Use of an isogenic mutant constructed in Moraxella catarrhalis To identify a protective epitope of outer membrane protein B1 defined by monoclonal antibody 11C6

Antimicrobial Photodynamic Therapy with Chlorin e6 Is Bactericidal against Biofilms of the Primary Human Otopathogens

Otitis media (OM), or middle ear disease, is the most prevalent bacterial infection in children and the primary reason for antibiotic use and surgical intervention in the pediatric population. Biofilm formation by the major bacterial otopathogens, Moraxella catarrhalis, Streptococcus pneumoniae, and nontypeable Haemophilus influenzae, has been shown to occur within the middle ears of OM patients and is a key factor in the development of recurrent disease, which may result in hearing impairment and developmental delays. Bacterial biofilms are inherently impervious to most antibiotics and present a significant challenge to the immune system. In this study, we demonstrate that antimicrobial photodynamic therapy (aPDT) using the photosensitizer chlorin e6 elicits significant bactericidal activity versus planktonic and biofilm-associated otopathogens and supports further analyses of this novel, efficacious, and promising technology as an adjunctive treatment for acute and recurrent OM.

Moraxella catarrhalis, Streptococcus pneumoniae, and nontypeable Haemophilus influenzae (NTHi) are ubiquitous upper respiratory opportunistic pathogens. Together, these three microbes are the most common causative bacterial agents of pediatric otitis media (OM) and have therefore been characterized as the primary human otopathogens. OM is the most prevalent bacterial infection in children and the primary reason for antibiotic administration in this population. Moreover, biofilm formation has been confirmed as a primary mechanism of chronic and recurrent OM disease. As bacterial biofilms are inherently metabolically recalcitrant to most antibiotics and these complex structures also present a significant challenge to the immune system, there is a clear need to identify novel antimicrobial approaches to treat OM infections. In this study, we evaluated the potential efficacy of antibacterial photodynamic therapy (aPDT) with the photosensitizer chlorin e6 (Ce6) against planktonic as well as biofilm-associated M. catarrhalis, S. pneumoniae, and NTHi. Our data indicate aPDT with Ce6 elicits significant bactericidal activity against both planktonic cultures and established biofilms formed by the three major otopathogens (with an efficacy of ≥99.9% loss of viability). Notably, the implementation of a novel, dual-treatment aPDT protocol resulted in this disinfectant effect on biofilm-associated bacteria and, importantly, inhibited bacterial regrowth 24 h posttreatment. Taken together, these data suggest this novel Ce6-aPDT treatment may be a powerful and innovative therapeutic strategy to effectively treat and eradicate bacterial OM infections and, significantly, prevent the development of recurrent disease.

IMPORTANCE Otitis media (OM), or middle ear disease, is the most prevalent bacterial infection in children and the primary reason for antibiotic use and surgical intervention in the pediatric population. Biofilm formation by the major bacterial otopathogens, Moraxella catarrhalis, Streptococcus pneumoniae, and nontypeable Haemophilus influenzae, has been shown to occur within the middle ears of OM patients and is a key factor in the development of recurrent disease, which may result in hearing impairment and developmental delays. Bacterial biofilms are inherently impervious to most antibiotics and present a significant challenge to the immune system. In this study, we demonstrate that antimicrobial photodynamic therapy (aPDT) using the photosensitizer chlorin e6 elicits significant bactericidal activity versus planktonic and biofilm-associated otopathogens and supports further analyses of this novel, efficacious, and promising technology as an adjunctive treatment for acute and recurrent OM.

Targeting a bacterial DNABII protein with a chimeric peptide immunogen or humanised monoclonal antibody to prevent or treat recalcitrant biofilm-mediated infections

Background:

Chronic and recurrent bacterial diseases are recalcitrant to treatment due to the ability of the causative agents to establish biofilms, thus development of means to prevent or resolve these structures are greatly needed. Our approach targets the DNABII family of bacterial DNA-binding proteins, which serve as critical structural components within the extracellular DNA scaffold of biofilms formed by all bacterial species tested to date. DNABII-directed antibodies rapidly disrupt biofilms and release the resident bacteria which promote their subsequent clearance by either host immune effectors or antibiotics that are now effective at a notably reduced concentration.

Methods:

First, as a therapeutic approach, we used intact IgG or Fab fragments against a chimeric peptide immunogen designed to target protective epitopes within the DNA-binding tip domains of integration host factor to disrupt established biofilms in vitro and to mediate resolution of existing disease in vivo. Second, we performed preventative active immunisation with the chimeric peptide to induce the formation of antibody that blocks biofilm formation and disease development in a model of viral-bacterial superinfection. Further, toward the path for clinical use, we humanised a monoclonal antibody against the chimeric peptide immunogen, then characterised and validated that it maintained therapeutic efficacy.

Findings:

We demonstrated efficacy of each approach in two well-established pre-clinical models of otitis media induced by the prevalent respiratory tract pathogen nontypeable Haemophilus influenzae, a common biofilm disease.

Interpretation:

Collectively, our data revealed two approaches with substantive efficacy and potential for broad application to combat diseases with a biofilm component.

Funding

Supported by R01 DC011818 to LOB and SDG.

Antibodies against the Majority Subunit (PilA) of the Type IV Pilus of Nontypeable Haemophilus influenzae Disperse Moraxella catarrhalis from a Dual-Species Biofilm

Middle ear infections (or otitis media [OM]) are highly prevalent among children worldwide and present a tremendous socioeconomic challenge for health care systems. More importantly, this disease diminishes the quality of life of young children. OM is often chronic and recurrent, due to the presence of highly antibiotic-resistant communities of bacteria (called biofilms) that persist within the middle ear space. To combat these recalcitrant infections, new and powerful biofilm-directed approaches are needed. Here, we describe the ability to disrupt a biofilm formed by the two most common bacteria that cause chronic and recurrent OM in children, via an approach that combines the power of vaccines with that of traditional antibiotics. An outcome of this strategy is that antibiotics can more easily kill the bacteria that our vaccine-induced antibodies have released from the biofilm. We believe that this approach holds great promise for both the prevention and treatment of OM.

