Generation of equine-specific local antibiograms: reproductive tract of mares and fillies in Western Australia.

Abstract

INTRODUCTION: Antimicrobial resistance (AMR) may lead to increasing inefficacy and treatment failure of bacterial infections in the future. Antimicrobial stewardship (AMS) programmes are critical to ensuring the continued efficacy of available antimicrobials. There is a lack of published evidence-based data on the susceptibility of isolates from common reproductive infections encountered in mares. This study aims to provide equine veterinarians in Western Australia (WA) with the most appropriate first-line empirical antimicrobials for infections of the mare reproductive tract. MATERIALS AND METHODS: A retrospective study was conducted on reproductive tract swab/fluid culture and sensitivity results of mares and fillies in WA from July 2015 to June 2020. An algorithm was generated using R to create an antibiogram for the mare reproductive system. RESULTS: The antibiogram included 767 reproductive tract isolates. Escherichia coli (E. coli) (277 of 767; 36%) was the most commonly isolated, followed by Streptococcus (240 of 767; 31%). Gram-negative isolates were most susceptible to enrofloxacin (84%), followed by ceftiofur (75%), gentamicin (72%) and tetracycline (65%). Gram-positive isolates were most susceptible to ampicillin (86%), followed by penicillin (83%), ceftiofur (83%) and trimethoprim-sulfonamide (TMS, 76%). The overall susceptibility of ceftiofur decreased across both Gram-negative and Gram-positive isolates during the time periods 2015-2017 and 2018-2020 from 79% to 69% and 91% to 75%, respectively. DISCUSSION: Gram-negative isolates were most susceptible to the high importance antimicrobials ceftiofur and enrofloxacin. However, these antimicrobials should be used judiciously only after culture and sensitivity testing have been performed, in accordance with the Australian Veterinary Prescribing Guidelines, as part of AMS. This study found that Gram-negative organisms are most susceptible to first-line empirical treatment with tetracycline if E. coli is suspected, or gentamicin when in doubt. Gram-positive isolates were most susceptible to first-line empirical treatment with ampicillin, penicillin or TMS. Regular updates to the antibiogram are required to provide contemporary empirical guidance for the use of antimicrobials.