed: 12/15/2022]
Abstract
Bacterial endophthalmitis is a potentially blinding intraocular infection. The bacterium Bacillus cereus causes a devastating form of this disease which progresses rapidly, resulting in significant inflammation and loss of vision within a few days. The outer surface of B. cereus incites the intraocular inflammatory response, likely through interactions with innate immune receptors such as TLRs. This study analyzed the role of B. cereus pili, adhesion appendages located on the bacterial surface, in experimental endophthalmitis. To test the hypothesis that the presence of pili contributed to intraocular inflammation and virulence, we analyzed the progress of experimental endophthalmitis in mouse eyes infected with wild type B. cereus (ATCC 14579) or its isogenic pilus-deficient mutant (ΔbcpA-srtD-bcpB or ΔPil). One hundred CFU were injected into the mid-vitreous of one eye of each mouse. Infections were analyzed by quantifying intraocular bacilli and retinal function loss, and by histology from 0 to 12 h postinfection. In vitro growth and hemolytic phenotypes of the infecting strains were also compared. There was no difference in hemolytic activity (1:8 titer), motility, or in vitro growth (p > 0.05, every 2 h, 0-18 h) between wild type B. cereus and the ΔPil mutant. However, infected eyes contained greater numbers of wild type B. cereus than ΔPil during the infection course (p ≤ 0.05, 3-12 h). Eyes infected with wild type B. cereus experienced greater losses in retinal function than eyes infected with the ΔPil mutant, but the differences were not always significant. Eyes infected with ΔPil or wild type B. cereus achieved similar degrees of severe inflammation. The results indicated that the intraocular growth of pilus-deficient B. cereus may have been better controlled, leading to a trend of greater retinal function in eyes infected with the pilus-deficient strain. Although this difference was not enough to significantly alter the severity of the inflammatory response, these results suggest a potential role for pili in protecting B. cereus from clearance during the early stages of endophthalmitis, which is a newly described virulence mechanism for this organism and this infection.
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Affiliation(s)
- Michelle C. Callegan
- Department of Ophthalmology, University of Oklahoma Health Sciences Center, 608 Stanton L. Young Blvd., Oklahoma City, OK 73104, USA,Department of Microbiology and Immunology, University of Oklahoma Health Sciences Center, 950 Stanton L. Young Blvd., Oklahoma City, OK 73104, USA,Dean A. McGee Eye Institute, Oklahoma City Oklahoma USA,Corresponding author: DMEI PA-418, 608 Stanton L. Young Blvd., Oklahoma City, OK 73104, USA. Phone: (405) 271-3674, Fax: (405) 271-8128,
| | - Salai Madhumathi Parkunan
- Department of Microbiology and Immunology, University of Oklahoma Health Sciences Center, 950 Stanton L. Young Blvd., Oklahoma City, OK 73104, USA
| | - C. Blake Randall
- Department of Ophthalmology, University of Oklahoma Health Sciences Center, 608 Stanton L. Young Blvd., Oklahoma City, OK 73104, USA
| | - Phillip S. Coburn
- Department of Ophthalmology, University of Oklahoma Health Sciences Center, 608 Stanton L. Young Blvd., Oklahoma City, OK 73104, USA
| | - Frederick C. Miller
- Department of Cell Biology, University of Oklahoma Health Sciences Center, 950 Stanton L. Young Blvd., Oklahoma City, OK 73104, USA
| | - Austin L. LaGrow
- Department of Ophthalmology, University of Oklahoma Health Sciences Center, 608 Stanton L. Young Blvd., Oklahoma City, OK 73104, USA
| | - Roger A. Astley
- Department of Ophthalmology, University of Oklahoma Health Sciences Center, 608 Stanton L. Young Blvd., Oklahoma City, OK 73104, USA
| | - Craig Land
- Department of Ophthalmology, University of Oklahoma Health Sciences Center, 608 Stanton L. Young Blvd., Oklahoma City, OK 73104, USA
| | - So-Young Oh
- Department of Microbiology, University of Chicago, 920 East 58
| | - Olaf Schneewind
- Department of Microbiology, University of Chicago, 920 East 58
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Mucosal fluid glycoprotein DMBT1 suppresses twitching motility and virulence of the opportunistic pathogen Pseudomonas aeruginosa. PLoS Pathog 2017; 13:e1006392. [PMID: 28489917 PMCID: PMC5440049 DOI: 10.1371/journal.ppat.1006392] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2017] [Revised: 05/22/2017] [Accepted: 04/28/2017] [Indexed: 12/22/2022] Open
Abstract
It is generally thought that mucosal fluids protect underlying epithelial surfaces against opportunistic infection via their antimicrobial activity. However, our published data show that human tear fluid can protect against the major opportunistic pathogen Pseudomonas aeruginosa independently of bacteriostatic activity. Here, we explored the mechanisms for tear protection, focusing on impacts of tear fluid on bacterial virulence factor expression. Results showed that tear fluid suppressed twitching motility, a type of surface-associated movement conferred by pili. Previously, we showed that twitching is critical for P. aeruginosa traversal of corneal epithelia, exit from epithelial cells after internalization, and corneal virulence. Inhibition of twitching by tear fluid was dose-dependent with dilutions to 6.25% retaining activity. Purified lactoferrin, lysozyme, and contrived tears containing these, and many other, tear components lacked the activity. Systematic protein fractionation, mass spectrometry, and immunoprecipitation identified the glycoprotein DMBT1 (Deleted in Malignant Brain Tumors 1) in tear fluid as required. DMBT1 purified from human saliva also inhibited twitching, as well as P. aeruginosa traversal of human corneal epithelial cells in vitro, and reduced disease pathology in a murine model of corneal infection. DMBT1 did not affect PilA expression, nor bacterial intracellular cyclicAMP levels, and suppressed twitching motility of P. aeruginosa chemotaxis mutants (chpB, pilK), and an adenylate cyclase mutant (cyaB). However, dot-immunoblot assays showed purified DMBT1 binding of pili extracted from PAO1 suggesting that twitching inhibition may involve a direct interaction with pili. The latter could affect extension or retraction of pili, their interactions with biotic or abiotic surfaces, or cause their aggregation. Together, the data suggest that DMBT1 inhibition of twitching motility contributes to the mechanisms by which mucosal fluids protect against P. aeruginosa infection. This study also advances our understanding of how mucosal fluids protect against infection, and suggests directions for novel biocompatible strategies to protect our surface epithelia against a major opportunistic pathogen.
