Molecular Characterization of Colistin-Resistant Isolated from Chickens: First Report from Nepal.

Dissemination of encoding colistin resistance in Gram-negative bacteria has created critical situation in poultry, livestock farming, and public health. In Nepal, for the first time, we initiated surveillance of colistin-resistant in broilers from seven different chicken farms. A total of 324 cloacal swabs were collected and 118 were isolated, of which 27 (22.8%) were colistin resistance all harboring gene, but lacking IS. Colistin-resistant isolates were characterized by antibiotic susceptibility testing, detecting antibiotic resistance genes, phylogenetic analysis, and plasmid replicon typing. These isolates belonged to the phylo-group A (70.37%) and phylo-group D (29.63%). In addition, most isolates (>80%) were resistant to ciprofloxacin, tetracycline, and sulfamethoxazole-trimethoprim. As much as 3 of the 27 encoding isolates were confirmed as extended-spectrum β-lactamase (ESBL) producer, all 3 isolates carrying gene. We performed the conjugation experiment to check transferability of , , and genes, and only two donors were found to have transferred resistance to ticarcillin. The transfer of colistin and tetracycline resistance was not detected, which suggests the chromosomal location of and genes. The prevalence of Inc K/B and Inc I1 was 96.3% and 81.48%, respectively. This study shows the co-existence of with , , , , and genes and dissemination of these resistant isolates in Nepalese chicken farms, which may pose huge threat to the livestock, especially chickens, and public health in Nepal.