Rapid Dissemination of bla NDM-5 Gene among Carbapenem-Resistant Escherichia coli Isolates in a Yellow-Feather Broiler Farm via Multiple Plasmid Replicon.

Although carbapenems have not been approved for animal use, carbapenem-resistant Escherichia coli (CREC) strains are increasingly being detected in food-producing animals, posing a significant public health risk. However, the epidemiological characteristics of CREC isolates in yellow-feather broiler farms remain unclear. We comprehensively investigated the genetic features of carbapenem-resistance genes among E. coli isolates recovered from a yellow-feather broiler farm in Guangdong province, China. Among the 172 isolates, 88 (51.2%) were recovered from chicken feces (88.5%, 54/61), the farm environment (51.1%, 24/47), and specimens of dead chickens (15.6%, 41/64). All CREC isolates were positive for the bla NDM-5 gene and negative for other carbapenem-resistance genes. Among 40 randomly selected isolates subjected to whole-genome sequencing, 10 belonged to distinct sequence types (STs), with ST167 (n = 12) being the most prevalent across different sources, suggesting that the dissemination of bla NDM-5 was mainly due to horizontal and clonal transmission. Plasmid analysis indicated that IncX3, IncHI2, and IncR-X1-X3 hybrid plasmids were responsible for the rapid transmission of the bla NDM-5 gene, and the genetic surrounding of bla NDM-5 contained a common mobile element of the genetic fragment designated "IS 5 -△IS Aba125 - bla NDM-5 - ble MBL - trpF - dsbC ". These findings demonstrate a critical role of multiple plasmid replicons in the dissemination of bla NDM-5 and carbapenem resistance.