Moraxella (Branhamella) catarrhalis - clinical and molecular aspects of a rediscovered pathogen

Abstract

Since its discovery at the end of the nineteenth century, Moraxella (Branhamella) catarrhalis has undergone several changes of nomenclature and periodic changes in its perceived status as either a commensal or a pathogen. Molecular analysis based on DNA hybridisation or 16s rDNA sequence comparisons has established its phylogenetic position as a member of the Moraxellaceae and shown that it is related more closely to Acinetobacter spp. than to the genus Neisseria in which it was placed formerly. However, confusion with phenotypically similar Neisseria spp. can occur in the routine diagnostic laboratory if appropriate identification tests are not performed. M. catarrhalis is now accepted as the third commonest pathogen of the respiratory tract after Streptococcus pneumoniae and Haemophilus injluenzae. It is a significant cause of otitis media and sinusitis in children and of lower respiratory tract infections in adults, especially those with underlying chest disease. Nosocomial spread of infection, especially within respiratory wards, has been reported. Invasive infection is uncommon, but analysis of reports for England and Wales between 1992 and 1995 revealed 89 cases of M. catarrhalis bacteraemia, with the peak incidence in children aged 1-2 years. Carriage rates of M. catarrhalis are high in children and in the elderly, but its role as a commensal organism has probably been overstated in the past. Approximately 90% of strains are now plactamase positive and, given that the first such strain was reported in 1976, this represents a dramatic increase in frequency over the last 20 years which has not been paralleled in any other species. The BRO-1 and BRO-2 P-lactamase enzymes of M. catarrhalis are found in other Moraxellaceae, but are not related to P-lactamases of any other species and their origin is therefore unknown. Molecular and typing studies have shown that the M. catarrhalis species is genetically heterogeneous and these methods have aided epidemiological investigation. Studies of factors that may be related to pathogenicity have shown the existence of three serotypes of lipooligosaccharide and the presence of fimbriae and a possible capsule. Some strains are serum-resistant, probably by virtue of interference with complement action, whilst transferrin-and lactoferrinbinding proteins enable the organism to obtain iron from its environment. An antibody response in humans to various M. catarrhalis antigens, including highly conserved outermembrane proteins, has been demonstrated. Increased understanding of the organism's pathogenic properties and the host response to it may help to identify suitable vaccine targets or lead to other strategies to prevent infection. Whilst it remains, at present, the third most important respiratory pathogen, the impact of immunisation strategies for other organisms may change this position. The speed with which M. catarrhalis acquired p-lactamase demonstrates the capacity of this organism to surprise us.

Molecular Aspects ofMoraxella catarrhalisPathogenesis

“…In the late 1990s, Enright and McKenzie suggested that the M. catarrhalis species has a population structure similar to that of N. meningitidis, which possesses a nonclonal (panmictic) population due to its high rate of genomic recombination, with an occasional emergence of successful clones (38). Subsequent MLST of N. meningitidis yielded 47 sequence types (STs) from 92 strains (128), and for M. catarrhalis, 173 MLST STs were observed among 268 isolates (153).…”

Development of a Disk Diffusion Method for Testing Moraxella catarrhalis Susceptibility Using Clinical and Laboratory Standards Institute Methods: a SENTRY Antimicrobial Surveillance Program Report

“…A total of 281 isolates were BRO-1, and 19 were BRO-2 (including one ATCC strain). Two strains had MICs to benzylpenicillin and ampicillin elevated above those of the wild type, suggesting the presence of either ␤-lactamases other than those of the BRO type (14) or polymorphisms in BRO genes preventing PCR amplification.…”

“…If the isolate comes from blood or another sterile body site culture (e.g., pleural fluid), treatment is clearly warranted. The organism is believed to be the third most common bacterium associated with acute exacerbations of chronic bronchitis and acute otitis media (4,5,14), both of which require antimicrobial treatment under certain circumstances. If resistance to commonly recommended agents is emerging, then regular testing would also be warranted.…”

Pulmonary thin-section CT findings in acuteMoraxella catarrhalispulmonary infection

“…The pathogen, also known as Micrococcus catarrhalis, Neisseria catarrhalis and Brahamella catarrhalis, is a clinically important pathogen and is a common cause of respiratory infections, particularly otitis media in children and lower respiratory tract infection in elderly patients [2][3][4][5]. M. catarrhalis is considered to be the third most common and most important cause of bronchopulmonary infections after Streptococcus pneumoniae and Haemophilus influenzae [6,7]. In the Alexander project in Europe and the US between 1992 and 1993, M. catarrhalis was identified in 13.5% of bacterial isolates [8].…”