Effects of gyrase mutation on the growth kinetics of ciprofloxacin-resistant strains of Clostridium perfringens

To investigate the effect of gyrA mutation on resistance of Clostridium perfringens to fluoroquinolones, a ciprofloxacin-resistant mutant was developed. The mutant had a single substitution in gyrA at position 87 (Asp to Tyr) and no additional mutations in gyrB, parC or parE. The MIC values of gatifloxacin and ciprofloxacin for this strain were 16 and 32-fold higher than those for the wild type, which were 0.125 and 0.250 μg/mL, respectively. The resistant mutant grew equally well in the presence or absence of 5 μg/mL of ciprofloxacin or 1 μg/mL of gatifloxacin and grew to lower cell densities with up to 30 μg/mL of ciprofloxacin or 5 μg/mL of gatifloxacin. Higher concentrations of fluoroquinolones resulted in increases in the time required to reach the end of the exponential phase and in lower cell densities at the end. The efflux pump inhibitor reserpine did not affect susceptibility to fluoroquinolones. The substitution of Asp 87 to Tyr in gyrA may have protected C. perfringens from low concentrations of ciprofloxacin and gatifloxacin and enabled survival and growth at higher concentrations.