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Prevalence and Characterization of Non-O157 EHEC/STEC on Pre-and Post-Intervention Cull Cow Carcasses and in Ground Beef


There are over 70 types of Shiga toxin-producing Escherichia coli (STEC) that have been found
to cause human illness. E. coli O157:H7 is the STEC most frequently isolated and most
commonly associated with serious human illness, including bloody diarrhea and hemolyticuremic syndrome (HUS). However, non-O157 STEC have also been found to cause sporadic
illness and outbreaks of bloody diarrhea and HUS. The most common non-O157 serogroups
reported by the Centers for Disease Control (CDC) to be associated with human disease were
O26 (22 percent), O111 (16 percent), O103 (12 percent), O121 (8 percent), O45 (7 percent) and
O145 (5 percent). Although infrequently isolated and reported, it is estimated that non-O157
STEC cause diarrhea at frequencies similar to those of other important enteric bacterial
pathogens such as Salmonella and Shigella. <P>

It is widely documented that cattle are a primary reservoir of many STEC serotypes, and a great
deal of research has focused on the prevalence of non-O157 STEC in fed cattle at the processing
level. There is currently a lack of information on the prevalence of non-O157 STEC found on
carcasses from plants that slaughter cull cows and bulls. A large percentage of these carcasses
are processed into ground beef. <P>
The objective of this project was to determine the prevalence of non-O157 STEC in commercial
ground beef, and on cull cow carcasses at two stages of slaughter—pre-evisceration and after inplant safety interventions have been applied.

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Findings: In this project approximately 3200 ground beef samples and 6400 carcass samples were used. Results showed that stx genes are present on 71% of pre-evisceration carcasses, and 3% of final carcasses and in 26% of ground beef samples. When STEC isolation was attempted, 30 to 48% of samples yielded one or more STEC. STEC of the common O-groups O26, O103, O113, O117, O121, O145, and O146 were identified. 389 other STEC were of other O-groups. The most frequent O-groups were O121 and O113. Virulence gene distribution showed that 19 (4%) STEC isolates total possessed multiple virulence associated genes: stx, intimin and enterohemolysin. Further categorization by OI122 analysis showed only 1.4% of STEC isolates belong to a putative group with severe disease potential. Results will be updated after all data is collected.

<P> For complete projects details, view the <a href="…; target="_blank">Project Summary. </a>

Koohmaraie, Mohammad
USDA - Agricultural Research Service
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