Antigenic characterization and analysis of the human immune response to outer membrane protein E of Branhamella catarrhalis

Otitis media: recent advances in otitis media vaccine development and model systems

Otitis media is an inflammatory disorder of the middle ear caused by airways-associated bacterial or viral infections. It is one of the most common childhood infections as globally more than 80% of children are diagnosed with acute otitis media by 3 years of age and it is a common reason for doctor's visits, antibiotics prescriptions, and surgery among children. Otitis media is a multifactorial disease with various genetic, immunologic, infectious, and environmental factors predisposing children to develop ear infections. Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis are the most common culprits responsible for acute otitis media. Despite the massive global disease burden, the pathogenesis of otitis media is still unclear and requires extensive future research. Antibiotics are the preferred treatment to cure middle ear infections, however, the antimicrobial resistance rate of common middle ear pathogens has increased considerably over the years. At present, pneumococcal and influenza vaccines are administered as a preventive measure against otitis media, nevertheless, these vaccines are only beneficial in preventing carriage and/or disease caused by vaccine serotypes. Otitis media caused by non-vaccine serotype pneumococci, non-typeable H. influenza, and M. catarrhalis remain an important healthcare burden. The development of multi-species vaccines is an arduous process but is required to reduce the global burden of this disease. Many novel vaccines against S. pneumoniae, non-typeable H. influenza, and M. catarrhalis are in preclinical trials. It is anticipated that these vaccines will lower the disease burden and provide better protection against otitis media. To study disease pathology the rat, mouse, and chinchilla are commonly used to induce experimental acute otitis media to test new therapeutics, including antibiotics and vaccines. Each of these models has its advantages and disadvantages, yet there is still a need to develop an improved animal model providing a better correlated mechanistic understanding of human middle ear infections, thereby underpinning the development of more effective otitis media therapeutics. This review provides an updated summary of current vaccines against otitis media, various animal models of otitis media, their limitations, and some future insights in this field providing a springboard in the development of new animal models and novel vaccines for otitis media.

Virulence determinants of Moraxella catarrhalis: distribution and considerations for vaccine development

Moraxella catarrhalis is a human-restricted opportunistic bacterial pathogen of the respiratory mucosa. It frequently colonizes the nasopharynx asymptomatically, but is also an important causative agent of otitis media (OM) in children, and plays a significant role in acute exacerbations of chronic obstructive pulmonary disease (COPD) in adults. As the current treatment options for M. catarrhalis infection in OM and exacerbations of COPD are often ineffective, the development of an efficacious vaccine is warranted. However, no vaccine candidates for M. catarrhalis have progressed to clinical trials, and information regarding the distribution of M. catarrhalis virulence factors and vaccine candidates is inconsistent in the literature. It is largely unknown if virulence is associated with particular strains or subpopulations of M. catarrhalis, or if differences in clinical manifestation can be attributed to the heterogeneous expression of specific M. catarrhalis virulence factors in the circulating population. Further investigation of the distribution of M. catarrhalis virulence factors in the context of carriage and disease is required so that vaccine development may be targeted at relevant antigens that are conserved among disease-causing strains. The challenge of determining which of the proposed M. catarrhalis virulence factors are relevant to human disease is amplified by the lack of a standardized M. catarrhalis typing system to facilitate direct comparisons of worldwide isolates. Here we summarize and evaluate proposed relationships between M. catarrhalis subpopulations and specific virulence factors in the context of colonization and disease, as well as the current methods used to infer these associations.

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.

Identification of an outer membrane lipoprotein involved in nasopharyngeal colonization by Moraxella catarrhalis in an animal model

Colonization of the human nasopharynx by Moraxella catarrhalis is presumed to involve attachment of this bacterium to the mucosa. DNA microarray analysis was used to determine whether attachment of M. catarrhalis to human bronchial epithelial (HBE) cells in vitro affected gene expression in this bacterium. Attachment affected expression of at least 454 different genes, with 163 being upregulated and 291 being downregulated. Among the upregulated genes was one (ORF113) previously annotated as encoding a protein with some similarity to outer membrane protein A (OmpA). The protein encoded by ORF113 was predicted to have a signal peptidase II cleavage site, and globomycin inhibition experiments confirmed that this protein was indeed a lipoprotein. The ORF113 protein also contained a predicted peptidoglycan-binding domain in its C-terminal half. The use of mutant and recombinant M. catarrhalis strains confirmed that the ORF113 protein was present in outer membrane preparations, and this protein was also shown to be at least partially exposed on the bacterial cell surface. A mutant unable to produce the ORF113 protein showed little or no change in its growth rate in vitro, in its ability to attach to HBE cells in vitro, or in its autoagglutination characteristics, but it did exhibit a reduced ability to survive in the chinchilla nasopharynx. This is the first report of a lipoprotein essential to the ability of M. catarrhalis to persist in an animal model.

