More than 40 percent of horses used in a Canadian study were found to be shedding multi-drug resistant E. coli in their feces.
The researchers also found that some of the horses in the Quebec study were passing E. coli carrying the ESBL/AmpC genes responsible for cephalosporin resistance, which is particularly worrisome.
The presence of ESBL/AmpC genes in horses is both a public and equine health concern, considering the close contact between horses and owners, the University of Montreal researchers reported in the journal Animals.
Antimicrobial resistance has been recognised as a global threat by the World Health Organisation.
The first bacteria resistant to antimicrobials in horses were reported in 1971, in Canada. Since then, the number of treatment failure reports due to resistance has risen.
In Europe, several studies have reported that healthy horses can carry multi-drug resistant bacteria at a relatively high prevalence and some countries are setting up surveillance monitoring.
Escherichia coli (E. coli) is common in the intestinal microbiota of mammals. Most strains do no harm, although some can cause disease in humans and animals.
Maud de Lagarde, John Fairbrother and Julie Arsenault set out in their study to see whether multidrug-resistant E. coli, and E. coli resistant to cephalosporins, were present in the feces of healthy horses in Quebec.
They tested rectal swabs from 225 horses across 32 premises.
Evidence of E. coli was found in 209 of the 225 rectal swabs, representing 93% of the horses. Of these 209 horses, 46.3% shed multi-drug-resistant E. coli, being resistant to three or more classes of antimicrobials tested.
Over 40% of the horses shed isolates that were not susceptible to ampicillin, streptomycin or amoxicillin plus clavulanic acid. More than 60% of premises housed horses that shed isolates non-susceptible to streptomycin, nalidixic acid, folate pathway inhibitors (trimethoprim-sulfamethoxazole and sulfisoxazole), ampicillin, amoxicillin plus clavulanic acid or tetracycline.
ESBL/AmpC genes, indicating resistance to cephalosporin were detected in E. coli from 7.3% of the 209 horses, across 18.8% of premises.
They found that 1.4% of horses shed isolates non-susceptible to nine classes of antimicrobials,
and therefore had the potential for extensive resistance.
Certain factors increased the chances of shedding multi-drug resistant E. coli, the researchers found. These included the number of staff and equestrian event participation within the preceding three months.
“To our knowledge, we demonstrated for the first time that participation in an equestrian event was a risk factor for shedding multi-drug resistant isolates at the horse level,” the study teams said.
“Considering the correlation between horse participation in an equestrian event and transportation, this effect could also be driven by contacts occurring during transportation.
“Based on this association, we could suggest isolating horses that are participating in equestrian events or at least the implementation of appropriate biosecurity measures.
“As an example, limiting contact between these horses and horses that stay at home or handling horses that stayed at home before horses that travelled might be beneficial to limit antimicrobial gene dissemination.
“However, more longitudinal studies are needed to establish the duration of shedding, and therefore be more accurate in these recommendations.”
The levels of resistant E. coli isolates found in healthy horses in Quebec were noteworthy, they said.
“Surveillance of ESBL/AmpC gene dissemination and the quantification of multi-drug resistant isolates would be beneficial to characterize the nature and the extent of the risk they represent, with the aim of limiting their transmission between horses, but also to other species including humans and to the environment.
“The detection of risk factors for multi-drug resistant shedding could be used to help equine veterinarians in managing at-risk populations.”
de Lagarde, M.; Fairbrother, J.M.; Arsenault, J. Prevalence, Risk Factors, and Characterization of Multidrug Resistant and ESBL/AmpC Producing Escherichia coli in Healthy Horses in Quebec, Canada, in 2015–2016.. Animals 2020, 10, 523.