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Genetic Determinants of Salmonella enterica Serovar Typhimurium Proliferation in the Cytosol of Epithelial Cells. Infect Immun 2016; 84:3517-3526. [PMID: 27698022 DOI: 10.1128/iai.00734-16] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2016] [Accepted: 09/26/2016] [Indexed: 11/20/2022] Open
Abstract
Intestinal epithelial cells provide an important colonization niche for Salmonella enterica serovar Typhimurium during gastrointestinal infections. In infected epithelial cells, a subpopulation of S Typhimurium bacteria damage their internalization vacuole, leading to escape from the Salmonella-containing vacuole (SCV) and extensive proliferation in the cytosol. Little is known about the bacterial determinants of nascent SCV lysis and subsequent survival and replication of Salmonella in the cytosol. To pinpoint S Typhimurium virulence factors responsible for these steps in the intracellular infectious cycle, we screened a S Typhimurium multigene deletion library in Caco-2 C2Bbe1 and HeLa epithelial cells for mutants that had an altered proportion of cytosolic bacteria compared to the wild type. We used a gentamicin protection assay in combination with a chloroquine resistance assay to quantify total and cytosolic bacteria, respectively, for each strain. Mutants of three S Typhimurium genes, STM1461 (ydgT), STM2829 (recA), and STM3952 (corA), had reduced cytosolic proliferation compared to wild-type bacteria, and one gene, STM2120 (asmA), displayed increased cytosolic replication. None of the mutants were affected for lysis of the nascent SCV or vacuolar replication in epithelial cells, indicating that these genes are specifically required for survival and proliferation of S Typhimurium in the epithelial cell cytosol. These are the first genes identified to contribute to this step of the S Typhimurium infectious cycle.
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Pinnock A, Shivshetty N, Roy S, Rimmer S, Douglas I, MacNeil S, Garg P. Ex vivo rabbit and human corneas as models for bacterial and fungal keratitis. Graefes Arch Clin Exp Ophthalmol 2016; 255:333-342. [PMID: 27844206 PMCID: PMC5285415 DOI: 10.1007/s00417-016-3546-0] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2016] [Revised: 10/23/2016] [Accepted: 10/31/2016] [Indexed: 11/25/2022] Open
Abstract
PURPOSE In the study of microbial keratitis, in vivo animal models often require a large number of animals, and in vitro monolayer cell culture does not maintain the three-dimensional structure of the tissues or cell-to-cell communication of in vivo models. Here, we propose reproducible ex vivo models of single- and dual-infection keratitis as an alternative to in vivo and in vitro models. METHODS Excised rabbit and human corneoscleral rims maintained in organ culture were infected using 108 cells of Staphylococcus aureus, Pseudomonas aeruginosa, Candida albicans or Fusarium solani. The infection was introduced by wounding with a scalpel and exposing corneas to the microbial suspension or by intrastromal injection. Post-inoculation, corneas were maintained for 24 and 48 h at 37 °C. After incubation, corneas were either homogenised to determine colony-forming units (CFU)/cornea or processed for histological examination using routine staining methods. Single- and mixed-species infections were compared. RESULTS We observed a significant increase in CFU after 48 h compared to 24 h with S. aureus and P. aeruginosa. However, no such increase was observed in corneas infected with C. albicans or F. solani. The injection method yielded an approximately two- to 100-fold increase (p < 0.05) in the majority of organisms from infected corneas. Histology of the scalpel-wounded and injection models indicated extensive infiltration of P. aeruginosa throughout the entire cornea, with less infiltration observed for S. aureus, C. albicans and F. solani. The models also supported dual infections. CONCLUSIONS Both scalpel wounding and injection methods are suitable for inducing infection of ex vivo rabbit and human cornea models. These simple and reproducible models will be useful as an alternative to in vitro and in vivo models for investigating the detection and treatment of microbial keratitis, particularly when this might be due to two infective organisms.
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Affiliation(s)
| | | | - Sanhita Roy
- LV Prasad Eye Institute, Banjara Hills, Hyderabad, 500034, India
| | | | - Ian Douglas
- University of Sheffield, Sheffield, S10 2TA, UK
| | - Sheila MacNeil
- University of Sheffield, Sheffield, S10 2TA, UK.
