Transposon-induced norfloxacin-sensitive mutants of Bacteroides thetaiotaomicron.
To elucidate the mechanism of norfloxacin (a fluoroquinolone) resistance of Bacteroides thetaiotaomicron, a member of the B. fragilis group, we isolated transposon-induced mutants sensitive to this agent using Tn4351. Four norfloxacin-sensitive mutants showed reduced levels of resistance, at least, to ethidium bromide. Cloning and sequencing of three chromosomal fragments adjacent to Tn4351 from the mutants revealed that two partial open reading frames (orfs) were disrupted by a transposon. Amino acid sequences of partial orf products had strong homologies to those of Escherichia coli RecB and B. ovatus transketolase. Two mutants carried a recB homolog inserted by Tn4351 together with R751 (cointegration) and by itself (simple transposition) at the amino- and carboxyl-terminal portions, respectively. Since mutations in recB produce E. coli cells sensitive to DNA-damaging treatments by quinolones, it is concluded that decreases of the minimum inhibitory concentrations (MICs) of the agents for B. thetaiotaomicron resulted from disruption of the recB homolog. Another mutant carried a transketolase gene inserted by Tn4351. There is no reasonable explanation why disruption of the transketolase gene caused a decrease of the MIC of norfloxacin for this organism, although Streptococcus pneumoniae RecP related to DNA recombination was reported to be transketolase.
Ueda
Ohmi
O
Department of Microbiology, School of Dentistry, Aichi-Gakuin University, Nagoya, Aichi 464-8650, Japan. volvo70@po.mdu.ac.jp
Yoshimura
Fuminobu
F
D000595:Amino Acid Sequence; D000890:Anti-Infective Agents / Q000494:pharmacology*; D001439:Bacteroides / Q000187:drug effects* / Q000235:genetics; D001442:Bacteroides Infections / Q000382:microbiology; D001483:Base Sequence; D003001:Cloning, Molecular; D003227:Conjugation, Genetic; D004251:DNA Transposable Elements / Q000235:genetics*; D024881:Drug Resistance, Bacterial / Q000235:genetics; D006801:Humans; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D009643:Norfloxacin / Q000494:pharmacology*; D016366:Open Reading Frames; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid
D000890:Anti-Infective Agents; D004251:DNA Transposable Elements; D009643:Norfloxacin