The influence of regular diets on intestinal microbiota is widely unknown. The current study examined fecal samples of vegetarians (n=144), vegans (n=105), and an equal number of control subjects consuming an omnivorous diet who were matched for age and gender. Classical bacteriological isolation was utilized and the main aerobic and anaerobic bacterial genera were identified and enumerated. Absolute and relative numbers were computed and compared between groups. Total counts of Bacteroides spp., Bifidobacterium spp., Escherichia coli and Enterobacteriaceae spp. were significantly lower (P=0.001, P=0.002, P=0.006 and P=0.008, respectively) in vegan samples than in controls, whereas others (E. coli biovars, Klebsiella spp., Enterobacter spp., other Enterobacteriaceae, Enterococcus spp., Lactobacillus spp., Citrobacter spp. and Clostridium spp.) were not. The total microbial count did not differ between the groups. In addition, subjects on a vegan or vegetarian diet showed significantly (P=0.0001) lower stool pH than did controls and stool pH and counts of E. coli and Enterobacteriaceae were significantly correlated across all subgroups. The authors concluded that maintaining a vegan or vegetarian diet results in a significant shift in the microbiota while total cell numbers remain unaltered. Eur J Clin Nutr. 2012 Jan;66(1):53-60. PMID: 21811294