- The Kroto Research Institute, North Campus, University of Sheffield, Broad Lane, Sheffield, S3 7HQ, UK.
| | - Prashant Garg
- LV Prasad Eye Institute, Banjara Hills, Hyderabad, 500034, India
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Shikata M, Hayashi N, Fujimoto A, Nakamura T, Matsui N, Ishiyama A, Maekawa Y, Gotoh N. The pilT gene contributes to type III ExoS effector injection into epithelial cells in Pseudomonas aeruginosa. J Infect Chemother 2016; 22:216-20. [PMID: 26809217 DOI: 10.1016/j.jiac.2015.12.012] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2015] [Revised: 12/16/2015] [Accepted: 12/19/2015] [Indexed: 01/12/2023]
Abstract
A type IV pilus filament, mainly composed of PilA, is retracted by the driving power generated by PilT and PilU ATPases. pilA is required for injection of type III ExoS effectors into epithelial cells thereby facilitating Pseudomonas aeruginosa penetration through the epithelial barrier by impairing the defense function of tight junctions. Here, we examined whether the pilT and pilU of the P. aeruginosa PAO1 strain are required for ExoS injection into epithelial cells. We measured the quantity of ExoS injected into epithelial cells, and found that within such cells its quantity decreased by 80% (ΔpilA strain), 75% (ΔpilT strain), and 30% (ΔpilU strain) compared with the wild-type strain. pilT deficiency decreased the disruption of human epithelial colorectal adenocarcinoma (Caco-2) cell monolayers to the same extent as that of pilA and exoS deficiency, whereas pilU deficiency decreased disruption of the monolayers less than deficiency of the other genes. pilT and pilU deficiency decreased bacterial penetration of the Caco-2 cell monolayers to the same level as pilA and exoS deficiency. Our data showed that the pilU gene expression level was reduced in the PAO1 strain after adhesion to Caco-2 cell surfaces, but the expression levels of the pilA and pilT genes did not change. We conclude that P. aeruginosa injects ExoS into cells through the function of type IV pilus retraction, and that pilT makes a greater contribution to this process than pilU.
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Affiliation(s)
- Mototsugu Shikata
- Department of Microbiology and Infection Control Science, Kyoto Pharmaceutical University, Yamashina, Kyoto 607-8414, Japan
| | - Naoki Hayashi
- Department of Microbiology and Infection Control Science, Kyoto Pharmaceutical University, Yamashina, Kyoto 607-8414, Japan
| | - Akiyo Fujimoto
- Department of Microbiology and Infection Control Science, Kyoto Pharmaceutical University, Yamashina, Kyoto 607-8414, Japan
| | - Takano Nakamura
- Department of Microbiology and Infection Control Science, Kyoto Pharmaceutical University, Yamashina, Kyoto 607-8414, Japan
| | - Naoyuki Matsui
- Department of Microbiology and Infection Control Science, Kyoto Pharmaceutical University, Yamashina, Kyoto 607-8414, Japan
| | - Ayana Ishiyama
- Department of Microbiology and Infection Control Science, Kyoto Pharmaceutical University, Yamashina, Kyoto 607-8414, Japan
| | - Yui Maekawa
- Department of Microbiology and Infection Control Science, Kyoto Pharmaceutical University, Yamashina, Kyoto 607-8414, Japan
| | - Naomasa Gotoh
- Department of Microbiology and Infection Control Science, Kyoto Pharmaceutical University, Yamashina, Kyoto 607-8414, Japan.
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The importance of the Pseudomonas aeruginosa type III secretion system in epithelium traversal depends upon conditions of host susceptibility. Infect Immun 2015; 83:1629-40. [PMID: 25667266 DOI: 10.1128/iai.02329-14] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Pseudomonas aeruginosa is invasive or cytotoxic to host cells, depending on the type III secretion system (T3SS) effectors encoded. While the T3SS is known to be involved in disease in vivo, how it participates remains to be clarified. Here, mouse models of superficial epithelial injury (tissue paper blotting with EGTA treatment) and immunocompromise (MyD88 deficiency) were used to study the contribution of the T3SS transcriptional activator ExsA to epithelial traversal. Corneas of excised eyeballs were inoculated with green fluorescent protein (GFP)-expressing PAO1 or isogenic exsA mutants for 6 h ex vivo before bacterial traversal and epithelial thickness were quantified by using imaging. In the blotting-EGTA model, exsA mutants were defective in capacity for traversal. Accordingly, an ∼16-fold variability in exsA expression among PAO1 isolates from three sources correlated with epithelial loss. In contrast, MyD88-/- epithelia remained susceptible to P. aeruginosa traversal despite exsA mutation. Epithelial lysates from MyD88-/- mice had reduced antimicrobial activity compared to those from wild-type mice with and without prior antigen challenge, particularly 30- to 100-kDa fractions, for which mass spectrometry revealed multiple differences, including (i) lower baseline levels of histones, tubulin, and lumican and (ii) reduced glutathione S-transferase, annexin, and dermatopontin, after antigen challenge. Thus, the importance of ExsA in epithelial traversal by invasive P. aeruginosa depends on the compromise enabling susceptibility, suggesting that strategies for preventing infection will need to extend beyond targeting the T3SS. The data also highlight the importance of mimicking conditions allowing susceptibility in animal models and the need to monitor variability among bacterial isolates from different sources, even for the same strain.
