Observations on Pseudomonas aeruginosa proteolytic and toxic activity in experimentally infected rats

To bypass natural resistance against Pseudomonas aeruginosa infection, a granuloma pouch model to be experimentally infected was established in rats. This experimental model also permitted easy collection of wound exudate. In general, the animals either died or became very ill and were consequently sacrificed within the first 12 days, or they (6 of 16) survived in good condition after 20 days. The virulence of recently isolated strains compared to twelve-months old subcultures of the same strains showed no major differences in clinical pattern. In the first seven days following the start of the infection, all animals presented a fall of elastase activity in the wound exudate. Toxin A was present in the exudate, sometimes in relatively high levels, but there was no correlation between toxin level and the clinical development. As a rule, spontaneous rupture of the granuloma pouch, apparently unrelated to the concentrations of either elastase or toxin A in the exudate, was beneficial to survival. In the present experimental infectious context, neither P. aeruginosa elastase nor toxin A seemed to play any isolated lethal nor pathogenetic role.