Induction of the SOS gene (umuC) by 4-quinolone antibacterial drugs

Induction by the 4-quinolone group of antibacterial drugs of the umuC gene, the SOS function most involved in error-prone DNA repair (together with umuD), was assessed in a strain of Escherichia coli harbouring a umuC::lacZ gene fusion. All 4-quinolones tested induced this umuC::lacZ fusion, with maximum induction at 4-quinolone concentrations close to their minimum inhibitory concentrations for this strain, and the SOS Inducing Potential (SOSIP) was closely related to antibacterial activity. Mitomycin C, a known mutagen, was a slightly better inducer (in terms of SOSIP) than any of the quinolones. In contrast, induction by 4-quinolones of the sfiA (sulA) gene, an SOS function involved in cell division inhibition, was better than induction by mitomycin C in an E. coli strain harbouring an sfiA::lacZ gene fusion. The umuC gene fusion was induced at lower concentrations of 4-quinolone than was the sfiA gene fusion.