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Eijkelkamp BA, Stroeher UH, Hassan KA, Paulsen IT, Brown MH. Comparative analysis of surface-exposed virulence factors of Acinetobacter baumannii. BMC Genomics 2014; 15:1020. [PMID: 25422040 PMCID: PMC4256060 DOI: 10.1186/1471-2164-15-1020] [Citation(s) in RCA: 82] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2014] [Accepted: 11/14/2014] [Indexed: 01/19/2023] Open
Abstract
Background Acinetobacter baumannii is a significant hospital pathogen, particularly due to the dissemination of highly multidrug resistant isolates. Genome data have revealed that A. baumannii is highly genetically diverse, which correlates with major variations seen at the phenotypic level. Thus far, comparative genomic studies have been aimed at identifying resistance determinants in A. baumannii. In this study, we extend and expand on these analyses to gain greater insight into the virulence factors across eight A. baumannii strains which are clonally, temporally and geographically distinct, and includes an isolate considered non-pathogenic and a community-acquired A. baumannii. Results We have identified a large number of genes in the A. baumannii genomes that are known to play a role in virulence in other pathogens, such as the recently studied proline-alanine-alanine-arginine (PAAR)-repeat domains of the type VI secretion systems. Not surprising, many virulence candidates appear to be part of the A. baumannii core genome of virulent isolates but were often found to be insertionally disrupted in the avirulent A. baumannii strain SDF. Our study also reveals that many known or putative virulence determinants are restricted to specific clonal lineages, which suggests that these virulence determinants may be crucial for the success of these widespread common clones. It has previously been suggested that the high level of intrinsic and adaptive resistance has enabled the widespread presence of A. baumannii in the hospital environment. This appears to have facilitated the expansion of its repertoire of virulence traits, as in general, the nosocomial strains in this study possess more virulence genes compared to the community-acquired isolate. Conclusions Major genetic variation in known or putative virulence factors was seen across the eight strains included in this study, suggesting that virulence mechanisms are complex and multifaceted in A. baumannii. Overall, these analyses increase our understanding of A. baumannii pathogenicity and will assist in future studies determining the significance of virulence factors within clonal lineages and/or across the species. Electronic supplementary material The online version of this article (doi:10.1186/1471-2164-15-1020) contains supplementary material, which is available to authorized users.
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Affiliation(s)
| | | | | | | | - Melissa H Brown
- School of Biological Sciences, Flinders University, Adelaide, Australia.
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Pseudomonas aeruginosa AlgR phosphorylation modulates rhamnolipid production and motility. J Bacteriol 2013; 195:5499-515. [PMID: 24097945 DOI: 10.1128/jb.00726-13] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
AlgR is a key Pseudomonas aeruginosa transcriptional response regulator required for virulence. AlgR activates alginate production and twitching motility but represses the Rhl quorum-sensing (QS) system, including rhamnolipid production. The role of AlgR phosphorylation is enigmatic, since phosphorylated AlgR (AlgR-P) is required for twitching motility through the fimU promoter but is not required for the activation of alginate production. In order to examine the role of AlgR phosphorylation in vivo, a PAO1 algRD54E strain (with algR encoding a D-to-E change at position 54), which constitutively activates fimU transcription and exhibits twitching motility, was created. A corresponding PAO1 algRD54N strain (with algR encoding a D-to-N change at position 54) that does not activate fimU or twitching motility was compared to PAO1, PAO1 algRD54E, PAO1 ΔalgZ (deletion of the algZ [fimS] gene, encoding a putative histidine kinase), and PAO1 ΔalgR for swarming motility, rhamnolipid production, and rhlA transcription. PAO1 and PAO1 algRD54E produced approximately 2-fold-higher levels of rhamnolipids than PAO1 algRD54N and PAO1 ΔalgZ, thereby indicating that phosphorylated AlgR is required for normal rhamnolipid production. Examination of purified AlgR, AlgR-P, AlgR D54N, and AlgR D54E showed that AlgR-P and AlgR D54E bound preferentially to the fimU and rhlA promoters. Additionally, AlgR-P bound specifically to two sites within the rhlA promoter that were not bound by unphosphorylated AlgR. Taken together, these results indicate that phosphorylated AlgR-P has increased affinity for the rhlA promoter and is required for the coordinate activation of twitching motility, rhamnolipid production, and swarming motility in P. aeruginosa.
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Evans DJ, Fleiszig SM. Why does the healthy cornea resist Pseudomonas aeruginosa infection? Am J Ophthalmol 2013; 155:961-970.e2. [PMID: 23601656 DOI: 10.1016/j.ajo.2013.03.001] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2012] [Revised: 03/01/2013] [Accepted: 03/04/2013] [Indexed: 10/26/2022]
Abstract
PURPOSE To provide our perspective on why the cornea is resistant to infection based on our research results with Pseudomonas (P) aeruginosa. We focus on our current understanding of the interplay between bacteria, tear fluid, and the corneal epithelium that determines health as the usual outcome, and propose a theoretical model for how contact lens wear might change those interactions to enable susceptibility to P aeruginosa infection. METHODS Use of "null-infection" in vivo models, cultured human corneal epithelial cells, contact lens-wearing animal models, and bacterial genetics help to elucidate mechanisms by which P aeruginosa survives at the ocular surface, adheres, and traverses multilayered corneal epithelia. These models also help elucidate the molecular mechanisms of corneal epithelial innate defense. RESULTS Tear fluid and the corneal epithelium combine to make a formidable defense against P aeruginosa infection of the cornea. Part of that defense involves the expression of antimicrobials such as β-defensins, the cathelicidin LL-37, cytokeratin-derived antimicrobial peptides, and RNase7. Immunomodulators such as SP-D and ST2 also contribute. Innate defenses of the cornea depend in part on MyD88, a key adaptor protein of TLR and IL-1R signaling, but the basal lamina represents the final barrier to bacterial penetration. Overcoming these defenses involves P aeruginosa adaptation, expression of the type III secretion system, proteases, and P aeruginosa biofilm formation on contact lenses. CONCLUSION After more than 2 decades of research focused on understanding how contact lens wear predisposes to P aeruginosa infection, our working hypothesis places blame for microbial keratitis on bacterial adaptation to ocular surface defenses, combined with changes to the biochemistry of the corneal surface caused by trapping bacteria and tear fluid against the cornea under the lens.
