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

• Main Authors: Claudine Fournier, Patrice Nordmann, Olivier Pittet, Laurent Poirel
• Format: Article
• Language: English
• Published: MDPI AG 2021-05-01
• Series: Antibiotics
• Subjects: ESBL; colistin; mobilized colistin resistance; pigs
• Online Access: https://www.mdpi.com/2079-6382/10/5/574

<i>Background.</i> 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 <i>Enterobacterales</i> among pigs from a Swiss farm attending an animal health and antibiotic stewardship program and to determine the associated mechanisms of resistance. <i>Materials/Methods</i>. Eighty-one fecal samples were recovered and screened for either β-lactam-resistant, colistin-resistant, or aminoglycoside-resistant <i>Enterobacterales</i>, 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. <i>Results.</i> A total of 38 ESBL-producing <i>Escherichia coli</i> and a single ESBL-producing <i>Enterobacter cloacae</i> were recovered from 81 pigs, corresponding to a prevalence of 50%, no other β-lactamase producer being identified. Among the 38 ESBL-producing <i>E. coli</i>, all belonged to sequence type (ST) ST10, except two ST34 and ST744 isolates. Among the ST10-<i>bla</i>_CTX-M-1 isolates, three subclones (<i>n</i> = 22, <i>n</i> = 13, and <i>n</i> = 1, respectively) were identified according to the PFGE analysis. The most commonly identified IncI1 plasmid harboring the <i>bla</i>_CTX-M-1 gene was 143 kb in size and coharbored other resistance genes. Only three colistin-resistant <i>Enterobacterales</i> isolates were recovered, namely two <i>Klebsiella pneumoniae</i> isolates and a single <i>E. cloacae</i> isolate. Screening for the plasmid-borne <i>mcr-1</i> to <i>mcr-9</i> genes in these three isolates gave negative results. The two <i>K. pneumoniae</i> isolates were clonally related, belonged to ST76, and harbored a truncated <i>mgrB</i> chromosomal gene being the source of colistin resistance. <i>Conclusion.</i> A high prevalence of fecal carriage of ESBL-producing <i>E. coli</i> was found, being mainly caused by the spread of a clonal lineage within the farm. By contrast, a low prevalence of colistin-resistant <i>Enterobacterales</i> was found.