Influence of adhesion force on croRS gene expression and antibiotic resistance of Enterococcus faecalis

Surface properties of materials influence bacterial adhesion and play important roles in biofilm antibiotic resistance. The two-component system CroRS of Enterococcus faecalis (E. faecalis) can be activated by antibiotics and is involved in cephalosporin resistance. We hypothesized that surfaces properties could influence the expression of croRS in E. faecalis biofilm and contribute to cephalosporin resistance. In this study, the hydrophobicity of poly-ethylene (PE) and stainless steel (SS) was characterized. Adhesion forces were measured using atomic force microscopy. The transcript levels of croRS in E. faecalis adhering to surfaces exerting different adhesion forces were compared, in presence and absence of cephalosporin. The ceftriaxone susceptibility of E. faecalis biofilms was investigated using colony forming units (CFU) counting. The water contact angles of PE and SS were 97.1 +/- 0.3 degrees and 33.5 +/- 0.3 degrees, respectively (p <.05). The adhesion force of E. faecalis on PE was 7.6 +/- 1.0 nN, which was higher than that on SS surfaces (3.5 +/- 0.5 nN, p < .05). The gene expression of croS and croR in E. faecalis was higher on PE compared to that on SS (p <.05). E. faecalis on the hydrophobic PE surfaces, exerting stronger adhesion force, was more resistant to ceftriaxone compared to that on more hydrophilic SS surfaces. Results revealed the surface properties of materials can modulate the expression of croRS system and interfere with the outcome of antimicrobial therapy of E. faecalis biofilm. The modification of surface properties of biomedical devices may be used as a strategy to increase the efficacy of antimicrobial therapy.