Purpose To analyze PASP in terms of its gene distribution and expression, its corneal pathologic effects, its enzymatic properties, and the protectiveness of the immune response to this protease. Methods Twenty-five strains of P. aeruginosa were analyzed for the PASP gene and secreted protein by PCR and Western blot analysis, respectively. Active recombinant (r)PASP (10 μg/20 μL) or heat-inactivated rPASP was intrastromally injected into rabbit corneas. Pathologic changes were monitored by slit lamp examination (SLE) and histopathology. Purified rPASP was assayed for cleavage of collagens and susceptibility to TLCK. Rabbit antibody to rPASP was produced and tested for enzyme inactivation, and actively immunized rabbits were challenged by intrastromal injection of active rPASP (5 μg). Results All 25 strains of P. aeruginosa analyzed were positive for the PASP gene and protein. SLE scores of eyes injected with active rPASP were significantly higher than control eyes at all postinjection times (PI; P ≤ 0.004). Histopathologic studies documented the destruction of the corneal epithelial layer and portions of the corneal stroma at 9 hours PI, and polymorphonuclear (PMN) leukocyte infiltration into the cornea by 24 hours after active rPASP injection. PASP cleaved type I and IV collagens and was susceptible to TLCK inhibition. PASP was present in the cytoplasm and periplasm, but only secreted PASP was enzymatically active. A high antibody titer (ELISA titer ≥ 10,000) was produced, but this antibody did not protect against active rPASP challenge. Conclusions PASP is a commonly produced Pseudomonas protease that can cleave collagens and cause corneal erosions.

CD-cholesterol is a potent inhibitor of alpha-toxin activity in vitro and an effective means to arrest corneal damage during S. aureus keratitis.

The S. pneumoniae noncapsular strain was as virulent in the rabbit cornea as was the encapsulated strain, but unlike the encapsulated strain, was avirulent in the mouse peritoneum.

Topical cholesterol is an effective treatment for S. pneumoniae keratitis. Cholesterol not only inhibits pneumolysin, it is also bactericidal.

Surfactant D is important to the ocular innate host defense against Pseudomonas keratitis.

Only one S. aureus strain, UMCR1, was able to cause a reproducible severe conjunctivitis. This conjunctival infection could be used to test new antimicrobials and to help understand the pathogenesis of conjunctivitis, especially in terms of overcoming the host defenses.

Lysostaphin was mostly effective in treating coagulase-negative staphylococcal experimental endophthalmitis.

Corneas and erythrocytes of young rabbits, relative to aged rabbits, are significantly more susceptible to S. aureus keratitis and to alpha-toxin.