Abstract
This study investigated the ecology, epidemiology and plasmid characteristics of extended-spectrum cephalosporin (ESC)-resistant E. coli in healthy pigs over a period of 4 years (2013–2016) following the withdrawal of ESCs. High carriage rates of ESC-resistant E. coli were demonstrated in 2013 (86.6%) and 2014 (83.3%), compared to 2015 (22%) and 2016 (8.5%). ESC resistance identified among E. coli isolates was attributed to the carriage of an IncI1 ST-3 plasmid (pCTXM1-MU2) encoding blaCTXM-1. Genomic characterisation of selected E. coli isolates (n = 61) identified plasmid movement into multiple commensal E. coli (n = 22 STs). Major STs included ST10, ST5440, ST453, ST2514 and ST23. A subset of the isolates belong to the atypical enteropathogenic E. coli (aEPEC) pathotype that harboured multiple LEE pathogenic islands. pCTXM1-MU2 was similar (99% nt identity) to IncI1-ST3 plasmids reported from Europe, encoded resistance to aminoglycosides, sulphonamides and trimethoprim, and carried colicin Ib. pCTXM1-MU2 appears to be highly stable and readily transferable. This study demonstrates that ESC resistance may persist for a protracted period following removal of direct selection pressure, resulting in the emergence of ESC-resistance in both commensal E. coli and aEPEC isolates of potential significance to human and animal health.
Highlights
The World Health Organisation (WHO) has recently warned of a post-antibiotic era after discovering widespreadThese authors contributed : Darren J
We evaluated the carriage of extended-spectrum cephalosporin (ESC)-resistant E. coli in a pig herd over a period of 4 years, and clarified the molecular characteristics of ESC-resistant E. coli and their associated plasmids responsible for ESC resistance
The major findings arising from this study are as follows: (i) ESC resistance identified among E. coli isolated in this study was attributed to the widespread dispersion and persistence of an IncI1 plasmid encoding the blaCTXM-1 gene. (ii) Genomic characterisation of ESCresistant E. coli demonstrated that the ESC-resistant plasmid had moved into multiple commensal and several atypical enteropathogenic E. coli clonal lineages that harboured multiple locus of enterocyte effacement (LEE) pathogenic island variants encoding the eae and/or ehx genes. (iii) Once ESC-resistant E. coli emerge in a livestock production system, it will take an extended period of time for significant reduction and/or elimination of ESC-resistant E. coli following withdrawal of the direct antimicrobial selection pressure. (iv) IncI1-blaCTXM-1 plasmids are globally disseminated, stable and highly transferable
Summary
The World Health Organisation (WHO) has recently warned of a post-antibiotic era after discovering widespread. Recent studies in humans and animals have shown that once ESC-resistance emerges in the host’s microbiota, it takes a considerable time for resistance genes distributed among autochthonous Enterobacteriaceae to be lost, even when direct antibiotic selection pressure is removed. This demonstrates the long-term impact of ESC-resistance on both human and animal health [15, 16]. Rectal swabs were obtained from randomly selected pigs from an Australian piggery with a history of off-label ceftiofur use on an individual animal basis over the preceding 4 years This investigation was performed by a specialist pig veterinarian as part of the herd health management plan for the piggery, and samples were submitted to the University of Adelaide Veterinary Diagnostic Laboratory for culture. An additional E. coli isolate was selected from the selective agar if two morphologically distinct E. coli colony types were identified on the selective agar plate and on SBA
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