Detection of lactobacilli and their interaction with clostridia in human gastrointestinal tracts and in vitro.

Culture counts of aerobic lactobacilli in the feces of vegetarians ([8.1 +/- 0.7] of log10 bacteria per gram dry weight) were higher than those of meat consumers ([5.2 +/- 0.1] of log10 bacteria per gram dry weight). Co-culture of Lactobacillus acidophilus and Clostridium perfringens in various media revealed that an interaction between these two species. The pH was the most important factor controlling their relative growth, which might explain the relative abundance of lactobacilli in feces of men and animals on vegetarian diets. Lactobacilli but not clostridia were detected in feces of newborn infants. These findings are discussed in relation to health.