Oxygen tolerance of anaerobic bacteria isolated from human feces

The large bowel intestinal flora of mammals is made up mostly of O2-intolerant anaerobic microorganisms which are irreversibly damaged by brief exposure to air. The aim of our work was to investigate the effect of atmospheric O2 on human intestinal anaerobic microorganisms. Thirty O2-intolerant bacterial strains that reached 100% mortality after 120 min of air exposure were isolated. Ten of these strains were tested for their atmospheric O2 sensitivity as a function of air exposure time; all tested microorganisms showed a similar mortality trend on exposure to air. In fact, 50% of cells survive, on the average, after 4–5 min of atmospheric O2; this percentage decreases to 3–5% after only 20 min, and after 40 min only one cell in a thousand survives; all strains reached 100% mortality in a time range of 100–120 min. The strains examined were identified as belonging to the generaEubacterium, Peptostreptococcus, andCoprococcus.