Effects of Vancomycin, Roxithromycin, and Rifampin on Biofilm Formed by Staphylococcus epidermidis

Lim, Yong Seong; Kim, Yang Ree; Choi, Jung Hyun; Yoo, Jin Hong; Shin, Wan Shik; Kang, Moon Won

Abstract

BACKGROUND: Catheter-associated peritonitis occurs frequently in patients with chronic renal failure with peritoneal dialysis. It can be controlled by antibiotics, but relapses are common due to biofilms that affect the pathogenesis of peritonitis. This study was designed to evaluate the efficacy of antibiotics against biofilm formed by Staphylococcus epidermidis which is the most common causative organism of peritonitis in patients with peritoneal dialysis.
METHODS
After incubation of silastic plates for 24 hours in peritoneal dialysis fluid containing S. epidermidis, the establishment of bacterial biofilm on the plates was confirmed by scanning electron microscopy. Then the plates were incubated in dialysate containing various concentrations of antimicrobial agents, such as vancomycin, roxithromycin or rifampin, in combination or alone. The quantification of organisms on silastic plates was performed for evaluation of antibiotic efficacy against biofilm formed by S. epidermidis after getting samples of plates at 0 hour, 4, 24, and 48 hours after incubation.
RESULTS
The reduction of colony counts in groups with antibiotics was significantly larger than that in the control group and the difference was increased as time passed. In vancomycin treated plates, the colony count per plate for 2xMIC (minimal inhibitory concentration) was significantly lower than that for 1/8xMIC or 1/64xMIC at 4 hour, but no significant differences were noted at 24 hours and 48 hours among those of the various concentrations. The reduction of colony counts in accordance with concentrations of roxithromycin was not significantly different at 4 hours, but the reduction for 1/8xMIC was larger than that for 1/64xMIC at 24 hours and 48 hours. The reduction of colony counts in accordance with concentrations of rifampin was not significantly different at 4 hours, but the reduction for 1/8xMIC was larger than that for 1/64xMIC at 24 hours and 48 hours. There was no significant difference in reduction of colony counts between groups of anti-biotic combination containing vancomycin and groups of vancomycin alone.
CONCLUSIONS
It is suggested that the sub-inhibitory concentrations of vancomycin, roxithromycin, and rifampin might be effective on biofilm-forming S. epidermidis in in vitro model of infection related with peritoneal dialysis catheter. This result may be applicable for development of a new method to control biofilm-associated peritonitis during peritoneal dialysis.