Table 2.

Gene mutations in quinolone resistance-determining region and antibacterial activities of various quinolones against the resistant mutantsa

StrainSelecting quinolone (concn [μg/ml])bNo. of isolatesMutation (codon)cMIC (μg/ml)
gyrAparCGatSpaTroLevCipNor
ParentNoneNone0.390.390.100.780.786.25
Mutant
 Type ITro (0.20)3NoneSer79(TCT)→Tyr(TAT)0.390.390.391.563.1325
Lev (3.13)1NoneAsp83(GAT)→Asn(AAT)0.390.390.391.563.1325
Lev (3.13)2NoneSer79(TCT)→Tyr(TAT)0.390.390.391.563.1325
Nor (12.5 or 25)3NoneSer79(TCT)→Tyr(TAT)0.390.390.391.563.1325
Cip (1.56)1NoneSer79(TCT)→Tyr(TAT)0.390.390.391.563.1325
Cip (1.56)2NoneAsp83(GAT)→Asn(AAT)0.390.390.391.563.1325
 Type IISpa (3.13 or 6.25)3Ser81(TCC)→Phe(TTC)None0.783.130.100.780.786.25
Gat (0.39)1Ser81(TCC)→Tyr(TAC)None0.783.130.100.780.786.25
 Type IIITro (0.20 or 0.39)3NoneNone0.390.780.390.780.786.25
  • a The mutants were selected on the plates containing the selecting agents after at least a 48 h of incubation at 37°C. On the other hand, the MICs were defined as the lowest concentrations at which no visible growth was observed after incubation at 37°C for 18 to 20 h. None of the strains possessed mutations in the QRDR of gyrB and parE genes. Abbreviations: Gat, gatifloxacin; Spa, sparfloxacin; Tro, trovafloxacin; Lev, levofloxacin; Nor, norfloxacin; Cip, ciprofloxacin.

  • b The concentrations of the agents used for selection.

  • c The codon positions of gyrA andparC are designated according to the numbering of Balas et al. (1) and Pan and Fisher (12), respectively.