Bactericidal antibody response against P6, protein D, and OMP26 of nontypeable Haemophilus influenzae after acute otitis media in otitis-prone children

The bactericidal antibody response to three nontypeable Haemophilus influenzae (NTHi) outer membrane proteins (D, P6, and OMP26) was studied in 24 otitis-prone children (aged 7-28 months) after an acute otitis media (AOM) caused by NTHi. The study was carried out to understand the contribution of antigen-specific bactericidal antibody responses in the class of children who are most vulnerable to recurrent otitis media infections. Levels of protein D (P = 0.005) and P6 (P = 0.026) but not OMP26 antibodies were higher in bactericidal sera compared with nonbactericidal sera. For five (24%) and 16 (76%) of 21 bactericidal sera tested, removal of anti-protein D and P6 antibody, respectively, resulted in a two- to fourfold drop in bactericidal antibody. Antibodies to OMP26 did not make any contribution to the overall bactericidal activity in any serum samples. Eleven of 21 sera (52%) had bactericidal activity against a heterologous NTHi (86-028 NP) strain but the titers were significantly lower (P < 0.05) as compared to the homologous strains. Future studies of protein D, P6, OMP26, and other potential NTHi vaccine antigens should include studies of bactericidal antibody in children who are otitis prone as a possible correlate of protection.

Antibiotics

This chapter describes the optimal approach to antibiotic treatment of exacerbations recognizing these limitations. Such an approach relies upon an accurate diagnosis of an exacerbation, including judicious application of diagnostic tests. Determining the severity of an exacerbation follows this. If antibiotics are indicated, then a risk stratification approach is described to choose an appropriate antibiotic. An increase in airway inflammation from the baseline level in a patient appears central to the pathogenesis of most acute exacerbations. Airway inflammation measured in induced or expectorated sputum, bronchoalveolar lavage or bronchial biopsy has revealed that increased inflammation accompanies exacerbations and resolves with treatment. Potential pathogens in chronic obstructive pulmonary disease (COPD) exacerbations include typical respiratory bacterial pathogens, respiratory viruses, and atypical bacteria. The current model of bacterial exacerbation pathogenesis involves both host and pathogen factors. Acquisition of strains of bacterial pathogens that are new to the host from the environment is the primary event that puts the patient with COPD at risk for an exacerbation. The traditional aims of treatment of an exacerbation are improvement in clinical status and the prevention of complications. The role of antibiotics in the treatment of COPD exacerbations has been a matter of controversy. Even more contentious has been the issue whether antibiotic choice is relevant to clinical outcome of exacerbations. Recommendations for antibiotic use among published guidelines are inconsistent.

Optimizing antibiotic selection in treating COPD exacerbations

Our understanding of the etiology, pathogenesis and consequences of acute exacerbations of chronic obstructive pulmonary disease (COPD) has increased substantially in the last decade. Several new lines of evidence demonstrate that bacterial isolation from sputum during acute exacerbation in many instances reflects a cause-effect relationship. Placebo-controlled antibiotic trials in exacerbations of COPD demonstrate significant clinical benefits of antibiotic treatment in moderate and severe episodes. However, in the multitude of antibiotic comparison trials, the choice of antibiotics does not appear to affect the clinical outcome, which can be explained by several methodological limitations of these trials. Recently, comparison trials with nontraditional end-points have shown differences among antibiotics in the treatment of exacerbations of COPD. Observational studies that have examined clinical outcome of exacerbations have repeatedly demonstrated certain clinical characteristics to be associated with treatment failure or early relapse. Optimal antibiotic selection for exacerbations has therefore incorporated quantifying the risk for a poor outcome of the exacerbation and choosing antibiotics differently for low risk and high risk patients, reserving the broader spectrum drugs for the high risk patients. Though improved outcomes in exacerbations with antibiotic choice based on such risk stratification has not yet been demonstrated in prospective controlled trials, this approach takes into account concerns of disease heterogeneity, antibiotic resistance and judicious antibiotic use in exacerbations.

