ALTERATIONS IN TOPOISOMERASE-IV AND DNA GYRASE IN QUINOLONE-RESISTANTMUTANTS OF MYCOPLASMA-HOMINIS OBTAINED IN-VITRO

Mycoplasma hominis mutants were selected stepwise for resistance to of loxacin and sparfloxacin, and their gyrA, gyrB, parC, and parE quinolo ne resistance-determining regions were characterized. For ofloxacin, f our rounds of selection yielded six first-, six second-, five third-, and two fourth-step mutants. The first-step mutants harbored a single Asp426-->Asn substitution in ParE. GyrA changes (Ser83-->Leu or Trp) w ere found only from the third round of selection. With sparfloxacin, t hree rounds of selection generated 4 first, 7 second-, and 10 third-st ep mutants. In contrast to ofloxacin resistance, GyrA mutations (Ser83 -->Leu or Ser84-->Trp) were detected in the first-step mutants prior t o ParC changes (Glu84-->Lys), which appeared only after the second rou nd of selection. Further analysis of eight multistep-selected mutants of ill hominis that were previously described (2) revealed that they c arried mutations in ParE (Asp426-->Asn), GyrA (Ser83-->Leu) and ParE ( Asp426-->Asn), GyrA (Ser83-->Leu) and ParC (Ser80-->Ile), or ParC (Ser 80-->Ile) alone, depending on the fluoroquinolone used for selection, i.e., ciprofloxacin, norfloxacin, ofloxacin, or pefloxacin, respective ly. These data indicate that in ill, hominis DNA gyrase is the primary target of sparfloxacin whereas topoisomerase TV is the primary target of pefloxacin, ofloxacin, and ciprofloxacin.