Using minimum inhibitory concentration values of common topical antibiotics to investigate emerging antibiotic resistance: A retrospective study of 134 dogs and 20 horses with ulcerative keratitis

Abstract

Objectives To identify the minimum inhibitory concentration (MIC) distribution for commonly used topical antibiotics from isolates of dogs and horses with ulcerative bacterial keratitis, and to investigate changes in MIC values over time and following treatment with topical fluoroquinolones. Animals studied One hundred thirty‐four client‐owned dogs and 20 client‐owned horses with bacterial ulcerative keratitis. Procedure Minimum inhibitory concentration values for 14 topical antibiotics were reported for canine and equine cases of bacterial ulcerative keratitis between 2013 and 2018. Changes in MIC values over time and after treatment with topical fluoroquinolones were reported. Results The three most common bacterial genera isolated were Staphylococcus, Streptococcus, and Pseudomonas. Together, these represented 79.4% of canine cases and 77.4% of equine cases. Overall, isolates from horses tended to have lower MIC values, as did Pseudomonas isolates from both dogs and horses, compared to other bacterial genera, especially Staphylococcus spp. The MIC values of erythromycin and trimethoprim sulfa for Staphylococcus spp., and the MIC value of moxifloxacin for Pseudomonas significantly increased over time. Previous topical fluoroquinolone use was associated with a significant increase in the MIC value of ofloxacin in canine and equine Staphylococcus isolates and current topical fluoroquinolone use was associated with significant increases in the MIC values of ciprofloxacin, moxifloxacin, and ofloxacin in canine Staphylococcus isolates. Conclusion Patients previously or currently treated with topical fluoroquinolones, particularly in Staphylococcus infections, may require alternative antibiotics or additional antibiotic classes other than fluoroquinolones. Bacterial culture with MIC susceptibility testing should be highly recommended when a Staphylococcal infection is suspected.

Comparison of antimicrobial resistance patterns in dogs with bacterial keratitis presented to a veterinary teaching hospital over two multi‐year time periods (1993–2003 and 2013–2019) in the Southeastern United States

“…Consistent with previous studies, 3‐6,15 brachycephalic breeds were more commonly affected with infected corneal ulcers. Brachycephalic conformation is associated with several craniofacial abnormalities that predispose to the development of corneal ulceration 6,7,16 and bacterial keratitis.…”

“…Consistent with previous studies, 3‐6,15 brachycephalic breeds were more commonly affected with infected corneal ulcers. Brachycephalic conformation is associated with several craniofacial abnormalities that predispose to the development of corneal ulceration 6,7,16 and bacterial keratitis. Additionally, more than half of the dogs had STT <15 mm/min, and nearly one‐third of these dogs were already receiving topical cyclosporine or tacrolimus.…”

Prevalence and Antibiotic Susceptibility of Bacterial Isolates From Dogs With Ulcerative Keratitis in Midwestern United States

“…and cephalosporins (cefazolin and ceftiofur) were higher than MIC values detected for Staphylococcus and Streptococcus species; further, MIC 50 and MIC 90 values for Streptococcus sp. and aminoglycosides (amikacin, gentamicin, neomycin, and tobramycin) were higher than MIC values identified for Staphylococcus or Pseudomonas isolates, as recently described in canine and equine patients ( 31 ).…”

Analysis of Virulence and Antimicrobial Resistance Gene Carriage in Staphylococcus aureus Infections in Equids Using Whole-Genome Sequencing

“…The major chloramphenicol resistance gene cat is carried on the plasmids pC221 and pC223 ( 25 ), while TMS drug resistance is mediated by the dfr genes ( 26 ). In horses, long-term treatment of staphylococcal eye infections with topical fluoroquinolones is a risk factor for developing resistance to fluroquinolones and other drug classes ( 27 ). The tet genes encode efflux pumps mediating tetracycline resistance, while the related multidrug efflux pump encoded by norA provides fluoroquinolone resistance ( 26 ).…”