Vancomycin-resistant bacteria in equine manure

Horses are not likely to play a major role in the spread of one type of antibiotic resistant micro-organism, to humans, according to a study in North West England.

Work reported at the International Conference on Antimicrobial Research in Valladolid in Spain November 2010 looked for vancomycin resistant enterococci (VRE) in equine faeces.

Lead researcher Dr Mohamed O Ahmed presented the results of the study, which looked at faecal samples from 66 hospitalised and 72 non-hospitalised horses.

Enterococci are enteric bacteria found in the digestive tract of many humans and animals. They may be responsible for urinary tract or wound infections (i.e. nosocomial infections). Also in patients with suppressed immune systems, they can cause serious conditions such as infection of the heart valves (endocarditis) and brain (meningitis).

Enterococci are naturally resistant to many antibiotics. One of the few last-choice antibiotics used for treating people with serious enterococcal infections is vancomycin.

Vancomycin-resistant enterococci is an emerging nosocomial organism, reportedly of zoonotic nature. There are several strains of vancomycin-resistant enterococci. The genes conferring resistance have probably been acquired from other types of bacteria that don't cause disease, but are already vancomycin resistant.

If specific vancomycin-resistant strains were present in horse faeces (i.e. VanA and VanB phenotypes) they could act as a zoonotic source of infection.

Overall, the researchers identified 47 suspected VRE isolates from a total of 264 faecal samples. Of those, only 9 were confirmed by polymerase chain reaction (PCR). Seven were confirmed as VanC genotype. Six of these were found in samples from hospitalised horses.

They identified one isolate each of VanA and VanD genotype. Both of these were in non-hospitalised horses, but neither could be typed by PCR.

The VanA genotype has been reported predominantly as the one involved in human infections. However, the VanC genotype, which was found most frequently in this study, is not commonly isolated in cases of human infection.

The researchers conclude that it is unlikely that horses play a major role in the transmission of VRE to humans in that specific geographic area. Also, the fact that most of the VRE isolates were found in hospitalised horses, suggests that hospitalisation could increase the risk of transmission between horses and possibly to humans too. Future research may be needed to look into this.

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