Inhibition of pathogenic enteric bacteria by hyperbaric oxygen: enhanced antibacterial activity in the absence of carbon dioxide.

The antibacterial effects of 24-h exposures to high-pressure oxygen in relation to environmental CO(2) were studied at 3 atm absolute (ata) and at 1 ata. Eight gram-negative, aerobic and facultatively aerobic, pathogenic enteric bacteria (Salmonella typhosa, Salmonella paratyphi, Salmonella schottmuelleri, Shigella dysenteriae, Shigella flexneri, Proteus vulgaris, Pseudomonas aeruginosa, and Escherichia coli) were exposed as shallow-broth cultures and agar surface cultures. Although broths supplemented with 0.2% glucose permitted some growth of Salmonella typhosa, Salmonella schottmuelleri, Shigella dysenteriae, and Shigella flexneri during exposure to high-pressure oxygen in the presence of CO(2), the other species grew only after the exposure, indicating a bacteriostatic effect. Both bacteriostatic and bactericidal effects were demonstrated on the surface of Trypticase soy agar, where killing of Salmonellea typhosa, Proteus vulgaris, and Pseudomonas aeruginosa was significantly greater after exposure to pure O(2) at 3 ata than at 1 ata. At 3 ata, significantly more killing occurred upon exposure of all species (except Shigella dysenteriae and S. flexneri) on an agar surface to 100% O(2) as compared with exposure to a mixture of 95% O(2) + 5% CO(2). Thus, deprivation of CO(2) during exposure to pure O(2) enhanced the bactericidal effect of high-pressure oxygen.