Colistin-Resistant Escherichia coli and the mcr-1 gene in the Argentine Poultry Chain, after the Colistin ban

Abstract

The increase in colistin resistance in diverse environments, including food production chains, led to the ban on colistin use in veterinary medicine in Argentina. This study assesses the presence and persistence of colistin resistance and the mcr genes in E. coli isolated from two Argentinian poultry supply chain points. The multidrug resistance profiles, the presence of the stx1, stx2, and eae virulence genes, and the clonal relationship among isolates were also analysed. At the slaughterhouse, 549 samples were collected, including caecal content, neck skin, and slaughterhouse wastewater. At the retail market, 241 breast skin samples were collected. The isolates were obtained from TBX agar supplemented with colistin, followed by determination of the uspA gene. Colistin agar test and agar microdilution were used to determine the minimum inhibitory concentration for colistin and other critical antibiotics. Multiplex polymerase chain reactions were used to determine the presence of mcr and virulence genes. Pulsed-field gel electrophoresis was used to compare different pulse-types. Forty-nine colistin-resistant E. coli were recovered from 35 samples from the slaughterhouse (6.37%), while two colistin-resistant E. coli were recovered from one sample from the retail market (0.41%). 54.90% of the colistin-resistant isolates carrying the mcr-1 gene, and 90.19% of their exhibited multidrug resistance. The highest proportion of colistin-resistant E. coli were grouped into 11 clusters. Stx1, stx2, and eae genes were identified in two isolates. This study highlights the need for continuous surveillance and proactive intervention throughout the poultry production chain to mitigate this persistent challenge