AEM Accepts, published online ahead of print on 15 January 2010

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Appl. Environ. Microbiol. doi:10.1128/AEM.01968-09
Copyright (c) 2010, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Presence and Characterization of Shiga Toxin-Producing Escherichia coli and Other Potentially Diarrheagenic E. coli in Retail Meats

Xiaodong Xia, Jianghong Meng^*, Patrick F. McDermott, Sherry Ayers, Karen Blickenstaff, Thu-Thuy Tran, Jason Abbott, Jie Zheng, and Shaohua Zhao

Department of Nutrition and Food Science, and Joint Institute for Food Safety and Applied Nutrition, University of Maryland, College Park, Maryland 20742; Center for Veterinary Medicine, Food and Drug Administration, Laurel, MD 20708; Center for Food Safety and Applied Nutrition, Food and Drug Administration, College Park, MD 20740

^* To whom correspondence should be addressed. Email: jmeng{at}umd.edu.

To determine the presence of Shiga toxin-producing Escherichia coli (STEC) and other potentially diarrheagenic E. coli in retail meats, 7,258 E. coli isolates collected by the U. S. National Antimicrobial Resistance Monitoring System (NARMS) retail meat program from 2002 to 2007 were screened for Shiga toxin genes. In addition, 1,275 of the E. coli isolates recovered in 2006 were examined for virulence genes specific for other diarrheagenic E. coli. Seventeen isolates (16 from ground beef and 1 from pork chop) were positive for stx genes, including five for both stx₁ and stx₂, two for stx₁ and 10 for stx₂. The 17 STEC belonged to 10 serotypes: O83:H8, O8:H16, O15:H16, O15:H17, O88:H38, ONT:H51, ONT:H2, ONT:H10, ONT:H7 and ONT:H46. None of the STEC isolates contained eae, whereas seven carried EHEC-hlyA. All except one STEC isolate exhibited toxic effects on Vero cells. DNA sequence analysis showed that stx₂ from five STEC isolates encoded mucus-activatable Stx2d. Subtyping of the 17 STEC isolates by PFGE yielded 14 distinct restriction patterns. Among the 1, 275 isolates from 2006, 11 atypical enteropathogenic E. coli (EPEC) isolates in addition to three STEC were identified. This study demonstrated that retail meats, mainly ground beef, were contaminated with diverse STEC strains. The presence of atypical EPEC strains in retail meat is also of concern due to their potential to cause human infections.