Mutations in GyrA and ParC in fluoroquinolone-resistant Mannheimia haemolytica isolates from cattle in Japan.

Nine isolates of Mannheimia haemolytica, comprising an enrofloxacin (ERFX)-resistant isolate, five nalidixic acid-resistant isolates and three susceptible isolates, from diseased cattle were subjected to sequence analysis of the quinolone resistance-determining regions (QRDRs) of the gyrA and parC genes. An ERFX-resistant isolate was shown to have two amino acid substitutions in GyrA (S83F and D87G) and one substitution in ParC (S80I). Three mutations in the QRDRs of GyrA were found in the NA-resistant isolates: S83Y in two isolates, S83F in two isolates and D87G in one isolate.