Outbreak of Moraxella catarrhalis in a respiratory unit

Preferred conformations of lipooligosaccharides and oligosaccharides of Moraxella catarrhalis

Moraxella catarrhalis (M. catarrhalis) is a pathogenic gram-negative bacterium that causes otitis media and sinusitis in children. Three major serotypes A, B and C are identified to account for approximately 95% of the clinical isolates. Understanding the conformational properties of different serotypes of M. catarrhalis provides insights into antigenic determinants. In this work, all-atom molecular dynamics simulations were conducted for M. catarrhalis lipooligosaccharide (LOS) bilayer systems and oligosaccharides (OS) in water solution to investigate the conformational similarities and differences of three serotypes. For up to 10 neutral monosaccharides in the core part, the conformational ensembles described by the pair-wise root mean square deviation distributions are similar among the three serotypes of either the LOS or OS. At the central β-($1\to4$)-linkage, anti-$\psi$ conformation in conjunction with the gauche-gauche (g-) conformation of the central trisubstituted glucosyl residue is observed as the dominant conformation to sustain the structural characteristics of M. catarrhalis three types, which is further supported by calculated transglycosidic ${}^3{J}_{C,H}\Big({\psi}_H\Big)$ of serotype A in comparison to experimental data. Interestingly, the conformational variability of three serotypes is more restricted for the OS in water solution than that in the LOS bilayer systems. The LOS-LOS interactions in the bilayer systems are responsible for the increased conformational diversity despite of tight packing. Solvent-accessible surface area analysis suggests that a trisaccharide attached to the β-($1\to 6$)-linked sugar in all three serotypes of LOS could be the common epitope and have the possibility to interact with antibodies.

Molecular epidemiology study of a nosocomial Moraxella catarrhalis outbreak in a neurological rehabilitation unit

BACKGROUND

Moraxella catarrhalis is a common agent causing upper and lower respiratory tract infections, particularly of ventilated patients. The bacteria are transmitted between humans by direct and indirect contacts. However, reports of nosocomial outbreaks by this pathogen are scarce.

AIM

To analyse M. catarrhalis strains isolated during an outbreak in a medical rehabilitation centre to reveal their clonal relationship and to elucidate potential transmission routes.

METHODS

Extensive environmental and medical staff sampling was performed. Phenotypic and genotypic analyses of 15 isolates were executed, including repetitive element palindromic polymerase chain reaction (repPCR) and whole-genome sequencing. Furthermore, an intensified hygiene regimen was installed.

FINDINGS

The clonal nature of nine patient isolates and a simultaneous presence of separate entities including a strain isolated from a physician during staff screening was confirmed. Although neither asymptomatic carriers among the staff persons nor outbreak strain-contaminated fomites were identified for a specific intervention, the outbreak ceased due to maximum general and specific hygiene precautions. Retrospective analysis showed the increasing prevalence of M. catarrhalis strains over a period of two years before the incidence. Since then and after returning to the regular hygiene regimen, only one patient with a phenotypically diverse M. catarrhalis isolate has been documented.

CONCLUSION

The first M. catarrhalis outbreak involving nine patients of a neurological and trauma rehabilitation centre was reported. Potential transmission pathways were discussed. Comprehensive outbreak analyses insinuated the extension of routine laboratory storage time for defined species.

Potential targets for next generation antimicrobial glycoconjugate vaccines

Cell surface carbohydrates have been proven optimal targets for vaccine development. Conjugation of polysaccharides to a carrier protein triggers a T-cell-dependent immune response to the glycan moiety. Licensed glycoconjugate vaccines are produced by chemical conjugation of capsular polysaccharides to prevent meningitis caused by meningococcus, pneumococcus and Haemophilus influenzae type b. However, other classes of carbohydrates (O-antigens, exopolysaccharides, wall/teichoic acids) represent attractive targets for developing vaccines. Recent analysis from WHO/CHO underpins alarming concern toward antibiotic-resistant bacteria, such as the so called ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter spp.) and additional pathogens such as Clostridium difficile and Group A Streptococcus. Fungal infections are also becoming increasingly invasive for immunocompromised patients or hospitalized individuals. Other emergencies could derive from bacteria which spread during environmental calamities (Vibrio cholerae) or with potential as bioterrorism weapons (Burkholderia pseudomallei and mallei, Francisella tularensis). Vaccination could aid reducing the use of broad-spectrum antibiotics and provide protection by herd immunity also to individuals who are not vaccinated.

