Effect of High Oxygen Tensions on the Growth of Selected, Aerobic, Gram-negative, Pathogenic Bacteria

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Abstract
The in vitro effects of high O2 tensions (PO2) on aerobic, enteric pathogens were examined at pressures of up to 3 atm absolute. Organisms from the genera Salmonella, Shigella, and Vibrio were usually subjected to 24-hr exposures. Tensions of 0.87, 1.87, and 2.87 atm absolute of O2 (plus traces of CO2 and N2) became progressively inhibitory for Salmonella and Shigella growth, but were bactericidal only for V. comma strains at tensions greater than 0.87 atm absolute of O2. Growth inhibition of enteric organisms resulted from increased PO2, rather than pressure per se, and could be mitigated nutritionally; an appropriate carbohydrate source is at least partially involved. Further studies with vibrios indicated that such mitigation was independent of medium pH. In addition, a synergistic relationship existed between O2 and sulfisoxazole when tensions from 0.87 to 2.87 atm absolute of O2 were maintained for 3 to 24 hr. Synergism occurred even under nutritional conditions which negated growth inhibition by O2 alone. Bactericidal concentrations of sulfisoxazole, in the presence of increased PO2, were reducible up to 4,000-fold. The combined procedure employed in this investigation, by use of an antimicrobial drug of known action, which also synergizes with O2, plus nutritional studies, suggests a means for establishing a site of O2 toxicity. These data support the concept that O2 inhibition of growth represents a metabolic disturbance and that metabolic pathways involving p-aminobenzoic acid may be O2-labile. Such an approach could also guide development of antimicrobial agents as O2 substitutes for promoting synergism.