Mining the Moraxella catarrhalis genome: identification of potential vaccine antigens expressed during human infection

Moraxella catarrhalis is an important cause of respiratory infections in adults and otitis media in children. Developing an effective vaccine would reduce the morbidity, mortality, and costs associated with such infections. An unfinished genome sequence of a strain of M. catarrhalis available in the GenBank database was analyzed, and open reading frames predicted to encode potential vaccine candidates were identified. Three genes encoding proteins having molecular masses of approximately 22, 75, and 78 kDa (designated Msp [Moraxella surface proteins]) (msp22, msp75, and msp78, respectively) were determined to be conserved by competitive hybridization using a microarray, PCR, and sequencing of the genes in clinical isolates of M. catarrhalis. The genes were transcribed when M. catarrhalis was grown in vitro. These genes were amplified by PCR and cloned into Escherichia coli expression vectors. Recombinant proteins were generated and then studied using enzyme-linked immunosorbent assays with preacquisition and postclearance serum and sputum samples from 31 adults with chronic obstructive pulmonary disease (COPD) who acquired and cleared M. catarrhalis. New antibody responses to the three proteins were observed for a small proportion of the patients with COPD, indicating that these proteins were expressed during human infection. These studies indicate that the Msp22, Msp75, and Msp78 proteins, whose genes were discovered using genome mining, are highly conserved among strains, are expressed during human infection with M. catarrhalis, and represent potential vaccine antigens.

Serum levels of soluble HLA and IL-2R molecules in patients with urogenital chlamydia infection

Cellular immunity plays a central role in immune response to chlamydial infection, and soluble forms of immune cell membrane antigens take part in the regulation of immune response. Using an immunoenzymatic method, we determined serum levels of soluble HLA molecules (sHLA-I and sHLA-DR) and soluble CD25 molecules (sCD25) in patients with genital chlamydial infection. Specimens from patients with nonspecific inflammation of the urogenital tract were studied and healthy volunteers served as controls. We revealed that serum levels of sHLA-DR and sCD25 increased 3.5- and 2.3-fold, respectively, during chlamydial infection, while the levels of sHLA-I were not changed. Nonspecific inflammation of the urogenital tract was characterized by a 1.5-fold increase in sHLA-I, a 1.6-fold decrease in sCD25, and no changes of sHLA-DR levels in comparison with healthy volunteers. We concluded that Th1 immune responses might dominate during genital chlamydial infection contrary to the state of nonspecific inflammation of urogenital tract.

Metabolic analysis of Moraxella catarrhalis and the effect of selected in vitro growth conditions on global gene expression

The nucleotide sequence from the genome of Moraxella catarrhalis ATCC 43617 was annotated and used both to assess the metabolic capabilities and limitations of this bacterium and to design probes for a DNA microarray. An absence of gene products for utilization of exogenous carbohydrates was noteworthy and could be correlated with published phenotypic data. Gene products necessary for aerobic energy generation were present, as were a few gene products generally ascribed to anaerobic systems. Enzymes for synthesis of all amino acids except proline and arginine were present. M. catarrhalis DNA microarrays containing 70-mer oligonucleotide probes were designed from the genome-derived nucleotide sequence data. Analysis of total RNA extracted from M. catarrhalis ATCC 43617 cells grown under iron-replete and iron-restricted conditions was used to establish the utility of these DNA microarrays. These DNA microarrays were then used to analyze total RNA from M. catarrhalis cells grown in a continuous-flow biofilm system and in the planktonic state. The genes whose expression was most dramatically increased by growth in the biofilm state included those encoding a nitrate reductase, a nitrite reductase, and a nitric oxide reductase. Real-time reverse transcriptase PCR analysis was used to validate these DNA microarray results. These results indicate that growth of M. catarrhalis in a biofilm results in increased expression of gene products which can function not only in energy generation but also in resisting certain elements of the innate immune response.

