Antimicrobial Activity of Ceftiofur and Penicillin With Gentamicin Against Escherichia coli and Streptococcus equi Subspecies zooepidemicus in an Ex Vivo Model of Equine Postpartum Uterine Disease.
Authors: Von Dollen Karen A, Jones Monica, Beachler Theresa, Harris Tonya L, Papich Mark G, Lyle Sara K, Bailey C Scott
Journal: Journal of equine veterinary science
Summary
# Editorial Summary Selecting appropriate antimicrobials for equine postpartum uterine disease typically relies on in vitro sensitivity testing or empirical protocols, yet these approaches may not accurately predict clinical efficacy within the infected uterine environment. Von Dollen and colleagues employed an ex vivo model using actual equine postpartum uterine fluid to directly compare the antimicrobial activity of ceftiofur and procaine penicillin G with gentamicin against two common bacterial isolates—*Escherichia coli* and *Streptococcus equi* subspecies *zooepidemicus*—testing both drugs in standard culture broth and native uterine fluid. Ceftiofur proved effective against *S. zooepidemicus* in uterine fluid but failed to suppress *E. coli* growth, whereas penicillin with gentamicin achieved bacteriostatic control of *E. coli* in both environments and bactericidal activity against *S. zooepidemicus* in both fluid types. These findings suggest that penicillin-gentamicin combinations warrant preference for intrauterine infusion in postpartum mares with confirmed or suspected *E. coli* or *Streptococcus* involvement, as they demonstrate superior performance under conditions more representative of the clinical setting than standard susceptibility panels alone. The ex vivo approach bridges a critical gap between laboratory results and clinical outcomes, highlighting the importance of validating antibiotic choices in physiologically relevant models before relying on empirical treatment protocols.
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Practical Takeaways
- •For mares with postpartum uterine disease caused by E. coli or S. zooepidemicus, intrauterine infusion of procaine penicillin G with gentamicin is more reliably effective than ceftiofur alone
- •In vitro sensitivity testing may not accurately predict antibiotic performance in the uterine environment; clinical outcomes should guide antimicrobial selection for postpartum uterine infections
- •Consider penicillin-gentamicin as first-line therapy for postpartum metritis when E. coli or Streptococcus are suspected, rather than relying solely on in vitro culture results
Key Findings
- •Ceftiofur effectively reduced S. zooepidemicus growth in equine postpartum uterine fluid but failed to reduce E. coli growth
- •Procaine penicillin G with gentamicin achieved bacteriostatic activity against E. coli and bactericidal activity against S. zooepidemicus in both standard culture broth and postpartum uterine fluid
- •Ex vivo uterine fluid model revealed significant differences in antibiotic efficacy compared to standard in vitro culture conditions
- •Penicillin-gentamicin combination demonstrated superior broad-spectrum coverage for common postpartum uterine pathogens in equine models