Modification of cycloserine cefoxitin fructose agar to supress growth of yeasts from stool specimens

Abstract

Cycloserine cefoxitin fructose agar is a widely used selective isolation medium for Clostridium difficile from stool specimens. Yeasts often colonize in the intestine of C. difficile disease patients and, if colonized heavily, pure culture of C. difficile can be delayed. The aim of this study was to modify cycloserine cefoxitin fructose agar to suppress the growth of yeasts. Antimicrobial activities of three commonly available antifungal agents were tested against recent clinical isolates of Candida species. Amphotericin B was most active in inhibiting all isolates by 0.5mg/L concentration. Cycloserine cefoxitin fructose agar was modified by adding 2mg/L of amphotericin B. Serial ten-fold dilution of stool specimens from 126 suspected C. difficile-associated diarrhea patients were cultured both on cycloserine cefoxitin fructose agar plates and modified agar plates. Yeasts grew from 60 specimens on cycloserine cefoxitin fructose agar, but none grew on the modified medium. Growth of C. difficile was detected from 37 and 39 of 126 specimens on cycloserine cefoxitin fructose agar and modified medium, respectively. The number of C. difficile colonies was similar on both media. In conclusion, 2mg/L of amphotericin B supplementation to cycloserine cefoxitin fructose agar can facilitate the isolation of C. difficile from stool specimens which are densely colonized with yeasts.