Otitis media (OM) is often polymicrobial, with nontypeable Haemophilus influenzae (NTHI) and Moraxella catarrhalis (Mcat) frequently cocultured from clinical specimens. Bacterial biofilms in the middle ear contribute to the chronicity and recurrence of OM; therefore, strategies to disrupt biofilms are needed. We have focused our vaccine development efforts on the majority subunit of NTHI type IV pili, PilA. Antibodies against a recombinant, soluble form of PilA (rsPilA) both disrupt and prevent the formation of NTHI biofilms in vitro. Moreover, immunization with rsPilA prevents and resolves NTHI-induced experimental OM. Here, we show that antibodies against rsPilA also prevent and disrupt polymicrobial biofilms. Dual-species biofilms formed by NTHI and Mcat at temperatures that mimic the human nasopharynx (34°C) or middle ear (37°C) were exposed to antiserum against either rsPilA or the OMP P5 adhesin of NTHI. NTHI+Mcat biofilm formation was significantly inhibited by antiserum directed against both adhesin proteins at either temperature. However, only anti-rsPilA disrupted NTHI+Mcat preestablished biofilms at either temperature and actively dispersed both NTHI and Mcat via interspecies quorum signaling. Newly released NTHI and Mcat were significantly more susceptible to killing by antibiotics. Taken together, these results revealed new opportunities for treatment of biofilm-associated diseases via a strategy that combines vaccine-induced antibody-mediated biofilm dispersal with traditional antibiotics, at a significantly reduced dosage to exploit the newly released, antibiotic-sensitive phenotype. Combined, our data strongly support the utility of rsPilA both as a preventative and as a therapeutic vaccine antigen for polymicrobial OM due to NTHI and Mcat.

Vaccine targets against Moraxella catarrhalis

INTRODUCTION

Moraxella catarrhalis is a prominent pathogen that causes acute otitis media in children and lower respiratory tract infections in adults, resulting in a significant socioeconomic burden on healthcare systems globally. No vaccine is currently available for M. catarrhalis. Promising M. catarrhalis target antigens have been characterized in animal models and should soon enter human clinical trials.

AREAS COVERED

This review discusses the detailed features and research status of current candidate target antigens for an M. catarrhalis vaccine. The approaches for assessing M. catarrhalis vaccine efficacy are also discussed.

EXPERT OPINION

Targeting the key molecules contributing to serum resistance may be a viable strategy to identify effective vaccine targets among M. catarrhalis antigens. Elucidating the role and mechanisms of the serum and mucosal immune responses to M. catarrhalis is significant for vaccine target selection, testing and evaluation. Developing animal models closely simulating M. catarrhalis-caused human respiratory diseases is of great benefit in better understanding pathogenesis and evaluating vaccine efficacy. Carrying out clinical trials will be a landmark in the progress of M. catarrhalis vaccine research. Combined multicomponent vaccines will be a focus of future M. catarrhalis vaccine studies.

Characterization of a trifunctional glucosyltransferase essential for Moraxella catarrhalis lipooligosaccharide assembly

The human respiratory tract pathogen Moraxella catarrhalis expresses lipooligosaccharides (LOS), glycolipid surface moieties that are associated with enhanced colonization and virulence. Recent studies have delineated the major steps required for the biosynthesis and assembly of the M. catarrhalis LOS molecule. We previously demonstrated that the glucosyltransferase enzyme Lgt3 is responsible for the addition of at least one glucose (Glc) molecule, at the β-(1-4) position, to the inner core of the LOS molecule. Our data further suggested a potential multifunctional role for Lgt3 in LOS biosynthesis. The studies reported here demonstrate that the Lgt3 enzyme possesses two glycosyltransferase domains (A1 and A2) similar to that of other bifunctional glycosyltransferase enzymes involved in surface polysaccharide biosynthesis in Escherichia coli, Pasteurella multocida and Streptococcus pyogenes. Each Lgt3 domain contains a conserved DXD motif, shown to be involved in the catalytic activity of other glycosyltransferases. To determine the function of each domain, A1 (N-terminal), A2 (C-terminal) and double A1A2 site-directed DAD to AAA mutants were constructed and the resulting LOS phenotypes of these modified strains were analyzed. Our studies indicate that the Lgt3 N-terminal A1 catalytic domain is responsible for the addition of the first β-(1-3) Glc to the first Glc on the inner core. The C-terminal catalytic domain A2 then adds the β-(1-4) Glc and the β-(1-6) Glc, confirming the bifunctional nature of this domain. The results from these experiments demonstrate that Lgt3 is a novel, multifunctional transferase responsible for the addition of three Glcs with differing linkages onto the inner core of M. catarrhalis LOS.

Respiratory syncytial virus promotes Moraxella catarrhalis-induced ascending experimental otitis media

Otitis media (OM) is a polymicrobial disease wherein prior or concurrent infection with an upper respiratory tract virus plays an essential role, predisposing the middle ear to bacterial invasion. In episodes of acute bacterial OM, respiratory syncytial virus (RSV) is the most commonly isolated virus and thus serves as an important co-pathogen. Of the predominant bacterial agents of OM, the pathogenesis of disease due to Moraxella catarrhalis is the least well understood. Rigorous study of M.catarrhalis in the context of OM has been significantly hindered by lack of an animal model. To bridge this gap, we assessed whether co-infection of chinchillas with M. catarrhalis and RSV would facilitate ascension of M. catarrhalis from the nasopharynx into the middle ear. Chinchillas were challenged intranasally with M. catarrhalis followed 48 hours later by intranasal challenge with RSV. Within 7 days, 100% of nasopharynges were colonized with M. catarrhalis and homogenates of middle ear mucosa were also culture-positive. Moreover, within the middle ear space, the mucosa exhibited hemorrhagic foci, and a small volume of serosanguinous effusion was present in one of six ears. To improve upon this model, and based on epidemiologic data, nontypeable Haemophilus influenzae (NTHI) was included as an additional bacterial co-pathogen via intranasal administration four days before M. catarrhalis challenge. With this latter protocol, M. catarrhalis was cultured from the nasopharynx and middle ear homogenates of a maximum of 88% and 79% animals, respectively, for up to 17 days after intranasal challenge with M. catarrhalis. Additionally, hemorrhagic foci were observed in 79% of middle ears upon sacrifice. Thus, these data demonstrated that co-infection with RSV and NTHI predisposed to M. catarrhalis-induced ascending experimental OM. This model can be used both in studies of pathogenesis as well as to investigate strategies to prevent or treat OM due to M. catarrhalis.

