Low Rates of Positive Bacterial Culture and High Prevalence of Antimicrobial Resistance in Equine Synovial Sepsis

Abstract

Introduction: Septic synovitis is both performance limiting and life-threatening in horses; however, accurate identification of pathogens can enhance outcomes. The objectives of this study were to identify: (1) variables associated with the likelihood of obtaining a positive culture, (2) commonly isolated microorganisms, and (3) antimicrobial resistance (AMR) patterns of isolates from horses with synovial sepsis.

Materials and Methods: Synovial fluid, synovium, and bone samples from equine cases with presumptive synovial sepsis that were submitted to the Cornell University Animal Health Diagnostic Center from 2000 to 2020 for microbial culture and antimicrobial sensitivity testing were included. Univariable and multivariable analyses were performed to determine the effect of multiple factors on the likelihood of positive culture. Frequency distributions for isolated organisms and AMR were generated. Multidrug resistance (MDR) patterns and associations were assessed with association rule mining.

Results: Positive culture rate ranged from 37.4% for cases with presumptive sepsis to 43% for cases with confirmed sepsis. Blood culture enrichment resulted in greater positive culture compared to samples submitted in serum tubes. Structure affected, tissue submitted, and horse age were associated with positive culture. Staphylococcus spp., Streptococcus spp., and Enterococcus spp. were commonly isolated. MDR prevalence ranged from 92 to 76% of gram-negative isolates and 60 to 52% of gram-positive isolates for 2000–2010 and 2011–2020, respectively.

Discussion/Conclusion: Positive culture rate from synovial fluid submissions with traditional sampling and culture methods remains low and may be optimized by submitting samples in blood culture vials. Overall, antimicrobial resistance was frequently observed but did not increase from the first to second decade for most genera.

Acknowledgements: Funding sources: Harry M. Zweig Memorial Fund for Equine Research (H.L.R., C.A., C.L.C.).

Publication History

Article published online:
16 September 2024