Prevalence of Salmonella and Pathogenic E. coli in Raw Wheat and the Need for Control

In a recently published study, the research shows that Salmonella and pathogenic E. coli is found in raw wheat, and with that, can be found in raw flour.   A total of 5,176 wheat samples were tested for enterohemorrhagic Escherichia coli (EHEC), Salmonella spp., Listeria spp., and L. monocytogenes.

• Salmonella was in 1.23% of the samples (average level of 0.110 MPN/g), 
• EHECs occurred in 0.44% of the samples (0.039 MPN/g), 
• Listeria spp. occurred in 0.08% of samples (0.020 MPN/g), but L. monocytogenes was not detected.

A few important discussion points:

• "Contamination sources are diverse and vary with several conditions, including weather, temperature, precipitation, time of flowering, and time of harvest."   So there is no silver bullet in eliminating this contamination from getting on the raw product.
• "There are two main pathways in which the presence of pathogens in wheat flour can cause human illness: (i) by the consumption of raw dough and (ii) through cross-contamination. The widespread use of wheat products in foods and the occurrence of outbreaks associated with wheat products confirm that eating raw wheat products poses a risk for foodborne illnesses."  As processors as well as consumers, these vegetative pathogens must be considered as being potentially present, and with that, we need to have a process to eliminate the organism (baking) and procedures against cross contamination with the raw flour (cleaning).

Journal of Food Protection
https://jfoodprotection.org/doi/full/10.4315/0362-028X.JFP-18-345
Occurrence and Levels of Salmonella, Enterohemorrhagic Escherichia coli, and Listeria in Raw Wheat
Volume 82, Issue 6 (June 2019) 

SAMUEL P.  MYODA,1  STEFANIE  GILBRETH,2  DEANN  AKINS-LEWENTHAL,3  SEANA K.  DAVIDSON,1 and  MANSOUR  SAMADPOUR1*
1IEH Laboratories & Consulting Group, 15300 Bothell Way N.E., Lake Forest Park, Washington 98155 
2The WhiteWave Foods Company, 1225 Seventeenth Street, Suite 1000, Denver, Colorado 80202 
3ConAgra Foods, Inc., One ConAgra Drive, Omaha, Nebraska 68102, USA 
 *Author for correspondence. Tel: 206-522-5432; Fax: 206-306-8883; E-mail: ms@iehinc.com. 

ABSTRACT


Wheat flour has been implicated in several outbreaks of foodborne illness in recent years, yet little information is available regarding microbial pathogens in wheat and wheat flour. Information about microbial pathogens in wheat is needed to develop effective methods to prevent foodborne illnesses caused by wheat products. From 2012 to 2014, we conducted a baseline study to determine the prevalence and levels of pathogens in wheat samples taken before milling. A total of 5,176 wheat samples were tested for enterohemorrhagic Escherichia coli (EHEC), Salmonella spp., Listeria spp., and L. monocytogenes. Positive samples were assayed for most probable numbers (MPNs), and isolates were fingerprinted by pulsed-field gel electrophoresis (PFGE). The rate of detection of each pathogen tested was as follows: Salmonella was in 1.23% of the samples (average level of 0.110 MPN/g), EHECs occurred in 0.44% of the samples (0.039 MPN/g), and Listeria spp. occurred in 0.08% of samples (0.020 MPN/g), but L. monocytogenes was not detected. The PFGE assessment found a high diversity for all organisms. All EHEC PFGE patterns (22 of 22) were unique, and 39 of 47 Salmonella patterns (83%) were unique. These results indicate a diverse background of naturally occurring organisms. These findings suggest that the microbial contamination is coming from diverse sources and provide no evidence in support of a specific pathogen load. Altogether, our surveillance study shows that contamination of wheat with pathogens is clearly evident and poses a foodborne illness risk.