This review analyzes structural and functional differences of the polysaccharides exposed on the surface of emerging pathogenic bacteria, combined with medical need and technological feasibility of corresponding glycoconjugate vaccines.

Seasonal variation of respiratory pathogen colonization in asymptomatic health care professionals: A single-center, cross-sectional, 2-season observational study

BACKGROUND

The purpose of this study was to determine the seasonal variance of potentially pathogenic bacterial and viral organisms in nasopharyngeal specimens obtained from asymptomatic health care professionals (HCPs) during the 2014 winter and summer months.

METHODS

Nasopharyngeal specimens from 100 HCPs were collected from Huntsville Hospital (Huntsville, AL) during the winter and from 100 HCPs during the summer. All subjects were tested for 22 viruses and 19 bacteria using Target Enriched Multiplex Polymerase Chain Reaction. Both seasonal cohorts were composed of students, nurses, physicians, and residents.

RESULTS

Of the 100 HCPs tested during the winter, 34 subjects were colonized with at least 1 bacterium, and 11 tested positive for at least 1 virus. Methicillin-resistant Staphylococcus aureus (MRSA), Moraxella catarrhalis, and coronavirus were the most frequently detected potentially infectious agents. Of the 100 HCPs tested during the summer, 37 tested positive for at least 1 bacterium, and 4 tested positive for a viral agent. The most prevalent bacteria were MRSA and Klebsiella pneumonia.

CONCLUSION

Nasopharyngeal carriage among asymptomatic HCPs was common, but the frequency and presence of potential pathogens varied with each season. Understanding the colonization and infection potential of upper respiratory organisms is important, particularly for viruses. Although asymptomatic HCPs certainly harbor a number of different potentially infectious agents, future studies are needed to determine whether colonized pathogens are transmitted or initiate infection in at-risk patient populations.

Pulmonary thin-section CT findings in acute Moraxella catarrhalis pulmonary infection

OBJECTIVE

Moraxella catarrhalis is an important pathogen in the exacerbation of chronic obstructive pulmonary disease. The aim of this study was to assess the clinical and pulmonary thin-section CT findings in patients with acute M. catarrhalis pulmonary infection.

METHODS

Thin-section CT scans obtained between January 2004 and March 2009 from 292 patients with acute M. catarrhalis pulmonary infection were retrospectively evaluated. Clinical and pulmonary CT findings in the patients were assessed. Patients with concurrent infection including Streptococcus pneumoniae (n = 72), Haemophilus influenzae (n = 61) or multiple pathogens were excluded from this study.

RESULTS

The study group comprised 109 patients (66 male, 43 female; age range 28-102 years; mean age 74.9 years). Among the 109 patients, 34 had community-acquired and 75 had nosocomial infections. Underlying diseases included pulmonary emphysema (n = 74), cardiovascular disease (n = 44) or malignant disease (n = 41). Abnormal findings were seen on CT scans in all patients and included ground-glass opacity (n = 99), bronchial wall thickening (n = 85) and centrilobular nodules (n = 79). These abnormalities were predominantly seen in the peripheral lung parenchyma (n = 99). Pleural effusion was found in eight patients. No patients had mediastinal and/or hilar lymph node enlargement.

CONCLUSIONS

M. catarrhalis pulmonary infection was observed in elderly patients, often in combination with pulmonary emphysema. CT manifestations of infection were mainly ground-glass opacity, bronchial wall thickening and centilobular nodules.

Molecular epidemiological study of Moraxella catarrhalis isolated from nosocomial respiratory infection patients in a community hospital in Japan

BACKGROUND

Moraxella catarrhalis, occasionally, plays the essential role in nosocomial respiratory infection (NRI). Few studies have reported the route by which this organism spreads in a nosocomial infection outbreak. We identified characteristics of the strains isolated from NRI and attempted to reveal the potential nosocomial transmission routes.

