Selective and differential medium for isolation of Clostridium difficile

Abstract

C. difficile is a recognized cause of pseudomembranous (antimicrobial agent-associated) colitis and may cause antimicrobial agent-induced diarrhea. A selective and differential agar medium that contains cycloserine, cefoxitin, fructose and egg yolk (CCFA) was developed to facilitate the isolation of C. difficile from fecal specimens. Quantitative cultures of 16 stock strains of C. difficile on this medium (and on a medium containing cycloserine, fructose and egg yolk) yielded counts equivalent to those obtained on blood agar; other media selective for clostridia, including Clostrisel agar, reinforced clostridial agar plus 0.2% p-cresol and egg yolk-neomycin agar (the latter was inoculated with cultures subjected to prior heat shocking), were also tested and were inhibitory to the growth of C. difficile. Of 28 fecal or colostomy effluent specimens cultured on the above media, 14 yielded C. difficle. CCFA was the most sensitive and selective of these media for the recovery of C. difficile. Colonies of C. difficile growing on CCFA had distinctive morphological and fluorescent properties which were sufficient for presumptive identification. CCFA should provide a rapid method for the screening of fecal specimens from patients with antimicrobial agent-associated diarrhea or colitis for C. difficile.