Induction of the SOS response by new 4-quinolones.

The 4-quinolones ciprofloxacin, difloxacin, enoxacin, norfloxacin, ofloxacin, and nalidixic acid were found to induce the SOS response in qualitative and quantitative tests on Escherichia coli K12 containing the sfiA::lacZ gene fusion. Maximum induction of the SOS-response was observed with the quinolone concentrations that produced the most killing. There was also a modest increase in the rate of mutation in the lactose and galactose operons in a GalE- background, provided there was a functioning SOS system.