<i>Notes from the Field:</i> An Outbreak of Shiga Toxin–Producing <i>Escherichia coli</i> O121 Infections Associated with Flour — Canada, 2016–2017

Morton, Vanessa; Cheng, Joyce; Sharma, D. K.; Kearney, Ashley

doi:10.15585/mmwr.mm6626a6

Cited by 14 publications

(9 citation statements)

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“…STEC O121 is among the top 6 non-O157 serotypes that are most frequently associated with human disease in the United States (Brooks et al, 2005;Gould et al, 2013;Luna-Gierke et al, 2014). Outbreaks of STEC O121 infection were reported worldwide with an HUS rate ranging from 7.1% to 27.3% (McCarthy et al, 2001;Yatsuyanagi et al, 2002;Luna-Gierke et al, 2014;Crowe et al, 2017;Morton et al, 2017). Besides waterborne illness, the common foods associated with STEC O121 infection include leafy greens, milk, cheese, and flours.…”

Section: Introductionmentioning

confidence: 99%

A Clonal Shiga Toxin–ProducingEscherichia coliO121:H19 Population Exhibits Diverse Carbon Utilization Patterns

Carter

Tan

Pham

et al. 2019

Foodborne Pathogens and Disease

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Shiga toxin-producing Escherichia coli (STEC) serotype O121:H19 is one of the major non-O157:H7 serotypes associated with severe human disease. Here we examined population structure, virulence potential, and metabolic profile of environmental STEC O121 strains recovered from a major produce production region in California and performed comparative analyses with STEC O121 clinical isolates. Multilocus sequence typing revealed that sequence type (ST)-655, a common ST in clinical strains, was the predominant genotype among the environmental strains. Phylotyping placed all STEC O121 strains in B1 group, a lineage containing other major non-O157 serogroups of STEC. Genes encoding different subtypes of Shiga toxin 1 and 2 were detected in O121, including stx 1a , stx 1d , stx 2a , and stx 2e. Furthermore, genes encoding intimin (eae) and enterohemolysin (ehxA) were detected in a majority of environmental strains (83.3%), suggesting that the majority of environmental STEC O121 strains are enterohemorrhagic E. coli. The STEC O121 strains with the same genotype were clustered together based on the carbon utilization pattern. Among the 122 carbon substrates that supported the growth of STEC O121 strains, 44 and 35 exhibited lineage (ST) and strain-specific metabolic profiles, respectively. Although clinical ST-655 strains displayed higher metabolic activity than environmental ST-655 strains for several carbon substrates, including l-alaninamide, 5-keto-d-gluconic acid, 3-O-b-dgalactopyranosyl-d-arabinose, a-ketoglutaric acid, and lactulose, a few environmental strains with the enhanced metabolic potential for the above substrates were detected. Variations in curli biogenesis and swimming motility were also observed in ST-655 strains, suggesting that phenotypic variants are widespread in STEC. Considering the ecological niches that STEC colonizes, increased metabolic potential for plant-derived carbohydrates, mucus-derived substrates, or secondary metabolites produced by the indigenous microorganisms might have been selected. Such traits would confer STEC competitive advantages and facilitate survival and adaptation of STEC population to a given niche, including infected humans.

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Section: Introductionmentioning

confidence: 99%

A Clonal Shiga Toxin–ProducingEscherichia coliO121:H19 Population Exhibits Diverse Carbon Utilization Patterns

Carter

Tan

Pham

et al. 2019

Foodborne Pathogens and Disease

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“…Changing stx1 detection may point to differences in insertion sites for the stx1 and stx2 phages of O121:H19 or may be related to an uncharacterized insertion sequence element in stx1 as previously documented [ 20 ] or proposed for stx2 [ 24 ]. In Canada, O121:H19 has been recently implicated in human disease outbreaks due to contaminated flour [ 60 ] and it is also likely not coincidental that serotypes of E. coli frequently implicated in human disease are those that show stability in stx1 and/or stx2 across laboratories and over time. O121 also showed the most diversity in STEC serotypes ( n = 4) detected upon initial isolation at LAB A and at LAB C. To our knowledge, one of these serotypes (O121:H32), has not been previously reported, and may be an emerging pathogen as the majority of serotypes in the present study with stable stx have been linked to human disease.…”

Section: Discussionmentioning

confidence: 99%

Variability in Characterizing Escherichia coli from Cattle Feces: A Cautionary Tale

Stanford¹,

Reuter²,

Hallewell

et al. 2018

Microorganisms

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Shiga toxin-producing Escherichia coli (STEC) are diverse bacteria, with seven serogroups (O26, O45, O103, O111, O121, O145, O157; “Top 7”) of interest due to their predominance in human disease. Confirmation of STEC relies on a combination of culturing, immunological and molecular assays, but no single gold standard for identification exists. In this study, we compared analysis of STEC between three independent laboratories (LAB) using different methodologies. In LAB A, colonies of Top 7 were picked after serogroup-specific immunomagnetic separation of feces from western-Canadian slaughter cattle. A fraction of each colony was tested by PCR (stx1, stx2, eae, O group), and Top 7 isolates were saved as glycerol stocks (n = 689). In LAB B, a subsample of isolates (n = 171) were evaluated for stx1 and stx2 using different primer sets. For this, approximately half of the PCR were performed using original DNA template provided by LAB A and half using DNA extracted from sub-cultured isolates. All Top 7 isolates were sub-cultured by LAB A and shipped to LAB C for traditional serotyping (TS) to determine O and H groups, with PCR-confirmation of virulence genes using a third set of primers. By TS, 76% of O groups (525/689) matched PCR-determined O groups. Lowest proportions (p < 0.05) of O group matches between PCR and TS (62.6% and 69.8%) occurred for O26 and O45 serogroups, respectively. PCR-detection of stx differed most between LAB A and LAB C. Excluding isolates where O groups by PCR and TS did not match, detection of stx1 was most consistent (p < 0.01) for O111 and O157:H7/NM. In contrast, for O45 and O103, stx1 was detected in >65% of isolates by LAB A and <5% by LAB C. Stx2 was only detected by LAB C in isolates of serogroups O121, O145, and O157:H7/NM. LAB B also detected stx2 in O26 and O157:H12/H29, while LAB A detected stx2 in all serogroups. Excluding O111 and O157:H7/NM, marked changes in stx detection were observed between initial isolation and sub-cultures of the same isolate. While multiple explanations exist for discordant O-typing between PCR and TS and for differences in stx detection across labs, these data suggest that assays for STEC classification may require re-evaluation and/or standardization.

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“…were identified as the hazard of concern. Wheat flour has been implicated in two outbreaks of O121 STEC infections in Canada between 2016 and 2017 (2,36).…”

Section: Highlightsmentioning

confidence: 99%

Microbiological Survey of Wheat Flour Sold at Retail in Canada, 2018 to 2019

Zhang

Yamamoto

Murphy

et al. 2021

Journal of Food Protection

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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.

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Notes from the Field: An Outbreak of Shiga Toxin–Producing Escherichia coli O121 Infections Associated with Flour — Canada, 2016–2017

Cited by 14 publications

References 0 publications

A Clonal Shiga Toxin–ProducingEscherichia coliO121:H19 Population Exhibits Diverse Carbon Utilization Patterns

A Clonal Shiga Toxin–ProducingEscherichia coliO121:H19 Population Exhibits Diverse Carbon Utilization Patterns

Variability in Characterizing Escherichia coli from Cattle Feces: A Cautionary Tale

Microbiological Survey of Wheat Flour Sold at Retail in Canada, 2018 to 2019

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