AUTHOR=Dor Ziv , Shnaiderman-Torban Anat , Kondratyeva Kira , Davidovich-Cohen Maya , Rokney Assaf , Steinman Amir , Navon-Venezia Shiri 

TITLE=Emergence and Spread of Different ESBL-Producing Salmonella enterica Serovars in Hospitalized Horses Sharing a Highly Transferable IncM2 CTX-M-3-Encoding Plasmid

JOURNAL=Frontiers in Microbiology

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.616032

DOI=10.3389/fmicb.2020.616032

ISSN=1664-302X

ABSTRACT=<p><italic>Salmonella enterica</italic> is a major causative pathogen of human and animal gastroenteritis. Antibiotic resistant strains have emerged due to the production of extended-spectrum β-lactamases (ESBLs) posing a major health concern. With the increasing reports on ESBL-producing Enterobacterales that colonize companion animals, we aimed to investigate ESBL dissemination among ESBL-producing <italic>Salmonella enterica</italic> (ESBL-S) in hospitalized horses. We prospectively collected ESBL-S isolates from hospitalized horses in a Veterinary-Teaching Hospital during Dec 2015–Dec 2017. Selection criteria for ESBL-S were white colonies on CHROMagarESBL plates and an ESBL phenotypic confirmation. <italic>Salmonella enterica</italic> serovars were determined using the Kaufmann-White-Le-Minor serological scheme. ESBL-encoding plasmids were purified, transformed and compared using restriction fragment length polymorphism (RFLP). Whole genome sequencing (Illumina and MinION platforms) were performed for detailed phylogenetic and plasmid analyses. Twelve ESBL-S were included in this study. Molecular investigation and Sequence Read Archive (SRA) meta-analysis revealed the presence of three unique <italic>Salmonella enterica</italic> serovars, Cerro, Havana and Liverpool, all reported for the first time in horses. PFGE revealed the clonal spread of <italic>S.</italic> Cerro between seven horses. All twelve isolates carried <italic>bla</italic><sub><italic>CTX–M–</italic></sub><sub>3</sub> and showed an identical multidrug resistance profile with co-resistance to trimethoprim/sulfamethoxazole and to aminoglycosides. Plasmid RFLP proved the inter-serovar horizontal spread of a single <italic>bla</italic><sub><italic>CTX–M–</italic></sub><sub>3</sub>-encoding plasmid. Complete sequence of a representative plasmid (<italic>S</italic>. Havana strain 373.3.1), designated pSEIL-3 was a -86.4 Kb IncM2 plasmid, that encoded nine antibiotic resistance genes. pSEIL-3 was virtually identical to pCTX-M3 from <italic>Citrobacter freundii</italic>, and showed high identity (&gt;95%) to six other <italic>bla</italic><sub><italic>CTX–M–</italic></sub><sub>3</sub> or <italic>bla</italic><sub><italic>NDM–</italic></sub><sub>1</sub> IncM2 broad host range plasmids from various Enterobacterales of human origin. Using a specific six gene-based multiplex PCR, we detected pSEIL-3 in various Enterobacterales species that co-colonized the horses’ gut. Together, our findings show the alarming emergence of ESBL-S in hospitalized horses associated with gut shedding and foal morbidity and mortality. We demonstrated the dissemination of CTX-M-3 ESBL among different <italic>Salmonella enterica</italic> serovars due to transmission of a broad host range plasmid. This report highlights horses as a zoonotic reservoir for ESBL-S, including highly transmissible plasmids that may represent a ‘One-Health’ hazard. This risk calls for the implementation of infection control measures to monitor and control the spread of ESBL-S in hospitalized horses.</p>