Comparative analyses of the Moraxella catarrhalis type-IV pilus structural subunit PilA

Moraxella catarrhalis is a Gram-negative aerobic diplococcus that is a mucosal pathogen of the upper and lower respiratory tracts in humans. In order to colonize the human host and establish an infection, M. catarrhalis must be able to effectively attach to the respiratory mucosal epithelia. Although little is known about M. catarrhalis pathogenesis, our laboratory has previously shown that expression of type IV pili (TFP) contributes to mucosal colonization. TFP are filamentous surface appendages primarily composed of a single protein subunit termed pilin, which is encoded by pilA in M. catarrhalis. These surface structures play a crucial role in the initiation of disease by a wide range of pathogenic bacteria. Our studies also indicate that unlike the pilin of the pathogenic Neisseria species, which exhibit both phase and antigenic variation, the pilin subunit of M. catarrhalis appears to be more highly conserved as there are no major pilin variants produced by a single strain and only two major PilA antigenic variants, termed clade 1 and clade 2, have been observed between strains. Moreover, we have determined that these highly conserved bacterial surface structures are expressed by all M. catarrhalis clinical isolates evaluated. Therapeutic or vaccine-based interventions that prevent or diminish nasopharyngeal colonization will likely decrease acute and recurrent M. catarrhalis infections in prone populations. Thus, our data indicate that additional studies aimed at elucidating the role of PilA in the pathogenesis and host response to M. catarrhalis infections are warranted.

Identification of a bacteriocin and its cognate immunity factor expressed by Moraxella catarrhalis

Background

Bacteriocins are antimicrobial proteins and peptides ribosomally synthesized by some bacteria which can effect both intraspecies and interspecies killing.

Results

Moraxella catarrhalis strain E22 containing plasmid pLQ510 was shown to inhibit the growth of M. catarrhalis strain O35E. Two genes (mcbA and mcbB) in pLQ510 encoded proteins predicted to be involved in the secretion of a bacteriocin. Immediately downstream from these two genes, a very short ORF (mcbC) encoded a protein which had some homology to double-glycine bacteriocins produced by other bacteria. A second very short ORF (mcbI) immediately downstream from mcbC encoded a protein which had no significant similarity to other proteins in the databases. Cloning and expression of the mcbI gene in M. catarrhalis O35E indicated that this gene encoded the cognate immunity factor. Reverse transcriptase-PCR was used to show that the mcbA, mcbB, mcbC, and mcbI ORFs were transcriptionally linked. This four-gene cluster was subsequently shown to be present in the chromosome of several M. catarrhalis strains including O12E. Inactivation of the mcbA, mcbB, or mcbC ORFs in M. catarrhalis O12E eliminated the ability of this strain to inhibit the growth of M. catarrhalis O35E. In co-culture experiments involving a M. catarrhalis strain containing the mcbABCI locus and one which lacked this locus, the former strain became the predominant member of the culture after overnight growth in broth.

Conclusion

This is the first description of a bacteriocin and its cognate immunity factor produced by M. catarrhalis. The killing activity of the McbC protein raises the possibility that it might serve to lyse other M. catarrhalis strains that lack the mcbABCI locus, thereby making their DNA available for lateral gene transfer.

Identification of a novel two-partner secretion locus in Moraxella catarrhalis

Although Moraxella catarrhalis continues to be a significant cause of disease in both children and adults, the steps involved in pathogenesis remain poorly understood. We have identified three open reading frames in the M. catarrhalis genome that encode homologues of the two-partner secretion system (TPS). The sequenced M. catarrhalis hemagglutinin-like locus of strain 7169 has a unique gene organization composed in the order of mchA1, mchB, and mchA2, where mchA1 is divergent. MchA1 and MchA2 are 74% identical at the amino acid level and diverge only in the C-terminal regions. The TPS motif identified in the common N-terminal regions of MchA1 and MchA2 was found to be homologous to the filamentous hemagglutinin of Bordetella pertussis, and MchB has homology to other TpsB transporters. The presence of MchA1 and MchA2 in outer membrane protein preparations and concentrated culture supernatants (CCSs) of strain 7169 was confirmed by immunoblotting using specific antisera. Nanoscale liquid chromatography-tandem mass spectrometry peptide sequencing of the antibody-reactive bands from the CCSs was performed and demonstrated that 13 different peptides mapped to identical regions of MchA1 and MchA2. Quantitative adherence assays revealed a decrease of binding to primary normal human bronchial epithelial cells by the mch mutants 7169mchB and 7169mchA1A2B compared to that by the wild-type strain. These studies show that MchA1, MchA2, and MchB are components of a novel TPS identified in M. catarrhalis and suggest that these proteins may be involved in colonization.

Plasmid pWW115, a cloning vector for use with Moraxella catarrhalis

The plasmid shuttle vector pWW102B is able to replicate in only a modest number of Moraxella catarrhalis strains. Plasmid pWW115, a spontaneous deletion mutant of pWW102B, was shown to lack both the pACYC184-derived origin of replication and the associated chloramphenicol-resistance gene but was able to replicate in every M. catarrhalis strain tested in this study, including one strain that had been previously refractory to all types of genetic manipulations. To test the utility of this plasmid, a M. catarrhalis gene encoding the UspA2 serum-resistance factor was cloned into pWW115 and the resultant recombinant plasmid was shown to confer serum-resistance on a serum-sensitive M. catarrhalis uspA2 mutant.

Development of a shuttle vector for Moraxella catarrhalis

Efforts to perform genetic analysis in Moraxella catarrhalis have been hampered by the lack of a cloning vector. M. catarrhalis strain E22 was previously shown to contain plasmid pLQ510 which lacked a selectable antibiotic resistance marker. Several methods were used to eliminate unnecessary DNA from pLQ510. Then, a 1.2 kb spectinomycin resistance cartridge, a multiple cloning site, and the origin of replication from pACYC184 were cloned into this plasmid backbone to obtain the 7.2 kb plasmid pWW102B. This new plasmid could replicate in M. catarrhalis as well as in both Escherichia coli and Haemophilus influenzae. This shuttle vector was used to clone and express two different M. catarrhalis genes, respectively, encoding an adhesin and a protein involved in serum resistance. When these two plasmids were introduced into appropriate M. catarrhalis mutants, they complemented the phenotypic deficiency of each mutant. This is the first report of functional complementation in trans in this pathogen.

