Biological Properties And Structure Of Virulence-related Genes In An Atypical L. Monocytogenes Strain Naturally Lacking InlAB Locus

Listeria monocytogenes is an important food-borne pathogen that can cause listeriosis in humans. Nowdays, Ministries of public health and food safety around the world have paid great attention to Listeria monocytogenens, which was listed as one of the four important food-borne pathogens by WHO.We found an atypical Listeria monocytogenes strain S10naturally lacking inlAB locus from115strains of different origins in our lab. This study focused on the following three parts.(1)Analysis of biological properties and virulence-related genes.The isolate S10, together with other7strains representing different serovars, were studied by biochemical profiling, genetic lineage analyses, adhesion assay in HeLa cells, virulence to mice, detection of virulence-associated genes detection and MLST. The results showed that the S10isolate belonged to lineage I and serovar1/2b, with carbohydrate fermentation and hemolytic characteristics typical of Listeria monocytogenes. This strain contained an almost whole set of infection-associasted genes and formed a sisiter branch with4b strain in the MLST scheme. However, this strain had reduced ability to adhere to HeLa cells and decreased pathogenicity to mice.(2)Analysis of gene structures surrounding the inlAB locus and estimation of their function. S10lacked the gene locus inlAB and their adjacent genes Imo0431, Imo0432, lmo0436and Imo0437, while Imo0430was the only gene amplified in this region, whose nucleotide identity was99.6%.94.0%and77.4%respectively compared to1/2a strain EGD,4b strain F2-365and4a strain HCC23.(3) Detection of different transcription level of internallin genes in S10using quantitative real-time PCR. Data showed that transcriptional levels of inlC2, inlD, inlE in S10were extremely higher than reference strain M1(p<0.01), while transcriptional levels of inlC, inlJ didn’t show remarkable differences(p>0.05). These results suggested that S10might upregulated transcriptional level of other internalin genes to successfully infect the host.In conclusion, the biological characteristics,virulence gene structure and differenece of transcriptional levels were studied in this assay, these results provided basis for further studying the internalization mechanism, and pathogenomics evolution of this organism.