Reduction of Salmonella Typhimurium following exposure to multiple hurdle treatments of heated, acidified organic acid salt solutions occurs via membrane destabilization. Salmonella enterica subsp. enterica serovar Typhimurium

The antimicrobial activity of organic acids in combination with non-chemical treatments was evaluated for inactivation of Salmonella Typhimurium. It was observed that the effectiveness of the multiple hurdle treatments were temperature and pH dependent and corresponded to the degree of organic acid lipophilicity. This led to the hypothesis that the loss in viability was due to cell membrane disruption. Evaluation of osmotic response, potassium ion leakage, and transmission electron micrographs confirmed effects on the cell membrane following treatment. Interestingly, all treatments, even those with no affect on viability, such as with sodium acetate, resulted in measurable cellular stress. Microarray experiments explored the specific response of S. Typhimurium to sodium acetate and sodium propionate, the most similar treatments in terms of pKa and ionic strength, and found little difference in the changes in gene expression following either treatment, despite their very different effects on viability. Taken together, the results reported support our hypothesis that following treatment with heated, acidified, organic acid salts, the loss of S. Typhimurium viability is at least in part due to membrane damage and the more lipophilic the organic acid the more effective the treatment. Overall, the data presented here indicate that a combined thermal, acidified sodium propionate treatment can provide a simple, yet effective antimicrobial treatment to combat Salmonella. Overall design: We have strategically designed a multiple hurdle intervention employing various organic acid salts [sodium acetate (SA), sodium lactate, and sodium propionate (SP)], pH, and temperature hurdles into one treatment against S. Typhimurium. Previous research in our lab has shown similar treatments to be highly effective against S. Typhimurium. Here, we further investigate the range of effectiveness as well as the mechanism of action behind this multiple hurdle treatment using viability, osmotic response, potassium leakage, and transmission electron microscopy studies. Total bacterial RNA was isolated as previously described and the RNA samples were then converted to fluorescently-labeled cDNA and hybridized to S. Typhimurium microarrays version 8 (NIAID's Pathogen Functional Genomics Resource Center).

本研究针对鼠伤寒沙门氏菌（Salmonella Typhimurium）的灭活效果，评估了有机酸与非化学处理联用的抗菌活性。研究发现，多屏障处理的有效性呈温度与pH依赖性，且与有机酸的亲脂性程度相关。据此我们提出假设：菌体活力丧失源于细胞膜破坏。通过渗透响应、钾离子渗漏及透射电子显微成像实验的评估，证实了处理后菌体细胞膜受到的影响。值得注意的是，所有处理（即便对菌体活力无影响的处理，如乙酸钠处理）均引发了可检测到的细胞应激反应。基因芯片（microarray）实验探究了鼠伤寒沙门氏菌对乙酸钠与丙酸钠的特异性响应——这两种处理在pKa与离子强度方面最为相似——结果发现，尽管二者对菌体活力的影响差异巨大，但处理后基因表达的变化几乎无显著差异。综上，本研究结果支持我们的假设：经加热酸化的有机酸盐处理后，鼠伤寒沙门氏菌的活力丧失至少部分源于细胞膜损伤，且有机酸亲脂性越强，处理效果越佳。本研究数据表明，联合使用热酸化丙酸钠的处理方式可作为一种简便且高效的抗沙门氏菌抗菌策略。实验整体设计：我们采用策略性设计，将多种有机酸盐[乙酸钠（SA）、乳酸钠及丙酸钠（SP）]、pH与温度屏障整合为一套针对鼠伤寒沙门氏菌的多屏障干预处理方案。本实验室此前的研究已证实，类似的处理方案对鼠伤寒沙门氏菌具有高效抑制效果。本研究进一步通过菌体活力检测、渗透响应实验、钾离子渗漏实验及透射电子显微镜观察，探究该多屏障处理方案的有效范围及其作用机制。按照此前报道的方法分离总细菌RNA，随后将RNA样本转化为荧光标记的互补DNA（cDNA），并与第8版鼠伤寒沙门氏菌基因芯片（由美国国家过敏和传染病研究所（NIAID）病原体功能基因组资源中心提供）进行杂交。