Quinolone Induction of qnrVS1 in Vibrio splendidus and Plasmid-Carried qnrS1 in Escherichia coli, a Mechanism Independent of the SOS System

Plasmid-carried qnrS1 is derived from Vibrio splendidus chromosomal qnrVS1. qnrVS1 transcripts increased 21- to 34-fold with subinhibitory concentrations of ciprofloxacin but much less with mitomycin. No LexA binding sites were upstream of qnrS1 or qnrVS1, and similar induction levels were observed in lexA-positive and lexA-negative Escherichia coli strains with native qnrS1 plasmid pMG306 but not with pUC18-cloned qnrS1 or qnrVS1. Thus, qnrS1 induction by quinolones is independent of the SOS system and requires sequence besides that of the structural gene.