Genetic diversity among strains of Moraxella catarrhalis cultured from thenasopharynx of young and healthy Brazilian, Angolan and Dutch children

The present study describes the carriage patterns and genetic variability o f Moraxella catarrhalis strains isolated from children living in different countries. Moraxella catarrhalis is genetically heterogeneous, but little i s known about its geographic distribution and phenotypic and genetic divers ity in warm-climate countries. A collection of 99 isolates from 30 Brazilia n, 19 Angolan and 50 Dutch healthy children, all less than 5 years of age, was investigated for phenotypic and genotypic relatedness. The isolates fro m the three countries were similar where biochemical reactivity was concern ed: 89 strains were beta -lactamase-producing and 87 were complement-resist ant as determined by phenotype. There was no geographical difference in the prevalence of beta -lactamase-producing isolates, but the carriage rate of complement-resistant strains was significantly higher in Dutch than in Ang olan children (P=0.004). Complement resistance of 66 randomly selected stra ins was genetically confirmed in a Southern hybridization assay by a novel DNA probe that is specific for complement-resistant strains and that demons trated a sensitivity of 97% and a specificity of 100%. PCR amplification ba sed on the probe sequence had a sensitivity of 98% and a specificity of 57% when compared to the outcome of a conventional culture spot test. PCR rest riction fragment length polymorphism analysis of the MU 46 locus and pulsed -field gel electrophoresis of SpeI DNA macrorestriction fragments revealed genetic heterogeneity of strains from within and between the three countrie s, and no geographical clustering could be established. In conclusion, simi lar phenotypic characteristics but genotypic heterogeneity was found among Moraxella catarrhalis strains colonizing children in three different contin ents.