Shiga Toxins Stay in the Forefront of E. coli Research

STEC cause more than 265,000 illnesses in the U.S. annually, according to the CDC. Consuming food contaminated with STEC or having direct contact with fecal matter from STEC infected cattle and other ruminants cause most of these illnesses.

The STEC CAP research is focusing on the seven most dangerous serogroups (i.e. O157) or serotypes (i.e. O157:H7) of STEC (O157:H7 and six non-O157), plus a new one, O104:H4 that made its first widespread appearance in an outbreak in Europe in 2011, Dr. Moxley relates.

“Based on the three core pillars of this project, pre-harvest, post-harvest, and consumer research, the long-term goal is to reduce the occurrence and public health risks from STEC in beef using a quantitative microbial risk assessment (QMRA) platform, while preserving an economically viable and sustainable beef industry,” he explains. “To that end, we are energized by our multi-institutional effort that brings together complementary teams of the nation’s experts whose expertise spans the entire beef chain continuum.”

According to Dr. Moxley, in addition to STEC CAP’s overall goal, the project’s five objectives relative to STEC in beef are: 1) detection, 2) biology, 3) intervention, 4) risk analysis and assessment, and 5) risk management and communication.

Accomplishments Aplenty

Dr. Moxley is quick to boast that the STEC CAP grant, with work ongoing through December 2018, has yielded many significant outcomes and impacts, including at least 104 refereed journal articles to date, not to mention other important activities and outputs.

Relative to Objective 1, detection, new reagents and methods for detection and quantification of STEC in the beef chain (culture- and DNA-based, as well as immunological) have been developed, optimized, and validated. “The development and optimization of reagents and methods of detection and quantification has improved food safety by enhancing the removal of these organisms or contaminated products across the beef chain,” Dr. Moxley says.

With reference to Objective 2, biology, epidemiological studies have generated data and identified factors that influence the prevalence and concentration of STEC organisms in cattle, their environments, and on carcasses. “For example, hides were identified as the major source of microbial contamination in beef processing plants,” Dr. Moxley notes. “Microbiome studies on feedlot cattle determined that lower levels of hide bacterial diversity corresponded with non-O157 and O157 STEC contamination, and the presence of certain bacterial populations typically associated with soil occurred in the absence of these STEC populations.”

Focusing on Objective 3, intervention, multiple interventions to control non-O157 STEC at different steps of beef processing in plants were validated through research. “Through modifications, such as use of electrostatic spray or sprayed lethality in container methods, it was found that antimicrobial agents had increased efficacy through more uniform contact with target surfaces, yet reduced cost through reduced water usage,” Dr. Moxley says. “Data collected from packing plants helped identify processing steps where water recycling and reduction was needed. Changes made to these could result in 30 percent to 50 percent reductions in water usage, savings that in turn could pay for enhanced antimicrobial intervention in the plant.”

Interventions effective for STEC O157:H7 on non-intact beef were equally effective against the regulated types of non-O157 STEC, Dr. Moxley adds. “This information appreciably reduced the nature and scope of additional scientific studies needed for mitigation of the risk of STEC in beef and obviated the need to modify existing processing technologies or develop additional interventions specific for the regulated non-O157 STEC.” he emphasizes.

The project also conducted studies focusing on STEC translocation and end-point cooking temperatures on mechanically tenderized non-intact steaks to fill key data gaps for determining risk of blade tenderized and brine injected steaks compared to non-tenderized beef. “Federal regulatory agencies used data to update risk assessments, and support rules for labeling beef products that have been tenderized and, therefore, rendered non-intact,” Dr. Moxley points out. “Through this, guidance was given to Canadian authorities for similar labeling and rulemaking initiatives. The veal industry was provided with scientifically validated and USDA-approved antimicrobial carcass interventions for application as part of an effective veal slaughter hazard analysis critical control point program to control STEC with no adverse effects.”

QMRA for STEC

Addressing Objective 4, risk analysis and assessment, a working computer model of the QMRA for STEC has been developed. “The QMRA is the STEC CAP’s centerpiece and is what drives all research, education, and extension activities,” Dr. Moxley emphasizes. “The QMRA model estimates the risk associated with each regulated STEC serogroup to provide a basis for decision-making and optimal risk management. In addition, it estimates the value of intervention in decreasing the risk of product contamination and human disease, including the sensitivity of the system to control components. The QMRA model will allow both policy makers and beef processors to develop operating procedures that reduce risk and improve food safety.”