Toxin A-deficient mutants of Pseudomonas aeruginosa PA103: isolation and characterization

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Abstract
An immunological assay utilizing double-diffusion principles was developed for identification of P. aeruginosa mutants deficient in toxin A. Mutations were chemically induced and mutants were isolated from P. aeruginosa strain PA103. Quantitative assays, enzymatic and immunological, indicated that 5 mutants produced toxin A in vitro at levels of 0.3% or less of parental strain levels. The mutants apparently fell into 4 classes. Multiple genes may be involved in the regulation of toxin A yields. Classes 1-3 produced less than 1% of parental levels of extracellular toxin A. Class 1 mutants are apparently specific for toxin A. Class 2 mutants are pleiotropic and produced toxin A, protease and other extracellular proteins at reduced yields. Class 3 mutants are pleiotropic and have relatively high levels of cell-bound toxin A. Class 4 mutants produce toxin A at levels > 1% of parental yields. Of 16 toxin A-deficient mutants examined, only 1 was a class 1 mutant. This mutant (PA103-29) was identical to the parental strain in all respcects tested except for its marked deficiency in toxin A. The suitability of this class 1 mutant for use in virulence studies is discussed.