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

Abstract

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.

Draft Genome Sequences of Salmonella enterica subsp. diarizonae Serotype IIIb_61:I,v:1,5,(7) Strains Isolated from Wheat Grains

“…The interest in the microbiological safety of wheat grains is because foodborne illness outbreaks linked to wheat flour have been reported ( 2 ). Salmonella illnesses linked to wheat flour have been reported in the United States and other countries ( 4 – 6 ).…”

Shiga toxin-producing Escherichia coli (STEC) and atypical enteropathogenic E. coli (aEPEC) in Swedish retail wheat flour

“…The recovered isolates included the known human-pathogenic serotypes O26:H11 and O103:H2. A larger, more recent study performed in Canada isolated STEC from 1.7 % of 347 retail flour samples and recovered a likely pathogenic strain of O103:H25 [ 20 ].…”

Pasteurization of Salmonella spp. in black fungus (Auricularia auricula) powder by radio frequency heating

“…It can be added to dough to make various flour products (Fan et al, 2021; Yuan et al, 2017). In recent years, a series of public foodborne outbreaks by pathogenic bacteria have been associated with powder foods which is the typical low water activity (a w ) foods, such as flour, milk powder, vegetable spices (Henry and Fouladkhah, 2019; Jernberg et al, 2015; Zhang et al, 2020a). A serious Salmonella outbreak in North America in 2020 was linked to dried black fungus from China, and Japan also found Salmonella positive in dried black fungus from China in import inspection and requested to strengthen the inspection of Salmonella in black fungus (CDC, 2020).…”