September 16, 2009

Researchers in Britain have discovered that Escherichia coli bacteria in a horse's gut appear to acquire antibiotic resistance while a horse is hospitalised.

The researchers working at Philip Leverhulme Equine Hospital in Liverpool found a significant increase in multiple drug resistance in E. coli samples isolated from horses' faeces after a period in hospital.

E. Coli is commonly found in the lower intestine of animals. Most strains are harmless and are part of normal gut flora.

The researchers, led by Adele Williams, collected faecal samples from randomly selected horses over an 18-month period from 2006 to 2008 at the hospital, run by the University of Liverpool.

Faecal samples were collected when the horse was admitted, and again after the horse had been hospitalised for seven days. The selected horses included horses treated and not treated with antibiotics, before and during hospitalisation.

E. coli bacteria cultured from the samples were tested for their sensitivity to eight antibiotics - neomycin, ampicillin, ceftiofur, gentamicin, chloramphenicol, ciprofloxacin, tetracycline and trimethoprim - using the Kirby-Bauer disk diffusion method. The antibiotics chloramphenicol and tetracycline are not used at the hospital.

The researchers found a significant increase in resistance during the week's hospitalisation for seven of the eight antibiotics. No significant difference was found for neomycin.

Antibiotic resistance increased even in horses not treated with antibiotics and to antibiotics that are not used in the hospital.

This may be due to the transfer of antibiotic resistant genes as a result of selection pressure for antibiotic resistance in the hospital environment, or it may be because the number of resistant E. coli is greatly increased due to selective pressure so that they are much easier to detect, or that resistant isolates have been acquired from the environment.

Further research is needed to understand the source of antibiotic resistance in the environment.

"Pathogenic bacteria are likely to be exposed to the same selection pressures or could receive the same resistant genes, so it is vital we improve hygiene in equine hospitals and reduce the overuse of antibiotics," said Williams, who had received funding for the work from equine charity The Horse Trust.

"People who work in equine hospitals need to pay strict attention to hygiene and should reserve antibiotics for essential cases only."

Williams carried out the research while undergoing a Horse Trust-funded clinical training programme in equine internal medicine at the University of Liverpool.

She presented her research at the European College of Equine Internal Medicine Congress in January 2009.

The other researchers involved in the project were R.M. Christley, S.M. McKane, V.L.H. Roberts, P.D Clegg and N.J Williams.