An investigation of Pseudomonas cepacia : flagellin characterization and virulence studies in a burned mouse model

Pseudomonas cepacia, a clinically important opportunist, was examined with respect to its flagellin characteristics and its virulence in the burned mouse model. Sodium dodecyl sulfate poly acrylamide gel electrophoresis was used to characterize the flagellins from several clinically important non-aeruginosa pseudomonads. The flagellin molecular weights were found to vary between species: P. maltophilia B69 Fla—33,000; P. stutzeri HEW—55,000; P. aeruqinosa M-2—53,000. Upon examination of ten clinical strains, the flagellins of P. cepacia were divided into two groups based on flagellin molecular weights and serological relationships, Type I is a homologous group with a molecular weight of 31,000, whereas Type II is a heterologous group with flagellin molecular weights from 44,000 to 46,000. The characteristics of the two groups are further reflected in their serological relationships. Hyperimmune antisera prepared against Type I FAg agglutinated only Type I strains. Based upon slide agglutination assays, subgroups were detected within Type II. The two flagellin types appear to be analogous to the two major flagellin groups of P. aeruginosa.

The virulence of Pseudomonas aeruginosa and non-aeruginosa pseudomonads was examined in a burned mouse model. Pseudomonas aeruginosa strain M-2 was highly virulent causing 100% mortality by 38 hours with injection of 10 CFU by either a subcutaneous or intra2 peritoneal route. Subcutaneous injection of 10² CFU resulted in rapid multiplication of the bacteria at the burn wound with 10⁸ CFU/g detectable in the burned skin by 28 hours post-injection, 10⁵ CFU/g liver and 10³ CFU/ml blood, markedly less virulent; injection of ≥ 10⁷ CFU caused ≤ 60% lethality. Pseudomonas cepacia SMH colonized the burn skin of thermally injured mice, persisting at levels of 10⁷ to 10⁸ CFU/g burned skin after an Pseudomonas cepacia persisted in the burn wound for at least three weeks. No organ invasion was detectable throughout this period. Studies with E. coli and two additional clinical isolates of P. cepacia yielded similar results. Injection of a 10² CFU dose of P. cepacia SMH revealed that the level of persistence is dose dependent. These results suggest that tenacious persistence of P. cepacia in the burn wound may provide a model for the study of persistent, nuisance infections in a compromised host.