METHODS

A follow-up study has been performed in a Japanese community hospital between July 2002 and January 2003. M. catarrhalis clinical isolates were identified and beta-lactamase production test as well as the minimal inhibitory concentrations (MICs) have been examined. Pulsed-field gel electrophoresis (PFGE) and the multi locus sequence typing method (MLST) have been introduced as the effective "fingerprinting" methods.

RESULTS

A total of 29 strains were isolated from 17 participants; 7 independent DNA fragment patterns were detected by PFGE. Pattern B (defined in this study) was dominant, and was detected both in strains from a health care worker (HCW) and inpatients. In the 9 selected strains analyzed by MLST, 7 unique MLST types were identified, which showed the congruence with the results of PFGE results.

CONCLUSION

Epidemiological analysis proved the transmission route from patient to patient, and suggested that more studies should be focused on identifying the possible transmission route between HCWs and inpatients.

The rise and spread of a new pathogen: seroresistant Moraxella catarrhalis

The nosocomial human pathogen Moraxella catarrhalis is one the most important agents of human respiratory tract infections. This species is composed of two distinct lineages, one of only moderate virulence, the so-called serosensitive subpopulation, and a second, the seroresistant one, which is enriched among strains that harbor two major virulence traits: complement resistance and adherence to epithelial cells. Using a suite of population genetics tools, we show that the seroresistant lineage is also characterized by higher homologous recombination and mutation rates at housekeeping genes relative to its less pathogenic counterpart. Thus, sex and virulence have evolved in tandem in M. catarrhalis. Moreover, phylogenetic and Bayesian analyses that take into account recombination between the two clades show that the ancestral group was avirulent, is possibly 70 million years old, and must have infected mammals prior to the evolution of humans, which occurred later. The younger seroresistant isolates went through an important population expansion some 5 million years ago, coincident with the hominid expansion. This rise and spread was possibly coupled with a host shift and the acquisition of virulence genes.

Pneumonia caused by Moraxella catarrhalis in haematopoietic stem cell transplant patients. Report of two cases and review of the literature

Moraxella catarrhalis is a gram negative diplococcus that causes a variety of upper and lower respiratory tract infections. Patients with malignant, hematological disorders treated with intensive cytotoxic chemotherapy, and recipients of various forms of haematopoietic stem cell transplant receiving immunosuppressive agents are at high risk of developing severe infections and septic complications. Early detection of the organism and prompt treatment with appropriate antibiotics provide both resolution of the infection and prevention of further consequences. Two patients with haematopoietic stem cell transplant who developed pneumonia caused by M. catarrhalis at King Faisal Specialist Hospital and Research Centre in Riyadh are reported and the literature is reviewed. To our knowledge, these are the first case reports of M. catarrhalis pneumonia in haematopoietic stem cell transplant patients.

Possible relationship of PFGE patterns of Moraxella catarrhalis between hospital- and community-acquired respiratory infections in a community hospital

We describe a prospective study of molecular analysis of Moraxella catarrhalis isolated from a community hospital. Our study was designed to investigate the possible relationship of pulsed-field gel electrophoresis (PFGE) patterns of M. catarrhalis between hospital- and community-acquired respiratory infections. A nosocomial outbreak of M. catarrhalis was observed between September 2000 and September 2001. During the study period, 40 strains of M. catarrhalis were isolated from a total of 32 patients with respiratory infections (26 strains from 18 inpatients, and 14 strains from 14 outpatients). We compared the PFGE patterns in 40 strains of M. catarrhalis isolated from the respiratory tract of the study patients. The genomic types of M. catarrhalis were classified into three PFGE patterns (A, B, and C). Interestingly, the nosocomial outbreak of M. catarrhalis included two patterns (A and B). Of the three patterns, two patterns (A and B) were found in both inpatients and outpatients. More interestingly, two subtypes of pattern B (B1 and B4) were simultaneously found in both inpatients and outpatients. Our results indicated that PFGE with SmaI chromosomal digestion is a suitable technique to establish the inter-strain genetic relatedness of M. catarrhalis, and suggested that the outbreak of M. catarrhalis occasionally included miscellaneous PFGE patterns. The results also showed that PFGE patterns of M. catarrhalis isolates were similar between hospital- and community-acquired respiratory infections. Analysis of the subtypes suggested that there might be some association between hospital- and community-acquired respiratory infections caused by M. catarrhalis.

