Inhibition of Pseudomonas aeruginosa by hyperbaric oxygen: interaction with mouse peritoneal exudate cells

Abstract

High pressure oxygen (HPO) therapy for P. aeruginosa infections of burn wounds has not been as effective as in vitro studies predicted. Mitigation of HPO toxicity for P. aeruginosa by nutrients present at the burn site could explain the lack of in vivo success. Alternatively, HPO induced depression of host defense mechanisms could negate beneficial effects arising from HPO's known toxicity for P. aeruginosa. Accordingly, mouse peritoneal exudate cells (PEC), preincubated for 24 hr in 1 atm of air CO2, were used to study the in vitro effects of HPO or air CO2 on phagocytosis of P. aeruginosa or sheep erythrocytes (SRBC). Subsequent 2 hr exposures of PEC to increasing numbers of bacteria, in an air CO2 atmosphere, decreased the percentage of bacteria cleared as well as PEC viability. Similar exposures of PEC to bacteria in an HPO atmosphere prevented the loss of PEC viability and increased bacterial clearance. In control experiments, increasing the number of SRBC relative to PEC decreased the percentage of SRBC cleared without decreasing PEC viability, as determined under air CO2; short (2 hr) exposure to HPO did not affect SRBC clearance. Microscopic examination of PEC indicated that a 24 hr preincubation in HPO decreased the percentage of PEC which could ingest SRBC during subsequent experimental exposures (2 hr) to air CO2 or HPO. These data suggest that short periods of exposure to HPO promote the ability of PEC to clear pseudomonads by adversely affecting the bacteria. This in turn prevents a pseudomonad induced depression of PEC viability and function. In contrast, prolonged HPO exposure may be detrimental to phagocytic activity.