Molecular characterization of Escherichia coli strains isolated from retail meat that harbor bla_CTX-Mand fosA3 genes

A total of 55 cefotaxime-resistant Escherichia coli isolates were obtained from retail meat products purchased in Shenzhen, China, during the period November 2012 to May 2013. Thirty-seven of these 55 isolates were found to harbor a blaCTX-Mgene, with the blaCTX-M-1group being the most common type. blaCMY-2 was detected in 16 isolates, alone or in combination with other extended-spectrum β-lactamase (ESBL) determinants. Importantly, the fosA3 gene, which encodes fosfomycin resistance, was detected in 12 isolates, with several being found to reside in the conjugative plasmid that harbored the blaCTX-Mgene. The insertion sequence IS26 was observed upstream of some of the blaCTX-M-55and fosA3 genes. Conjugation experiments showed that blaCTX-Mgenes from 15 isolates were transferrable, with Inc I1 and Inc FII being the most prevalent replicons. High clonal diversity was observed among the blaCTX-Mproducers, suggesting that horizontal transfer of the blaCTX-Mgenes among E. coli strains in retail meats is a common event and that such strains may constitute an important reservoir of blaCTX-Mgenes, which may be readily disseminated to other potential human pathogens.