Does subinhibitory concentrations of clinically important antibiotic induce biofilm production of Enterococcus faecium strains?

Abstract

Biofilm structures are the most resistant form of active microorganisms against sanitation, disinfection, and sterilization processes. One of the specific properties of biofilm is the development of antibiotic resistance that can be up to 1,000-fold greater than planktonic cells. Enterococcus faecium is a human pathogen that causes nosocomial bacteremia and at the present time, it is well known that most of the chronic infections are biofilm-based. Recent evidence suggested that subinhibitory concentrations (sub-MICs) of antibiotics have an important role in the evolution of antibiotic resistance and induction on biofilm formation. Based on this information, we aimed to determine the effect of subinhibitory antibiotic concentrations on biofilm formation and the role of the antibiotic concentrations on the enterococcal surface protein gene (esp). To determine the impact of clinically important antibiotics on biofilm production, crystal violet assay was used. Then, the effect of sub-MICs of antibiotics on the expression of the esp gene was investigated by quantitative real-time PCR. Biofilm production assays show that MIC/2 of erythromycin (ERT; 512 μg/ml), MIC/32 of vancomycin (VAN; 16 μg/ml), MIC/64 of streptomycin (STR; 32 μg/ml), and MIC/128 of kanamycin (KAN; 4 μg/ml) values induce maximum biofilm production compared with the control. According to q-PCR results, sub-MIC values of ERT, VAN, and STR antibiotics were found to enhance esp gene expression. In addition, despite the increasing biofilm production after KAN treatment, the antibiotic was not effective on the esp expression.