Category Archives: E.coli O121

Research – Microbiological Survey of Wheat Flour Sold at Retail in Canada, 2018-2019

Journal of Food Protection

Following two O121 STEC outbreaks linked to wheat flour, this study was conducted to gain baseline information on the occurrence of bacterial pathogens and levels of indicator organisms in wheat flour in Canada. A total of 347 pre-packaged wheat flour samples were analyzed for Salmonella spp., Shiga Toxin-Producing Escherichia coli (STEC), Listeria monocytogenes ( L. monocytogenes ) , aerobic colony count (ACC), total coliforms, and generic Escherichia coli ( E. coli ) . Salmonella spp. and O157 STEC were not detected in any of the samples. L. monocytogenes was identified in two samples (0.6%) at levels below the limit of detection (<0.7 log CFU/g). Non-O157 STEC were isolated from six samples (1.7%) and were characterized for the presence of STEC virulence genes: stx 1, stx 2 and subtypes, eae , hlyA, and aggR . One O103:H25 STEC isolate carried virulence genes ( stx 1 a + eae ) that are known to be capable of causing diarrhea and/or bloody diarrhea in humans. Of the five remaining non-O157 STEC isolates, four carried single stx 2a or stx 2c genes and were considered to have the potential of causing diarrhea. The remaining non-O157 STEC isolate ( stx 2 ), while not a priority non-O157 STEC was not available for sequencing and thus its potential to cause illness is unknown. ACC, total coliforms, and generic E. coli were detected   in 98.8%, 72.6% and 0.6% of the flour samples. The mean counts of ACC were greater in whole-wheat flour as compared to the other flour types tested ( p <0.001). The results of this study suggest that the occurrence of O157 STEC and Salmonella  is low, but the occurrence of non-O157 STEC in wheat flour with the potential to cause human illness of diarrhea is relatively common. Therefore, the consumption of raw flour could increase the likelihood of STEC infections. Further research is merited for potential risk mitigation strategies within the food production system and with consumers.

Research – Thermal Resistance of Single Strains of Shiga Toxin-Producing Escherichia coli O121:H19 and O157:H7 Based on Culture Preparation Method and Osmolyte-Reduced Water Activity

Journal of Food Protection

Pathogen thermal resistance studies on low-water activity foods (LWAF) use a variety of methods to inoculate food, as well as strategies to reduce water activity, which can influence thermal resistance observations. This study investigated effects of culture preparation method and osmolyte-induced water activity on thermal resistance of two Shiga toxin-producing Escherichia coli (STEC; O121:H19, O157:H7) challenged with isothermal conditions, determining D – and z -values for each isolate (56, 59, and 62 ° C). Tryptic Soy Broth (TSB) and Agar (lawn cultures) were compared. D -values of broth cultures were significantly and consistently larger than those of lawn cultures, and O121 was significantly more resistant than O157, but only at 56 ° C ( p < 0.05). To compare potential effects of water activity on STEC thermal resistance, cells were suspended in osmolyte solutions with varying water activity: high (TSB, a w 0.99), intermediate (61% glycerol or 26% NaCl, a w 0.75), and low (82% glycerol, a w 0.5). In most instances, STEC in high-water activity broth exhibited greater heat resistance compared to reduced-water activity solutions, except the glycerol intermediate-water activity solution (a w 0.75). Magnitudes varied with strain and temperature. The z -values of lawn cultures were significantly lower than those of broth cultures ( p < 0.05), but there were only some differences between high-a w and reduced-a w samples. There were no significant differences of z -values based on strain type. These results highlight that thermal resistance can be affected by culture preparation and that osmolyte-induced changes to water activity influence thermal inactivation of STEC by varying magnitudes. These results emphasize the challenges between extrapolating results from lab inactivation kinetic experiments to determine the inactivation of low water activity foods, especially those considered dry in nature.

USA -USDA Will Expand non-O157 STEC Testing to Ground Beef

Food Poisoning Bulletin

According to an announcement in the Federal Register, the USDA will expand non-O157 STEC (Shiga toxin-producing E. coli) testing to ground beef, bench trim, and other raw ground beef components. The non-O157 strains include what’s called the “Big Six” E. coli strains: E. coli O26, O45, O103, O111, O121, and O145.

