Detection of nucleotide variability in rpoB in both rifampin-sensitive and rifampin-resistant strains of Chlamydia trachomatis.

A 656-bp PCR fragment from rpoB was sequenced from five rifampin-resistant Chlamydia trachomatis variants selected in vitro from a wild-type parent with a surprising level of genetic variability in this region. Three variants (MIC, 4 microg/ml) showed Ala522-->Val in cluster I (codons 507 to 533), which harbors mutations in most rifampin-resistant bacteria. Two high-level resistance variants (MICs, 64 and 256 microg/ml) showed His526-->Tyr in cluster I with additional genetic variation, some of which resulted in amino acid substitutions. None of the latter was situated in clusters related to rifampin resistance in other bacteria.