Characterization of a cluster of three glycosyltransferase enzymes essential for Moraxella catarrhalis lipooligosaccharide assembly

Moraxella catarrhalis isolates express lipooligosaccharide (LOS) molecules on their surface, which share epitopes similar to that of the Neisseria and Haemophilus species. These common LOS epitopes have been implicated in various steps of pathogenesis for the different organisms. In this study, a cluster of three LOS glycosyltransferase genes (lgt) were identified in M. catarrhalis 7169, a strain that produces a serotype B LOS. Mutants in these glycosyltransferase genes were constructed, and the resulting LOS phenotypes were consistent with varying degrees of truncation compared to wild-type LOS. The LOS structures of each lgt mutant were no longer detected by a monoclonal antibody (MAb 4G5) specific to a highly conserved terminal epitope nor by a monoclonal antibody (MAb 3F7) specific to the serotype B LOS side chain. Mass spectrometry of the LOS glycoforms assembled by two of these lgt mutants indicated that lgt1 encodes an alpha(1-2) glucosyltransferase and the lgt2 encodes a beta(1-4) galactosyltransferase. However, these structural studies could not delineate the function for lgt3. Therefore, M. catarrhalis lgt3 was introduced into a defined beta(1-4) glucosyltransferase Haemophilus ducreyi 35000glu- mutant in trans, and monoclonal antibody analysis confirmed that Lgt3 complemented the LOS defect. These data suggest that lgt3 encodes a glucosyltransferase involved in the addition of a beta(1-4)-linked glucose to the inner core. Furthermore, we conclude that this enzymatic step is essential for the assembly of the complete LOS glycoform expressed by M. catarrhalis 7169.

Identification of a conserved Moraxella catarrhalis haemoglobin-utilization protein, MhuA

Moraxella catarrhalis is a leading cause of acute otitis media in children and is a cause of respiratory disease in adults with underlying lung disease. This organism is a strict human pathogen that has an absolute requirement for iron in order to grow and cause disease. Previous studies identified transferrin and lactoferrin receptors used by M. catarrhalis to obtain iron from the human host, yet other iron-acquisition systems remain undefined. In this study, it is demonstrated that this strict mucosal pathogen can utilize haemoglobin (Hb) as a sole source of iron for growth. A novel 107 kDa outer-membrane protein involved in Hb utilization by this pathogen was also identified. An isogenic mutant defective in this Moraxella Hb-utilization protein (MhuA), 7169 : : mhuA, showed a significant lag during growth in the presence of Hb as the sole iron source. This protein appears to be expressed constitutively, regardless of growth conditions, and a mAb directed to MhuA demonstrated that this protein contains highly conserved, surface-exposed epitopes. Data demonstrating that expression of MhuA may be highly specific to isolates of M. catarrhalis are also presented, suggesting a potential role as a diagnostic marker. To our knowledge, this is the first report demonstrating that M. catarrhalis expresses an Hb-binding protein and that this bacterium can utilize Hb as a sole iron source for growth.

Moraxella catarrhalis strains with reduced expression of the UspA outer membrane proteins belong to a distinct subpopulation

The outer membrane proteins UspA1 and UspA2 are candidate antigens for a Moraxella catarrhalis vaccine. We previously reported that 103 of 108 isolates (95%) from young children expressed UspA1 detected by reactivity with the monoclonal antibody mAb24B5. The aim of the present study was to investigate mechanisms controlling UspA1 expression by analysis of five mAb24B5 non-reactive isolates. Four of these strains were characterized by (i) decreased or absent transcription of uspA1 and uspA2 and (ii) clustered mutations and deletions in the promoter region of both uspA1 and uspA2. Antigenic or phase variation were not responsible for reduced levels of UspA1 expression. While mAb24B5-positive isolates expressing normal levels of uspA1 and uspA2 mRNA belonged to the previously described 16S rRNA type 1 phylogenetic group, these four mAb24B5-negative isolates were found to belong to the 16S rRNA gene types 2 or 3. The remaining mAb24B5-negative isolate (#610) belonged to 16S rRNA type 1 and exhibited a posttranscriptional defect of UspA1 expression defined by normal levels of uspA1 mRNA and both recombinant and in vitro expression of mAb24B5-reactive UspA1. In conclusion, M. catarrhalis clinical isolates exhibiting reduced expression of UspA1 and UspA2 belonged to a distinct phylogenetic subpopulation. A UspA-based vaccine is unlikely to be effective against such isolates.

Expression of type IV pili by Moraxella catarrhalis is essential for natural competence and is affected by iron limitation

Type IV pili, filamentous surface appendages primarily composed of a single protein subunit termed pilin, play a crucial role in the initiation of disease by a wide range of pathogenic bacteria. Although previous electron microscopic studies suggested that pili might be present on the surface of Moraxella catarrhalis isolates, detailed molecular and phenotypic analyses of these structures have not been reported to date. We identified and cloned the M. catarrhalis genes encoding PilA, the major pilin subunit, PilQ, the outer membrane secretin through which the pilus filament is extruded, and PilT, the NTPase that mediates pilin disassembly and retraction. To initiate investigation of the role of this surface organelle in pathogenesis, isogenic pilA, pilT, and pilQ mutants were constructed in M. catarrhalis strain 7169. Comparative analyses of the wild-type 7169 strain and three isogenic pil mutants demonstrated that M. catarrhalis expresses type IV pili that are essential for natural genetic transformation. Our studies suggest type IV pilus production by M. catarrhalis is constitutive and ubiquitous, although pilin expression was demonstrated to be iron responsive and Fur regulated. These data indicate that additional studies aimed at elucidating the prevalence and role of type IV pili in the pathogenesis and host response to M. catarrhalis infections are warranted.

