Role of Exotoxin and Protease as Possible Virulence Factors in Experimental Infections with Pseudomonas aeruginosa

Evidence is presented which suggests that both the proteases and the exotoxin produced by Pseudomonas aeruginosa multiplying in situ in a burned mouse model are virulence factors. A 50% decrease in functional elongation factor 2 (EF-2) was seen 16 h postinfection in the liver of mice infected with the toxigenic, protease-producing P. aeruginosa strain M-2; at the time of death EF-2 was depleted by 80%. This correlates with a reduction in the level of protein synthesis in the liver of infected animals. Treatment with specific antitoxin extended the mean time to death and blocked depletion of EF-2. Administration of gentamicin 24 h after infection caused rapid clearance of bacteria and extended the mean time to death, but all animals treated with either antitoxin or gentamicin eventually died. In contrast, treatment with both antitoxin and gentamicin provided virtually complete protection. Infection of mice with P. aeruginosa WR5 (protease-producing, nontoxigenic) or with P. aeruginosa PA103 (toxigenic, slow protease producer) required several logs more bacteria and did not result in the same extensive depletion in EF-2 content. When challenge with PA103 was supplemented by injection of purified Pseudomonas protease, the mean time to death was shortened and significant reduction in liver EF-2 was observed. It is suggested that both toxin and proteases are required for the full expression of virulence in Pseudomonas infections.