The Challenges of Shiga
Toxigenic E. coli (STEC)
Detection
The potential public health risk of the non-O157 Shiga toxigenic Es- cherichia coli (STEC) continues to top the list of concerns for many food safety professionals. The U.S. Department of Agriculture
(USDA) Food Safety Inspection Service (FSIS)
introduced its first internal method for detec-
tion and isolation of the top six non-O157
STEC in October 2010. More recently, in a
special session at the International Association
of Food Protection meeting in Milwaukee ear-
lier this year, U.S. Secretary of Agriculture Tom
Vilsack indicated that the USDA is moving for-
ward with plans to develop regulations pertain-
ing to these top STEC in food as early as
spring 2012. In the meantime, several leading
food companies announced plans to imple-
ment testing programs for the top six non-
O157 STEC in addition to their existing E. coli
O157:H7 testing efforts. However, accurate
detection of this group of organisms repre-
sents a new and unique challenge to the food
industry.
www.biocontrolsys.com
The Rapid Method Dilemma
The top six non-O157 STEC (Top STEC)
have been defined by USDA FSIS as E. coli belonging to serogroups O26,
O111, O103, O121, O145 or O45 and possessing both the eae gene and
either the stx1 or stx2 genes. Because this definition includes both an immunological component of the O-antigen and a genetic component of specific pathogenicity genes, rapid methods employing only a single detection
technology will generate a high frequency of false positives. Because many
strains of E. coli and other bacteria belonging to these six serogroups do
not possess the necessary pathogenicity genes, traditional antibody-based
tests such as lateral flows or enzyme-linked immunoabsorbent assays will
inaccurately detect many non-Top STEC organisms. Similarly, because
there are over 200 other serotypes of E. coli that contain the eae and/or stx
genes, genetic-based methods that target only these genes are subject to
inaccuracy, resulting in a high rate of false-positive results. These false
positives would have to be sorted out either with a series of secondary genetic tests for the O-group genes or through labor-intensive traditional culture methods.
Detection methods that combine both immunological and genetic technologies can greatly increase the specificity and accuracy of Top STEC detection. The Assurance GDS® pathogen detection system from BioControl
Systems, Inc. incorporates a proprietary PickPen® immunomagnetic separation (IMS) sample preparation procedure prior to PCR-based detection of
the gene targets. The PickPen procedure captures and isolates bacteria
belonging to the target serogroups. As such, the downstream reaction for
detection of the target pathogenicity genes is performed on a unique subset of organisms that belong only to the serogroups of concern.
A Building-block Approach to
STEC Testing
The unparalleled collection of Assurance GDS STEC assays provides food
processors with the building blocks necessary to assemble a comprehensive and
cost-effective STEC testing program. The
new Assurance GDS MPX Top 7 STEC
assay provides definitive positive/negative
results for both E. coli O157:H7 and Top
STEC in just 12 hours. Following enrichment and IMS capture of the top seven
serogroups, including O157, the Top
STEC results are based on the presence
of the eae, stx1 and stx2 genes, while the E.
coli O157:H7 result is based on the same
proven gene target found in the Assurance
GDS E. coli O157:H7 kit, utilized extensively throughout the industry.
For organizations that want to maintain
a separate E. coli O157:H7 testing strategy, the Assurance GDS MPX Top 6 STEC
assay captures the top six non-O157
serogroups and then provides a definitive
result based on the eae, stx1 and stx2
genes. Still more flexibility can be had with
the Assurance GDS Top STEC (eae) and
Assurance GDS Shiga Toxin Gene assays.
Both are available with either Top 6 or Top
7 serogroup IMS capture options, allowing
users to implement a sequential approach
to testing that provides Shiga toxin gene
results for only those samples already determined to be positive for eae. The extensive collection of Assurance GDS STEC
assays allows organizations to assemble
custom testing strategies to fit their specific food safety program needs for the
detection and confirmation of E. coli
O157:H7 and the six non-O157
serogroups of STEC.
The Assurance GDS pathogen detection system includes a comprehensive offering of assays for detection of the major
foodborne pathogens, including Top
STEC, E. coli O157:H7, Shiga toxin genes,
Salmonella, Listeria spp., Listeria monocytogenes and Cronobacter spp. The system is internationally recognized and
accepted based on its extensive third-party validations and approvals from organizations such as AOAC, AFNOR,
NordVal, Health Canada and the Brazilian
Ministry of Agriculture. The flexible, easy-to-run assays provide the fast and accurate results food processors and testing
labs require to both affordably and economically ensure the safety and integrity
of their products. For more information regarding Assurance GDS, contact BioControl Systems at 800.245.0113 or visit the
website at www.biocontrolsys.com.
