Trends in antimicrobial resistance in equine bacterial isolates: 1999-2012.
Authors: Johns I C, Adams E-L
Journal: The Veterinary record
Summary
# Editorial Summary: Trends in Antimicrobial Resistance in Equine Bacterial Isolates (1999–2012) Between 1999 and 2012, antimicrobial resistance in common equine pathogens increased markedly, prompting Johns and Adams to examine 464 clinical isolates of *Escherichia coli* and *Streptococcus* species from laboratory records, comparing susceptibility patterns across six drug classes between early (1999–2004) and late (2007–2012) periods. *E. coli* resistance showed particularly concerning trends: cephalosporin resistance (*Ceftiofur*) tripled from 7.3% to 22.7%, gentamicin resistance nearly doubled from 28.5% to 53.9%, and tetracycline resistance increased from 48.4% to 74.2%, with multiple drug resistance (≥3 antimicrobial classes) rising from 26.6% to 49.4%. Streptococcal species demonstrated dramatic emergence of enrofloxacin resistance—from zero to 63% depending on species—whilst *Streptococcus zooepidemicus* exhibited increasing tetracycline and multidrug resistance over the study period. These findings underscore the urgent need for judicious antimicrobial prescribing in equine practice, particularly regarding fluoroquinolones, cephalosporins and tetracyclines, and highlight the value of antimicrobial susceptibility testing to guide treatment decisions rather than relying on empirical therapy.
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Practical Takeaways
- •Antimicrobial resistance in common equine pathogens is increasing significantly; routine culture and sensitivity testing is increasingly important before starting treatment rather than relying on historical empirical choices
- •Commonly used first-line antimicrobials (tetracyclines, gentamicin, ceftiofur) are showing reduced effectiveness; consult current resistance patterns and consider alternatives when treating E. coli and Streptococcus infections
- •Responsible antimicrobial stewardship—using narrower-spectrum agents, shorter courses, and culture-guided therapy—is critical to slow the development of further resistance in equine practice
Key Findings
- •E. coli resistance to ceftiofur increased from 7.3% to 22.7% between early (1999-2004) and late (2007-2012) periods (P=0.002)
- •E. coli resistance to gentamicin more than doubled from 28.5% to 53.9% (P<0.001) and tetracycline resistance increased from 48.4% to 74.2% (P=0.002)
- •Streptococcal species resistance to enrofloxacin increased from 0% to 63% depending on species, with S. zooepidemicus showing increased tetracycline resistance and multiple drug resistance over time
- •Multiple drug-resistant E. coli isolates nearly doubled from 26.6% to 49.4% (P=0.007) over the 13-year study period