The Moraxella catarrhalis autotransporter McaP is a conserved surface protein that mediates adherence to human epithelial cells through its N-terminal passenger domain

The protein McaP was previously shown to be an adhesin expressed by the Moraxella catarrhalis strain O35E, which also displays esterase and phospholipase B activities (J. M. Timpe et al., Infect. Immun. 71:4341-4350, 2003). In the present study, sequence analysis suggests that McaP is a conventional autotransporter protein that contains a 12-stranded beta-barrel transporter module (amino acids [aa] 383 to 650) linked to a surface-exposed passenger domain exhibiting lipolytic activity (aa 62 to 330). An in-frame deletion removing most of this predicted N-terminal passenger domain was engineered, and Escherichia coli expressing the truncated McaP protein exhibited greatly reduced adherence to A549 human lung epithelial cells compared to E. coli expressing wild-type McaP. Site-directed mutagenesis of a serine residue at position 62 of McaP, predicted to be important for the lipolytic activity of the protein, resulted in loss of hydrolysis of p-nitrophenyl ester of caproate. E. coli expressing this mutated McaP, however, adhered to A549 monolayers at levels greater than recombinant bacteria expressing the wild-type adhesin. These results indicate that the predicted passenger domain of McaP is involved in both the binding and the lipolytic activity of the molecule and demonstrate that the adhesive properties of McaP do not require its lipolytic activity. Sequence analysis of mcaP from eight Moraxella catarrhalis strains revealed that the gene product is highly conserved at the amino acid level (98 to 100% identity), and Western blot analysis demonstrated that a panel of 16 isolates all express McaP. Flow cytometry experiments using antibodies raised against various portions of McaP indicated that its predicted passenger domain as well as transporter module contain surface-exposed epitopes. In addition to binding to the surface of intact bacteria, these antibodies were found to decrease adherence of M. catarrhalis to A549 human lung cells by up to 47% and to reduce binding of recombinant E. coli expressing McaP by 98%. These results suggest that McaP should be considered as a potential vaccine antigen.

Human antibody response to outer membrane protein G1a, a lipoprotein of Moraxella catarrhalis

Moraxella catarrhalis is an important cause of respiratory infections in adults with chronic obstructive pulmonary disease (COPD) and of otitis media in children. Outer membrane protein (OMP) G1a is an approximately 29-kDa surface lipoprotein and is a potential vaccine candidate. The gene that encodes OMP G1a was expressed and purified using a novel plasmid vector. [(3)H]palmitic acid labeling demonstrated that both native and recombinant OMP G1a contain covalently bound palmitic acid. To assess the expression of OMP G1a during human infection, paired sera and sputum supernatants from adults with COPD followed prospectively were studied by enzyme-linked immunosorbent assays with recombinant lipidated OMP G1a to detect antibodies made specifically during carriage of M. catarrhalis. Overall, 23% of patients developed either a serum immunoglobulin G (IgG) response (9%) or sputum IgA response (21%) to OMP G1a, following 100 episodes of acquisition and clearance of M. catarrhalis. Patients developed antibody responses at similar rates following episodes of clinical exacerbation compared to asymptomatic colonization. Serum IgG antibodies following natural infection were directed predominantly at OMP G1a epitopes that are not exposed on the bacterial surface. These data show that OMP G1a is expressed during infection of the human respiratory tract and is a target of systemic and mucosal antibodies. These observations indicate that OMP G1a, a highly conserved surface protein, should be evaluated further as a vaccine candidate.

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.

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.

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.

Chronic obstructive pulmonary disease: role of bacteria and guide to antibacterial selection in the older patient

Chronic obstructive pulmonary disease (COPD) is a common problem in the elderly. The disease is characterised by intermittent worsening of symptoms and these episodes are called acute exacerbations. The best estimate, based on several lines of evidence, is that approximately half of all exacerbations are caused by bacteria. These lines of evidence include studies of lower respiratory tract bacteriology during exacerbations, correlation of airways' inflammation with results of sputum cultures during exacerbations, analysis of immune responses to bacterial pathogens, and the observation in randomised, prospective, placebo-controlled trials that antibacterial therapy is of benefit. The most important bacterial causes of exacerbations of COPD are nontypeable Haemophilus influenzae, Moraxella catarrhalis, Streptococcus pneumoniae and Chlamydia pneumoniae. In approaching the elderly patient with an exacerbation, it is useful to consider the severity of the exacerbation based on three cardinal symptoms: increased sputum volume, increased sputum purulence and increased dyspnoea compared with baseline. Patients experiencing moderate (two symptoms) or severe (all three symptoms) exacerbations benefit from antibacterial therapy. Consideration of underlying host factors allows for a rational choice of antibacterial agent. Patients are considered to have 'simple COPD' or 'complicated COPD' based on: (i) the severity of underlying lung disease; (ii) the frequency of exacerbations; and (iii) the presence of comorbid conditions. It is proposed that patients with simple COPD are treated with doxycycline, a newer macrolide, or an extended-spectrum oral cephalosporin; and patients with complicated COPD are treated with amoxicillin/clavulanate or a fluoroquinolone. The major goals of antibacterial therapy for exacerbations of COPD are acceleration of symptom resolution and prevention of the complications of exacerbation.

