Naim F, Leblanc D, Messier S, Saucier L, Piette G, Houde A
Faculty of Veterinary Medicine, Department of Microbiology and Pathology, University of Montreal, C.P. 5000, Saint-Hyacinthe, Quebec, Canada, J2S 7C6.
Food Microbiol. 2006 May;23(3):231-40. doi: 10.1016/j.fm.2005.04.006. Epub 2005 Aug 1.
In order to study the effects of the fermentation-drying procedure and subsequent in vitro digestion on Shiga toxins (Stx) production by Escherichia coli O157:H7, dry sausages were inoculated during the formulation step with pure cultures of strains 5-1 and ATCC 43895. The inoculated sausages were submitted to a minimum (30 min, pH between 3.1 and 3.5) or a maximum (120 min at stepwise adjusting the pH downward) gastric challenge followed by a 240-min pancreatic challenge at pH 8.0 and 37 degrees C. Production of toxins by the overnight culture controls, assessed using the Vero cell assay, was dependent on the pathogen cell concentration. The effect of cell concentration was not relevant in sausage samples and data showed: (a) higher Stx production in contaminated sausage samples than in overnight cultures; (b) the lowest Stx levels were detected with undigested sausage samples; (c) the maximum gastric challenge enhanced Stx production, compared to minimally digested and undigested samples. Reverse transcriptase polymerase chain reaction (RT-PCR) performed on extracts from inoculated, digested (4.5-6 h process) and undigested sausages produced amplicons for both stx1 and stx2 mRNA, suggesting that post-stress expression of stx genes had occurred. Our data suggest that sub-lethal stresses imposed by the fermentation-drying procedure and subsequent digestion of ingested food (i.e. contaminated sausages) may affect the degree to which the surviving E. coli O157:H7 cells express their virulence in vivo.
为了研究发酵干燥过程及随后的体外消化对大肠杆菌O157:H7产生志贺毒素（Stx）的影响，在配方步骤中用5-1株和ATCC 43895菌株的纯培养物接种干香肠。对接种后的香肠进行最低限度（30分钟，pH值在3.1至3.5之间）或最大限度（逐步将pH值调低至120分钟）的胃部刺激，随后在pH值8.0和37摄氏度下进行240分钟的胰腺刺激。使用Vero细胞试验评估过夜培养对照产生毒素的情况，其取决于病原体细胞浓度。细胞浓度的影响在香肠样品中不相关，数据显示：（a）受污染香肠样品中的Stx产量高于过夜培养物；（b）未消化的香肠样品中检测到的Stx水平最低；（c）与最低限度消化和未消化的样品相比，最大程度的胃部刺激增强了Stx的产生。对接种、消化（4.5 - 6小时过程）和未消化香肠的提取物进行逆转录聚合酶链反应（RT-PCR），产生了stx1和stx2 mRNA的扩增子，表明stx基因在应激后发生了表达。我们的数据表明，发酵干燥过程以及随后摄入食物（即受污染的香肠）的消化所施加的亚致死应激可能会影响存活的大肠杆菌O157:H7细胞在体内表达其毒力的程度。
