Cumulative antibiogram and multidrug-resistant organisms in a regional equine referral hospital

Prudent use of antimicrobials is paramount to slow the development of resistance and for successful treatment. The use of cumulative antibiograms will allow evidence-based antimicrobial selection with consideration of local resistance patterns. We generated a "first-isolate-per-patient" cumulative antibiogram for a regional equine referral hospital. Bacterial organisms cultured from horses between 2011 and 2018, sample origin, antimicrobial susceptibilities, and multidrug-resistant (MDR) status were tabulated. Of 1,176 samples, 50% were culture positive. Overall, 93 of 374 (25%) were MDR. Of the MDR isolates, 11 (12%) were susceptible to high-importance antimicrobials only (as defined by the Australian Strategic and Technical Advisory Group on antimicrobial resistance). β-hemolytic streptococci were uniformly susceptible to penicillin (76 of 76); 17 of 20 (85%) non-β-hemolytic Streptococcus spp. were susceptible to penicillin. Despite veterinary-specific challenges in constructing an antibiogram, our study provides an exemplar of the clinical utility of regional-, farm-, or hospital-specific cumulative antibiograms for evidence-based empirical antimicrobial selection by veterinarians prior to susceptibility result availability.