Deficiency of quorum sensing system inhibits the resistance selection of Pseudomonas aeruginosa to ciprofloxacin and levofloxacin in vitro

Abstract Objectives The objective was to investigate how deficient of quorum sensing system (QS) affects minimal inhibitory concentrations (MICs) of Pseudomonas aeruginosa strains to ciprofloxacin (CIP) and levofloxacin (LEV) in vitro. Methods Collected the clinical Pseudomonas aeruginosa isolates. Screened the strains deficient of QS genes by the PCR agarose electrophoresis, and then randomly picked out normal strains with the same number of deficient ones. All strains incubated on the different CIP-concentration Mueller-Hinton agars for five days, the different concentrations of CIP respectively refered to 0.5 × MIC, 1 × MIC, 2 × MIC and 4 × MIC. Strains incubated on the first, third and fifth days were saved. MICs of saved strains to CIP and LEV were measured by the agar dilution method. Statistical analysis methods were the repeated measures analysis of variance and the rank sum test. Results The study totally collected 40 Pseudomonas aeruginosa isolates. 5 deficient strains screened were as follows: one strain lacked of rhlR and lasI genes, one strain lacked of lasI , lasR , rhlI and rhlR genes, four strains lacked of lasR gene. All the final selected strains were sensitive to both CIP and LEV. Statistical analysis results showed deficient strains became resistant more slowly and difficultly than normal strains, whether the resistance was to CIP or LEV. What’s more, MICs to LEV showed the half and delayed increase than those to CIP in the vitro selection. Conclusions Deficient of QS inhibits the resistance selection of P. aeruginosa to CIP and LEV in vitro.