Molecular Characterization of Escherichia coli Strains Isolated from Retail Meat That Harbor bla CTX-M and fosA3 Genes

Abstract

ABSTRACT 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 bla CTX-M gene, with the bla CTX-M-1 group being the most common type. bla CMY-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 bla CTX-M gene. The insertion sequence IS 26 was observed upstream of some of the bla CTX-M-55 and fosA3 genes. Conjugation experiments showed that bla CTX-M genes from 15 isolates were transferrable, with Inc I1 and Inc FII being the most prevalent replicons. High clonal diversity was observed among the bla CTX-M producers, suggesting that horizontal transfer of the bla CTX-M genes among E. coli strains in retail meats is a common event and that such strains may constitute an important reservoir of bla CTX-M genes, which may be readily disseminated to other potential human pathogens.