High prevalence of ESBLs in retail chicken meat despite reduced use of antimicrobials in chicken production, France

Abstract

Extended-spectrum cephalosporins (ESCs) are critically important antibiotics for humans and their use in animals poses a potential threat for public health. Chicken represents an increasing part of the human diet and has also been regarded as a source of ESC-resistant Enterobacteriaceae because of the worldwide off-label use of ceftiofur, a broad-spectrum cephalosporin. Thus, numerous studies pointed out chicken as a reservoir of ESBL/pAmpC genes, plasmids and/or clones at risk for humans. In France, late 2011, strong political pressure led to a drastic reduction of ceftiofur use and all other antibiotics in chicken production. Here, we ascertained the potential impact of those efforts on the prevalence of ESC-resistant E. coli in retail chicken. From October 2015 to January 2016, of 48 unrelated pieces of meat (chicken legs) belonging to four different brands, 44 (91.7%) were positive for ESC-resistant E. coli. The blaCTX-M-1 gene was highly prevalent (68/74, 91.9%), mostly located on IncI1/ST3 plasmids (65/68, 95.6%). Other ESBL/pAmpC genes (blaTEM-52, blaSHV-12, blaCMY-2) were carried by IncX1, IncI1/ST36, IncI1/ST95, IncA/C or IncK plasmids. The positive isolates were non-clonal, suggesting a horizontal spread of the ESBL/pAmpC genes. Obviously, the strong decrease of antimicrobial use in chicken farms had no impact yet on the ESBL/pAmpC prevalence in retail chicken meat in France. A human source of these ESBL/pAmpC genes is unlikely as blaCTX-M-1 IncI1/ST3 plasmids are dominant in animals and rare in humans. Our data question the real impact of the decrease of antimicrobial use in chicken production on ESBL contamination of chicken meat and point out the risk of ESBL/AmpCs human transfer through the food chain.