Molecular characterization of Moraxella catarrhalis
Moraxella catarrhalis is a gram-negative diplococcus which until recently was thought to be a harmless commensal. Increasing awareness has established the pathogenic nature of this organism and it is now recognised as a major cause of otitis media in children, exacerbations of chronic bronchitis in elderly patients and an occasional cause of invasive disease. M. catarrhalis is spread nosocomially especially in respiratory wards containing elderly patients. This study evaluated four methods for typing nosocomially spread isolates:- immunoblotting with normal human serum (NHS), and three DNA fingerprinting methods. The most discriminatory method found was restriction endonuclease analysis (REA) using Taq I, although immunoblotting with NHS and pulsed-field gel electrophoresis (PFGE) using Sma I sub-divided isolates grouped together by the other methods. PFGE using Not I only confirmed groupings made by other methods. A study of M. catarrhalis and phenotypically similar organisms was performed using comparisons of partial 16S rDNA sequence. 16S rDNA of M. catarrhalis strains from disparate geographical locations was found to be extremely conserved M. catarrhalis 16S rDNA was very similar to that of other Moraxella species whilst Moraxella species were found to be generally distinct from the Neisseria and Kingella species studied. These results confirm M. catarrhalis as a genuine member of the Moraxellae.