Abstract
The objective of this study was to describe bacterial culture and antibiotic susceptibility results in 476 dogs presenting with suspected bacterial keratitis in Iowa and surrounding Midwestern states, further detailing trends in patient characteristics, seasonality, and antimicrobial resistance. Corneal swabs yielded 465 bacterial isolates and 220 cultures (46.2%) with no apparent growth (0–5 isolates per culture). The most frequent bacterial genera were Staphylococcus (32.3%), Streptococcus (19.1%), and Pseudomonas (12.5%), while the most common bacterial species were Staphylococcus pseudintermedius (26.7%), Streptococcus canis (12%), and Pseudomonas aeruginosa (7.5%). Compared to mixed-breed dogs, canine breeds most likely to be examined for ulcerative keratitis included Boston terrier, Cavalier King Charles spaniel, miniature pinscher, pug, rat terrier, Saint Bernard, shih tzu, and silky terriers. In summer, the likelihood to yield a negative culture was reduced while the likelihood to culture Pseudomonas species was increased. Bacteria considered multidrug resistant (MDR, resistant to ≥ 3 antibiotic classes) represented 20% of all canine isolates and were most prevalent for Staphylococcus species (33%). An alarming, escalating trend of MDR prevalence was noted between 2016 (5%) and 2020 (34%). Individual ophthalmic preparations (i.e., single antibiotics or commercially available antibiotic combinations) with highest efficacy against all bacterial isolates included chloramphenicol (83%), ceftiofur (79%), amikacin (77%), neomycin-polymyxin B-bacitracin (77%), and gentamicin (74%). Efficacy of systemic antibiotics and combinations of ophthalmic preparations was also evaluated. Based on the present findings, triple antibiotic (Neo-Poly-Bac) is recommended as empirical monotherapy for prophylactic antibiotic therapy in dogs with simple corneal ulcers, while a chloramphenicol-ciprofloxacin combination is empirically recommended for therapeutic management of infected corneal ulcers. Pending culture and susceptibility results, appropriate selection of empiric antibiotic therapy is important to enhance therapeutic outcome and reduce antibacterial resistance in dogs with corneal ulceration.
Highlights
MATERIALS AND METHODSBacterial keratitis is a major global cause of ocular discomfort and visual impairment in dogs and other species
To our knowledge, specific comparisons of antibiotic combination efficacies on bacterial isolates has not been described in dogs or other species, and only selected canine reports have described the efficacy of systemic antibiotics for corneal disease (16, 17)
Patients Characteristics Between March 2014 and June 2020, corneal swabs were obtained from 476 dogs with suspected bacterial keratitis and submitted in-house (ISU LVMC, n = 317) or as mail-in to Iowa State University’s Veterinary Diagnostic Laboratory (ISU VDL) for aerobic bacterial culture and susceptibility testing
Summary
MATERIALS AND METHODSBacterial keratitis is a major global cause of ocular discomfort and visual impairment in dogs and other species. Rapid and appropriate use of antibiotics is critical in mitigating the potential devastating effects of bacterial keratitis in dogs, including keratomalacia (corneal melting), corneal perforation, scarring, and loss of vision or the entire eye (4, 5). Successful management requires the clinician to be aware of the most common bacterial isolates and their susceptibility profiles to antibiotics, as there is often a lag period of several days until corneal samples collected from the patient provide results for bacterial culture and sensitivity testing. Most previous reports in veterinary literature are limited to describing the prevalence of bacterial isolates and susceptibility profiles for individual antibiotics (6, 7, 10). Such information is useful but is generally insufficient to provide optimized recommendations for clinicians managing bacterial keratitis in dogs. Less antibiotic resistance in the environment will benefit both veterinary and human medicine
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