Temporal trends in in vitro antimicrobial susceptibility patterns of bacteria isolated from foals with sepsis: 1979-2010.
Authors: Theelen M J P, Wilson W D, Edman J M, Magdesian K G, Kass P H
Journal: Equine veterinary journal
Summary
# Editorial Summary: Antimicrobial Resistance Trends in Equine Neonatal Sepsis Over three decades of laboratory data (1979–2010) from 1,091 bacterial isolates cultured from 588 septic foals, researchers tracked how pathogenic resistance to first-line antimicrobials has evolved, revealing both encouraging stability and concerning shifts that should inform clinical decision-making in neonatal cases. Key pathogens including Enterobacteriaceae, Actinobacillus spp. and β-haemolytic Streptococcus spp. demonstrated progressive resistance to gentamicin and rising minimum inhibitory concentrations (MICs) for amikacin across successive time periods, whilst ceftiofur efficacy against Enterobacteriaceae declined significantly; Enterococcus spp. presented additional challenges, developing resistance to imipenem and reduced susceptibility to ticarcillin/clavulanic acid. Despite these trends, amikacin and ampicillin combined remain the recommended empirical therapy for foal sepsis pending culture results, though clinicians must recognise that aminoglycoside resistance is steadily increasing and monitor treatment responses accordingly. The notable decline in ceftiofur's in vitro activity against Gram-negative enteric pathogens warrants caution in relying on this agent alone, particularly given the widespread use of cephalosporins in equine practice. Prudent antimicrobial stewardship—including targeted use based on culture results and regional resistance patterns rather than blanket prophylaxis—is essential to preserve the effectiveness of these critical drugs for neonatal foals with life-threatening infections.
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Practical Takeaways
- •Continue using amikacin plus ampicillin as first-line empirical therapy for septic foals while awaiting culture results, but monitor resistance trends closely as amikacin resistance is increasing
- •Avoid ceftiofur as monotherapy or primary choice for Enterobacteriaceae infections in foals due to documented declining susceptibility over time
- •Request susceptibility testing on all foal sepsis cultures and adjust therapy accordingly—do not rely solely on empirical protocols, as resistance patterns are shifting
Key Findings
- •Enterobacteriaceae, Actinobacillus spp., and β-haemolytic Streptococcus spp. showed decreasing susceptibility to gentamicin over the 31-year study period
- •Increasing minimum inhibitory concentrations (MIC) to amikacin were documented across Enterobacteriaceae, Actinobacillus spp., and β-haemolytic Streptococcus spp., indicating developing resistance
- •Ceftiofur showed decreased in vitro activity against Enterobacteriaceae, and Enterococcus spp. developed resistance to imipenem
- •Amikacin and ampicillin combination remains recommended for empirical treatment of foal sepsis pending culture results, despite increasing amikacin resistance