Intestinal carriage of mcr-1 and mcr-5 mediated colistin-resistant Escherichia coli in avian species: First report from broiler breeders and laying hens in Algeria.

Abstract

Colistin, a critical last-resort antibiotic in human medicine, is commonly used in veterinary practice both as a growth promoter and for the treatment and prevention of enterobacterial infections in livestock. However, its extensive use has been linked to the emergence of colistin-resistant Gram-negative bacteria. The co-occurrence of mcr genes with other multidrug resistance determinants increases the risk of pan-drug-resistant strains, posing a significant threat to public health and potentially limiting therapeutic options. This study aimed to investigate the occurrence of colistin resistance in Escherichia coli isolates from apparently healthy poultry in Algeria. A total of 360 E. coli isolates collected from broilers, broiler breeders, breeding hens, and laying hens were tested for colistin susceptibility using the broth microdilution method. Phenotypic resistance was observed in 14 isolates (3.9 %) with MICs ranging from 4 to 32 μg/mL. All resistant isolates exhibited a multidrug-resistant phenotype. PCR screening and Sanger sequencing revealed that 78.6 % (11/14) of the colistin-resistant isolates carried the mcr-1 gene, and 57.1 % (8/14) harboured both mcr-1 and mcr-5. The mcr-2, mcr-3, and mcr-4 genes were not detected. Additionally, conjugation assays demonstrated the transferability of the mcr-1 gene in one isolate, indicating its potential for horizontal dissemination. This is the first documented report of mcr-1 and mcr-5 in E. coli from broiler breeders and laying hens in Algeria, highlighting its significant public health implications. These findings underscore the need for enhanced surveillance and stringent control measures to prevent the spread of colistin resistance from animal reservoirs to humans.