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H-NS plays a role in expression of Acinetobacter baumannii virulence features. Infect Immun 2013; 81:2574-83. [PMID: 23649094 DOI: 10.1128/iai.00065-13] [Citation(s) in RCA: 78] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Acinetobacter baumannii has become a major problem in the clinical setting with the prevalence of infections caused by multidrug-resistant strains on the increase. Nevertheless, only a limited number of molecular mechanisms involved in the success of A. baumannii as a human pathogen have been described. In this study, we examined the virulence features of a hypermotile derivative of A. baumannii strain ATCC 17978, which was found to display enhanced adherence to human pneumocytes and elevated levels of lethality toward Caenorhabditis elegans nematodes. Analysis of cellular lipids revealed modifications to the fatty acid composition, providing a possible explanation for the observed changes in hydrophobicity and subsequent alteration in adherence and motility. Comparison of the genome sequences of the hypermotile variant and parental strain revealed that an insertion sequence had disrupted an hns-like gene in the variant. This gene encodes a homologue of the histone-like nucleoid structuring (H-NS) protein, a known global transcriptional repressor. Transcriptome analysis identified the global effects of this mutation on gene expression, with major changes seen in the autotransporter Ata, a type VI secretion system, and a type I pilus cluster. Interestingly, isolation and analysis of a second independent hypermotile ATCC 17978 variant revealed a mutation to a residue within the DNA binding region of H-NS. Taken together, these mutants indicate that the phenotypic and transcriptomic differences seen are due to loss of regulatory control effected by H-NS.
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Type IV pilus protein PilA of Pseudomonas aeruginosa modulates calcium signaling through binding the calcium-modulating cyclophilin ligand. J Infect Chemother 2013; 19:653-64. [DOI: 10.1007/s10156-012-0536-y] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2012] [Accepted: 12/06/2012] [Indexed: 01/07/2023]
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Teuchner B, Eitzinger C, Lutz M, Hager T, Schmid E, Bechrakis NE, Zuck M, Jekle A, Debabov D, Anderson M, Nagl M. N-chlorotaurine and its analogues N,N-dichloro-2,2-dimethyltaurine and N-monochloro-2,2-dimethyltaurine are safe and effective bactericidal agents in ex vivo corneal infection models. Acta Ophthalmol 2012; 90:e632-7. [PMID: 22971221 DOI: 10.1111/j.1755-3768.2012.02501.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
PURPOSE N-chlorotaurine (NCT) and its analogues N-monochloro-2,2-dimethyltaurine (NVC-612) and N-dichloro-2,2-dimethyltaurine (NVC-422) are new anti-infectives for topical treatment for conjunctivitis. The aim of this study was to show that these compounds are safe in an EpiOcular model and effective in corneas infected ex vivo. METHODS Corneal buttons were excised from porcine eyes. In 183 of the 229 corneas, erosion and artificial superficial stromal incision were induced. They were bathed in suspensions of Pseudomonas aeruginosa or Staphylococcus aureus for 24 hr at 37°C and incubated in solutions of the test substances at 37°C and pH 7.1. Subsequently, they were subjected to histology (n = 20) or homogenized followed by quantitative bacterial cultures (n = 209). Ocular irritation was tested using the EpiOcular™ tissue system (MatTek Corporation). RESULTS Bacterial accumulations were detected histologically both on the corneal surface and also in the anterior third of the stroma of incised corneal buttons. All three test compounds at a concentration of 55 mm (equals 1% NCT) reduced the bacterial counts of P. aeruginosa and S. aureus by approximately 5 log10 after 60- and 120-min incubation, respectively. Significant killing was observed as early as after 5-min incubation. Also intrastromal bacteria were inactivated. In the EpiOcular™ tissue model, NCT, NVC-422 and NVC-612 had no or very low potential to irritate corneal tissue. CONCLUSION N-chlorotaurine, NVC-422 and NVC-612 are non-irritating in cornea and kill P. aeruginosa and S. aureus, even following penetration into the deeper corneal stromal layers.
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Affiliation(s)
- Barbara Teuchner
- Department of Ophthalmology, Innsbruck Medical University, Innsbruck, Austria
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Affiliation(s)
- Lori L. Burrows
- Department of Biochemistry and Biomedical Sciences, Michael G. DeGroote Institute for Infectious Disease Research, McMaster University, Hamilton, ON L8N 3Z5, Canada;
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Burrows LL. Prime time for minor subunits of the type II secretion and type IV pilus systems. Mol Microbiol 2012; 86:765-9. [PMID: 22998166 DOI: 10.1111/mmi.12034] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/07/2012] [Indexed: 10/27/2022]
Abstract
The type II secretion system (T2SS) exports folded proteins from the periplasms of Gram-negative bacteria. The type IV pilus system (T4PS) is a multifunctional machine used for adherence, motility and DNA transfer in bacteria and archaea. Partial sequence identity between the two systems suggests that they are related and might function via a similar mechanism, the dynamic assembly and disassembly of pseudopilus (T2SS) or pilus (T4PS) filaments. The major subunit in each system is thought to form the bulk of the (pseudo)pilus, while minor (low-abundance) subunits have proposed roles in assembly initiation, antagonism of disassembly, or modulation of (pseudo)pilus functional properties. In this issue, Cisneros et al. () extend their previous finding that pseudopilus assembly is primed by the minor pseudopilins, showing that the same proteins can initiate assembly of Escherichia coli T4P. Similarly, they show that the E. coli minor pilins prime the polymerization of T2S pseudopili, although unlike genuine pseudopili, the chimeric filaments did not support secretion. This work reinforces the notion of a common assembly mechanism for the T2S and T4P systems.
