Effect of Gyrase Inhibitors on the Activity of φBA 1

The effect of DNA gyrase inhibitors, which contained a new quinolone compound enoxacin, nalidixic acid, and, on the two activities (plaque-forming and killing) of a phage (φBA1) of Bacillus aneurinolyticus was studied. The results obtained are as follows : 1) Minimum inhibitory concentration (MIC) of enoxacin against B. aneurinolyticus KA10 and KA23 were 6.25μg/ml and 3.13μg/ml, respectively: MICs of nalidixic acid against both strains were approx. 100μg/ml. MICs of novobiocin against the strains were 12.5μg/ml and 1.56μg/ml, respectively. 2) In the case of enoxacin and nalidixic acid, plaque-forming activity of oBA1 at the one-half concentration of MIC was reduced to about 40% compared with that of no-drug control. 3) Killing activity of φBA1 was not effected by the drugs as long as the host cell could grow.