Microevolution through DNA exchange among strains of Neisseria meningitidis isolated during an outbreak in the Czech Republic

Neisseria meningitidis is a highly variable bacterium. Indeed, N. meningiti dis is naturally competent for transformation, and horizontal DNA exchange between strains may lead to mosaic genetic loci in N. meningitidis. We stud ied such an exchange in nature during an epidemic provoked by N. meningitid is. This epidemic started in the Czech Republic in 1993 and the original ep idemic clone was shown to have the antigenic formula (serogroup:serotype:se rosubtype) C:2a:P1.2,5. We analysed 145 meningococcal strains isolated in t he Czech Republic between 1993 and 1997 using serological and genetic typin g methods (multilocus enzyme electrophoresis and polymorphism of pilA and p ilD genes). This analysis showed that genetic exchange between epidemic and endemic strains had occurred. Exchanges involved mostly surface-exposed st ructures such as the capsule, giving rise to new meningococcal variants. Th e expansion of these variants should be kept under close surveillance. (C) Elsevier, Paris.