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 LISA and the complement-resistant resistant variant of M. catarrhalis has been considered particularly pathog enic. A collection of geographically diverse, complement-sensitive (n = 28) and -resistant strains (n = 47) of M. catarrhalis was assembled in order t o analyse the bacterial population structure. All strains were identified a s M. catarrhalis by conventional microbiological and biochemical methods. A mplification of the small subunit (ssu) ribosomal RNA gene followed by rest riction fragment length polymorphism (RFLP) analysis did not reveal consist ent differences between serum-susceptible and -resistant M. catarrhalis iso lates. Interestingly, upon automated ribotyping using the Qualicon RiboPrin ter(R) microbial characterisation system, the complement-sensitive and -res istant strains segregated into two groups. This suggested the existence of two clearly distinguishable lineages within the species M. catarrhalis. Thi s observation was corroborated by pulsed field gel electrophoresis (PFGE) o f DNA macro-restriction fragments, a non-ribosomal PCR RFLP procedure and r andom amplification of polymorphic DNA (RAPD) analysis. All procedures grou ped the two variants similarly. Redefinition of the taxonomic status of com plement-resistant M. catarrhalis or even the definition of a new species ma y be opportune. (C) 2000 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.