Published: 04 Feb 2015 | Last Updated: 05 Sep 2016 09:09:36

A new paper from Imogen Johns, Senior Lecturer in Equine Medicine at the RVC equine hospital, has been published in the Veterinary Record describing trends in antimicrobial resistance in equine bacterial isolates.  

The study looked at laboratory records of samples from horses submitted between 1999 and 2012 from which the bacteria Escherichia coli or Streptococcus species was isolated. The susceptibility of the bacteria to the antimicrobials enrofloxacin, ceftiofur, gentamicin, penicillin G, trimethoprim sulfamethoxazole (TMPS) and tetracyclines was noted.  

Isolates were divided into those identified between 1999 and 2004 (Early) and between 2007 and 2012 (Late). The proportion of isolates resistant to each antimicrobial and multiple drug-resistant (MDR) isolates (≥3 antimicrobial classes) was compared between time periods.  

A significant increase in the percentage of E coli isolates resistant to ceftiofur, gentamicin, tetracyclines and MDR was identified. There was a significant increase over time in the percentage of all streptococcal species that were resistant to enrofloxacin, ranging from 0 per cent (Early) up to 63 per cent (Late) depending on species. For Streptococcus zooepidemicus, resistance over time to tetracyclines and MDR increased. There was also a decrease in the proportion of S zooepidemicus resistant to TMPS over time.  

An increase in resistance over time of common equine pathogens to a number of commonly used antimicrobials supports the responsible use of antimicrobials.

Research Reference

Trends in antimicrobial resistance in equine bacterial isolates: 1999–2012, Veterinary Record 2015 176 334 doi:10.1136/vr.102708