Bacterial studies of Clindamycin-associated colitis. A preliminary report.

The cause of pseudomembraneous colitis is not known but has been attributed to an alteration in the microbial flora of the colon. To test this hypothesis, a blind, prospective study was undertaken in which fecal samples were cultured quantitatively for aerobic and anaerobic organisms. The patients from which these samples were taken were all receiving clindamycin and had diarrhea secondary to the use of the drug. We were able to show definite differences in the colonic microflora which correlated with the presence of pseudomembranes on biopsy. Those patients who had diarrhea and pseudomembranous colitis showed a striking decrease, both quantitatively and qualitatively, in the number of anaerobes present. Those patients who had diarrhea but no pseudomembranes had large numbers of anaerobes which qualitatively approximated normal fecal cultures but quantitatively were fewer in number. A third group of patients, which had resolving pseudomembranous colitis, and were no longer symptomatic, had large numbers of anaerobic organisms which approximated those found in normal fecal cultures. There were no differences among the three groups with regard to facultative anaerobic microflora. Thus, the presence of pseudomembranous colitis correlated directly with a striking quantitative and qualitative decrease in the anaerobic microflora of the colon. The symptom of diarrhea alone appeared to have no meaning with regard to changes in the bacterial flora. Resolution of pseudomembranous colitis was associated with a return of the anaerobic microflora.