Analysis of Pseudomonas aeruginosa clinical isolates for possible variations within the virulence genes exotoxin A and exoenzyme S.

We have previously characterized several Pseudomonas aeruginosa isolates that were obtained from patients with tracheal, urinary tract, or wound infections (A. H. Hamood, J. A. Griswold, and C. M. Duhan, 1996, J. Surg. Res. 61: 425). Analysis of additional isolates showed that regardless of the isolation site, some isolates produced significantly higher or significantly lower levels of either exotoxin A or exoenzyme S proteins. These variations did not correlate with the mucoid phenotype of the isolates. One aim of this study was to determine if the variations in the level of exotoxin A or exoenzyme S are due to DNA rearrangements within either the toxA or the exoS gene. This was accomplished by Southern blot hybridization experiments using a toxA internal probe, a toxA upstream probe, or an exoS internal probe. Hybridization with the toxA internal probe produced a 0.8-kb hybridizing fragment, whereas hybridization with the exoS internal probe produced either a 2.0- or a 2.3-kb hybridizing fragment. Hybridization with the toxA upstream probe, however, produced hybridizing fragments of varying sizes, regardless of their isolation site. Isolates that showed a similar hybridization fragment with either the toxA upstream probe or the exoS internal probe produced variable levels of exotoxin A or exoenzyme S. These results suggest that: [1] specific location within the host has no effect on either the mucoid phenotype of the isolate or the level of exotoxin A or exoenzyme S produced by the isolates; [2] although restriction polymorphism exists within the toxA upstream region, both the toxA and the exoS structural genes are relatively conserved; and [3] variations in the level of exoenzyme S and exotoxin A produced by different isolates do not correlate with either the observed heterogeneity within the toxA upstream region or the mucoid phenotype of the isolates.