Antibiograms of field and hospital acquired equine neonatal bacterial fluid cultures in the Midwestern United States: 149 samples (2007-2018)

Abstract

Background: Contemporary data reflecting local pathogens and their antibiograms is necessary to select empirical antimicrobial therapy for equine neonates. Hypothesis/Objectives: Describe bacterial isolates associated with equine neonatal infection and their antibiograms in the Midwestern United States. An increase in gram-positive infection and antibiotic resistance compared to previous literature was expected. Animals: Data from 149 fluid samples from 133 foals <30 days of age submitted for bacterial culture between January 2007 and December 2018. Methods: A retrospective evaluation of equine neonatal fluid cultures was performed. Fluid submission type, bacterial culture and antibiogram, empirical antibiotic treatment, and foal outcome was included. Isolate susceptibility to individual antimicrobials and combination protocols relevant to equine practice were recorded. The effect of recorded variables on foal survival was evaluated using Fisher's exact or chi-squared tests. Results: Ninety bacterial isolates (78 aerobes and 12 anaerobes) were identified and gram-positive organisms predominated (n = 50/90, 56%). Greater than 70% of aerobic isolates were susceptible to ampicillin, ceftiofur, chloramphenicol, trimethoprim/sulfamethoxazole, and all penicillin/aminopenicillin and aminoglycoside combinations. Seventy-seven (n = 81/105) percent of foals survived. Survival was associated with a negative fluid culture and was not associated with empirical antimicrobial choice. Conclusions and Clinical Importance: Gram positive and anaerobic isolates associated with equine neonatal fluid cultures exceed that of previous reports. Historical empirical antimicrobial choices for equine neonatal infection in the Midwestern United States are supported by local antibiogram results.