Co-occurrence of mcr-1 mediated colistin resistance and β-lactamase-encoding genes in multidrug-resistant Escherichia coli from broiler chickens with colibacillosis in Tunisia.

Colibacillosis caused by avian pathogenic Escherichia coli (APEC) is considered a major hindrance in poultry farming worldwide. This study aimed to characterize the genetic content and the relatedness between multidrug-resistant E. coli isolates from broiler chickens died due to colibacillosis from three farms from Tunisia. One hundred samples were collected from chickens' fresh carcasses from three poultry farms in Tunisia. E. coli isolation and identification were performed. Then, antimicrobial susceptibility regarding antibiotics, the ability to produce β-lactamases and minimum inhibitory concentration for colistin were determined according to Clinical and Laboratory Standards Institute guidelines. β-Lactam and non-β-lactam antimicrobial resistance genes, integrons, virulence genes, and phylogenetic groups were investigated using polymerase chain reaction. The genetic relatedness of the E. coli isolates was analysed by pulsed field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). A high infection rate of E. coli (50%) in infected organs of chickens was observed. The majority of E. coli isolates were multidrug resistant (96%); among them, 24% were colistin resistant and 30% were ESBL producing. Seven of 12 colistin-resistant isolates harboured the mcr-1 gene; among them, 10 were ESBL producing and carried bla This is the first report of ESBL-mcr-1-carrying E. coli isolates of a clinically relevant phylogenetic group (B2) from chickens that died due to colibacillosis in Tunisian poultry farms.

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