Colonization of equine patients with Extended-spectrum β-lactamase-producing Enterobacteriaceae (ESBL-E) upon admission and during hospitalization at a veterinary clinic

Extended-Spectrum Beta-Lactamase (ESBL)-producing-resistant Enterobacteriaceae are recognized by the Center of Disease Control and Prevention (CDC) as serious threats because antibiotic classes to treat these infections are limited and often last-line antibiotics such as carbapenems are the remaining options. Horses may act as reservoirs and also show an increasing prevalence in the last years. To evaluate the situation in Austria, fecal samples of 40 horses attending and staying in the equine hospital of Veterinary Medicine in Vienna were collected upon admission (T1), at 48h (T2) and at 72h/release (T3). Species identification was performed using MALDI-TOF, while the isolates were assessed for phenotypic resistance through VITEK2. Different classes of antibiotics were tested, including aminopenicillins, 3rd generation cephalosporins, aminoglycosides, quinolones, tetracyclines and sulfonamides. Additionally, a carbapenem screening with imipenem was conducted. Among the 40 horses, 21 (52.5 %) of them were positive at either T1, T2 or T3 or several time points. In total, 28 of ESBL-producing Enterobacteriaceae were isolated but 8 of them contained two or three different colonies which made a total of 37 identifications. The percentage of ESBL-positive samples increased with the duration of hospitalization, starting at 2.5 % upon admission, rising to 25 % at the second time point, and reaching 42.5 % at the final sample. These results can be compared to other studies researching prevalence of ESBL in horses . Two of the isolates showed resistance to imipenem and one showed an intermediated result. There was a moderate statistical association between antimicrobial use in general and age, and ESBL carriage, but not surgery. Although further research is needed, there has been a significant increase in the percentage of ESBL-positive horses in relation to the duration of hospitalization. This trend highlights a potential public health risk, particularly within the One Health concept, where the interconnectedness of human, animal and environmental health must be considered.