Identification of a hemin utilization protein of Moraxella catarrhalis (HumA)

Moraxella catarrhalis is a major cause of acute otitis media in young children and has also been implicated as an important cause of exacerbations in adults with underlying pulmonary disease. Due to the considerable level of antibiotic resistance and the high degree of carriage rates in young children, it is likely that the incidence of M. catarrhalis infections will continue to rise. M. catarrhalis is a strict human respiratory pathogen, and this bacterium uses both transferrin and lactoferrin receptors to fulfill the essential iron requirement for survival in vivo. However, these are the only described iron acquisition systems for this organism. In this report we have demonstrated that M. catarrhalis can also utilize hemin as a sole source of iron for growth. In addition, we have identified and characterized an outer membrane protein with homology (26 to 28% similarity) to other known hemin binding and uptake proteins in related gram-negative organisms (i.e., Bordetella and Yersinia spp.). This newly described M. catarrhalis protein, termed HumA, is capable of directly binding to hemin coupled to a solid-phase matrix. M. catarrhalis HumA expressed on the surface of an Escherichia coli hemA-deficient strain (K-12 EB53) is fully capable of complementing the defect and thus restoring the ability of this strain to grow in the presence of hemin. When M. catarrhalis is grown in the presence of hemin, HumA expression is clearly increased as shown by Western blotting with polyclonal antiserum developed against a HumA peptide. In addition, growth analyses revealed that a HumA-deficient mutant of M. catarrhalis (7169::humA) is restricted for growth in the presence of hemin as the sole iron source compared to the wild-type strain. We conclude that HumA is an essential component of a hemin uptake and utilization system previously undescribed for M. catarrhalis, thus providing another mechanism of iron acquisition that may facilitate persistent colonization of the mucosal surface.

Identification and characterization of outer membrane proteins G1a and G1b of Moraxella catarrhalis

Moraxella catarrhalis is an important cause of otitis media, sinusitis, and lower respiratory tract infections in patients with chronic obstructive pulmonary disease. The purified outer membrane of M. catarrhalis contains a 29 kDa band, previously named outer membrane protein G1 (OMP G1). Polyclonal antiserum to the OMP G1 band was used to screen a genomic lambda phage library and the gene for OMP G1a was cloned and sequenced. Analysis of outer membrane by isoelectric focusing and amino-terminal protein sequence of the 29 kDa band revealed that the band is actually two individual proteins designated OMP G1a and OMP G1b. OMP G1a is a lipoprotein with an isoelectric point of 4. OMP G1b contains an unblocked amino-terminus and has an isoelectric point of 9. Analysis of the sequence of OMP G1a and OMP G1b from 25 clinical isolates revealed a high degree of conservation among strains. The sequence conservation of OMP G1a and OMP G1b among strains, combined with previous observations that OMP G1a and OMP G1b contain epitopes on the bacterial surface, indicate that OMP G1a and OMP G1b are potential vaccine antigens for M. catarrhalis.

The Moraxella catarrhalis porin-like outer membrane protein CD is an adhesin for human lung cells

The outer membrane protein CD (OMPCD) of Moraxella catarrhalis is an outer membrane protein with several attributes of a potential vaccine antigen. We isolated four transposon mutants of strain O35E on the basis of their reduced binding to A549 human lung cells in microcolony formation assays, and we determined that they contain a transposon in ompCD. We also found that these transposon insertions had pleiotropic effects: mutants grew slower, became serum sensitive, bound approximately 10-fold less to A549 cells, and appeared transparent when grown on solid medium. We confirmed that these various phenotypes could be attributed solely to disruption of ompCD by constructing the isogenic strain O35E.CD1. O35E-ompCD was cloned, and recombinant Escherichia coli bacteria expressing the gene product exhibited a 10-fold increase in adherence to A549 cells. This is the first report of M. catarrhalis ompCD mutants, and our findings demonstrate that this gene product is an adhesin for human lung cells.

Identification of a 3-deoxy-D-manno-octulosonic acid biosynthetic operon in Moraxella catarrhalis and analysis of a KdsA-deficient isogenic mutant

Lipooligosaccharide (LOS), a predominant surface-exposed component of the outer membrane, has been implicated as a virulence factor in the pathogenesis of Moraxella catarrhalis infections. However, the critical steps involved in the biosynthesis and assembly of M. catarrhalis LOS currently remain undefined. In this study, we used random transposon mutagenesis to identify a 3-deoxy-D-manno-octulosonic acid (KDO) biosynthetic operon in M. catarrhalis with the gene order pyrG-kdsA-eno. The lipid A-KDO molecule serves as the acceptor onto which a variety of glycosyl transferases sequentially add the core and branch oligosaccharide extensions for the LOS molecule. KdsA, the KDO-8-phosphate synthase, catalyzes the first step of KDO biosynthesis and is an essential enzyme in gram-negative enteric bacteria for maintenance of bacterial viability. We report the construction of an isogenic M. catarrhalis kdsA mutant in strain 7169 by allelic exchange. Our data indicate that an LOS molecule consisting only of lipid A and lacking KDO glycosylation is sufficient to sustain M. catarrhalis survival in vitro. In addition, comparative growth and susceptibility assays were performed to assess the sensitivity of 7169kdsA11 compared to that of the parental strain. The results of these studies demonstrate that the native LOS molecule is an important factor in maintaining the integrity of the outer membrane and suggest that LOS is a critical component involved in the ability of M. catarrhalis to resist the bactericidal activity of human sera.

The Hag protein of Moraxella catarrhalis strain O35E is associated with adherence to human lung and middle ear cells

Previous studies have demonstrated that the Moraxella catarrhalis surface antigen UspA1 is an adhesin for Chang human conjunctival cells. The present report demonstrates that lack of UspA1 expression does not affect the adherence of strain O35E to A549 human lung cells or primary cultures of human middle ear epithelial (HMEE) cells. These results imply that another molecule mediates the adherence of M. catarrhalis to these two cell lines. To identify this adhesin, strain O35E was mutagenized with a transposon and 1,000 mutants were screened in a microcolony formation assay using A549 cells. Nine independent isolates exhibited an 8- to 19-fold reduction in adherence and contained a transposon in the same locus. Nucleotide sequence data and PCR analysis indicated that the transposons were inserted in different locations in the gene encoding the surface protein Hag. Quantitative assays using one representative transposon mutant, O35E.TN2, showed considerably decreased binding to A549 as well as HMEE cells. However, this mutant adhered at wild-type levels to Chang conjunctival cells. These findings suggest that the M. catarrhalis Hag protein is an adhesin for cell lines derived from human lung and middle ear tissues.

