Alterations in mouse fecal flora associated with hyperbaric stress

The effect of hyperbaric stress on the composition of fecal microflora was investigated in the mouse. Mice were exposed to 35 ATA with normoxic PO2 concentration in a helium atmosphere at 35 degrees C to prevent body heat loss or to 1 ATA oxygen-helium at 25 degrees C. Freshly discharged fecal pellets were cultured under strict anaerobic conditions, replica plated, and then cultured both aerobically and anaerobically. From experiment to experiment there was considerable variation in the total number of cultured bacteria. By replica plating, however, a consistent reduction in the relative numbers of obligate anaerobes was demonstrated, from a mean of 71% to 44%, in the pressurized mice. Bacteroids distasonis and B. multiacidus were the obligately anaerobic species most frequent identified from mice exposed at 35 and 1 ATA. Major changes in species distribution were not encountered.