Research – Shiga toxin-producing Escherichia coli (STEC) and food: attribution, characterization, and monitoring


Strains of pathogenic Escherichia coli that are characterized by their ability to
produce Shiga toxins are referred to as Shiga toxin-producing E. coli (STEC). STEC
are an important cause of foodborne disease and infections have been associated with a wide range of human clinical illnesses ranging from mild non-bloody
diarrhoea to bloody diarrhoea (BD) and haemolytic uraemic syndrome (HUS)
which often includes kidney failure. A high proportion of patients are hospitalized,
some develop end-stage renal disease (ESRD) and some die.
The Codex Committee on Food Hygiene (CCFH) has discussed the issue of STEC
in foods since its 45th Session, and at the 47th Session, in November 2015, it was
agreed that it was an important issue to be addressed (REP 16/FH, 2015)2
. To
commence this work, the CCFH requested the Food and Agriculture Organization
(FAO) and the World Health Organization (WHO) to develop a report compiling
and synthesizing available relevant information, using existing reviews where
possible, on STEC. The CCFH noted that further work on STEC in food, including
the commodities to be focused on, would be determined based on the outputs of
the FAO/WHO consultation.
The information requested by CCFH is divided into three main areas: the global
burden of disease and source attribution; hazard identification and characterization; and monitoring, including the status of the currently available analytical
methods. This report provides an overview of the work undertaken in response to
the request from the CCFH and provides the conclusions and advice of the Expert
Group based on the currently available information.

Research – Evaluation of Bactericidal Effects of Phenyllactic Acid on Escherichia coli O157:H7 and Salmonella Typhimurium on Beef Meat

Journal of Food Protection


Bactericidal effects of various concentrations of phenyllactic acid on Shiga toxin–producing Escherichia coli (STEC), including E. coli O157:H7, O26:H11, O103:H2, and O121:H19, and on Salmonella Typhimurium DT104 in pure culture and microplates assays were studied. Beef cuts were surface sprayed with phenyllactic acid or lactic acid for inactivation of E. coli O157:H7 and Salmonella Typhimurium. The 1.5% phenyllactic acid inactivated all inoculated E. coli O157:H7, O26:H11, O103:H2, and O121:H19 and Salmonella Typhimurium DT104 (>6-log reduction) within 1 min of contact at 21°C, whereas 1.5% lactic acid did not result in microbial reduction. Microplate assays (for STEC and Salmonella Typhimurium DT104 at 10 to 100 CFU per well) indicated that concentrations of 0.25% phenyllactic acid or 0.25% lactic acid inhibited the growth of STEC and Salmonella Typhimurium DT104 incubated at 37°C for 24 h. Treatment of beef with 1.5% lactic acid or 1.5% phenyllactic acid reduced E. coli O157:H7 by 0.22 and 0.38 log CFU/cm2, respectively, within 5 min and reduced Salmonella Typhimurium DT104 by 0.12 and 0.86 log CFU/cm2, respectively. When meat treated with 1.5% phenyllactic acid was frozen at −20°C, inactivation of E. coli O157 and Salmonella Typhimurium DT104 was enhanced by 1.06 and 1.46 log CFU/cm2, respectively. Thus, treatment of beef with 1.5% phenyllactic acid significantly reduced the population of E. coli O157:H7 and Salmonella.

  • Phenyllactic acid at 1.5% killed STEC and Salmonella (>6-log reduction) within 1 min.

  • The MIC of lactic and phenyllactic acids was 0.25%.

  • The bactericidal effect of phenyllactic acid on beef was enhanced by freezing.

Research -Shiga toxin-producing Escherichia coli survives storage in wheat flour for two years

Science Direct


Wheat flour has recently been recognised as an exposure vehicle for the foodborne pathogen Shiga toxin-producing Escherichia coli (STEC). Wheat flour milled on two sequential production days in October 2016, and implicated in a Canada wide outbreak of STEC O121:H19, was analysed for the presence of STEC in November 2018. Stored in sealed containers at ambient temperature, the water activity of individual flour samples was below 0.5 at 6 months post-milling and remained static or decreased slightly in individual samples during 18 months of additional storage. STEC O121 was isolated, with the same genotype (stx2aeaehlyA) and core genome multilocus sequence type as previous flour and clinical isolates associated with the outbreak. The result of this analysis demonstrates the potential for STEC to persist in wheat flour at levels associated with outbreak infections for periods of up to two years. This has implications for the potential for STEC to survive in other foods with low water activity.

