Risk reduction: Irradiation of strawberries

Strawberries are vulnerable to harboring microbial pathogens because they are generally not washed due to their perishable nature. The focus of this study was to quantify the reduction in infection risks associated with non-O157 Shiga toxin producing E. coli serotypes contaminated strawberries if the strawberries are exposed to low doses ∼1 kGy (kiloGray) of electron beam (eBeam) irradiation.

strawberry.irradiationA cocktail of six serotypes of non O157 E. coli namely, O26:H11, O45:H2, O103:H2, O111:NM, O121:H19, and O145 was employed. Strawberry puree rather than whole strawberries were used in this study to ensure dose uniformity that is critical for accurate interpretation of microbial reduction.

The results show that when these serotypes are exposed to ≤1 kGy eBeam dose, there is approximately 4-log reduction in their numbers when they are present within a strawberry matrix (puree). Quantitative microbial risk assessments suggest that if a typical strawberry serving (150 g) was heavily contaminated (∼105 CFU/serving size), 2 out of 10 susceptible individuals (20%) would get sick (without eBeam treatment). However, if these contaminated strawberries had been treated with 1 kGy of eBeam dose, the infection risks would have be significantly reduced to approximately 4 out of every 100,000 individuals (0.004%). Similarly, even at low levels of contamination (∼102 CFU/serving), the infection risks would be reduced from 6 out of 10,000 susceptible individuals to approximately 4 out of 100 million susceptible individuals.

Quantifying the reduction in potential infection risks from non-O157 Shiga toxin producing E. coli in strawberries by low dose electron beam processing

Food Control; Available online 7 May 2016; doi:10.1016/j.foodcont.2016.04.057

Shima Shayanfara, Kristina Menab, Suresh D. Pillaia


Listeria: Is zero tolerance consistent with risk-reduction

Tom Karst of The Packer writes it doesn’t seem quite right that many fresh produce processors aren’t testing for listeria on food contact surfaces in their facilities. Aren’t belts and other parts of a processing plant that touch product an important place to look for pathogens that might be present on food? 

listeria4Yet, that is the way it is, based on industry’s evaluation of Food and Drug Administration Guidance. Because any finding of listeria on food contact surfaces could result in an immediate recall situation, many in the industry believe the FDA’s zero-tolerance policy inhibits companies from testing food contact surfaces. 

The FDA is considering changing some of their guidance on listeria testing. Industry experts a new version of the guidance by late this year or early next year.  Perhaps the FDA will give more flexibility for companies to test for the listeria species – indicating the presence of the family of bacteria, but not necessarily the dangerous Listeria monocytogenes strain. Perhaps the FDA will establish a tolerance level for Listeria monocytogenes, though that doesn’t seem likely.

Karst got some standard answers from government spokesthingies, but got a more proactive answer from Martin Bucknavage, a Pennsylvania State University Department of Food Science food safety extension specialist, who said fresh produce and other food companies have to do a better job of understanding the presence of listeria within their operations and take stronger corrective actions. Most of the testing now being done for listeria is pre-operational and on nonfood contact areas, which he said has limited use.

“They have got to get more proactive and get rid of it,” he said. “I think it is time to batten down the hatches, get aggressive on sampling and put this thing to bed.”

Summertime Blues: lowering bacterial loads from farm-to-fork means fewer sick people

Every summer, government agencies at the local state and federal level in Western countries around the world warn consumers to be extra super-duper careful when barbecuing, because the incidence of foodborne illness, especially E. coli O157:H7, goes up in the warm summer months, and this is because consumers are doing dumb things at the grill.

I never believed it – consumers, food service workers, humans are capable of doing dumb things wherever they are cooking – but it was another standard line in the blame-the-consumer approach to food safety risk reduction.

There has been plenty of evidence over the years to show that the increase in human illnesses in summer months is strongly correlated to overall increases in E. coli O157:H7 loads in cattle in summer months.

Lower the loads, reduce the risk.

Most food safety interventions are designed to reduce or eliminate pathogen loads – to lower the number of harmful bugs from farm-to-fork. A piece of highly-contaminated meat can wreck cross-contamination havoc in a food service or home kitchen.

A new paper in Foodborne Pathogens and Disease by researchers from the U.S. Department of Agriculture and the University of Nebraska-Lincoln uses models representing seasonal variation in E. coli O157:H7 loads in the farm-to-fork continuum, and concludes that summertime cooking is as risky as the rest of the year.

The authors write:

“A plausible explanation for the increase in E. coli O157:H7 illness during the summer is poor consumer storage and cooking practices associated with meals prepared and cooked outdoors (e.g., picnics and barbeques). If these practices are major contributors to human illness, then an effective mitigation strategy could be additional labeling and consumer education regarding the need to maintain meat products at temperatures sufficiently low to avoid bacterial growth during transportation to outdoor venues and to cook products to a sufficient temperature when grilling. Conversely, if summer storage and cooking practices are not responsible for a large proportion of summer illnesses, a more effective mitigation strategy would reduce the seasonal effect of E. coli O157:H7 contamination at the preharvest stage or during the production and processing of beef. …

“The seasonal change in the probability of exposure to a contaminated serving is the primary driver of the season pattern in illnesses, rather than any seasonal changes in consumer storage and handling.”

The complete abstract is below.

Determining relationships between the seasonal occurrence of Escherichia coli O157:H7 in live cattle, ground beef, and humans
Foodborne Pathogens and Disease. October 2010, 7(10): 1247-1254
Michael S. Williams, James L. Withee, Eric D. Ebel, Nathan E. Bauer, Wayne D. Schlosser, William T. Disney, David R. Smith, Rodney A. Moxley
The prevalence and concentration of many foodborne pathogens exhibit seasonal patterns at different stages of the farm-to-table continuum. Escherichia coli O157:H7 is one such pathogen. While numerous studies have described the seasonal trend of E. coli O157:H7 in live cattle, ground beef, and human cases, it is difficult to relate the results from these different studies and determine the interrelationships that drive the seasonal pattern of beef-related human illnesses. This study uses a common modeling approach, which facilitates the comparisons across data sets, to relate prevalence in live cattle to raw ground beef and human illness. The results support an intuitive model where a seasonal rise of E. coli O157:H7 in cattle drives increased ground beef prevalence and a corresponding rise in the human case rate. We also demonstrate the use of these models to assess the public health impact of consumer behaviors. We present an example that suggests that the probability of illness, associated with summertime cooking and handling practices, is not substantially higher than the baseline probability associated with more conventional cooking and handling practices during the remainder of the year.