Molecular Epidemiology of Escherichia coli Producing CTX-M and pAmpC β-Lactamases from Dairy Farms Identifies a Dominant Plasmid Encoding CTX-M-32 but No Evidence for Transmission to Humans in the Same Geographical Region

Abstract

Third-generation cephalosporins (3GCs) are critically important antibacterials, and 3GC resistance (3GC-R) threatens human health, particularly in the context of opportunistic pathogens such as Escherichia coli . There is some evidence for zoonotic transmission of 3GC-R E. coli through food, but little work has been done examining possible transmission via interaction of people with the local near-farm environment. We characterized acquired 3GC-R E. coli found on dairy farms in a geographically restricted region of the United Kingdom and compared these with E. coli from people living in the same region, collected in parallel. While there is strong evidence for recent farm-to-farm transmission of 3GC-R strains and plasmids—including one epidemic plasmid that has a remarkable capacity to be transmitted—there was no evidence that 3GC-R E. coli found on study farms had a significant impact on circulating 3GC-R E. coli strains or plasmids in the local human population.