Simple Summary The spread and development of extended spectrum beta-lactamase (ESBL)-mediated antimicrobial resistance is a significant concern in healthcare with impacts to animal and public health alike. While the occurrence of the ESBL phenotype in Escherichia coli has been investigated in depth by numerous studies, there is still a lack of information regarding ESBL-producing bacterial isolates from clinical specimens of equine origin. In this study, we investigated the incidence of ESBL-producing E. coli in hospitalized horses. Overall, 207 E. coli isolates were analyzed for their antimicrobial susceptibility and 13 ESBL-producing E. coli isolates were genotypically characterized. Seven out of the 13 E. coli isolates were found to harbor the resistance genes bla(CTX-M-1) or bla(SHV-1) and a novel beta-lactamase TEM gene variant, bla(TEM-233) was discovered. Furthermore, despite being phenotypically susceptible to tested carbapenems, 1 out of 13 E. coli isolates was PCR-positive for the carbapenemase gene, bla(IMP-1). The latter is an alarming finding because the presence of carbapenemase resistance genes in equine pathogens is extremely rare. In conclusion, equines can be reservoirs for ESBL-producing Enterobacteriaceae, and further investigation into this species group is necessary to understand their impact in the spread and development of antibiotic resistance genes. AbstractEscherichia coli isolates were recovered from clinical specimens of equine patients admitted to the Texas A&M Veterinary Medical Teaching Hospital over a five-year period. Ceftiofur resistance was used as a marker for potential extended-spectrum beta-lactamase (ESBL)-activity, and of the 48 ceftiofur-resistant E. coli isolates, 27.08% (n = 13) were phenotypically ESBL-positive. Conventional PCR analysis followed by the (large-scale)bla Finder multiplex PCR detected the ESBL genes, CTX-M-1 and SHV, in seven out of the 13 isolates. Moreover, beta-lactamase genes of TEM-1-type, BER-type (AmpC), and OXA-type were also identified. Sequencing of these genes resulted in identification of a novel TEM-1-type gene, called bla(TEM-233), and a study is currently underway to determine if this gene confers the ESBL phenotype. Furthermore, this report is the first to have found E. coli ST1308 in horses. This subtype, which has been reported in other herbivores, harbored the SHV-type ESBL gene. Finally, one out of 13 E. coli isolates was PCR-positive for the carbapenemase gene, bla(IMP-1) despite the lack of phenotypically proven resistance to imipenem. With the identification of novel ESBL gene variant and the demonstrated expansion of E. coli sequence types in equine patients, this study underscores the need for more investigation of equines as reservoirs for ESBL-producing pathogens.
