Data_Sheet_1_Influence of temperature and pH on induction of Shiga toxin Stx1a in Escherichia coli.PDF

Shiga toxin-producing strains represent pathogenic group that is of concern in food production. The present study evaluated forty-eight E. coli isolates (11 with intact stx gene, while remaining isolates presented only stx-fragments) for Shiga toxin production. The four most expressive stx-producers (O26, O103, O145, and O157) were selected to evaluate effects of pH (3.5, 4.5, and 7) and temperature (35, 40, and 50°C). After determining acid stress effects in media on Stx-induction, we mimicked “in natura” conditions using milk, apple, and orange juices. Only isolates that showed the presence of intact stx gene (11/48) produced Shiga toxin. In addition, acid pH had a role in down-regulating the production of Shiga toxin, in both lactic acid and juices. In contrast, non-lethal heating (40°C), when in neutral pH and milk was a favorable environment to induce Shiga toxin. Lastly, two isolates (O26 and O103) showed a higher capacity to produce Shiga toxin and were included in a genomic cluster with other E. coli involved in worldwide foodborne outbreaks. The induction of this toxin when subjected to 40°C may represent a potential risk to the consumer, since the pathogenic effect of oral ingestion of Shiga toxin has already been proved in an animal model.

志贺毒素产生菌株构成了一类在食品生产中引起关注的致病菌群。本研究评估了48株大肠杆菌分离株（其中11株携带完整的stx基因，而其余分离株仅呈现stx片段）的志贺毒素产生能力。选取了四种表达最强的stx产生菌株（O26、O103、O145和O157）以评估pH值（3.5、4.5和7）和温度（35、40和50°C）的影响。在确定培养基中酸胁迫对Stx诱导作用后，我们使用牛奶、苹果汁和橙汁模拟“自然状态”条件。仅有携带完整stx基因的分离株（48株中的11株）能够产生志贺毒素。此外，酸性pH值在降低乳酸和果汁中志贺毒素的产生中起到了作用。相反，非致命性加热（40°C）在pH中性且存在牛奶的环境中，成为了诱导志贺毒素的有利条件。最后，两个分离株（O26和O103）表现出较高的志贺毒素产生能力，并被纳入与其他参与全球食源性疾病爆发的肠杆菌相关的基因组聚类中。在40°C条件下，该毒素的诱导可能对消费者构成潜在风险，因为志贺毒素经口摄入的致病效应已在动物模型中得到证实。