Food Safety Science Directorate, Science Branch, Canadian Food Inspection Agency, 1400 Merivale Road, Ottawa, Ontario, Canada K1A 0Y9.
ORCID: https://orcid.org/0000-0003-4786-3535 [H.Z.].
J Food Prot. 2021 Apr 1;84(4):647-654. doi: 10.4315/JFP-20-297.
Following two O121 Shiga toxin-producing Escherichia coli (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 prepackaged wheat flour samples were analyzed for Salmonella species, STEC, Listeria monocytogenes, aerobic colony count (ACC), total coliforms, and Escherichia 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: stx1, stx2, and their subtypes, eae, hlyA, and aggR. One O103:H25 STEC isolate carried virulence genes (stx1a+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 stx2a or stx2c genes and were considered to have the potential of causing diarrhea. The remaining non-O157 STEC isolate (stx2), while not a priority non-O157 STEC, was not available for sequencing; thus, its potential to cause illness is unknown. ACC, total coliforms, and E. coli were detected (≥0.48 log CFU/g) in 98.8, 72.6, and 0.6% of the flour samples. The mean counts of ACC were greater in whole wheat flour compared with 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 that 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.
在与小麦粉有关的两起 O121 型志贺毒素产生大肠杆菌（STEC）暴发之后，本研究旨在获取加拿大小麦粉中细菌病原体和指示菌水平的基线信息。对 347 份预包装小麦粉样品进行了沙门氏菌、STEC、单核细胞增生李斯特菌、需氧菌落计数（ACC）、总大肠菌群和大肠杆菌的分析。在任何样本中均未检测到沙门氏菌和 O157 STEC。在 2 份样本（0.6%）中检出低于检测限（<0.7 log CFU/g）的单核细胞增生李斯特菌。从 6 份样本（1.7%）中分离出非 O157 STEC，并对其 STEC 毒力基因：stx1、stx2 及其亚型、eae、hlyA 和 aggR 的存在情况进行了鉴定。一个 O103：H25 STEC 分离株携带已知能够引起人类腹泻和/或血性腹泻的毒力基因（stx1a+eae）。在其余 5 个非 O157 STEC 分离株中，有 4 个携带单个 stx2a 或 stx2c 基因，被认为有引起腹泻的潜力。其余非 O157 STEC 分离株（stx2）虽然不是优先非 O157 STEC，但无法进行测序；因此，其引起疾病的潜力尚不清楚。在 98.8%、72.6%和 0.6%的面粉样品中检测到 ACC、总大肠菌群和大肠杆菌（≥0.48 log CFU/g）。与其他测试的面粉类型相比，全麦面粉中 ACC 的平均计数更大（P < 0.001）。本研究结果表明，O157 STEC 和沙门氏菌的发生率较低，但具有引起人类腹泻疾病潜力的非 O157 STEC 在小麦粉中的发生率相对较高。因此，食用生面粉会增加 STEC 感染的可能性。需要进一步研究在食品生产系统和消费者中可能的风险缓解策略。