Conservation of outer membrane protein E among strains of Moraxella catarrhalis

Outer membrane protein E (OMP E) is a 50-kDa protein of Moraxella catarrhalis which has several features that suggest that the protein may be an effective vaccine antigen. To assess the conservation of OMP E among strains of M. catarrhalis, 22 isolates were studied with eight monoclonal antibodies which recognize epitopes on different regions of the protein. Eighteen of 22 strains were reactive with all eight antibodies. The sequences of ompE from 16 strains of M. catarrhalis were determined, including the 4 strains which were nonreactive with selected monoclonal antibodies. Analysis of sequences indicate a high degree of conservation among strains, with sequence differences clustered in limited regions of the gene. To assess the stability of ompE during colonization of the human respiratory tract, the sequences of ompE of isolates collected from patients colonized with the same strain for 3 to 9 months were determined. The sequences remained unchanged. These results indicate that OMP E is highly conserved among strains of M. catarrhalis, and preliminary studies indicate that the gene which encodes OMP E remains stable during colonization of the human respiratory tract.

Bacterial infection in chronic obstructive pulmonary disease in 2000: a state-of-the-art review

Chronic obstructive pulmonary disease (COPD) is the fourth leading cause of death in the United States. The precise role of bacterial infection in the course and pathogenesis of COPD has been a source of controversy for decades. Chronic bacterial colonization of the lower airways contributes to airway inflammation; more research is needed to test the hypothesis that this bacterial colonization accelerates the progressive decline in lung function seen in COPD (the vicious circle hypothesis). The course of COPD is characterized by intermittent exacerbations of the disease. Studies of samples obtained by bronchoscopy with the protected specimen brush, analysis of the human immune response with appropriate immunoassays, and antibiotic trials reveal that approximately half of exacerbations are caused by bacteria. Nontypeable Haemophilus influenzae, Moraxella catarrhalis, and Streptococcus pneumoniae are the most common causes of exacerbations, while Chlamydia pneumoniae causes a small proportion. The role of Haemophilus parainfluenzae and gram-negative bacilli remains to be established. Recent progress in studies of the molecular mechanisms of pathogenesis of infection in the human respiratory tract and in vaccine development guided by such studies promises to lead to novel ways to treat and prevent bacterial infections in COPD.

Vaccines for Moraxella catarrhalis

Vaccine development for Moraxella catarrhalis is in the antigen identification stage. M. catarrhalis does not appear to synthesize secreted antigens such as exotoxins, nor does it appear to possess a carbohydrate capsule. Modified forms of these antigens are usually good vaccine components. There is some interest in whole bacterial cells and membrane fractions, but the search has largely focused on purified outer surface antigens. All of the present antigens have been selected based on the response seen in animals, although the antibody response seen in people exposed to the bacterium provides some guidance. The antibody response provides information related to the cross-strain preservation of epitopes and whether they are surface exposed. Antigens that elicit antibodies that have complement dependent bactericidal capacity, opsonophagocytic activity or interfere with one of the antigen's known functions such as adhesion or nutrient acquisition are particularly valued. In addition to examining the antibody response, some antigens have been evaluated in a murine pulmonary clearance model. Using these assays and model, several vaccine candidates have been identified. The antigens may be roughly classified by the function they serve the bacterium. One set appears to promote adhesion to host tissues and includes the hemagglutinins, ubiquitous surface protein A1 (UspA1), and possibly the CD protein. A second set is involved in nutrient acquisition. This set includes the lactoferrin binding protein A (LbpA) and lactoferrin binding protein B (LbpB), the transferrin binding protein A (TbpA) and transferrin binding protein B (TbpB), the CD and E porins, and the Catarrhalis outer membrane protein B (CopB). A third set is comprised of antigens involved in virulence and it includes lipooligosaccharide (LOS) and the ubiquitous surface protein A2 (UspA2). Antigens of unknown function, such as the 200K protein, may also be vaccine candidates. The antigens that are most suitable will be determined in clinical studies that are only beginning now.

