Equine Science Update
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Horses can be a source of antibiotic-resistant bacteria, presenting a threat to human health, according to a recent study.

Research carried out in northwest England, examined faeces samples collected from horses in an equine hospital and in two livery yards. From a total of 264 samples, 296 isolates of antibiotic-resistant Escherichia coli were identified.

Although some strains of E. coli can cause disease, the organism is generally non-pathogenic, and is found as a normal occupant of the gut. However the microorganism can play an important role in transferring antimicrobial resistance to more dangerous bacteria.

Mohamed Ahmed, of the Department of Veterinary Microbiology and Parasitology, at AL Fatah, University, Tripoli, Libya, working with colleagues at the Liverpool Vet School, examined fecal samples collected from the University’s equine hospital and from livery yards.

They found antibiotic resistant E. coli in faeces from both locations.

Hospitalised horses were more likely to have antibiotic resistant E. coli in their faeces and were more likely to carry organisms that were resistant to multiple drugs than those maintained on livery yards.

Of the 109 faeces samples collected in the hospital, 89 contained at least one antibiotic resistant E. coli isolate. In contrast only 35 of 155 faeces samples from the livery yards yielded antibiotic resistant E. coli.

Another problem that was more common in hospitalised horses was multiple drug resistance (MDR) - in which resistance to four of more antimicrobial agents occurs. Nearly half (48%) of the resistant isolates from the hospital environment showed multiple drug resistance phenotypes, compared with only 12% from the livery yards.

The scientists identified genes responsible for conferring resistance to four antibacterial agents (trimethoprim, ampicillin tetracycline and chloramphenicol) using PCR amplification techniques. They found that many of the genes were those commonly found in E. coli in other species of domestic animals and humans.

When susceptible bacteria are exposed to antibacterial agents, many will be killed. however, some may survive and multiply, producing a generation of resistant organisms (selective pressure).  

But resistance to antibacterial agents does not only increase as a result of selection. Some bacteria can transfer antimicrobial resistance to others by direct contact  - passing pieces of genetic code, (plasmids and integrons), from one microorganism to another in a well-reported mechanism known as conjugation.

The researchers conclude that, in the UK, horses may provide both recipients, and sources, of antibiotic resistance, MDR, and be an extensive reservoir of antimicrobial resistance genes that could pose a potential threat to human health.

The full, open access, report is available:

Antimicrobial resistance in equine faecal Escherichia coli isolates from north-west England.
MO Ahmed, PD Clegg, NJ Williams, KE Baptiste, M Bennett.
Annals of Clin Microb Antimicrob (2010) 9, 12


Written by Mohamed O Ahmed/Mark Andrews.
Published online 19.06.10
 © Copyright Equine Science Update  2010
Antibiotic resistance in equine faeces
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