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Affiliation(s)
- Lori L Burrows
- Department of Biochemistry and Biomedical Sciences, the Michael G. DeGroote Institute for Infectious Diseases Research, McMaster University, Hamilton, Ontario, Canada, L8S4K1.
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Extracellular stress and lipopolysaccharide modulate Acinetobacter baumannii surface-associated motility. J Microbiol 2012; 50:434-43. [PMID: 22752907 DOI: 10.1007/s12275-012-1555-1] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2011] [Accepted: 02/07/2012] [Indexed: 10/28/2022]
Abstract
Acinetobacter baumannii is a nosocomial bacterial pathogen, and infections attributed to this species are further complicated by a remarkable ability to acquire antimicrobial resistance genes and to survive in a desiccated state. While the antibiotic resistance and biofilm formation of A. baumannii is well-documented, less is known about the virulence attributes of this organism. Recent studies reported A. baumannii strains display a motility phenotype, which appears to be partially dependent upon Type IV pili, autoinducer molecules, and the response to blue light. In this study, we wanted to determine the prevalence of this trait in genetically diverse clinical isolates, and any additional required factors, and environmental cues that regulate motility. When strains are subjected to a wide array of stress conditions, A. baumannii motility is significantly reduced. In contrast, when extracellular iron is provided or salinity is reduced, motility is significantly enhanced. We further investigated whether the genes required for the production of lipopolysaccharide (lpsB) and K1 capsule (epsA/ptk) are required for motility as demonstrated in other Gram-negative bacteria. Transposon mutagenesis resulted in reduced motility by the insertion derivatives of each of these genes. The presence of the parental allele provided in trans, in the insertion mutant background, could only restore motility in the lpsB mutant. The production of core LPS directly contributes to the motility phenotype, while capsular polysaccharide may have an indirect effect. Further, the data suggest motility is regulated by extracellular conditions, indicating that A. baumannii is actively sensing the environment and responding accordingly.
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Skiebe E, de Berardinis V, Morczinek P, Kerrinnes T, Faber F, Lepka D, Hammer B, Zimmermann O, Ziesing S, Wichelhaus TA, Hunfeld KP, Borgmann S, Gröbner S, Higgins PG, Seifert H, Busse HJ, Witte W, Pfeifer Y, Wilharm G. Surface-associated motility, a common trait of clinical isolates of Acinetobacter baumannii, depends on 1,3-diaminopropane. Int J Med Microbiol 2012; 302:117-28. [PMID: 22560766 DOI: 10.1016/j.ijmm.2012.03.003] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2011] [Revised: 02/22/2012] [Accepted: 03/05/2012] [Indexed: 01/05/2023] Open
Abstract
While flagella-independent motility has long been described in representatives of the genus Acinetobacter, the mechanism of motility remains ambiguous. Acinetobacter baumannii, a nosocomial pathogen appearing increasingly multidrug-resistant, may profit from motility during infection or while persisting in the hospital environment. However, data on the frequency of motility skills among clinical A. baumannii isolates is scarce. We have screened a collection of 83 clinical A. baumannii isolates of different origin and found that, with the exception of one isolate, all were motile on wet surfaces albeit to varying degrees and exhibiting differing morphologies. Screening a collection of transposon mutants of strain ATCC 17978 for motility defects, we identified 2 akinetic mutants carrying transposon insertions in the dat and ddc gene, respectively. These neighbouring genes contribute to synthesis of 1,3-diaminopropane (DAP), a polyamine ubiquitously produced in Acinetobacter. Supplementing semi-solid media with DAP cured the motility defect of both mutants. HPLC analyses confirmed that DAP synthesis was abolished in ddc and dat mutants of different A. baumannii isolates and was re-established after genetic complementation. Both, the dat and ddc mutant of ATCC 17978 were attenuated in the Galleria mellonella caterpillar infection model. Taken together, surface-associated motility is a common trait of clinical A. baumannii isolates that requires DAP and may play a role in its virulence.
