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Rifampicin resistance in Neisseria meningitidis: evidence from a study of sibling strains, description of new mutations and notes on population genetics.

To provide direct evidence for the mechanism leading to resistance to rifampicin, two Neisseria meningitidis strains from one clonal lineage (so-called sibling strains) were studied; one of these strains was resistant, the other sensitive to rifampicin. The polymerase chain reaction (PCR) was used to amplify fragments of the known rifampicin resistance region on the rpoB gene coding for the beta subunit of DNA-directed RNA polymerase and the amplimers were then sequenced. In addition to the DNA from the sibling strains, DNA from further strains was analysed, including two Spanish, rifampicin-resistant strains, eight further N. meningitidis strains, strains of four further Neisseria spp. and one reference strain. The results demonstrated how quickly and easily N. meningitidis can acquire resistance to rifampicin, and also suggest a clonal population structure within the collection of strains studied. This finding is discussed with respect to recent studies that indicate a more panmictic population structure within particular serogroups of N. meningitidis.