Epidemic population structure of Pseudomonas aeruginosa: Evidence for a clone that is pathogenic to the eye and that has a distinct combination of virulence factors

The genetic structure of a population of Pseudomonas aeruginosa, isolated f rom patients with keratitis, endophthalmitis, and contact lens-associated r ed eye, contact lens storage cases, urine, ear, blood, lungs, wounds, feces , and the environment was determined by multilocus enzyme electrophoresis. The presence and characteristics of virulence factors were determined by re striction fragment length polymorphism analysis with DNA probes for lasA, 1 asB, aprA, exoS, exoT, exoU, and ctx and by zymography of staphylolysin, el astase, and alkaline protease. These analyses revealed an epidemic populati on structure of P. aeruginosa, characterized by frequent recombination in w hich a particular successful clone may increase, predominate for a time, an d then disasappear as a result of recombination. Epidemic clones were found among isolates from patients with keratitis. They were characterized by hi gh activity of a hitherto-un recognized size variant of elastase, high alka line protease activity, and possession of the exoU gene encoding the cytoto xic exoenzyme U. These virulence determinants are not exclusive traits in s trains causing keratitis, as strains with other properties may cause kerati tis in the presence of predisposing conditions. There were no uniform patte rns of characteristics of isolates from other types of infection; however, all strains from urinary tract infections possessed the exoS gene, all stra ins from environment and feces and the major part of keratitis and wound is olates exhibited high elastase and alkaline protease activity, and all stra ins from feces showed high staphylolysin activity, indicating that these vi rulence factors may be important in the pathogenesis of these infectious di seases.