Occurrence and molecular characteristics of ESBL/AmpC-producing Escherichia coli in faecal samples from horses in an equine clinic

Objectives: To investigate the occurrence and characteristics of ESBL/AmpC-producing Escherichia coli in faecal samples from horses at one equine clinic in the Netherlands. Methods: A total of 91 horses, including residents and patients, were sampled. ESBL/AmpC-producing E. coli were identified by a combination disc diffusion test. Phylogenetic groups and MLST were determined. ESBL/AmpC genes were analysed using PCR and sequencing. Plasmids were characterized by transformation and PCR-based replicon typing. Subtyping of plasmids was done by plasmid MLST. Results: At least one E. coli isolate with a confirmed ESBL/AmpC gene was found in samples from 76 horses (84%). Although phylogenetic group B1 E. coli bla(CTX-M-1) predominated, a diverse E. coli population was found, indicating that clonal nosocomial spread was not the only reason for the high occurrence found. MLST analysis revealed the presence of 47 E. coli STs, organized in four clusters of genetically related strains. ST10, ST641, ST1079 and ST1250 were most commonly found. With regard to the genes, bla(CTX-M-1) was most prevalent (n = 91), followed by bla(CTX-M-2) (n = 26). The most frequently found plasmid type was IncHI1, but plasmids belonging to the IncF, IncI1 and IncN groups were also identified. Conclusions: A high occurrence of ESBL-producing E. coli in faecal samples was found among horses in an equine clinic and the variety of STs, ESBL genes and plasmid types suggests nosocomial transmission. ESBL E. coli can cause difficult-to-treat infections in horses and prudent use of antimicrobials is warranted. A further assessment of the risks of transmission to persons in close contact with horses, such as caretakers or veterinarians, is crucial.