Salmonella Typhimurium is Attracted to Egg Yolk and Repelled by Albumen.

Salmonella Typhimurium is the causative agent of non-typhoidal, foodborne salmonellosis. Contamination of hen eggs by the bacterium is a common source of S. Typhimurium infection. S. Typhimurium is peritrichous, and flagellum-dependent motility and chemotaxis are believed to facilitate egg contamination despite the presence of many antimicrobial egg components. We performed motility and chemotaxis assays to demonstrate that S. Typhimurium cells are attracted to egg yolks and are repelled by albumen. The bacterial flagellar motor shows bidirectional rotation, and counterclockwise-biased rotation allows cells to swim smoothly. A rotation assay for a single flagellum showed that, in comparison with thin albumen, the thick albumen more strongly affected the directional bias of the flagellar rotation, resulting in a remarkable suppression of the migration distance. Nevertheless, the S. Typhimurium cells retained positive chemotaxis toward the yolk in the presence of the albumens, suggesting that motility facilitates the growth of S. Typhimurium and survival in eggs.

Membrane vesicle protein PagC as a novel biomarker for detecting pathogenic Salmonella in the viable but not culturable state.

The viable but non-culturable (VBNC) state is a remarkable survival mechanism in which cells exist in a physiologically inactive state. Bacteria in the VBNC state do not form colonies, and thus, are difficult to detect using colony-based methods. As a result, VBNC bacteria are potentially virulent and can cause widespread contamination during food production. In the present study, we reported a novel biomarker, the membrane vesicle protein PagC, for the detection of VBNC Salmonella. Salmonella cells were chemically induced into the VBNC state by H2O2 treatment. The bacterial cells retained their shapes but were observed to release numerous membrane vesicles, which were accompanied by a transient PagC overexpression. Immunoblotting was performed to detect PagC in pathogenic strains, including Salmonella Enteritidis and S. Typhimurium, which are harmful and known to cause food-borne gastroenteritis in humans and other animals. Therefore, our findings demonstrated the potential use of PagC as a biomarker for the detection of VBNC Salmonella in food production.

Immortalization of Fetal Bovine Colon Epithelial Cells by Expression of Human Cyclin D1, Mutant Cyclin Dependent Kinase 4, and Telomerase Reverse Transcriptase: An In Vitro Model for Bacterial Infection.

Cattle are the economically important animals in human society. They are essential for the production of livestock products such as milk and meats. The production efficiency of livestock products is negatively impacted by infection with zoonotic pathogens. To prevent and control infectious diseases, it is important to understand the interaction between cattle tissue and pathogenic bacteria. In this study, we established an in vitro infection model of an immortalized bovine colon-derived epithelial cell line by transducing the cells with lentiviral vectors containing genes encoding cell cycle regulators cyclin D1, mutant cyclin dependent kinase 4 (CDK4), and human telomerase reverse transcriptase (TERT). The established cell line showed continuous cell proliferation, expression of epithelial markers, and an intact karyotype, indicating that the cells maintained their original nature as colon-derived epithelium. Furthermore, we exposed the established cell line to two strains of Salmonella enterica and EHEC. Interestingly, S. Typhimurium showed higher affinity for the established cell line and invaded the cytoplasm than S. Enteritidis. Quantitative RT-PCR revealed that gene expression of Toll-like receptor 1 (TLR1), TLR 2 and TLR 3, whereas TLR 4, 5 and 6 were not detectable in established cells. Our established immortalized colon-derived epithelial cell should be a useful tool for studies evaluating the molecular mechanisms underlying bacterial infection.