PSEUDOMONAS KERATITIS - THE ROLE OF AN UNCHARACTERIZED EXOPROTEIN, PROTEASE-IV, IN CORNEAL VIRULENCE

Purpose. The role of exoproteins in the pathogenesis of Pseudomonas ae ruginosa keratitis was investigated in three animal models by assessin g the relationship between corneal virulence and the activities of exo toxin A, elastase, alkaline protease, and an uncharacterized protease, protease IV. Methods. The four Pseudomonas strains tested included a prototype strain (ATCC 27853) producing exotoxin A, elastase, and alka line protease; a parent strain (PA103) producing only exotoxin A and p rotease IV; a mutant (PA103-29) producing only protease IV; and a muta nt (PA103-AP1) producing exotoxin A and having only approximately 5% o f the protease IV activity of its parent Corneal virulence was evaluat ed in the mouse scratch, rabbit scratch, and rabbit intrastromal model s in terms of clinical signs (slit lamp examination, slit lamp examina tion), and viable bacteria. Results. Protease IV, the only protease pr oduced by PA103 and PA103-29, was found to produce a unique band on zy mograms (120 kDa) and to react distinctively with a synthetic substrat e. Evidence for the role of protease IV in corneal virulence included two findings: PA103-29, which produced protease TV but not the other e xoproteins, caused infections that were as severe as those caused by t he prototype strain (ATCC 27853) in an three models (P > 0.24); and PA 103-AP1, the strain deficient in 95% of the parent protease IV activit y, mediated infections characterized by slit lamp examination scores s ignificantly lower than those of infections caused by the parent (PA10 3) or the prototype strain (ATCC 27853) in the rabbit and mouse scratc h models (P < 0.02). Conclusions. Protease IV was found to be a novel Pseudomonas protease contributing to corneal virulence in rabbits and mice when infections were initiated at the corneal surface. Furthermor e, production of protease IV in low quantities was sufficient for viru lence when the topical stages of keratitis were bypassed by an intrast romal injection of Pseudomonas.