How to Treat Bacterial Keratitis

How to Treat Bacterial Keratitis Bacterial keratitis in dogs is a common disease that can be aggressive and may threaten vision. The exact pathogenesis is unknown. Culture of the cornea should be done when bacterial keratitis is suspected, and many suspected or confirmed cases are treated with cefazolin and tobramycin or with ciprofloxacin alone. All of these regimens provide a broad spectrum of coverage for most pathogenic bacteria. In human bacterial keratitis, there are regional differences in the organisms isolated and resistance patterns are seen among bacterial isolates that vary both regionally and temporally. This retrospective, cross-sectional study evaluated the clinical characteristics of dogs with bacterial keratitis, as well as regional and temporal changes in the species of bacteria isolated and their patterns of resistance to antimicrobials. Medical records from 2 veterinary teaching hospitals for the years 1993 through 2003 were reviewed, and 97 dogs with bacterial keratitis were identified. Sixty-six percent of the dogs were brachycephalic, and the odds of a diagnosis of bacterial keratitis were significantly higher for Pekingese, shih tzus, pugs, Boston terriers, miniature pinschers, and bichon frise. Of dogs in which Schirmer’s tear tests were done, 54% had tear production < 15 mm/min, suggesting that keratoconjunctivitis sicca (KCS) may play a role in the pathogenesis of bacterial keratitis. In addition, at the time of initial examination, 29% of the dogs were receiving a corticosteroid, although the authors noted that they were unable to evaluate corticosteroid use as a risk factor for bacterial keratitis. The most commonly isolated bacteria were Staphylococcus intermedius (29%), beta-hemolytic Streptococcus species (17%), and Pseudomonas aeruginosa (21%). In comparing antimicrobial susceptibility, S. intermedius isolates had limited resistance to certain antimicrobials; more than 80% of beta-hemolytic Streptococcus species were resistant to neomycin, polymyxin B, and tobramycin; P. aeruginosa isolates were susceptible to tobramycin and gentamicin with limited resistance to ciprofloxacin and enrofloxacin. Unlike in humans, no significant changes in antimicrobial resistance patterns were noted over the 11-year period of this study. The authors concluded that administration of ciprofloxacin or a combination of a first-generation cephalosporin and tobramycin may be used to treat bacterial keratitis in dogs while awaiting results of bacterial culture and sensitivity. They also suggest that corneal ulcers in brachycephalic dogs and dogs with KCS be managed more aggressively and that dogs being treated with corticosteroids should be monitored for corneal ulceration.