Spread of multidrug-resistant IncHI1 plasmids carrying ESBL gene bla(CTX-M-1) and metabolism operon of prebiotic oligosaccharides in commensal Escherichia coli from healthy horses, France

The objective of the study was to identify the genetic determinants and characteristics of expanded-spectrum cephalosporin (ESC) resistance in commensal Escherichia coli from healthy horses in France in 2015. Faecal samples from 744 adult horses were screened for ESC-resistant E. coli isolates. The extended-spectrum beta-lactamase (ESBL)/AmpC resistance genes were identified using polymerase chain reaction (PCR) and sequencing. ESC phenotypes were horizontally transferred by conjugation or transformation. Plasmids carrying ESBL/AmpC genes were typed by PCR-based replicon typing, restriction fragment length polymorphism (RFLP), and plasmid multilocus sequence typing (pMLST). The ESC-resistant E. coli isolates were typed by XbaI macrorestriction analysis. Sixteen of 41 stables harboured at least one horse carrying ESC-resistant E. coli. The proportion of individually tested horses carrying ESC-resistant E. coli was 8.5% (28/328). Fifty non-redundant ESC-resistant E. coli isolates showing a great diversity of XbaI macrorestriction profiles belonged mainly to phylogroup B1, and were negative for major E. coli virulence genes, indicating they are commensal isolates. ESBL bla(CTX-M) genes were dominant (bla(CTX-M-1 ), n=34; bla(CTX-M-2), n=8; bla(CTX-M-14), n=2) and located on conjugative plasmids belonging to various incompatibility groups (IncHI1, IncI1, IncN, IncY, or non-typeable). Among these, the multidrug-resistant IncHI1-pST9 plasmids were dominant and simultaneously harboured the bla(CTX-M-1/2) genes and an operon enabling the metabolism of short-chain fructo-oligosaccharides (scFOS). In conclusion, commensal E. coli of French horses displayed a significant distribution of IncHI1-pST9 plasmids carrying both the bla(CTX-M-1/2) gene and the fos metabolism operon. This finding highlights the risk of co-selection of multidrug-resistant IncHI1 plasmids carrying ESBL genes possibly mediated by the use of scFOS as prebiotic in horses. (C) 2020 Elsevier B.V. and International Society of Chemotherapy. All rights reserved.