Investigate the pathogenesis and environmental fitness of Listeria monocytogenes emerging clone SL87

L. monocytogenes is a life-threatening foodborne pathogen and the main etiology of human listeriosis, where it crosses intestinal barrier to cause systemic infection with a high mortality up to 30%. Further crossing of the placental barrier in pregnant women can result in miscarriage and fetal loss. Multilocus sequence typing (MLST) shows that in serogroup 4b the clonal complex (CC) 1, CC2, CC4 and CC6 are hypervirulent with high clinical frequency, whereas CC121 of serogroup 1/2a is associated to a food origin mainly infecting highly immunocompromised individuals. The hypervirulent CCs colonize better the intestinal tissues of mice, and the hypovirulent CCs show high prevalence of stress tolerance genes and better biofilm formation capacity in the presence of surface disinfectants. These findings highlight the heterogeneity in virulence and environmental fitness of L. monocytogenes, which reflects the ecological niches it evolves. Listeriosis has been a notifiable disease in Taiwan since 2018. We employed whole genome sequencing and core genome MLST to analyze the phylogeny of L. monocytogenes from patients and contaminated foods in Taiwan. From 2014 to 2019, we found that less than 8% of human infections were due to the hypervirulent MLST clones, while more than 35% of human infections and 50% of maternal-neonatal infections were due to sublineage (SL) 87 of serogroup 1/2b in Taiwan. Moreover, SL87 was the predominant (31.7%) SL in food. SL87 also has been one of the most prevalent clones in food products and maternal-neonatal infections in China, highlighting that SL87 may hold particular features in infection and environmental persistence, both of which had not been observed in one single CC in previous studies. However, the pathogenicity and environmental fitness of SL87 have never been studied. We aim to identify microbial factors that confer virulence and environmental persistence of SL87 to reduce listeriosis burden in Asia, which would even help to restrict its spread in the world. Whole genome sequencing shows that all the genomes of SL87 isolates contain LIPI-4, a gene cluster contributes to L. monocytogenes placental and brain invasion but is absent in most hypervirulent clones except for CC4, yet the underlying mechanism remains uncharacterized. We hypothesize that LIPI-4 is implicated in SL87 virulence and environmental adaptation. In this research proposal, we will study the virulence of SL87 as compared to that of the hyper- and hypo-virulent clones in the receptor-humanized mouse model and identified the implicated tissues as well as the cells by immunofluorescence staining (Aim 1). In vitro cell models based on the implicated tissues from in vivo mouse modeling will be employed to investigate bacterial invasion and intracellular proliferation efficiency, as well as immune responses of the infected cells (Aim 2). We will study environmental stress tolerance of SL87 as compared to that of other prevalent clones, and address potential correlation between the environmental fitness and intracellular survival (Aim 3). The implication of LIPI-4 in SL87 virulence and environmental adaptation will be investigated by LIPI-4 deletion mutants to study underlying molecular mechanism of LIPI-4 in SL87 (Aim 4). We anticipate to fully characterize the property of the emerging clone SL87 that mainly causes deadly listeriosis in Taiwan and Asia. Our findings will add a missing part to understand L. monocytogenes pathophysiology in a global manner, leading to better strategies to control L. monocytogenes food contaminations and treat listeriosis.

Project ID:PG11401-0048
External Project ID:NHRI-EX114-11120SC