Changes in genetic types and population dynamics of Moraxella catarrhalis in hospitalized children are not associated with an exacerbation of existing disease

Pulsed-field gel electrophoresis typing was performed on a retrospective set of 129 Moraxella catarrhalis isolates obtained over a 20 month period from 70 children admitted to, or presenting at, the Erasmus University Medical Center, Rotterdam, The Netherlands. The mean age of the children (at the end of the study) was 2.5 years, with a range of 6 months to 15 years. Fifty-one different M. catarrhalis types were isolated from the hospitalized children, with 31 % (22/70) being infected with two particularly prevalent M. catarrhalis types. These two prevalent types also exhibited different protein profiles. The majority (72%; 16/22) of the children infected with these two predominant types had spent at least 1 week on two paediatric intensive care wards. No exacerbation of existing disease or new disease was observed in children who experienced M. catarrhalis type changes.

Gram-negative Diplococcal Respiratory Infections

Human respiratory tract infections caused by gram- negative diplococci continue to remain significant issues in health care. Although not addressed as frequently as the classical diplococcal pneumonia, the gram-positive Streptococcus pneumoniae (the pneumococcus), infections due to Neisseria meningitidis (the meningococcus), and Moraxella catarrhalis (formerly called both Neisseria catarrhalis and Branhamella catarrhalis) are addressed here including their microbiology, respiratory tract manifestations, antimicrobial treatment, and potential prevention with immunization.

Quantitative detection of Moraxella catarrhalis in nasopharyngeal secretions by real-time PCR

The recognition of Moraxella catarrhalis as an important cause of respiratory tract infections has been protracted, mainly because it is a frequent commensal organism of the upper respiratory tract and the diagnostic sensitivity of blood or pleural fluid culture is low. Given that the amount of M. catarrhalis bacteria in the upper respiratory tract may change during infection, quantification of these bacteria in nasopharyngeal secretions (NPSs) by real-time PCR may offer a suitable diagnostic approach. Using primers and a fluorescent probe specific for the copB outer membrane protein gene, we detected DNA from serial dilutions of M. catarrhalis cells corresponding to 1 to 10(6) cells. Importantly, there was no difference in the amplification efficiency when the same DNA was mixed with DNA from NPSs devoid of M. catarrhalis. The specificity of the reaction was further confirmed by the lack of amplification of DNAs from other Moraxella species, nontypeable Haemophilus influenzae, H. influenzae type b, Streptococcus pneumoniae, Streptococcus oralis, Streptococcus pyogenes, Bordetella pertussis, Corynebacterium diphtheriae, and various Neisseria species. The assay applied to NPSs from 184 patients with respiratory tract infections performed with a sensitivity of 100% and a specificity of up to 98% compared to the culture results. The numbers of M. catarrhalis organisms detected by real-time PCR correlated with the numbers detected by semiquantitative culture. This real-time PCR assay targeting the copB outer membrane protein gene provided a sensitive and reliable means for the rapid detection and quantification of M. catarrhalis in NPSs; may serve as a tool to study changes in the amounts of M. catarrhalis during lower respiratory tract infections or following vaccination against S. pneumoniae, H. influenzae, or N. meningitidis; and may be applied to other clinical samples.

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.

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.

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.

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.

Moraxella catarrhalis: clinical significance, antimicrobial susceptibility and BRO beta-lactamases

Moraxella catarrhalis is an important pathogen of humans. It is a common cause of respiratory infections, particularly otitis media in children and lower respiratory tract infections in the elderly. Colonisation of the upper respiratory tract appears to be associated with infection in many cases, although this association is not well understood. Nosocomial transmission is being increasingly documented and the emergence of this organism as a cause of bacteremia is of concern. The widespread production of a beta-lactamase enzyme renders Moraxella catarrhalis resistant to the penicillins. Cephalosporins and beta-lactamase inhibitor combinations are effective for treatment of beta-lactamase producers, and the organism remains nearly universally susceptible to the macrolides, fluoroquinolones, tetracyclines and the combination of trimethoprim and sulfamethoxazole. Two major beta-lactamase forms, BRO-1 and BRO-2, have been described on the basis of their isoelectric focusing patterns. The BRO-1 enzyme is found in the majority of beta-lactamase-producing isolates and confers a higher level of resistance to strains than BRO-2. The BRO enzymes are membrane associated and their production appears to be mediated by chromosomal determinants which are transmissible by an unknown mechanism. The origin of these novel proteins is unknown.

