Efficacies of alkaline protease, elastase and exotoxin A toxoid vaccines against gut-derived Pseudomonas aeruginosa sepsis in mice

The protective efficacies of vaccines prepared from Pseudomonas aeruginosa alkaline protease, elastase and exotoxin A toxoids against gut-derived P. aeruginosa sepsis in mice were evaluated. Specific pathogen-free mice given P. aeruginosa strain D4 orally followed by cyclophosphamide (to promote translocation across the gut wall) died of bacteraemia. Mice immunised with one of the three individual toxoid vaccines were not significantly protected when compared to control mice immunised with bovine serum albumin. Combined immunisation with alkaline protease and elastase toxoids likewise showed no significant protective activity. However, combined immunisation with alkaline protease and exotoxin A toxoids significantly increased the survival rate, which reached 60% (compared with a 7.1% survival rate in the control group). These results show that alkaline protease and exotoxin A play important roles as pathogenic factors in gutderived sepsis and that a combination of the two exoenzyme toxoids represents a logical candidate for vaccination against P. aeruginosa sepsis.