Amoxicillin resistance in urinary E. coli in pets from the Midwest

Abstract

BACKGROUND: Antibiograms are stewardship tools that provide antimicrobial resistance data for regional bacterial isolates to guide treatment of infections. OBJECTIVES: To develop regional antibiograms of urinary Escherichia coli isolates from cats and dogs. ANIMALS: Escherichia coli isolates cultured from feline (N = 143) and canine (640) urine from 2013 to 2017, from Kansas State University (N = 335) and private practice (N = 448) patients in the Midwestern United States. METHODS: Retrospective review of urine culture and susceptibility results. Antibiograms were created for 10 commonly used antimicrobial agents using Clinical and Laboratory Standards Institutes guidelines. RESULTS: No isolates from cats were susceptible to amoxicillin-clavulanate (susceptibility [S] ≤ 0.25/0.12) or amoxicillin (S ≤ 0.25); isolates from dogs had low susceptibility to amoxicillin 53% (S ≤ 8). Conversely, isolates from dogs had high susceptibility to amoxicillin-clavulanate 92% (S ≤ 8/4), despite equal 90th percentile minimum inhibitory concentrations (8 μg/mL) for feline and canine populations. Resistance to other antimicrobials was uncommon (≤7% for isolates from cats, ≤14% for isolates from dogs). CONCLUSIONS AND CLINICAL IMPORTANCE: The disparity in susceptibility for amoxicillin and amoxicillin-clavulanate between isolates from cats and dogs likely reflects higher breakpoints for urinary tract infections (UTIs) in dogs. Urine concentration data for these antimicrobials in cats might support a UTI-specific breakpoint for cats and increase potential therapeutic options for managing UTIs in cats with first-line antimicrobials. Decreased susceptibility among isolates from dogs to amoxicillin (53%) compared to amoxicillin-clavulanate (92%) might support amoxicillin-clavulanate as a better empirical choice for UTIs in dogs in this geographical region.