Establishment of Non-O157 Shiga-toxin Producing E. coli (STEC) Baseline in Raw Ground Beef in the US

Shiga toxin-producing Escherichia coli (STEC), which are capable of producing Shiga toxin 1 and/or
2, have been associated with foodborne outbreaks and caused severe human illness such as bloody
diarrhea, hemolytic uremic syndrome (HUS), and kidney failure, since 1982 when E. coli O157:H7
was frequently isolated from the undercooked hamburger beef patties. Although not all non-O157
STEC are pathogenic to humans, some non-O157 STEC strains have been related to sporadic cases
of human illness, and are able to cause disease as severe as E. coli O157:H7, such as bloody diarrhea,
hemorrhagic colitis, HUS or even death. STEC primarily resides in the gastrointestinal tract of
ruminants, especially cattle, and will not cause any illness to their hosts. These strains can be easily
disseminated to the environment or other surfaces through direct fecal contamination, which is also
the primary food safety issue during the production of beef products. Centers for Disease Control
and Prevention (CDC) estimated that six non-O157 STEC strains, including serotypes O26, O45,
O103, O111, O121, and O145, accounted for over 70% of non-O157 STEC outbreaks in the
United States. Due to the increasing number of non-O157 STEC-associated illness and capability of
developing severe disease, USDA’s Food Safety and Inspection Service (FSIS) has declared the six
most prevalent non-O157 STEC (O26, O45, O103, O111, O121, and O145) as adulterants in
ground beef or other non-intact beef products.<P>
Due to non-phenotypic characteristics of non-O157 STEC, it has been a challenge to detect these
bacteria with the fast and accurate methods; therefore, illness associated with non-O157 STEC has
always been under-estimated. Polymerase chain reaction (PCR)-based detection methods have been
considered as valuable tools to trace outbreaks of bacterial pathogens in the food supplies. The BAX
system is one of the commercial PCR-based systems that utilize the amplification of a specific target
DNA sequence for the detection of pathogens in the food.<P>To date, unlike E. coli O157:H7, the information regarding the prevalence of non-O157 STEC in
commercial ground beef samples from the retailers is scarce. Therefore, there is a need to set up the
baseline of non-O157 STEC in the commercial ground beef samples and to determine fast and
reliable methods to detect those stains.<P>

The objective of this study was to identify the prevalence of the six pathogenic non-O157
STECs (serotypes O26, O45, O103, O111, O121, O145) in commercial ground beef
products, and their association with different harvest parts from carcass, and lean/fat
proportion.