|Koohmaraie, Mohammad -|
Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 12, 2011
Publication Date: March 1, 2011
Citation: Bosilevac, J.M., Koohmaraie, M. 2011. Prevalence and characterization of non-O157 Shiga toxin producing Escherichia coli isolates from commercial ground beef in the United States. Applied and Environmental Microbiology. 77(6):2103-2112. Interpretive Summary: Escherichia coli O157:H7 is one of many different types of Shiga toxin (stx) producing E. coli (STEC) that can cause severe illness in humans. E. coli O157:H7 is highly regulated in beef products because, in the U.S., it is the type of E. coli that most often causes outbreaks of disease. The other types of Shiga toxin producing E. coli (non-O157 STEC) are associated with diseases of varying severity. Recently, the presence of non-O157 STEC in cattle and beef products has gained the attention of the beef industry, regulatory officials, and the public. There are few reports describing STEC in ground beef, therefore this study reports on the prevalence and characterization of non-O157 STEC in 4,133 samples of U.S. ground beef obtained from numerous manufacturers from across the U.S. over a period of 24 months. The results showed that Shiga toxin genes were present in 24.3% (1,006 of 4,133) of the ground beef samples. At least one STEC could be obtained from 300 of the 1,006 samples that contained Shiga toxin genes (7.3% of the total 4,133 samples). A total of 338 different STEC isolates were obtained from the 300 samples because some samples contained more than one type. All the STEC isolates were characterized and tested for the presence of different genes that help predict their ability to cause severe disease. Results of this characterization identified ten STEC (0.2% of the total 4,133) that may be considered significant food safety threats.
Technical Abstract: Escherichia coli O157:H7 is a Shiga toxin (stx) producing E. coli (STEC) that has been classified as an adulterant in U.S. beef, and its presence is rigorously monitored. However, there are numerous non-O157 STEC that are associated with diseases of varying severity. Non-O157 STEC are an increasing concern to the beef industry, regulatory officials, and the public, but little data exists for STEC prevalence in ground beef. This study reports the prevalence and characterization of non-O157 STEC in commercial ground beef (n = 4,133) obtained from numerous commercial ground beef manufacturers from across the U.S. for a period of 24 months. All samples were screened by DNA amplification for the presence of stx1, stx2, intimin (eae) and enterohemorrhagic E. coil hemolysin (ehx). The suggested prevalence of STEC based on the presence of stx1 and stx2 genes in ground beef was 24.3% (1,006 of 4,133). Culture isolation of a STEC from all samples that contained stx1 and/or stx2 was attempted. Of the 1,006 stx screened positive ground beef samples, 300 (7.3% of the total 4,133) were confirmed to have at least one variant of STEC present by culture isolation. In total, 338 unique STEC isolates were recovered in the 300 samples that yielded a STEC. All unique STEC isolates were serotyped and had various virulence factors characterized. These included Shiga toxin subtypes, intimin subtypes, and accessory virulence factors related to adherence (saa, iha, lifA), toxicity (cnf, subA, astA), iron acquisition (chuA), the presence of the large 60MDa virulence plasmid (espP, etpD, toxB, katP, toxB) and a pathogenicity molecular risk assessment (MRA, based on presence of various O-Island nle genes). Results of this characterization identified ten STEC (0.2% of total 4,133) that may be considered significant food safety threats.