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.

Applications of flow cytometry to clinical microbiology

Classical microbiology techniques are relatively slow in comparison to other analytical techniques, in many cases due to the need to culture the microorganisms. Furthermore, classical approaches are difficult with unculturable microorganisms. More recently, the emergence of molecular biology techniques, particularly those on antibodies and nucleic acid probes combined with amplification techniques, has provided speediness and specificity to microbiological diagnosis. Flow cytometry (FCM) allows single- or multiple-microbe detection in clinical samples in an easy, reliable, and fast way. Microbes can be identified on the basis of their peculiar cytometric parameters or by means of certain fluorochromes that can be used either independently or bound to specific antibodies or oligonucleotides. FCM has permitted the development of quantitative procedures to assess antimicrobial susceptibility and drug cytotoxicity in a rapid, accurate, and highly reproducible way. Furthermore, this technique allows the monitoring of in vitro antimicrobial activity and of antimicrobial treatments ex vivo. The most outstanding contribution of FCM is the possibility of detecting the presence of heterogeneous populations with different responses to antimicrobial treatments. Despite these advantages, the application of FCM in clinical microbiology is not yet widespread, probably due to the lack of access to flow cytometers or the lack of knowledge about the potential of this technique. One of the goals of this review is to attempt to mitigate this latter circumstance. We are convinced that in the near future, the availability of commercial kits should increase the use of this technique in the clinical microbiology laboratory.

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.

Applications of flow cytometry to clinical microbiology

Classical microbiology techniques are relatively slow in comparison to other analytical techniques, in many cases due to the need to culture the microorganisms. Furthermore, classical approaches are difficult with unculturable microorganisms. More recently, the emergence of molecular biology techniques, particularly those on antibodies and nucleic acid probes combined with amplification techniques, has provided speediness and specificity to microbiological diagnosis. Flow cytometry (FCM) allows single- or multiple-microbe detection in clinical samples in an easy, reliable, and fast way. Microbes can be identified on the basis of their peculiar cytometric parameters or by means of certain fluorochromes that can be used either independently or bound to specific antibodies or oligonucleotides. FCM has permitted the development of quantitative procedures to assess antimicrobial susceptibility and drug cytotoxicity in a rapid, accurate, and highly reproducible way. Furthermore, this technique allows the monitoring of in vitro antimicrobial activity and of antimicrobial treatments ex vivo. The most outstanding contribution of FCM is the possibility of detecting the presence of heterogeneous populations with different responses to antimicrobial treatments. Despite these advantages, the application of FCM in clinical microbiology is not yet widespread, probably due to the lack of access to flow cytometers or the lack of knowledge about the potential of this technique. One of the goals of this review is to attempt to mitigate this latter circumstance. We are convinced that in the near future, the availability of commercial kits should increase the use of this technique in the clinical microbiology laboratory.

Analysis of antigenic structure and human immune response to outer membrane protein CD of Moraxella catarrhalis

Moraxella catarrhalis is an important cause of otitis media in children and lower respiratory tract infections in adults with chronic obstructive pulmonary disease (COPD). Outer membrane protein CD (OMP CD) is a 45-kDa protein which is a potential vaccine antigen to prevent infections caused by M. catarrhalis. Eight monoclonal antibodies were used to study the antigenic structure of the OMP CD molecule by assaying recombinant peptides corresponding to the sequence of the protein. This approach identified two surface-exposed epitopes, including one near the amino terminus (amino acids 25 to 44) and one in the central region of the molecule (amino acids 261 to 331). Assays with serum and sputum supernatants of adults with COPD revealed variable levels of antibodies to OMP CD among individuals. To determine which portions of the OMP CD molecule were recognized by human antibodies, three human serum samples were studied with six recombinant peptides which span the sequence of OMP CD. All three sera contained immunoglobulin G antibodies which recognized exclusively the peptide corresponding to amino acids 203 to 260 by immunoblot assay. Adsorption experiments with whole bacteria established that some of the human antibodies are directed at surface-exposed epitopes on OMP CD. We conclude that OMP CD is a highly conserved molecule which contains at least two separate epitopes which are exposed on the bacterial surface. While individual adults with COPD show variability in the immune response to OMP CD, a specific region of the OMP CD molecule (amino acids 203 to 260) is important as a target of the human immune response.