Fecal carriage of Extended Spectrum beta-Lactamase (ESBL)/ AmpC-producing Escherichia coli in horses

Extended Spectrum ß-Lactamase (ESBL) or AmpC-type ß-Lactamase (AmpC) producing Escherichia coli have been described in horses, mainly hospitalized, but also non-hospitalized. The association of blaCTX-M-1 with incHI1 plasmids has been reported in different countries in Europe. We performed a nationwide study on non-hospitalized horses in the Netherlands on the occurrence of ESBL/AmpC. Molecular characterization and questionnaires were analyzed to identify determinants associated with carriage. In total, 796 horse owners were approached to participate, of which 281 submitted a fecal sample of their horse. Some submitted a sample of multiple horses, resulting in 362 samples. All samples were cultured qualitatively in LB broth and MacConkey agar, supplemented with 1 mg/L cefotaxime (LB+ and MC+). Positive samples were subsequently cultured quantitatively on MC+. Initial ESBL/AmpC screening was performed by PCR, followed by whole genome sequencing for a selection of strains. Association between ESBL/AmpC carriage and questionnaire items were analyzed using a univariate generalized estimating equation (GEE) regression analysis, followed by a multiple GEE model for relevant factors.In total, 39 out of 362 samples (11%) were positive for ESBL/AmpC. In total, 77% of positive samples carried blaCTX-M-1 (n=30). Other ESBL/AmpC genes observed were blaCTX-M-2, blaCTX-M-14, blaCTX-M-15, blaCTX-M-32, blaSHV-12, blaCMY-2, blaACT-10. In four strains the ESBL/AmpC gene could be directly linked to a plasmid type; IncN (n=2), IncK/BO (n=1) and IncI (n=1). Although without a direct link, a high association of blaCTX-M-1 to IncHI1 was observed (46% of samples; n=18). Based on core genome analysis (n=48 isolates), six E. coli clusters could be identified, of which three represented 80% of the isolates. A negative association between ESBL/AmpC carriage and horses being in contact with other horses at a different site was observed. The presence of a dog on the premises and housing in a more densely human-populated region were positively associated.