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Affiliation(s)
- Evelyn Skiebe
- Robert Koch-Institute, Wernigerode Branch, D-38855 Wernigerode, Germany
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Ramirez JC, Fleiszig SMJ, Sullivan AB, Tam C, Borazjani R, Evans DJ. Traversal of multilayered corneal epithelia by cytotoxic Pseudomonas aeruginosa requires the phospholipase domain of exoU. Invest Ophthalmol Vis Sci 2012; 53:448-53. [PMID: 22167094 DOI: 10.1167/iovs.11-8999] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
PURPOSE Pseudomonas aeruginosa isolates from microbial keratitis are invasive or cytotoxic toward mammalian cells, depending on their type III secreted toxins. Cytotoxic strains express ExoU, a phospholipase that contributes to corneal virulence. This study determined whether the ExoU phospholipase domain is required for P. aeruginosa traversal of the human corneal epithelium. METHODS P. aeruginosa traversal of airlifted, multilayered, human corneal epithelial cells was quantified in vitro up to 8 hours after apical inoculation with ∼10⁶ cfu of strain PA14, or an isogenic exoU mutant (PA14ΔexoU). In addition, PA14ΔexoU or its triple effector mutant PA14ΔexoUΔexoTΔexoY, were complemented with exoU (pUCPexoU), phospholipase-inactive exoU (pUCPexoUD344A), or control plasmid (pUCP18). Transepithelial resistance (TER) was measured (by epithelial volt ohmmeter), and cytotoxicity was determined by trypan blue staining. RESULTS PA14 traversed more efficiently than its exoU mutant at 4, 6, and 8 hours after inoculation (100-, 20-, and 8-fold, respectively; P < 0.05), but not at 2 hours. Cells exposed to PA14 lost TER to baseline (P < 0.05). Controls confirmed PA14 cytotoxicity toward these corneal epithelial cells that was absent with exoU mutants. Epithelial traversal, cytotoxicity, and lost TER were restored for PA14ΔexoU, or PA14ΔexoUΔexoTΔexoY, by complementation with pUCPexoU, but not by complementation with pUCPexoUD344A. CONCLUSIONS Traversal of multilayered corneal epithelia in vitro by cytotoxic P. aeruginosa requires ExoU with an active phospholipase domain. Correlative loss of TER with traversal by wild-type, or exoU-complemented, bacteria suggests involvement of epithelial cell death and/or lost tight junction integrity. However, traversal by exoU mutants without reduced TER suggests that additional mechanisms are also operative.
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Affiliation(s)
- Julio C Ramirez
- School of Optometry, University of California, Berkeley, California, USA
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Tam C, LeDue J, Mun JJ, Herzmark P, Robey EA, Evans DJ, Fleiszig SMJ. 3D quantitative imaging of unprocessed live tissue reveals epithelial defense against bacterial adhesion and subsequent traversal requires MyD88. PLoS One 2011; 6:e24008. [PMID: 21901151 PMCID: PMC3162028 DOI: 10.1371/journal.pone.0024008] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2010] [Accepted: 08/03/2011] [Indexed: 12/15/2022] Open
Abstract
While a plethora of in vivo models exist for studying infectious disease and its resolution, few enable factors involved in the maintenance of health to be studied in situ. This is due in part to a paucity of tools for studying subtleties of bacterial-host interactions at a cellular level within live organs or tissues, requiring investigators to rely on overt outcomes (e.g. pathology) in their research. Here, a suite of imaging technologies were combined to enable 3D and temporal subcellular localization and quantification of bacterial distribution within the murine cornea without the need for tissue processing or dissection. These methods were then used to demonstrate the importance of MyD88, a central adaptor protein for Toll-Like Receptor (TLR) mediated signaling, in protecting a multilayered epithelium against both adhesion and traversal by the opportunistic bacterial pathogen Pseudomonas aeruginosa ex vivo and in vivo.
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Affiliation(s)
- Connie Tam
- School of Optometry, University of California, Berkeley, California, United States of America
| | - Jeffrey LeDue
- School of Optometry, University of California, Berkeley, California, United States of America
| | - James J. Mun
- Program in Vision Science, University of California, Berkeley, California, United States of America
| | - Paul Herzmark
- Department of Molecular and Cell Biology, University of California, Berkeley, California, United States of America
| | - Ellen A. Robey
- Department of Molecular and Cell Biology, University of California, Berkeley, California, United States of America
| | - David J. Evans
- School of Optometry, University of California, Berkeley, California, United States of America
- College of Pharmacy, Touro University California, Vallejo, California, United States of America
| | - Suzanne M. J. Fleiszig
- School of Optometry, University of California, Berkeley, California, United States of America
- Program in Vision Science, University of California, Berkeley, California, United States of America
- Programs in Infectious Diseases and Immunity and Microbiology, University of California, Berkeley, California, United States of America
- * E-mail:
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Eijkelkamp BA, Stroeher UH, Hassan KA, Papadimitrious MS, Paulsen IT, Brown MH. Adherence and motility characteristics of clinical Acinetobacter baumannii isolates. FEMS Microbiol Lett 2011; 323:44-51. [PMID: 22092679 DOI: 10.1111/j.1574-6968.2011.02362.x] [Citation(s) in RCA: 115] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2011] [Revised: 06/06/2011] [Accepted: 06/30/2011] [Indexed: 11/30/2022] Open
Abstract
Acinetobacter baumannii continues to be a major health problem especially in hospital settings. Herein, features that may play a role in persistence and disease potential were investigated in a collection of clinical A. baumannii strains from Australia. Twitching motility was found to be a common trait in A. baumannii international clone I strains and in abundant biofilm formers, whereas swarming motility was only observed in isolates not classified within the international clone lineages. Bioinformatic analysis of the type IV fimbriae revealed a correlation between PilA sequence homology and motility. A high level of variability in adherence to both abiotic surfaces and epithelial cells was found. We report for the first time the motility characteristics of a large number of A. baumannii isolates and present a direct comparison of A. baumannii binding to nasopharyngeal and lung epithelial cells.
