Extended-spectrum β-lactamase-producing <i>Escherichia coli</i> isolated from healthy Thoroughbred racehorses in Japan

Abstract

Extended-spectrum β-lactamase-producing Escherichia coli (ESBLEC) have become a major health concern in both human and veterinary medicine. These bacteria could become a critical problem in equine medicine due to the limited number of antimicrobial drugs available. However, there are no previous reports of ESBLEC isolated from horses in Japan. The objectives of this study were to investigate the occurrence of ESBLEC isolated from feces in healthy Thoroughbred racehorses in Japan. Feces samples were collected from 147 healthy Thoroughbred racehorses by equine veterinarians at the Japan Racing Association (103 from Miho Training Center and 44 from Ritto Training Center) between March 2017 and April 2018. Samples were screened for ESBLECs using MacConkey agar supplemented with 1 µg/ml cefotaxime. Detection of ESBL genes was performed by PCR and confirmed by DNA sequencing. Horizontal transmission was demonstrated by conjugation assay. In this study, 24 ESBLECs were isolated from twelve horse feces samples (8.2%). All ESBLECs harbored bla CTX-M-2 , and both bla TEM-1 and bla CTX-M-2 were detected in nine isolates (37.5%). ESBLECs showed resistance to all β-lactam antibiotics (100%) tested, followed by trimethoprim (66.7%), streptomycin (62.5%), tetracycline (25.0%), and oxytetracycline (25.0%). Horizontal transmission was successfully demonstrated by conjugation assay in eight of 13 isolates, and bla CTX-M-2 was detected by PCR in all transconjugants. This study showed that racehorses in Japan are potential reservoirs of ESBLECs.

IncI1 Plasmid Associated with blaCTX-M-2 Transmission in ESBL-Producing Escherichia coli Isolated from Healthy Thoroughbred Racehorse, Japan

“…Horses can serve as a natural reservoir of antibiotic-resistant microorganisms, a characteristic which has implications on the health, treatment efficiency and epidemiological safety of people working in close contact with horses [13]. Racehorses have been described as potential reservoirs of ESBLECs in Japan [9]. In the current study, we evaluated the horizontal transmission of ESBLECs detected from 10.8% of samples collected from healthy Thoroughbred racehorses at JRA Training Centers.…”

“…These isolates were derived from 23 healthy Thoroughbred racehorse feces samples in JRA Training Centers in Japan. Thirteen isolates were selected from ESBLEC collection isolates, which were isolated from 12 of 147 Thoroughbred racehorse feces samples in a previous study [9]. Additional non-repetitive isolates (one isolate, one horse) were collected from 65 feces samples from the JRA Ritto Training Center between May and August 2018.…”

“…A total of 212 racehorse feces samples were investigated between April 2017 and August 2018 in this study. The isolation of ESBLEC was as described in a previous study [9]. All isolates were confirmed for the ESBL phenotype using an AmpC and ESβL Detection Set (D68C) Kit, and the results were interpreted based on the manufacturer's guidelines (Mast Diagnostics, Merseyside, UK).…”

“…As a potentially zoonotic bacteria, ESBL-producing Escherichia coli (ESBLEC) have received special attention in the area of equine medicine [9]. Most studies of ESBLEC in horses refer to clinical isolates [7], where healthy horses are also potential reservoirs of ESBL-producing bacteria.…”

“…In our previous study, ESBLECs were isolated from 8.2% of healthy Thoroughbred racehorses in Japan Racing Association (JRA) Training Centers in Japan. CTX-M-2 was identified as the most prevalent type of ESBL and some of these were predicted to be located on a conjugative plasmid [9]. The aim of this study was to evaluate the diversity of plasmid replicon types of ESBLEC isolated from healthy Thoroughbred racehorses in Japan.…”