Amino acid substitutions in gyrA and parC are associated with fluoroquinolone resistance in mycoplasma bovis isolates from Japanese dairy calves

Abstract

We investigated the contribution of quinolone resistance-determining region (QRDR) mutations to fuoroquinolone (enrofoxa-cin, orbifoxacin and danofoxacin) susceptibility in 58Mycoplasma bovis isolates from dairy cattle in Japan. Fluoroquinolone non-resistant isolates (fuoroquinolone-MICs≤2 μg/ml) possessed no QRDR mutations (19 isolates) or Ser83Leu in GyrA (32 isolates). Fluoroquinolone-resistant isolates (fuoroquinolone-MICs≥4 μg/ml) possessed Ser83Leu in GyrA and Ser81Pro in ParC (3 isolates) or Ser83Phe in GyrA and Ser80Ile in ParC (4 isolates). Laboratory-derived fuoroquinolone-resistant mutants selected from 2 isolates (possessing Ser83Leu in GyrA) had an amino acid substitution in ParC at the same position (Ser80Ile or Ser81Tyr) as fuoroquinolone-resistant isolates, suggesting a concurrent amino acid substitution in ParC (Ser80 or Ser81) is important in fuoroquinolone resistance inM. bovis isolates. © 2013 The Japanese Society of Veterinary Science..