Pseudomonas aeruginosa keratitis in leukopenic rabbits

To study the role of the host inflammatory response in Pseudomonas aeruginosa keratitis, rabbits were made leukopenic with intravenous injections of cyclophosphamide and dexamethasone. Twenty-four hr later, keratitis was initiated in all rabbits with an intrastromal injection of 1,000 log phase P. aeruginosa strain 27853. Slit lamp examination of eyes showed that leukopenic rabbits had significantly less (P < 0.0001) ocular pathology at 16, 22, and 27 hr postinfection. The number of viable bacteria recovered from corneas of leukopenic rabbits was the same as the number recovered from nonleukopenic rabbits (P = 0.95). These results suggest that the host inflammatory response significantly contributes to the overall ocular pathology associated with P. aeruginosa keratitis, but does not influence the survival of the infecting organism in the cornea at the height of the infection.

Prednisolone acetate or prednisolone phosphate concurrently administered with ciprofloxacin for the therapy of experimental Pseudomonas aeruginosa keratitis

This study was conducted to determine the therapeutic efficacy of 3.0 mg/ml ciprofloxacin administered concurrently with one of two salts of prednisolone for the treatment of experimental pseudomonal keratitis. Rabbit corneas were injected intrastromally with Pseudomonas aeruginosa ATCC strain 27853. Sixteen hr after injection, rabbits were randomly divided into four treatment groups (3 rabbits, 6 eyes per group): 1) ciprofloxacin plus prednisolone acetate; 2) ciprofloxacin plus prednisolone phosphate; 3) ciprofloxacin only; 4) untreated. Signs of inflammation were graded in a masked fashion by slit lamp examination (SLE) and by estimating polymorphonuclear leukocyte (PMN) numbers in corneas 27 hr after injection. SLE scores and PMN numbers were significantly lower (P < 0.02) in eyes receiving either salt of prednisolone plus ciprofloxacin compared to the untreated controls. In contrast, SLE scores and PMN numbers were not significantly different in eyes treated with ciprofloxacin alone, compared to untreated controls (P > 0.13). No viable bacteria were recovered from any eye treated with ciprofloxacin (groups 1, 2, and 3). Ciprofloxacin concentrations in the aqueous humor of eyes in groups 1, 2, and 3 were greater than 15-fold higher than the MIC for P. aeruginosa 27853. These results suggest that either salt of prednisolone, when combined with ciprofloxacin, reduces ocular inflammation without affecting the antimicrobial efficacy of the antibiotic.

Bioassays for quantitating ciprofloxacin and tobramycin in aqueous humor

Development of new therapies for bacterial keratitis requires assays of antibiotics in infected ocular tissues; however, methods for such drug quantitation can be expensive and can lack precision and sensitivity. To develop a more suitable assay for quantitating tobramycin and ciprofloxacin in the aqueous humor, sixteen bioassays were compared. Variables assessed included: the strain of bacteria used as indicator (Staphylococcus aureus ATCC 25923 versus Klebsiella pneumoniae ATCC 10031), the application of bacteria to the agar surface versus inclusion in molten agar, the volume of the agar, and the application of antibiotic on paper discs versus instillation into agar wells. The best results were obtained when the appropriate indicator organism (S. aureus for tobramycin and K. pneumoniae for ciprofloxacin) was applied to the surface of the agar, antibiotic solution was put into agar wells, and the volume of agar was 30 ml per plate. The best sensitivity for assays of tobramycin and ciprofloxacin diluted in water were 0.98 and 0.12 micrograms/ml, respectively. These sensitivities improved as much as fourfold when antibiotics were diluted in aqueous humor or normal saline. The precision of all assays tested was high as determined by regression coefficients (r > 0.90). The sensitivity and precision of these assays indicate their utility for quantitating fluoroquinolones and aminoglycosides in aqueous humor.

Collagen shields containing tobramycin for sustained therapy (24 hours) of experimental Pseudomonas keratitis

We compared collagen shields hydrated in 1.36% tobramycin with topical 1.36% tobramycin for sustained treatment of experimental Pseudomonas keratitis in rabbits. Antibiotic therapy for a total of 24 hours was initiated 14 hours after an intrastromal injection of 10(3) logarithmic phase Pseudomonas aeruginosa. Seven groups were treated as follows: groups 1-3, collagen shields hydrated in tobramycin supplemented with topical 1.36% tobramycin drops at 4, 6, or 8 hour intervals; group 4, collagen shields hydrated in tobramycin without any further topical supplementation; group 5, topical tobramycin therapy, initially every half-hour for 4 hours, then hourly; group 6, collagen shields hydrated in balanced saline solution; and group 7, no treatment. Each group contained four eyes. The groups treated with collagen shields supplemented every 4 or 6 hours with topical tobramycin had significantly fewer colony forming units (CFU) than those receiving topical or collagen shield therapy alone (P < 0.001). The group treated with collagen shields hydrated in sterile saline had 10(7) CFU per cornea, which was not significantly different from the untreated group (P > 0.2). Collagen shields hydrated in tobramycin and supplemented with topical tobramycin were effective in sustained treatment of experimental Pseudomonas keratitis.