Variations in the anaerobic faecal flora of ten healthy human volunteers with special reference to the Bacteroides fragilis-group and Clostridium difficile.

Ninety nine stool specimens of ten healthy human volunteers were collected over a one year period, and processed anaerobically. The individual variations in intestinal colonization with bacteria of the Bacteroides fragilis-group were detected, using the Bacteroides Bile Esculin medium and an identification scheme for bile-resistant Bacteroides species. Clostridium difficile agar supplemented with cycloserine/cefoxtin was used to detect the incidence of C. difficile in this group. The species of the B. fragilis-group most often detected were: B. vulgatus (in 31 samples from ten persons), B. uniformis (22/9), B. fragilis (19/7). C. difficile was never detected in this group. The mean total anaerobic cultural counts (log) of the ten volunteers varied between 9.94 and 10.91. This shows that interindividual variations in anaerobic cultural counts of about one log are common. In spite of these moderate interindividual variations, intraindividual variations in time of up to three log were detected. The mean Bacteroides cultural counts showed a variation between 8.83 and 10.24. The mean DMCCs of the ten volunteers were between 10.22 and 10.73. We conclude that at least a three to four log difference from the control samples will be required to establish a significant change in anaerobic cultural count due to antibiotic treatment.