Assessment of protease (elastase) as a Pseudomonas aeruginosa virulence factor in experimental mouse burn infection

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Abstract
In experimental P. aeruginosa infection of mice, protease may enhance the virulence of the organism. Anesthetized CBA/Lu mice were subjected to a 15 s flame burn and infected with a wild-type protease-producing strain And 2 of its protease-deficient mutants. The average bacterial cell LD50 of 3.8 .+-. 0.3 SD (log10) for mice infected with the protease-producing P. aeruginosa was at least 1 log lower than the LD50 of the protease-deficient mutants (0.02 > P > 0.01). The addition of purified protease to the infecting inoculum of protease-deficient strains reduced the LD50. Although the generation time in vitro was the same for all 3 bacterial strains used, there were consistently fewer viable bacteria in the blood of mice infected with protease-deficient strains than in those infected with the protease-producing strain. When a protease-deficient strain was mixed with the protease-producing wild-type strain, the number of protease-producing Pseudomonas found in the blood remained constant, whereas the number of protease-deficient organisms increased, suggesting that protease contributed to the invasiveness of the organisms. The survival of mice infected with protease-producing Pseudomonas was enhanced by anti-protease serum. Anti-protease serum had no effect in mice infected with protease-deficient mutants.