Genetic approaches to study Pseudomonas aeruginosa protein antigens

Pseudomonas aeruginosa produces a large number of extracellular products which may play a role in pathogenesis. We have used genetic techniques to elucidate the relative contribution of these proteins to virulence, and as a method of producing safe toxoids. A mutant has been isolated which produces an immunologically reactive nontoxic form of toxin A, the most toxic extracellular protein produced by P. aeruginosa. Although there are difficulties in production of sufficient quantities of this CRM toxoid, these are likely to be solved by further genetic manipulation. Protection studies with toxin A antibody and studies of mutants deficient in toxin A have confirmed that toxin A plays a role in pathogenesis while clearly showing that toxin A alone cannot totally account for the virulence of P. aeruginosa. Studies of mutants specifically altered in three other products, exoenzyme S, and the two major proteases of P. aeruginosa, elastase and alkaline protease, have clarified the contribution of these products to virulence. Demonstration by genetic studies that exoenzyme S was a major factor in the virulence for one P. aeruginosa strain allowed us to correctly predict that antibody to this product would be protective against infection with that strain.