Prevalence and characterization of hybrid bla_CTX-M among Escherichia coli isolates from livestock and other animals

This study investigated 248 extended-spectrum β-lactamase-producing Escherichia coli isolates from 2012 to 2013 for hybrid bla_CTX-M genes. bla_CTX-M genes were detected in 228 isolates of which 14 isolates were hybrid bla_CTX-M positive (6 bla_CTX-M-123, 6 bla_CTX-M-64, and 2 bla_CTX-M-132). The 14 hybrid bla_CTX-M-carrying isolates (8 from chickens, 2 each from pigs and cattle, 1 each from dog and rodent) were genetically diverse. All but 2 hybrid bla_CTX-M were carried on IncI1 (5 bla_CTX-M-123) and IncI2 (6 bla_CTX-M-64 and one bla_CTX-M-132) plasmids. Our IncI1 and IncI2 plasmids had pHNAH4-1-like and pHN1122-1-like restriction fragment length polymorphism patterns, respectively. Genetic relatedness of the plasmids to pHNAH4-1 and pHN1122-1 were confirmed by complete sequencing of 3 plasmids, pCTXM123_C0996, pCTXM64_C0967, and pCTXM132_P0421. Plasmids closely related to pHNAH4-1 and pHN1122-1 and carrying different bla_CTX-M alleles have been reported from multiple geographic areas in China previously. The findings highlighted the wide dissemination of hybrid bla_CTX-M variants in different parts of China.