Research – Survey of Intact and Nonintact Raw Pork Collected at Retail Stores in the Mid-Atlantic Region of the United States for the Seven Regulated Serogroups of Shiga Toxin–Producing Escherichia coli

Journal of Food Protection


A total of 514 raw pork samples (395 ground or nonintact and 119 intact samples) were purchased at retail stores in Pennsylvania, Delaware, and New Jersey between July and December 2017. All raw pork samples were screened for serogroup O26, O45, O103, O111, O121, O145, or O157:H7 cells of Shiga toxin–producing Escherichia coli (STEC-7) using standard microbiological and molecular methods. In short, 21 (5.3%) of the 395 ground or nonintact pork samples and 3 (3.4%) of the 119 intact pork samples tested positive via the BAX system real-time PCR assay for the stx and eae virulence genes and for the somatic O antigens for at least one of the STEC-7 serogroups. However, none of these 24 presumptive-positive pork samples subsequently yielded a viable isolate of STEC displaying a STEC-7 serogroup-specific surface antigen in combination with the stx and eae genes. These data suggest that cells of STEC serogroups O26, O45, O103, O111, O121, O145, or O157:H7 are not common in retail raw pork samples in the mid-Atlantic region of the United States.

  • None of the 514 retail raw pork samples were positive for STEC-7.

  • Four of 514 raw pork samples harbored E. coli of unknown serogroup containing stx and eae.

  • STEC-7 are uncommon in retail raw pork samples in the U.S. mid-Atlantic region.


USA – Outbreak Investigation of E. coli Linked to Ground Bison from Northfork Bison Distributions, July 2019


September 13, 2019

The U.S. Food and Drug Administration (FDA), along with the Centers for Disease Control and Prevention (CDC), state and local partners in the U.S., and with the support of the Canadian Food Inspection Agency (CFIA), investigated a multistate outbreak of E. coli O121 and E. coli O103 illnesses likely linked to ground bison supplied by Northfork Bison Distributions Inc. of Saint-Leonard, Québec, Canada.

On September 13, 2019, CDC announced that the outbreak appears to be over.

During the investigation, FDA and CDC analyzed traceback and epidemiological information to determine that ground bison supplied by Northfork Bison Distributions Inc. was the likely cause of the illnesses. FDA laboratory analysis of bison patties packed by the firm on February 26th, 2019, confirmed the presence of one of the outbreak strains of E. coli.

Northfork Bison Distributions Inc. was forthcoming with information to aid in the investigation, and publicly announced a voluntary recall on July 16, 2019. This recall included ground bison meat and bison patties produced between February 22 and April 30, 2019.

FDA regulates bison meat because the authority is not assigned specifically to the United States Department of Agriculture’s (USDA) Food Safety Inspection Service (FSIS) in the Federal Meat Inspection Act (FMIA).


Because the product is frozen and may still be in freezers, distributors, retailers and restaurants should not distribute, use or serve ground bison (including bison burgers) recalled by Northfork Bison Distributions Inc.

Consumers should not eat products prepared using recalled ground bison (including bison burgers) sold under the Northfork Bison label including bison burgers sold to retailers in 4 x 4-ounce packages with expiration dates through October 8, 2020.

Buffalo Burger Canadian Bison Meat

Research – Desiccation and Thermal Resistance of Escherichia coli O121 in Wheat Flour

Journal of Food Protection


Non-O157 Shiga toxin–producing Escherichia coli infections have recently been associated with wheat flour on two separate accounts in the United States and Canada. However, there is little information regarding the thermal resistance and longevity of non-O157 Shiga toxin–producing Escherichia coli during storage in low-moisture environments. The objectives of this study were to determine the thermal inactivation kinetics of E. coli O121 in wheat flour and to compare the thermal inactivation rates with those of other pathogens. Wheat flour, inoculated with E. coli O121, was equilibrated at 25°C to a water activity of 0.45 in a humidity-controlled conditioning chamber. Inoculated samples were treated isothermally at 70, 75, and 80°C, and posttreatment population survivor ratios were determined by plate counting. D– and z-values calculated with a log-linear model, were compared with those obtained in other studies. At 70, 75, and 80°C, the D-values for E. coli O121 were 18.16 ± 0.96, 6.47 ± 0.50, and 4.58 ± 0.40 min, respectively, and the z-value was 14.57 ± 2.21°C. Overall, E. coli O121 was observed to be slightly less thermally resistant than what has been previously reported for Salmonella Enteritidis PT30 in wheat flour as measured under the same conditions with the same methods.

  • Thermal resistance of E. coli O121 in wheat flour was studied.

  • E. coli O121 exhibited greater survival upon desiccation than E. coli O157:H7.

  • E. coli O121 was slightly less thermally resistant than was previously reported for Salmonella in wheat flour.

Information – Two varieties of E. coli behind multiple U.S. outbreak infections – O103 and O121

Food Safety News

This is a link to a  list of outbreaks in recent years that were caused by E. coli O103 and E. coli O121.