Mobile genetic elements facilitate the transmission of antibiotic resistance genes in multidrug-resistant Enterobacteriaceae from duck farms

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Multidrug-resistant (MDR) Enterobacteriaceae critically threaten duck farming and public health. The phenotypes, genotypes, and associated mobile genetic elements (MGEs) of MDR Enterobacteriaceae isolated from six duck farms in Zhejiang province, China, were investigated. A total of 215 isolates were identified as Escherichia coli (64.65%), Klebsiella pneumoniae (12.09%), Proteus mirabilis (10.23%), Salmonella (8.84%), and Enterobacter cloacae (4.19%). Meanwhile, all isolates were resistant to at least two antibiotics. Most isolates carried tet(A) (85.12%), blaTEM (78.60%) and sul1 (67.44%) resistance genes. Gene co-occurrence analysis showed that the resistance genes were associated with IS26 and integrons. A conjugative IncFII plasmid pSDM004 containing all the above MGEs was detected in Proteus mirabilis isolate SDM004. This isolate was resistant to 18 antibiotics and carried the blaNDM-5 gene. MGEs, especially plasmids, are the primary antibiotic resistance gene (ARG) transmission route in duck farms. These findings provide a theoretical basis for the rational use of antibiotics in farms which are substantial for evaluating public health and food safety.