Inactivation of the Moraxella catarrhalis 7169 ferric uptake regulator increases susceptibility to the bactericidal activity of normal human sera

Moraxella catarrhalis is a strict human pathogen and a significant cause of respiratory disease and otitis media. In direct response to these infections, research efforts have focused primarily on the identification of potential vaccine targets. The general biology of M. catarrhalis, however, including the mechanisms utilized to survive in the human host, remains poorly understood. Previous work has demonstrated that M. catarrhalis expresses iron-repressible proteins, suggesting the presence of iron acquisition systems under the control of a ferric uptake regulator (Fur). In this study M. catarrhalis fur has been cloned and sequenced from strain 7169. A deletion-insertion mutation of 7169 fur resulted in upregulation of iron-repressible outer membrane proteins in the absence and presence of iron. This mutant strain, 7169fur1, was significantly more sensitive to the bactericidal activity of normal human serum than the resistant wild-type strain. These data suggest that constitutive expression of iron-regulated proteins may provide multiple targets for human antibodies. In addition, the 7169 fur mutant provides an important tool for further investigation of the iron acquisition mechanisms utilized by M. catarrhalis.

Mucosal immune response to specific outer membrane proteins of Moraxella catarrhalis in young children

BACKGROUND

Moraxella catarrhalis is an important cause of otitis media. A number of candidate antigens for a future infant otitis media vaccine have been identified, but their mucosal immunogenicity induced by nasopharyngeal M. catarrhalis colonization has not been characterized. The aim of this study was to determine the salivary IgA response to M. catarrhalis outer membrane proteins (OMP) in young children.

METHODS

Children ages 1 to 24 months evaluated for acute respiratory tract infection were prospectively enrolled. M. catarrhalis nasopharyngeal colonization was determined by (1) selective culture and (2) detection by reverse transcription-PCR of messenger RNA specific for the OMP UspA1 and UspA2. Salivary IgA responses were detected by immunoblot analysis of M. catarrhalis OMP. Isogenic knockout mutants for UspA1, UspA2, hemagglutinin (Hag), transferrin-binding protein B (TbpB) and CopB were constructed for identification of specific target OMP.

RESULTS

Sixty-six patients were studied. The rates of M. catarrhalis colonization by culture, reverse transcription-PCR for messenger RNA and mRNA were 40, 94 and 58%, respectively. Anti-M. catarrhalis salivary IgA was detected in 62 patients (94%). IgA directed against a >250-kDa antigen (assigned to UspA1/UspA2 by mutant analysis) and a 200-kDa antigen (Hag) were detected in 65 and 70% of patients, respectively. Bands at 80 to 85 kDa (82%) consisted of IgA directed against monomeric UspA2, TbpB and CopB.

CONCLUSIONS

colonization occurring in early infancy is associated with a consistent mucosal immune response directed against the UspA proteins, Hag and other OMP. The data suggest that several M. catarrhalis OMP are immunogens of the nasopharyngeal mucosal immune system of infants.

A hag mutant of Moraxella catarrhalis strain O35E is deficient in hemagglutination, autoagglutination, and immunoglobulin D-binding activities

Previous studies correlated the presence of a 200-kDa protein on the surface of Moraxella catarrhalis with the ability of this organism to agglutinate human erythrocytes (M. Fitzgerald, R. Mulcahy, S. Murphy, C. Keane, D. Coakley, and T. Scott, FEMS Immunol. Med. Microbiol. 18:209-216, 1997). In the present study, the gene encoding the 200-kDa protein (designated Hag) of M. catarrhalis strain O35E was subjected to nucleotide sequence analysis and then was inactivated by insertional mutagenesis. The isogenic hag mutant was unable to agglutinate human erythrocytes and lost its ability to autoagglutinate but was still attached at wild-type levels to several human epithelial cell lines. The hag mutation also eliminated the ability of this mutant strain to bind human immunoglobulin D. The presence of the Hag protein on the M. catarrhalis cell surface, as well as that of the UspA1 and UspA2 proteins (C. Aebi, I. Maciver, J. L. Latimer, L. D. Cope, M. K. Stevens, S. E. Thomas, G. H. McCracken, Jr., and E. J. Hansen, Infect. Immun. 65:4367-4377, 1997), was investigated by transmission electron and cryoimmunoelectron microscopy. Wild-type M. catarrhalis strain O35E possessed a dense layer of surface projections, whereas an isogenic uspA1 uspA2 hag triple mutant version of this strain did not possess any detectable surface projections. Examination of a uspA1 uspA2 double mutant that expressed the Hag protein revealed the presence of a relatively sparse layer of surface projections, similar to those seen on a uspA2 hag mutant that expressed UspA1. In contrast, a uspA1 hag mutant that expressed UspA2 formed a very dense layer of relatively short surface projections. These results indicate that the surface-exposed Hag protein and UspA1 and UspA2 have the potential to interact both with each other and directly with host defense systems.

Inactivation of the Moraxella catarrhalis superoxide dismutase SodA induces constitutive expression of iron-repressible outer membrane proteins

Many pathogens produce one or more superoxide dismutases (SODs), enzymes involved in the detoxification of endogenous and exogenous reactive oxygen species that are encountered during the infection process. One detectable cytoplasmic SOD was identified in the human mucosal pathogen Moraxella catarrhalis, and the gene responsible for the SOD activity, sodA, was isolated from a recent pediatric clinical isolate (strain 7169). Sequence analysis of the cloned M. catarrhalis 7169 DNA fragment revealed an open reading frame of 618 bp encoding a polypeptide of 205 amino acids with 48 to 67% identity to known bacterial manganese-cofactored SODs. An isogenic M. catarrhalis sodA mutant was constructed in strain 7169 by allelic exchange. In contrast to the wild-type 7169, the 7169::sodK20 mutant was severely attenuated for aerobic growth, even in rich medium containing supplemental amino acids, and exhibited extreme sensitivity to the redox-active agent methyl viologen. The ability of recombinant SodA to rescue the aerobic growth defects of E. coli QC774, a sodA sodB-deficient mutant, demonstrated the functional expression of SOD activity by cloned M. catarrhalis sodA. Indirect SOD detection assays were used to visualize both native and recombinant SodA activity in bacterial lysates. This study demonstrates that M. catarrhalis SodA plays a critical role in the detoxification of endogenous, metabolically produced oxygen radicals. In addition, the outer membrane protein (OMP) profile of 7169::sodK20 was consistent with iron starvation in spite of growth under iron-replete conditions. This novel observation indicates that M. catarrhalis strains lacking SodA constitutively express immunogenic OMPs previously described as iron repressible, and this potentially attenuated mutant strain may be an attractive vaccine candidate.

