Persistence of MCR-1-Positive Colistin-Resistant E. coli ST162, ST93, and ST3941 Clones in Poultry Farms, Algeria

Plasmid-mediated colistin resistance in food animals is a major public health concern, but longitudinal farm data remain limited. We screened 10 broiler farms in Guelma, Algeria, for mcr-1-positive colistin-resistant Escherichia coli and monitored three positive farms over 8 months. Among 186 pooled animal and environmental samples, 54 isolates were recovered, and all carried mcr-1. Positive isolates were detected in chicken feces and environmental niches, including drinking water, wastewater, wall swabs, and soil. The population was polyclonal, comprising 28 sequence types, but ST162, ST93, and ST3941 recurred across farms or sampling periods. Four ST162 isolates from farm C recovered from successive flocks differed by only 12-14 SNPs, supporting local persistence or repeated reintroduction from a common reservoir. All isolates were multidrug resistant and carried mcr-1 on an IncI2 (delta) plasmid. These findings support a mixed epidemiology combining persistence of selected clones with horizontal dissemination of a conserved mcr-1-bearing plasmid in poultry farms.