Effects of sub-minimum inhibitory concentrations of ciprofloxacin on biofilm formation and virulence factors of Escherichia coli

Abstract Objective To evaluate the influence of sub-minimum inhibitory concentrations (MICs) of ciprofloxacin (CIP) on biofilm formation and virulence factors of Escherichia coli clinical isolates. Methods Sub-MICs of CIP were determined using growth curve experiments. The biofilm-forming capacity of E. coli clinical isolates and E. coli ATCC 25922 treated or untreated with sub-MICs of CIP was assessed using a crystal violet staining assay. The biofilm structure of E. coli isolate was assessed with scanning electron microscopy (SEM). The expression levels of the virulence genes fim , usp , and iron and the biofilm formation genes of the pgaABCD locus were measured using quantification RT-PCR (qRT-PCR) in E. coli isolates and E. coli ATCC 25922. Results Based on our results, the sub-MICs of CIP were 1/4 MICs. Sub-MICs of CIP significantly inhibited biofilm formation of E. coli clinical isolates and E. coli ATCC 25922 ( p E. coli changed significantly after treatment with sub-MICs of CIP. Expression levels of the virulence genes fim , usp , and iron and the biofilm formation genes of the pgaABCD locus were also suppressed. Conclusions The results revealed that treatment with sub-MICs of CIP for 24 h inhibited biofilm formation and reduced the expression of virulence genes and biofilm formation genes in E. coli .