Salmonella enters a dormant state within human epithelial cells for persistent infection

PLoS Pathog. 2021 Apr 30;17(4):e1009550. doi: 10.1371/journal.ppat.1009550. eCollection 2021 Apr.

Abstract

Salmonella Typhimurium (S. Typhimurium) is an enteric bacterium capable of invading a wide range of hosts, including rodents and humans. It targets different host cell types showing different intracellular lifestyles. S. Typhimurium colonizes different intracellular niches and is able to either actively divide at various rates or remain dormant to persist. A comprehensive tool to determine these distinct S. Typhimurium lifestyles remains lacking. Here we developed a novel fluorescent reporter, Salmonella INtracellular Analyzer (SINA), compatible for fluorescence microscopy and flow cytometry in single-bacterium level quantification. This identified a S. Typhimurium subpopulation in infected epithelial cells that exhibits a unique phenotype in comparison to the previously documented vacuolar or cytosolic S. Typhimurium. This subpopulation entered a dormant state in a vesicular compartment distinct from the conventional Salmonella-containing vacuoles (SCV) as well as the previously reported niche of dormant S. Typhimurium in macrophages. The dormant S. Typhimurium inside enterocytes were viable and expressed Salmonella Pathogenicity Island 2 (SPI-2) virulence factors at later time points. We found that the formation of these dormant S. Typhimurium is not triggered by the loss of SPI-2 effector secretion but it is regulated by (p)ppGpp-mediated stringent response through RelA and SpoT. We predict that intraepithelial dormant S. Typhimurium represents an important pathogen niche and provides an alternative strategy for S. Typhimurium pathogenicity and its persistence.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 3T3 Cells
  • Animals
  • Caco-2 Cells
  • Epithelial Cells / microbiology*
  • Epithelial Cells / pathology
  • Genomic Islands / genetics
  • HeLa Cells
  • Humans
  • Mice
  • Salmonella Infections / microbiology*
  • Salmonella Infections / pathology
  • Salmonella typhimurium / genetics
  • Salmonella typhimurium / pathogenicity
  • Salmonella typhimurium / physiology*
  • THP-1 Cells
  • Vacuoles / microbiology
  • Vacuoles / pathology
  • Virulence Factors / genetics
  • Virus Latency / genetics
  • Virus Latency / physiology*

Substances

  • Virulence Factors

Grants and funding

This research was supported by fellowships from Croucher Foundation (HK) and Fondation pour la Recherche Médicale (FRM) to C.H.L. and Y.Y.C.. C.H.L. is part of the Pasteur - Paris University (PPU) International PhD Program. J.E. is supported by the ERC-CoG “Endosubvert”. The Enninga lab is part of the LabEx IBEID and Milieu Interieure. AM and PB are supported for equipment from the French Government Programme Investissements d’Avenir France BioImaging (FBI, N° ANR-10-INSB-04-01) and are also members of the LabEx IBEID. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.