Sheng L, Olsen S A, Hu J, Yue W, Means W J, Zhu M J
School of Food Science, Washington State University, Pullman, WA 99164, USA.
Department of Animal Science, University of Wyoming, Laramie, WY 82071, USA.
Int J Food Microbiol. 2016 Jul 16;229:24-32. doi: 10.1016/j.ijfoodmicro.2016.04.001. Epub 2016 Apr 8.
Non-O157 Shiga toxin producing Escherichia coli (STECs) have become a growing concern to the food industry. Grape seed extract (GSE), a byproduct of wine industry, is abundant in polyphenols that are known to be beneficial to health. The objective of this study was to evaluate the effect of GSE on the growth, quorum sensing, and virulence factors of Centers for Disease Control and Prevention (CDC) "top-six" non-O157 STECs. Minimal inhibitory concentration (MIC) of GSE was 2mg/ml against E. coli O26:H11, and 4mg/ml against the other non-O157 STECs tested. Minimal bactericidal concentration (MBC) was the same as MIC for all six non-O157 STECs tested. At 5×10(5)CFU/ml inoculation level, 4mg/ml GSE effectively inhibited the growth of all tested strains, while 0.25-2mg/ml GSE delayed bacterial growth. At a higher inoculation level (1×10(7)CFU/ml), GSE had less efficacy against the growth of the selected six non-O157 STECs. Its impact on bacterial virulence was then assessed at this inoculation level. Autoinducer-2 (AI-2) is a universal signal molecule mediating quorum sensing (QS). GSE at concentration as low as 0.5mg/ml dramatically reduced AI-2 production of all non-O157 STECs tested, with the inhibitory effect proportional to GSE levels. Consistent with diminished QS, GSE at concentration of 0.125mg/ml caused marked reduction of swimming motility of all motile non-O157 STECs tested. In agreement, GSE treatment reduced the production of flagella protein FliC and its regulator FliA in E. coli O103:H2 and E. coli O111:H2. Furthermore, 4mg/ml GSE inhibited the production of Shiga toxin, a major virulence factor, in E. coli O103:H2 and E. coli O111:H2. In summary, GSE inhibits the growth of "top-six" non-O157 STECs at the population level relevant to food contamination. At higher initial population, GSE suppresses QS with concomitant decrease in motility, flagella protein expression and Shiga toxin production. Thus, GSE has the potential to be used in food industry to control non-O157 STEC.
非O157产志贺毒素大肠杆菌（STECs）已成为食品行业日益关注的问题。葡萄籽提取物（GSE）是葡萄酒行业的副产品，富含已知对健康有益的多酚。本研究的目的是评估GSE对疾病控制和预防中心（CDC）“六大”非O157 STECs的生长、群体感应和毒力因子的影响。GSE对大肠杆菌O26:H11的最低抑菌浓度（MIC）为2mg/ml，对其他测试的非O157 STECs为4mg/ml。所有六种测试的非O157 STECs的最低杀菌浓度（MBC）与MIC相同。在5×10⁵CFU/ml的接种水平下，4mg/ml GSE有效抑制了所有测试菌株的生长，而0.25 - 2mg/ml GSE延迟了细菌生长。在较高的接种水平（1×10⁷CFU/ml）下，GSE对所选六种非O157 STECs生长的抑制效果较差。然后在此接种水平下评估其对细菌毒力的影响。自诱导物-2（AI-2）是介导群体感应（QS）的通用信号分子。低至0.5mg/ml浓度的GSE显著降低了所有测试的非O157 STECs的AI-2产生，抑制作用与GSE水平成正比。与群体感应减弱一致，0.125mg/ml浓度的GSE导致所有可运动的测试非O157 STECs的游动能力显著降低。同样，GSE处理降低了大肠杆菌O103:H2和大肠杆菌O111:H2中鞭毛蛋白FliC及其调节因子FliA的产生。此外，4mg/ml GSE抑制了大肠杆菌O103:H2和大肠杆菌O111:H2中主要毒力因子志贺毒素的产生。总之，GSE在与食品污染相关的群体水平上抑制“六大”非O157 STECs的生长。在较高的初始菌量下，GSE抑制群体感应，同时降低运动性、鞭毛蛋白表达和志贺毒素产生。因此，GSE有潜力在食品工业中用于控制非O157 STEC。
