Comparison of Media for the Isolation ofClostridium difficileFrom Fecal Specimens

Abstract

Dowell reported in 1980 that two selective media, cycloserine mannitol agar (CMA) and cycloserine mannitol blood agar (CMBA), developed at the Centers for Disease Control (CDC), gave better results than cycloserine fructose egg-yolk agar or cycloserine cefoxitin fructose egg-yolk agar in the isolation of Clostridium difficile from feces and in the quantitative recovery of the organism from pure cultures. In 1983, Bartley and Dowell modified the basal medium for CMA and CMBA by deleting L-leucine and Lserine; since then, the modified media has been used for isolating C difficile from feces. In this study, we compared the modified CMA and CMBA media with cycloserine cefoxitin fructose agar (CCFA) in the quantitative recovery of C difficile isolates and modified CCFA from two vendors in the isolation of C difficile from feces. In addition, all fecal specimens were cultured on CDC anaerobe blood agar (BA) after treatment for 1 hour with 95% ethyl alcohol (BA-ETOH). Of 350 fecal specimens examined using all media, 105 yielded C difficile. Of the 105 specimens, 80 were positive with CMBA (76%), 68 with CMA (65%), 44 with CCFA (vendor A) (42%), 38 with CCFA (vendor B) (36%), and 95 with BA-ETOH (90%). The selective media ranked as follows in quantitative recovery of 24 C difficile strains from pure cultures: CMBA>CMA>CCFA. We conclude that the modified CMBA and CMA media are superior to modified CCFA medium for recovery of C difficile and that culture on BA following alcohol treatment is a superior and costeffective method for detecting C difficile from clinical fecal specimens.