Study On The Pathogenicity Of Listeria Monocytogenes ST87 Strains In China

Listeria monocytogenes (LM) is a major food-borne pathogen that has the capacity to cause severe infections, such as febrile gastroenteritis, fetal loss, abortion, septicemia, meningitis. Listeriosis is uncommon in China but L. monocytogenes has been isolated from foods and food processing environments in China. Some Chinese strains had the same sequence type with the isolates related to human listeriosis in some developed coutries. We study the pathogenicity of the LM isolates from food and patients belonging to ST87 which was prevalent in China Here we employ molecular and phenotypic subtyping schemes and virulent traits analyses tools to characterize these strains, and to evaluate its possible harmfulness in human and food. In vitro invasion assays, significant differences in invasion were detected, which divided the strains into two groups:highly-invasive strains and weakly-invasive strains. Clinical isolates were more invasive to HT-29 cells than the food isolates. A positive correlation was observed for most isolates; i.e. the isolates with high invasion to HT-29 cells also expressed high levels of inlA mRNA while isolates with low invasion had low levels of inlA mRNA. The strains showed significantly different hemolytic activity, but there were no difference between human isolates and food isolates. Most strains had similar cytotoxic to HT-29 cells. We also measured the levels of cytokines interleukin-1?(IL-1?),IL-6,IL-8, monocyte chemotactic protein-1(MCP-1) and RANTES, and found these cytokines production levels were in accordance with the invasion capacities of the strains, with a high invasion capacity corresponding to high cytokines production.In conclusion, the results of this study indicated that ST87 Listeria monocytogenes strains from listerisis patients in China had high virulence properties, and the same as some food isolates, suggested that they have the potential to cause humans listeriosis outbreak in humans in China although it is unknown why seldom listeriosis occurs in China. So there is a need to develop surveillance and prevention strategies to prevent emergence and outbreaks of human L. monocytogenes infections in China.This study established a research platform of L.monocytogenes pathogenic mechanism, and provided the basis for a more in-depth study.