Prevalence, risk factors, and characterization of multidrug resistant and extended spectrum β-lactamase/AmpC β-lactamase producing Escherichia coli in healthy horses in France in 2015.

Background: Although antimicrobial resistance is increasingly common in equine medicine, molecular and epidemiological data remains scarce.

Objectives: We estimated the prevalence of, and risk factors for, shedding of multidrug resistant (MDR), extended spectrum β-lactamase (ESBL)-producing, and AmpC β-lactamase-producing, or some combination of these in Escherichia coli in horses in France. We characterized ESBL/AmpC isolates for antimicrobial susceptibility and the presence of virulence and ESBL/AmpC-associated resistance genes.

Animals: Fecal samples from healthy adult horses at 41 premises were collected. A questionnaire was completed by each premises manager. A subset of these samples was tested to build 2 bacterial collections.

Methods: Indicator (without enrichment) and specific (enrichment with ceftriaxone) E. coli tested for antimicrobial susceptibility. Prevalence of isolates nonsusceptible to antimicrobials was estimated at the horse and the premises level. The ESBL/AmpC and virulence genes were identified by PCR. Multivariable logistic regression was used to investigate risk factors for MDR and ESBL/AmpC isolates at premises.

Results: Approximately 44% of horses shed MDR E. coli. Resistance most commonly was observed to ampicillin, streptomycin, and amoxicillin/clavulanic acid. Twenty-nine percent of premises housed horses shedding ESBL/AmpC-producing isolates. The ESBL/AmpC gene most commonly identified was bla . Virulence gene iutA was identified in 1 ESBL/AmpC-producing isolate. Medical treatment, staff numbers, and activity were identified as risk factors for housing horses shedding ESBL/AmpC-producing E. coli isolates.

Conclusions And Clinical Importance: Prevalence of healthy horses harboring ESBL/AmpC genes and MDR isolates in their intestinal microbiota is substantial. Risk factors could be used to elaborate guidelines to prevent their dissemination.