Does an Antibiotic Stewardship Applied in a Pig Farm Lead to Low ESBL Prevalence?

The aim of the present study was to prospectively evaluate the prevalence of intestinal carriage of colistin-resistant and extended-spectrum β-lactamase (ESBL)-producing among pigs from a Swiss farm attending an animal health and antibiotic stewardship program and to determine the associated mechanisms of resistance. . Eighty-one fecal samples were recovered and screened for either β-lactam-resistant, colistin-resistant, or aminoglycoside-resistant , using respective screening media. All recovered isolates were tested for antimicrobial susceptibility and their clonal relationship (PFGE and MLST). Plasmid typing was performed by plasmid-based replicon typing (PBRT). Resistance genes were searched by PCR and sequencing. A total of 38 ESBL-producing and a single ESBL-producing were recovered from 81 pigs, corresponding to a prevalence of 50%, no other β-lactamase producer being identified. Among the 38 ESBL-producing , all belonged to sequence type (ST) ST10, except two ST34 and ST744 isolates. Among the ST10- isolates, three subclones ( = 22, = 13, and = 1, respectively) were identified according to the PFGE analysis. The most commonly identified IncI1 plasmid harboring the gene was 143 kb in size and coharbored other resistance genes. Only three colistin-resistant isolates were recovered, namely two isolates and a single isolate. Screening for the plasmid-borne to genes in these three isolates gave negative results. The two isolates were clonally related, belonged to ST76, and harbored a truncated chromosomal gene being the source of colistin resistance. A high prevalence of fecal carriage of ESBL-producing was found, being mainly caused by the spread of a clonal lineage within the farm. By contrast, a low prevalence of colistin-resistant was found.