VACCINE EFFICACIES OF ELASTASE, EXOTOXIN-A, AND OUTER-MEMBRANE PROTEIN-F IN PREVENTING CHRONIC PULMONARY INFECTION BY PSEUDOMONAS-AERUGINOSA IN A RAT MODEL

The protective efficacies of eight vaccine preparations consisting of Pseudomonas aeruginosa outer-membrane protein F, elastase and exotoxin A toxoid, administered either individually or in various combinations, were determined in a rat model of chronic pulmonary infection. Rats were immunised intramuscularly at 2-week intervals (days 0, 14 and 28). On day 42, blood was collected and antisera were obtained from each vaccine group for use in an enzyme-linked immunosorbent assay which determined the titre of IgG antibodies elicited by each vaccine. Also on day 42, rats were challenged by intratracheal inoculation of a clinical isolate of P. aeruginosa encased within agar beads. On day 49, the animals were killed and the lungs were examined macroscopically for the presence of lesions and fixed for histological examination. When compared with control rats immunised with bovine serum albumin, rats immunised with protein F alone as a vaccine received significant protection against the development of severe pulmonary lesions. Elastase used alone as a vaccine provided some protection against severe lung lesions and reduced the incidence of microscopic peribronchial inflammation. However, the combination of protein F plus elastase as a vaccine did not afford protection from severe lesions, and there was an increased incidence of necrotising granulomas in the lungs from this vaccine group. Protection against lung lesions from the three-component vaccine consisting of protein F, elastase and exotoxin A toxoid was similar to that provided by the protein F vaccine. Neither macroscopic nor histological evidence showed any enhancement of protective efficacy for the three-component vaccine over that of the protein F vaccine. No combination of elastase or exotoxin A toxoid with protein F improved the protective efficacy of the protein F vaccine alone.