title: Molecular characterisation of the quinolone resistance-determining region (QRDR) of the parC gene locus in viridans-group streptococci.
abstract: Forty-eight isolates of viridans-group streptococci (VGS) from adults and children in the community are examined for their resistance to ciprofloxacin phenotypically by determination of the minimum inhibitory concentration (MIC). In addition, the parC gene locus is amplified and sequenced in all isolates and mutations noted. Overall, 44 VGS organisms were found to be susceptible to ciprofloxacin by the broth microdilution method, and the remaining four strains had intermediate susceptibility. Reduced MICs were observed with intermediate strains when reserpine was added to the broth, inhibiting any efflux activity. Overall, the effect of adding reserpine to the broth medium was to add one doubling dilution to the MIC in the case of Streptococcus mitis, S. oralis and S. salivarius, as well as to increase the MIC by two doubling dilutions in two of the three S. parasanguinis isolates. Amino acid sequence analysis of the quinolone resistance-determining region (QRDR) of the parC gene locus showed good correlation to the phenotypic resistance to ciprofloxacin, where no confirmed mutation conferring quinolone resistance was found. Eleven amino acid positions showed discordance with S. pneumoniae R6 and eight (S52, F55, S58, N91, E135, K137, F141 and S167) were common in the VGS species examined. In addition, minor substitutions were found at three positions (D51, T54 and V86). In conclusion, this study demonstrates the low occurrence of ciprofloxacin resistance in a population of VGS isolated from the community. In addition, several silent mutations were noted in VGS organisms without any increase in MIC against ciprofloxacin.
authors.affiliation: Northern Ireland Public Health Laboratory, Department of Bacteriology, Belfast City Hospital, Belfast.
authors.forename: M
authors.initials: M
authors.lastname: Murayama
authors.forename: Y
authors.initials: Y
authors.lastname: Maeda
authors.forename: C E
authors.initials: CE
authors.lastname: Goldsmith
authors.forename: W A
authors.initials: WA
authors.lastname: Coulter
authors.forename: C
authors.initials: C
authors.lastname: Masons
authors.forename: B C
authors.initials: BC
authors.lastname: Millar
authors.forename: M
authors.initials: M
authors.lastname: Matsuda
authors.forename: J E
authors.initials: JE
authors.lastname: Moore
mesh_terms: D000328:Adult; D000890:Anti-Infective Agents / Q000494:pharmacology*; D002675:Child, Preschool; D002939:Ciprofloxacin / Q000494:pharmacology*; D027101:DNA Topoisomerase IV / Q000235:genetics*; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D006801:Humans; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D009660:Northern Ireland; D015363:Quinolones; D013296:Streptococcus pneumoniae / Q000235:genetics; D034363:Viridans Streptococci / Q000187:drug effects / Q000235:genetics*
chemical_list: D000890:Anti-Infective Agents; D015363:Quinolones; D002939:Ciprofloxacin; D027101:DNA Topoisomerase IV