Aerobic uterine isolates and antimicrobial susceptibility in mares with post-partum metritis.
Authors: Ferrer M S, Palomares R
Journal: Equine veterinary journal
Summary
# Editorial Summary: Aerobic Bacterial Isolates and Antimicrobial Susceptibility in Equine Post-Partum Metritis Post-partum metritis poses a genuine threat to mare survival, yet veterinarians frequently must initiate antibiotic therapy before culture results become available—a clinical reality that underscores the critical need for evidence-based guidance on empirical antimicrobial selection. Ferrer and Palomares examined uterine bacterial cultures and susceptibility testing from 45 mares with metritis (yielding 88 bacterial isolates), with particular attention to infection patterns and resistance profiles. Mixed infections dominated the clinical picture, occurring in 62% of cases and typically comprising both Gram-negative and Gram-positive species; *Escherichia coli* was the most prevalent organism at 30.7%, and multidrug resistance was substantially higher in Gram-negative isolates (85.4%) compared with Gram-positive bacteria (23.5%). Penicillin combined with amikacin proved effective in 90.7% of cases and penicillin with enrofloxacin in 81.4%, whereas trimethoprim/sulfonamide combinations—widely used in equine practice—were effective in only 48.8% of mares, suggesting this combination is inadequate as a first-line empirical choice. These findings have practical implications for initial therapy protocols; whilst penicillin plus gentamicin may suffice for some mares, substituting amikacin or enrofloxacin for gentamicin significantly improves coverage against the multidrug-resistant Gram-negative organisms frequently encountered in post-partum metritis.
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Practical Takeaways
- •When empirical treatment is needed before culture results, consider penicillin with amikacin or enrofloxacin as first-line therapy for post-partum metritis rather than gentamicin or potentiated sulfonamides
- •Expect mixed aerobic infections in most metritis cases (60%+), often combining Gram-negative and Gram-positive organisms, which should influence initial antimicrobial selection
- •Be aware that Gram-negative bacteria in equine metritis frequently exhibit multidrug resistance; obtaining culture and sensitivity results remains important for refining therapy in treatment failures
Key Findings
- •Mixed bacterial infections occurred in 62.2% of mares with metritis, more frequently than pure infections
- •Escherichia coli was the most common isolate at 30.7%, with 85.4% of Gram-negative bacteria showing multidrug resistance
- •Penicillin combined with amikacin (90.7% effective) or enrofloxacin (81.4% effective) provided superior antimicrobial coverage compared to gentamicin or trimethoprim/sulfonamide (48.8% effective)
- •Gram-negative bacteria demonstrated significantly higher multidrug resistance (85.4%) than Gram-positive bacteria (23.5%)