Branhamella catarrhalis: epidemiology, surface antigenic structure, and immune response

Over the past decade, Branhamella catarrhalis has emerged as an important human pathogen. The bacterium is a common cause of otitis media in children and of lower respiratory tract infections in adults with chronic obstructive pulmonary disease. B. catarrhalis is exclusively a human pathogen. It colonizes the respiratory tract of a small proportion of adults and a larger proportion of children. Studies involving restriction enzyme analysis of genomic DNA show that colonization is a dynamic process, with the human host eliminating and acquiring new strains frequently. The surface of B. catarrhalis contains outer membrane proteins, lipooligosaccharide, and pili. The genes which encode several outer membrane proteins have been cloned, and some of these proteins are being studied as potential vaccine antigens. Analysis of the immune response has been limited by the lack of an adequate animal model of B. catarrhalis infection. New information regarding outer membrane structure should guide studies of the human immune response to B. catarrhalis. Immunoassays which specifically detect antibodies to determinants exposed on the bacterial surface will elucidate the most relevant immune response. The recognition of B. catarrhalis as an important human pathogen has stimulated research on the epidemiology and surface structures of the bacterium. Future studies to understand the mechanisms of infection and to elucidate the human immune response to infection hold promise of developing new methods to treat and prevent infections caused by B. catarrhalis.

Outer membrane protein CD of Branhamella catarrhalis: sequence conservation in strains recovered from the human respiratory tract

Branhamella catarrhalis causes lower respiratory tract infections in patients with chronic obstructive pulmonary disease. The outer membrane protein CD (OMP-CD) of B. catarrhalis is a major, heat-modifiable OMP. The goals of this study are to characterize the degree of conservation of OMP-CD among strains and to investigate if OMP-CD maintains its homogeneity under the effect of host immune selective pressure. Isolates of B. catarrhalis were collected prospectively from patients with bronchiectasis and chronic bronchitis. We studied the OMP-CD gene by analysis of PCR restriction fragment length polymorphisms (PCR-RFLP) and further determined DNA sequence of the CD gene of eight selected isolates. Five patterns of PCR-RFLP of the OMP-CD gene were observed among all isolates when the gene was digested with Sau3AI. The sequence analysis revealed a high degree of homogeneity in OMP-CD among strains of B. catarrhalis. Three regions of OMP-CD with minimal sequence heterogeneity were identified. The sequences of the OMP-CD gene of isolates collected from patients colonized with the same strain for up to 6 months was identical. These observations establish that the OMP-CD of B. catarrhalis recovered from clinical isolates is highly conserved among strains.

Assessment of complement-mediated killing of Moraxella (Branhamella) catarrhalis isolates by a simple method

Recently, we showed that complement resistance is an important virulence factor of Moraxella (Branhamella) catarrhalis. Our study used a serum bactericidal assay to determine complement resistance in M. catarrhalis. Although the serum bactericidal assay is considered the "gold standard" for determining complement resistance, it is laborious and time-consuming and therefore not well suited for large-scale studies. Using a large number (n = 324) of M. catarrhalis isolates obtained from the sputa of patients with lower respiratory tract infections (n = 200) and young carriers (n = 124), we assessed the value of a simple "culture-and-spot" test as an alternative to the serum bactericidal assay. For both groups of isolates, the degree of concordance between the two tests used was very significant (P < 0.0001). The agreement between the two assays was estimated to be "excellent beyond chance" (as determined by Cohen's kappa test). The culture-and-spot assay is a valuable alternative to the serum bactericidal assay, not only for screening purposes as shown here but also for studying the mechanism of complement resistance in M. catarrhalis at the molecular level.