Canadian Research Institute for Food Safety, Department of Food Science, University of Guelph, Guelph, ON, N1G 2W1, Canada.
Department of Food Science, University of Guelph, Guelph, ON, N1G 2W1, Canada.
Probiotics Antimicrob Proteins. 2020 Jun;12(2):577-588. doi: 10.1007/s12602-019-09574-1.
Invasion of Salmonella into host intestinal epithelial cells requires the expression of virulence genes. In this study, cell culture models of human intestinal cells (mucus-producing HT29-MTX cells, absorptive Caco-2 cells, and combined cocultures of the two) were used to determine the effects of Lactococcus lactis subsp. cremoris treatments (exopolysaccharide producing and nonproducing strains) on the virulence gene expression of Salmonella Typhimurium and its mutant lacking the oligopeptide permease subunit A (ΔoppA). During the course of epithelial cell (HT29-MTX, Caco-2, and combined) infection by Salmonella Typhimurium DT104, improved barrier function was reflected by increased transepithelial electrical resistance in cells treated with both strains of L. lactis subsp. cremoris. In addition, virulence gene expression was downregulated, accompanied with lower numbers of invasive bacteria into epithelial cells in the presence of L. lactis subsp. cremoris treatments. Similarly, virulence gene expression of Salmonella was also suppressed when coincubated with overnight cultures of both L. lactis subsp. cremoris strains in the absence of epithelial cells. However, in medium or in the presence of cell cultures, Salmonella lacking the OppA permease function remained virulent. HT29-MTX cells and combined cultures stimulated by Salmonella Typhimurium DT104 showed significantly lower secretion levels of pro-inflammatory cytokine IL-8 after treatment with L. lactis subsp. cremoris cell suspensions. Contrarily, these responses were not observed during infection with S. Typhimurium ΔoppA. Both the exopolysaccharide producing and nonproducing strains of L. lactis subsp. cremoris JFR1 exhibited an antivirulence effect against S. Typhimurium DT104 although no significant difference between the two strains was observed. Our results show that an intact peptide transporter is essential for the suppression of Salmonella virulence genes which leads to the protection of the barrier function in the cell culture models studied.
沙门氏菌侵入宿主肠道上皮细胞需要表达毒力基因。在这项研究中，使用了人肠道细胞（产生粘液的 HT29-MTX 细胞、吸收性 Caco-2 细胞以及两者的混合培养物）的细胞培养模型，以确定乳球菌乳亚种（产外多糖和非产外多糖菌株）处理对肠炎沙门氏菌及其突变体（缺乏寡肽渗透酶亚基 A 的突变体）毒力基因表达的影响。在沙门氏菌 Typhimurium DT104 感染上皮细胞（HT29-MTX、Caco-2 和混合培养物）的过程中，用两种乳球菌乳亚种处理的细胞的跨上皮电阻增加，这反映了屏障功能得到改善。此外，在乳球菌乳亚种处理存在的情况下，侵袭性细菌进入上皮细胞的数量减少，同时伴随着毒力基因表达下调。同样，当不存在上皮细胞时，将两种乳球菌乳亚种 overnight 培养物共同孵育也会抑制沙门氏菌的毒力基因表达。然而，在培养基或存在细胞培养物的情况下，缺乏 OppA 渗透酶功能的沙门氏菌仍然具有毒力。用沙门氏菌 Typhimurium DT104 刺激的 HT29-MTX 细胞和混合培养物在用乳球菌乳亚种细胞悬浮液处理后，促炎细胞因子 IL-8 的分泌水平明显降低。相反，在用 S. Typhimurium ΔoppA 感染时，未观察到这些反应。产外多糖和非产外多糖的乳球菌乳亚种 JFR1 对肠炎沙门氏菌 DT104 均表现出抗病毒作用，尽管两种菌株之间没有观察到显著差异。我们的研究结果表明，完整的肽转运体对于抑制沙门氏菌毒力基因至关重要，这导致了所研究的细胞培养模型中屏障功能的保护。