Vaccination of ducks with recombinant outer membrane protein (OmpA) and a 41 kDa partial protein (P45N') of Riemerella anatipestifer

The generation of protective immunity against Riemerella anatipestifer infection in ducks were investigated by immunizations with recombinant glutathione sulfatransferase (GST) fusion's proteins of OmpA, a 42kDa major outer membrane protein, and P45N', a 41kDa N-terminal fragment of a newly identified 45kDa potential surface protein from R. anatipestifer. The DNA encoding OmpA and P45N' were isolated from R. anatipestifer serotype 15 (field strain 110/89) and serotype 19 (reference strain 30/90), respectively. Immunoblotting and ELISA results showed that the purified recombinant proteins induced the production of antibodies in immunized ducks. However, neither was protective against subsequent challenge with the virulent serotype 15 strain, 34/90. All the five ducks immunized with formalinized R. anatipestifer strain 34/90 survived the challenge with the homologous strain whereas six out of seven ducks in the non-immunized control group died within a week following the challenge.

Moraxella catarrhalis: from emerging to established pathogen

Moraxella catarrhalis (formerly known as Branhamella catarrhalis) has emerged as a significant bacterial pathogen of humans over the past two decades. During this period, microbiological and molecular diagnostic techniques have been developed and improved for M. catarrhalis, allowing the adequate determination and taxonomic positioning of this pathogen. Over the same period, studies have revealed its involvement in respiratory (e.g., sinusitis, otitis media, bronchitis, and pneumonia) and ocular infections in children and in laryngitis, bronchitis, and pneumonia in adults. The development of (molecular) epidemiological tools has enabled the national and international distribution of M. catarrhalis strains to be established, and has allowed the monitoring of nosocomial infections and the dynamics of carriage. Indeed, such monitoring has revealed an increasing number of B-lactamase-positive M. catarrhalis isolates (now well above 90%), underscoring the pathogenic potential of this organism. Although a number of putative M. catarrhalis virulence factors have been identified and described in detail, their relationship to actual bacterial adhesion, invasion, complement resistance, etc. (and ultimately their role in infection and immunity), has been established in a only few cases. In the past 10 years, various animal models for the study of M. catarrhalis pathogenicity have been described, although not all of these models are equally suitable for the study of human infection. Techniques involving the molecular manipulation of M. catarrhalis genes and antigens are also advancing our knowledge of the host response to and pathogenesis of this bacterial species in humans, as well as providing insights into possible vaccine candidates. This review aims to outline our current knowledge of M. catarrhalis, an organism that has evolved from an emerging to a well-established human pathogen.

Antigenic structure of outer membrane protein E of Moraxella catarrhalis and construction and characterization of mutants

Outer membrane protein E (OMP E) is a 50-kDa protein of Moraxella catarrhalis which possesses several characteristics indicating that the protein will be an effective vaccine antigen. To study the antigenic structure of OMP E, eight monoclonal antibodies were developed and characterized. Three of the antibodies recognized epitopes which are present on the bacterial surface. Fusion peptides corresponding to overlapping regions of OMP E were constructed, and immunoblot assays were performed to localize the areas of the molecule bound by the monoclonal antibodies. These studies identified a surface-exposed epitope in the region of amino acids 80 through 180. To further study the protein, two mutants which lack OMP E were constructed. In bactericidal assays, the mutants were more readily killed by normal human serum compared to the isogenic parent strains. These results indicate that OMP E is involved in the expression of serum resistance of M. catarrhalis.

Lipooligosaccharide P(k) (Galalpha1-4Galbeta1-4Glc) epitope of moraxella catarrhalis is a factor in resistance to bactericidal activity mediated by normal human serum

Moraxella catarrhalis is a respiratory pathogen responsible for acute bacterial otitis media in children and exacerbation of chronic bronchitis in adults. M. catarrhalis strains are frequently resistant to the bactericidal activity of normal human serum. In order to determine if the lipooligosaccharide (LOS) of M. catarrhalis has a role in serum resistance, the UDP-glucose-4-epimerase (galE) gene was identified, cloned, and sequenced and a deletion/insertion mutation was introduced into M. catarrhalis strain 2951. GalE enzymatic activity, measured in whole-cell lysates, was ablated in M. catarrhalis 2951 galE. Mass spectrometric analysis of LOS isolated with hot phenol-water confirmed that strain 2951 produced a type A LOS. These studies showed that the LOS from 2951 galE had lost two hexose residues due to the galE mutation and that the resultant LOS structure lacked the (Galalpha1-4Galbeta1-4Glc) P(k) epitope found on M. catarrhalis 2951. Wild-type M. catarrhalis 2951 is resistant to complement-mediated serum bactericidal activity. In contrast, a greater than 2-log(10)-unit reduction in CFU occurred after incubation of 2951 galE in either 50 or 25% pooled human serum (PNHS), and CFU in 10% PNHS decreased by about 1 log(10) unit. These studies suggest that the P(k) epitope of the LOS may be an important factor in the resistance of M. catarrhalis to the complement-mediated bactericidal effect of normal human serum.

Progress toward the development of a vaccine to prevent Moraxella (Branhamella) catarrhalis infections

Moraxella catarrhalis is a major cause of otitis media and respiratory disease. Vaccine development is at the antigen identification stage. This review examines the more promising antigens, including the 200K protein, the hemagglutinins, the lactoferrin-binding proteins, the UspA proteins, the CopB protein, the transferrin-binding proteins, the CD protein, the E protein and lipooligosaccharide conjugates. Clinical testing of some of these antigens should begin soon.

