Exposure of Pseudomonas aeruginosa to Hyperbaric Oxygen: Inhibited Growth and Enhanced Activity of Polymyxin B.

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Abstract
The growth of P. aeruginosa was studied in stationary broth cultures (11 mm deep)"exposed to 100% O2 at 3 atmospheres absolute (3 ATA). During exposure, growth was greatly inhibited. Cultures transferred to air after high pressure O2 (HPO) resumed logarithmic growth at rates similar to unexposed cultures, but lag periods increased. The minimal inhibitory concentration (MIC) of polymyxin B was determined for 6 strains of P. aeruginosa after exposure to HPO for 3, 6 and 12 hr. The longer the exposure, the lower the MIC. Regardless of the strain, after 3 hr. exposure to HPO about 75% of the amount of antibiotic required for the MIC of unexposed cultures was needed; after 6 hr. exposure, about 50%; and after 12 hr. exposure, about 30%. It may be possible to increase the therapeutic effectiveness of an antibiotic administered at its maximum dosage if exposure of the patient to HPO can also bathe the infecting microorganisms with O2.