In Vitro Effect of Roxithromycin on Biofilm Formed by Pseudomonas aeruginosa

Kim, Yang Ree; Kim, Mi Young; Choi, Jung Hyun; Yoo, Jin Hong; Shin, Wan Shik; Kang, Moon Won

Abstract

BACKGROUND
Many patients discontinue peritoneal dialysis because they suffer from peritonitis associated with biofilm, which is mainly composed of microorganisms and glycocalyx. Pseudomonas aeruginosa produces more glycocalyx than any other gram-negative organism. Macrolide antibiotics are known to be effective against such glycocalyx-producing organisms.
METHODS
We evaluated the effect of subinhibitory concentrations of roxithromycin on the biofilm formed by P. aeruginosa obtained from the clinical specimen of a patient with peritonitis. After seeding the organism in the dialysis fluid on silicone discs attached to the sampling plugs of a modified Robbins device for 18 hours, subinhibitory concentrations of roxithromycin-containing dialysis fluid were passed through the device. Sampling plugs were removed at 0, 4-, 24-, 48- hour intervals. Quantifications of the organisms and the glycocalyx were performed, and silicone discs were examined with scanning electron microscope.
RESULTS
The colony count decreased at 4 hours of exposure to 1/2xMIC roxithromycin, and at 24 hours after exposure to 1/4xMIC or 1/8xMIC(P<0.05). At 48 hours, the colony count was the lowest in 1/2xMIC, followed by 1/4xMIC and 1/8xMIC, in successive order. The effect seemed to be concentration-dependent. On scanning electron microscopic examination, the production of glycocalyx decreased definitely as time passed, but it was not easy to exactly differentiate the amounts of the three concentration groups. Furthermore, quantification of glycocalyx by tryptophan assay was influenced by time (P<0.05).
CONCLUSION
The subinhibitory concentrations of roxithromycin are effectively enough to decrease the biofilm formed by P. aeruginosa colonized on a silicone disc in this in vitro model of peritoneal dialysis.