Subinhibitory concentrations of ciprofloxacin induce SOS response and mutations of antibiotic resistance in bacteria

Abstract

In this work, Salmonella typhimurium strains (Sal94) containing plasmid-borne fusions of Vibrio fischeri lux to the recA promoter was used to test the SOS response induced by sub-minimum inhibitory concentration (sub-MIC) of ciprofloxacin. The SOS response of Sal94 strain was rapidly increased during 20 min when supplemented with sub-MIC ciprofloxacin, but came down thereafter. The induction level of 1/2 MIC was higher than that of 1/4 MIC, showing some dose-dependency. Both mutation frequencies (MF) of anti-ciprofloxacin resistance and transformation frequency of pMD18-T Vector (lacZ ori Ampr) caused by the treatment of 1/4 and 1/2 MIC ciprofloxacin in Escherichia coli AB1157 strain (wild-type recA, SOS inducible) were markedly increased, but there were no or only slight changes in Escherichia coli IC400 strain (recA mutant, deficient in SOS response). These results, combining the positive relationship between the induction factor and the MF of anti-ciprofloxacin induced by sub-MIC ciprofloxacin in AB1157 strain, indicated that SOS response played an important role in the acquirement of antibiotic resistance resulting from sub-MIC ciprofloxacin treatment.