Moraxella catarrhalis: a review of an important human mucosal pathogen

Moraxella catarrhalis has again been recognized as a significant pathogen. The past decade has witnessed an increased amount of research and understanding of the pathogenesis of the organism. This review will summarize the research pertaining to the epidemiology and components of pathogenesis in M. catarrhalis.

Complement-resistant Moraxella catarrhalis forms a genetically distinct lineage within the species

Moraxella catarrhalis is a bacterial species that has been implicated in 15-20% of all cases of otitis media in the USA and the complement-resistant variant of M. catarrhalis has been considered particularly pathogenic. A collection of geographically diverse, complement-sensitive (n=28) and -resistant strains (n=47) of M. catarrhalis was assembled in order to analyse the bacterial population structure. All strains were identified as M. catarrhalis by conventional microbiological and biochemical methods. Amplification of the small subunit (ssu) ribosomal RNA gene followed by restriction fragment length polymorphism (RFLP) analysis did not reveal consistent differences between serum-susceptible and -resistant M. catarrhalis isolates. Interestingly, upon automated ribotyping using the Qualicon RiboPrinter(R) microbial characterisation system, the complement-sensitive and -resistant strains segregated into two groups. This suggested the existence of two clearly distinguishable lineages within the species M. catarrhalis. This observation was corroborated by pulsed field gel electrophoresis (PFGE) of DNA macro-restriction fragments, a non-ribosomal PCR RFLP procedure and random amplification of polymorphic DNA (RAPD) analysis. All procedures grouped the two variants similarly. Redefinition of the taxonomic status of complement-resistant M. catarrhalis or even the definition of a new species may be opportune.

The UspA1 protein and a second type of UspA2 protein mediate adherence of Moraxella catarrhalis to human epithelial cells in vitro

The UspA1 and UspA2 proteins of Moraxella catarrhalis are structurally related, are exposed on the bacterial cell surface, and migrate as very high-molecular-weight complexes in sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Previous analysis of uspA1 and uspA2 mutants of M. catarrhalis strain 035E indicated that UspA1 was involved in adherence of this organism to Chang conjunctival epithelial cells in vitro and that expression of UspA2 was essential for resistance of this strain to killing by normal human serum (C. Aebi, E. R. Lafontaine, L. D. Cope, J. L. Latimer, S. R. Lumbley, G. H. McCracken, Jr., and E. J. Hansen, Infect. Immun. 66:3113-3119, 1998). In the present study, isogenic uspA1, uspA2, and uspA1 uspA2 mutations were constructed in three additional M. catarrhalis strains: 012E, TTA37, and 046E. The uspA1 mutant of strain 012E had a decreased ability to attach to Chang cells. However, inactivation of the uspA1 gene in both strain TTA37 and strain 046E did not cause a significant decrease in attachment ability. Inactivation of the uspA2 gene of strain TTA37 did result in a loss of attachment ability. Nucleotide sequence analysis revealed that the predicted protein encoded by the uspA2 genes of both strains TTA37 and 046E had a N-terminal half that resembled the N-terminal half of UspA1 proteins, whereas the C-terminal half of this protein was nearly identical to those of previously characterized UspA2 proteins. The gene encoding this "hybrid" protein was designated uspA2H. PCR-based analysis revealed that approximately 20% of M. catarrhalis strains apparently possess a uspA2H gene instead of a uspA2 gene. The M. catarrhalis uspA1, uspA2, and uspA2H genes were cloned and expressed in Haemophilus influenzae cells, which were used to prove that both the UspA1 and UspA2H proteins can function as adhesins in vitro.

Construction and characterization of Moraxella catarrhalis mutants defective in expression of transferrin receptors

We have previously reported the construction of an isogenic mutant defective in expression of OmpB1, the TbpB homologue, in Moraxella catarrhalis 7169. In this report, we have extended these studies by constructing and characterizing two new isogenic mutants in this clinical isolate. One mutant is defective in expression of TbpA, and the other mutant is defective in expression of both TbpA and TbpB. These isogenic mutants were confirmed by using PCR analysis, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and sequencing. In vitro growth studies, comparing all three mutants, demonstrated that the tbpA mutant and the tbpAB mutant were severely limited in their ability to grow with human holotransferrin as the sole source of iron. In contrast, the ompB1 (tbpB) mutant was capable of utilizing iron from human transferrin, although not to the extent of the parental strain. While affinity chromatography with human holotransferrin showed that each Tbp was capable of binding independently to transferrin, solid-phase transferrin binding studies using whole cells demonstrated that the tbpA mutant exhibited binding characteristics similar to those seen with the wild-type bacteria. However, the ompB1 (tbpB) mutant exhibited a diminished capacity for binding transferrin, and no binding was detected with the double mutant. These data suggest that the M. catarrhalis TbpA is necessary for the acquisition of iron from transferrin. In contrast, TbpB is not essential but may serve as a facilitory protein that functions to optimize this process. Together these mutants are essential to provide a more thorough understanding of iron acquisition mechanisms utilized by M. catarrhalis.

Evaluation of a 74-kDa transferrin-binding protein from Moraxella (Branhamella) catarrhalis as a vaccine candidate

An outer membrane protein from Moraxella catarrhalis with a mass of 74-kDa was isolated and evaluated as a vaccine candidate. The 74-kDa protein binds transferrin, and appears to be related to the other proteins from the organism that are reported to bind transferrin. The 74-kDa protein possessed conserved epitopes exposed on the bacterial surface. This is based on the reactivity with whole bacterial cells as well as complement dependent bactericidal activity of sera from mice immunized with the isolated proteins from the O35E and TTA24 isolates. However, there was divergence in the degree of antibody cross-reactivity with the protein from one strain to another. This serotypic divergence was reflected in both the complement-dependent bactericidal activities of the antibodies elicited in mice and the capacity of immune mice to clear the bacteria in a murine pulmonary model. Antibodies affinity purified from human plasma lacked bactericidal activity even though they were reactive with all the tested isolates. The 74-kDa protein appears to be a good vaccine candidate, but more studies are needed to understand its antigenic variability and whether antibodies toward it are protective.