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Affiliation(s)
- Bart A Eijkelkamp
- School of Biological Sciences, Flinders University, Adelaide, SA, Australia
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Alarcon I, Tam C, Mun JJ, LeDue J, Evans DJ, Fleiszig SMJ. Factors impacting corneal epithelial barrier function against Pseudomonas aeruginosa traversal. Invest Ophthalmol Vis Sci 2011; 52:1368-77. [PMID: 21051692 DOI: 10.1167/iovs.10-6125] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
PURPOSE Mechanisms determining epithelial resistance versus susceptibility to microbial traversal in vivo remain poorly understood. Here, a novel murine model was used to explore factors influencing the corneal epithelial barrier to Pseudomonas aeruginosa penetration. METHODS Murine corneas were blotted with tissue paper before inoculation with green fluorescent protein-expressing P. aeruginosa. The impact of blotting on epithelial integrity was evaluated by susceptibility to fluorescein staining and histology. Using fluorescence imaging, blotted corneas were compared to nonblotted corneas for susceptibility to bacterial binding and epithelial penetration after 5 hours or were monitored for disease development. In some experiments, inoculation was performed ex vivo to exclude tear fluid or corneas were pretreated with EGTA to disrupt Ca(2+)-dependent factors. The role of surfactant protein D (SP-D), which inhibits P. aeruginosa cell invasion in vitro, was examined using knockout mice. RESULTS Blotting enabled fluorescein penetration through the epithelium into the underlying stroma without obvious disruption to corneal morphology. Although blotting enabled bacterial binding to the otherwise adhesion-resistant epithelial surface, adherent bacteria did not penetrate the surface or initiate pathology. In contrast, bacteria penetrated blotted corneas after EGTA treatment and in SP-D knockouts. Visible disease occurred and progressed only in aged, blotted, and EGTA-treated, SP-D knockout mice. CONCLUSIONS Neither fluorescein staining nor bacterial adhesion necessarily predict or enable corneal susceptibility to bacterial penetration or disease. Corneal epithelial defenses limiting traversal by adherent bacteria include EGTA-sensitive factors and SP-D. Understanding mechanisms modulating epithelial traversal by microbes could improve our understanding of susceptibility to infection and may indicate new strategies for preventing disease.
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Affiliation(s)
- Irania Alarcon
- Program in Microbiology, University of California, Berkeley, Berkeley, California, USA
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Yang L, Chen L, Shen L, Surette M, Duan K. Inactivation of MuxABC-OpmB transporter system in Pseudomonas aeruginosa leads to increased ampicillin and carbenicillin resistance and decreased virulence. J Microbiol 2011; 49:107-14. [PMID: 21369987 DOI: 10.1007/s12275-011-0186-2] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2010] [Accepted: 10/05/2010] [Indexed: 10/18/2022]
Abstract
Resistance-Nodulation-Cell Division (RND) pumps play important roles in bacterial resistance to antibiotics. Pseudomonas aeruginosa is an important human pathogen which exhibits high level resistance to antibiotics. There are total of 12 RND pumps present in the P. aeruginosa PAOl genome. The recently characterized MuxABC-OpmB system has been shown to play a role in resistance to novobiocin, aztreonam, macrolides, and tetracycline in a multiple knockout mutation. In this study, we examined the expression levels of all the 12 RND pump gene clusters and tested the involvement of MuxABC-OpmB in pathogenicity. The results indicated that in addition to the four known constitutively expressed RND pumps, mexAB-oprM, mexGHI-opmD, mexVW, and mexXY, relatively high levels of expression were observed with mexJK and muxABC-opmB in the conditions tested. Inactivation of muxA in the muxABC-opmB operon resulted in elevated resistance to ampicillin and carbenicillin. The mutant also showed attenuated virulence in both Brassica rapa pekinensis and Drosophila melanogaster infection models. The decreased virulence at least in part was due to decreased twitching motility in the mutant. These results indicate that the RND pump MuxABC-OpmB is associated with ampicillin and carbenicillin susceptibility and also involved in pathogenesis in P. aeruginosa.
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Affiliation(s)
- Liang Yang
- Molecular Microbiology Laboratory, Key Laboratory of Resources Biology and Biotechnology in Western China, Ministry of Education, Faculty of Life Sciences, Northwest University, Shaanxi, 710069, PR China
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Role of defensins in corneal epithelial barrier function against Pseudomonas aeruginosa traversal. Infect Immun 2010; 79:595-605. [PMID: 21115716 DOI: 10.1128/iai.00854-10] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Studies have shown that epithelium-expressed antimicrobial peptides (AMPs), e.g., β-defensins, play a role in clearing bacteria from mouse corneas already infected with Pseudomonas aeruginosa. Less is known about the role of AMPs in allowing the cornea to resist infection when healthy. We previously reported that contact lens exposure, a major cause of P. aeruginosa keratitis, can inhibit the upregulation of human β-defensin 2 (hBD-2) by corneal epithelial cells in response to P. aeruginosa antigens in vitro. Here, we studied the role of AMPs in maintaining the corneal epithelial barrier to P. aeruginosa penetration using both in vitro (human) and in vivo (mouse) experiments. Results showed that preexposing human corneal epithelial multilayers to bacterial antigens in a culture supernatant (known to upregulate AMP expression) reduced epithelial susceptibility to P. aeruginosa traversal up to 6-fold (P < 0.001). Accordingly, small interfering RNA (siRNA) knockdown of any one of four AMPs expressed by human epithelia promoted P. aeruginosa traversal by more than 3-fold (P < 0.001). The combination knockdown of AMPs further enhanced susceptibility to bacterial traversal by ∼8-fold (P < 0.001). In vivo experiments showed that the loss of murine β-defensin 3 (mBD-3), a murine ortholog of hBD-2, enhanced corneal susceptibility to P. aeruginosa. The uninjured ocular surface of mBD-3(-/-) mice showed a reduced capacity to clear P. aeruginosa, and their corneal epithelia were more susceptible to bacterial colonization, even when inoculated ex vivo to exclude tear fluid effects. Together, these in vitro and in vivo data show functional roles for AMPs in normal corneal epithelial cell barrier function against P. aeruginosa.
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