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Barcoded Consortium Infections Resolve Cell Type-Dependent Salmonella enterica Serovar Typhimurium Entry Mechanisms
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Biochemistry and Microbiology. Uppsala University, Science for Life Laboratory, SciLifeLab.ORCID iD: 0000-0002-9491-4000
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Biochemistry and Microbiology. Uppsala University, Science for Life Laboratory, SciLifeLab.
Swiss Fed Inst Technol, Inst Microbiol, Zurich, Switzerland.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Biochemistry and Microbiology. Uppsala University, Science for Life Laboratory, SciLifeLab.
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2019 (English)In: mBio, ISSN 2161-2129, E-ISSN 2150-7511, Vol. 10, no 3, article id e00603-19Article in journal (Refereed) Published
Abstract [en]

Bacterial host cell invasion mechanisms depend on the bacterium's virulence factors and the properties of the target cell. The enteropathogen Salmonella enterica serovar Typhimurium (S. Tm) invades epithelial cell types in the gut mucosa and a variety of immune cell types at later infection stages. The molecular mechanism(s) of host cell entry has, however, been studied predominantly in epithelial cell lines. S. Tm uses a type three secretion system (TTSS-1) to translocate effectors into the host cell cytosol, thereby sparking actin ruffle-dependent entry. The ruffles also fuel cooperative invasion by bystander bacteria. In addition, several TTSS-1-independent entry mechanisms exist, involving alternative S. Tm virulence factors, or the passive uptake of bacteria by phagocytosis. However, it remains ill-defined how S. Tm invasion mechanisms vary between host cells. Here, we developed an internally controlled and scalable method to map S. Tm invasion mechanisms across host cell types and conditions. The method relies on host cell infections with consortia of chromosomally tagged wild-type and mutant S. Tm strains, where the abundance of each strain can be quantified by qPCR or amplicon sequencing. Using this methodology, we quantified cooccurring TTSS-1-dependent, cooperative, and TTSS-1-independent invasion events in epithelial, monocyte, and macrophage cells. We found S. Tm invasion of epithelial cells and monocytes to proceed by a similar MOI-dependent mix of TTSS-1-dependent and cooperative mechanisms. TTSS-1-independent entry was more frequent in macrophages. Still, TTSS-1-dependent invasion dominated during the first minutes of interaction also with this cell type. Finally, the combined action of the SopB/SopE/SopE2 effectors was sufficient to explain TTSS-1-dependent invasion across both epithelial and phagocytic cells. IMPORTANCE Salmonella enterica serovar Typhimurium (S. Tm) is a widespread and broad-host-spectrum enteropathogen with the capacity to invade diverse cell types. Still, the molecular basis for the host cell invasion process has largely been inferred from studies of a few selected cell lines. Our work resolves the mechanisms that Salmonellae employ to invade prototypical host cell types, i.e., human epithelial, monocyte, and macrophage cells, at a previously unattainable level of temporal and quantitative precision. This highlights efficient bacterium-driven entry into innate immune cells and uncovers a type III secretion system effector module that dominates active bacterial invasion of not only epithelial cells but also monocytes and macrophages. The results are derived from a generalizable method, where we combine barcoding of the bacterial chromosome with mixed consortium infections of cultured host cells. The application of this methodology across bacterial species and infection models will provide a scalable means to address host-pathogen interactions in diverse contexts.

Place, publisher, year, edition, pages
AMER SOC MICROBIOLOGY , 2019. Vol. 10, no 3, article id e00603-19
Keywords [en]
Salmonella, bacterial invasion, genome barcoding, epithelial cells, macrophages, monocytes
National Category
Cell and Molecular Biology Microbiology in the medical area
Identifiers
URN: urn:nbn:se:uu:diva-390532DOI: 10.1128/mBio.00603-19ISI: 000473596500046PubMedID: 31113898OAI: oai:DiVA.org:uu-390532DiVA, id: diva2:1342278
Funder
Swedish Research Council, 2018-02223Swedish Research Council, 2015-00635Knut and Alice Wallenberg Foundation, 2016.0063Available from: 2019-08-13 Created: 2019-08-13 Last updated: 2019-08-13Bibliographically approved

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Di Martino, Maria LetiziaEk, ViktorEriksson, JensSellin, Mikael E.
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