Mutations in the gyrA and parC genes in ciprofloxacin-resistant clinical isolates of Acinetobacter baumannii in Korea

Mutation with Ser-83-->Leu in gyrA gene was associated with the principal mutation for ciprofloxacin resistance in clinical isolates of Acinetobacter baumannii. Double mutation, Ser-83-->Leu in gyrA gene and Ser-80-->Leu in parC gene, was the most frequently detected among ciprofloxacin-resistant isolates. A novel mutation with Ser-80-->Trp in parC gene, in addition to mutation in gyrA gene, was associated with a high-level ciprofloxacin resistance. These results suggested that the presence of an additional mutation in the parC gene contributed to a higher-level of ciprofloxacin resistance than a single mutation in the gyrA gene (geometric mean MICs of ciprofloxacin, 44.1 versus 16 microg/ml, P < 0.05).