Lee S. Engel

EFFECTIVENESS OF SPECIFIC ANTIBIOTIC/STEROID COMBINATIONS FOR THERAPY OF EXPERIMENTAL PSEUDOMONAS AERUGINOSA KERATITIS

Ciprofloxacin and prednisolone, but not an aminoglycoside and dexamethasone, were previously found to be effective in killing bacteria and reducing inflammation for the treatment of Pseudomonas keratitis. We investigated the therapeutic effectiveness of tobramycin/prednisolone and ciprofloxacin/dexamethasone in a rabbit model of experimental keratitis to increase our understanding of the effectiveness of antibiotic/steroid combinations. To our knowledge, this is the first analysis of the effectiveness of a combination of ciprofloxacin and dexamethasone for experimental keratitis. Two experiments were conducted. In the first experiment, 36 rabbits were divided into six groups: 1) untreated; 2) prednisolone acetate, 1.0%; 3) prednisolone phosphate, 1.0%; 4) tobramycin, 1.36%; 5) tobramycin plus prednisolone acetate; 6) tobramycin plus prednisolone phosphate. In the second experiment, 23 rabbits were divided into four groups: 1) untreated; 2) ciprofloxacin, 0.3%, plus dexamethasone alcohol, 0.1%; 3) ciprofloxacin; 4) dexamethasone alcohol. Topical antibiotic and/or steroid was given for 10 h, from 16 to 26 h postinfection, one drop every 15 min for the first hour and then every 30 min for the remaining 9 h. At 27 h postinfection, eyes were evaluated by slit lamp examination (SLE) and assayed for the presence of bacteria in terms of colony forming units (CFU) per cornea. Both prednisolone acetate and prednisolone phosphate reduced ocular inflammation (as determined by SLE), compared with no treatment (P < or = 0.036); the phosphate was more effective (P = 0.005). Tobramycin alone and in combination with prednisolone also significantly reduced SLE, compared with no treatment (P < or = 0.006). The bactericidal activity of tobramycin was not affected by either steroid formulation.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Growth and virulence of a complement-activation-negative mutant of Streptococcus pneumoniae in the rabbit cornea

Our previous work has demonstrated the importance of pneumolysin in the virulence of S. pneumoniae in a rabbit intracorneal model. This was accomplished by showing that deletion of the gene encoding pneumolysin resulted in reduced virulence, whereas restoration of the wild-type gene resulted in restoration of the virulent phenotype. To assess the importance of a particular domain in the pneumolysin molecule, we have now constructed a strain which produces a pneumolysin molecule which is hemolytic but which bears a site-specific mutation in the domain known to be associated with the complement-activating properties of this molecule. Comparison of the virulence of this strain with that of a strain bearing the wild-type gene showed statistically significantly lower total slit lamp examination (SLE) scores at 12, 18, 24, and 36 h (particularly with respect to fibrin formation), but no difference at 48 h. Determination of colony forming units (CFU) in eyes infected with the two strains showed approximately 10(6) bacteria per cornea until 36 h. Between 36 and 48 h, the bacteria were almost completely cleared with very few bacteria recoverable at the later time point. The loss of virulence observed with this mutation in the complement-activation domain of pneumolysin, though less than that observed with the gene deletion mutant, suggests that complement activation by pneumolysin has a significant role in the pathology observed in this model of corneal infection.

Effectiveness of ciprofloxacin-polystyrene sulfonate (PSS), ciprofloxacin and ofloxacin in a Staphylococcus keratitis model

PURPOSE Staphylococcus aureus causes severe corneal infections that often result in corneal scarring and blindness. Presently, therapy often involves the use of a fluoroquinolone antibiotic. This study, employing an experimental rabbit model of Staphylococcus keratitis, compared the effectiveness of two commonly prescribed formulations of fluoroquinolones to an experimental formulation, ciprofloxacin with polystyrene sulfonate (ciprofloxacin-PSS). The ciprofloxacin-PSS formulation uses an ion exchange resin to aid in the delivery of drug to the cornea. METHODS Early (4-9 h postinfection, PI) and late (10-15 h PI) therapies were studied, employing 5 groups: ciprofloxacin-PSS, ciprofloxacin, ofloxacin, PSS vehicle. and untreated. Dosing regimens were: every 30 min, 60 min, or a single drop applied at 9 h PI. Eyes were observed by slit lamp examination (SLE) and bacterial colony forming units (CFU) per cornea were determined. RESULTS Early phase therapy with ciprofloxacin-PSS, ciprofloxacin, or ofloxacin administered every 30 or 60 min were equally effective (P > or = 0.2880), decreasing CFU per cornea by >5 log. Ciprofloxacin was significantly more active than ciprofloxacin-PSS or ofloxacin (P < or = 0.0410) when applied as a single drop. Late therapy with ciprofloxacin-PSS, ciprofloxacin, or ofloxacin administered every 30 or 60 min resulted in >3 log decrease in CFU per cornea relative to controls (P < or = 0.0001). CONCLUSIONS Topical treatment of experimental Staphylococcus keratitis with ciprofloxacin-PSS, ciprofloxacin, or ofloxacin was effective. The effectiveness of ciprofloxacin-PSS suggests that improved drug delivery systems employing an ion exchange resin could be useful in an ocular fluoroquinolone formulation.

Efficacy of tobramycin drops applied to collagen shields for experimental staphylococcal keratitis

Treatment of staphylococcal keratitis includes tobramycin drops at repeated intervals, a prolonged therapy that is disruptive to the patient. To identify a regimen involving less frequent drug application, we compared the efficacy of fortified tobramycin (1.36%) administered by collagen shields or in topical drop form to rabbit corneas intrastromally infected with staphylococci. Eyes were treated with shields hydrated in and supplemented with fortified tobramycin drops (1.36%) applied every 1, 2, 5, or 10 h, from 10 to 20 h postinfection. For topical drop treatment alone, tobramycin was applied following the identical regimen. Untreated corneas contained 10(6) colony forming units. Shields supplemented with tobramycin drops applied every 1, 2, or 5 h sterilized 100% of the corneas. Shields supplemented with tobramycin drops applied at 10 h sterilized 58% of the corneas. Topical delivery of tobramycin every h sterilized all corneas; drops alone applied at longer intervals, such as 2, 5, or 10 h, sterilized 83%, 17%, and 0% of the corneas, respectively. Collagen shield delivery of tobramycin with supplemental topical drops can eradicate staphylococci in this model with less frequent dosing intervals than are required with topical therapy alone.