Evidence of bacteremia and endotoxemia in mice undergoing hyperbaric stress

Swiss albino mice were exposed to normoxic (PO2 approximately 0.2 ATA) helium at 1, 20 or 35 ATA for 2 or 48 h and examined for the presence of bacteria and endotoxin in selected tissues. Among mice exposed to 35 ATA for 48 h and tested immediately after decompression for bacteria in liver and peritoneal cavities, 6 of 30 (20%) contained gram-negative rods and 27 of 30 (90%) contained gram-positive cocci. Incidence of infection was considerably less in mice exposed to 35 ATA for 2 h or exposed to 1 ATA. Evidence of presence of gram-negative rods and /or escape of free endotoxin from the intestine was provided by demonstration that limulus lysate is coagulated (presumptive evidence of endotoxin) by liver homogenates in 70% of the mice exposed to 35 ATA for 48 h, 68% of those exposed to 20 ATA and 14% of those exposed to 1 ATA. Mice subjected to the hyperbaric stress of 35 ATA for 48 h were shown to be increasingly susceptible to injection with purified lipopolysaccharide. The LD50 was 0.24 mg for hyperbaric exposed mice and 0.39 mg for the control groups. These data suggest that hyperbaric stress, but not necessarily decompression, results in a short-term presence in mouse tissues of microbial agents originating from the gut. This invasion temporarily renders that host more susceptible to additional endotoxic challenge.