title: Mechanisms of 4-quinolone resistance in quinolone-resistant and methicillin-resistant Staphylococcus aureus isolates from Japan and China.
abstract: Ninety-two and 33 methicillin-resistant Staphylococcus aureus (MRSA) strains were isolated in Japan and China respectively. They were categorised as ofloxacin-susceptible (MIC < 12.5 mg/L), moderately (MIC 12.5-25 mg/L) or highly (MIC > or = 50 mg/L) ofloxacin-resistant. 4-Quinolone concentrations required to inhibit purified DNA gyrase from the moderately and highly quinolone-resistant MRSA were at least 20 times higher than those required to inhibit the equivalent enzyme from quinolone-susceptible strains. Reconstitution assays demonstrated that the 4-quinolone-resistant MRSA had a mutation in subunit A of DNA gyrase. A portion of the gyrA gene from amino acids codons 40-115 was sequenced. Four moderately resistant and seven highly resistant MRSA contained a Ser-->Leu substitution at amino acid 84; one moderately and one highly resistant MRSA and one moderately resistant methicillin-susceptible S. aureus (MSSA) strain contained a Glu-->Lys substitution at amino acid 88. Eight MRSA, including one quinolone-susceptible strain and one MSSA contained a silent mutation at amino acid 86. Uptake of ofloxacin in moderately resistant strains was almost the same in the presence or absence of carbonyl cyanide m-chlorophenylhydrazone (CCCP), whereas in highly resistant strains, uptake increased when CCCP was added. Restriction fragment length analysis of the norA gene with the restriction endonuclease SfcI showed a mutation of nucleotide position 1085 in all MRSA strains tested except for one highly quinolone-resistant strain. Thus the mechanisms of 4-quinolone-resistance in these MRSA isolates involved alterations in both DNA gyrase and antimicrobial uptake and efflux.
authors.affiliation: Exploratory Research Laboratories 1, Daiichi Pharmaceutical Co. Ltd, Tokyo, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Tanaka
authors.forename: Y X
authors.initials: YX
authors.lastname: Zhang
authors.forename: H
authors.initials: H
authors.lastname: Ishida
authors.forename: T
authors.initials: T
authors.lastname: Akasaka
authors.forename: K
authors.initials: K
authors.lastname: Sato
authors.forename: I
authors.initials: I
authors.lastname: Hayakawa
mesh_terms: D000890:Anti-Infective Agents / Q000494:pharmacology*; D001483:Base Sequence; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D002681:China; D004250:DNA Topoisomerases, Type II / Q000235:genetics; D004352:Drug Resistance, Microbial / Q000235:genetics; D005798:Genes, Bacterial; D006801:Humans; D007564:Japan; D016106:Methicillin Resistance; D008826:Microbial Sensitivity Tests; D015242:Ofloxacin / Q000378:metabolism / Q000494:pharmacology; D017354:Point Mutation; D012150:Polymorphism, Restriction Fragment Length; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D059005:Topoisomerase II Inhibitors
chemical_list: D000890:Anti-Infective Agents; D059005:Topoisomerase II Inhibitors; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D015242:Ofloxacin; D004250:DNA Topoisomerases, Type II