Bacterial interference between Clostridium difficile and normal fecal flora.

Clostridium difficile has been shown to be the cause of virtually all cases of pseudomembranous colitis related to the administration of antimicrobial agents. It is possible that some antimicrobial agents alter the normal bacterial flora of the gastrointestinal tract so as to permit colonization and/or proliferation by C. difficile. The inhibitory activity of representative fecal bacteria from 23 anaerobic and aerobic genera against C. difficile was examined using two in vitro procedures. Strains of bacteria in six of the genera inhibited the multiplication of C. difficile, with Lactobacillus organisms and group D enterococci displaying the most antagonistic activity. C. difficile was examined for its ability to inhibit the multiplication of several fecal strains of anaerobic and aerobic bacteria. All eight strains of C. difficile tested inhibited the growth of particular strains of bacteria in the genera Bacteroides, Peptococcus, and Peptostreptococcus.