A Comparison of the ATP Generating Pathways Used by S. Typhimurium to Fuel Replication within Human and Murine Macrophage and Epithelial Cell Lines.

Amanda C Chidlaw,Arthur Thompson,Gwenaelle Le Gall,Karsten Tedin,Steven D Bowden,Enriqueta Garcia-Gutierrez,Yousef Abu Kwaik,David J Kelly

doi:10.1371/journal.pone.0150687

Abstract

The metabolism of S. Typhimurium within infected host cells plays a fundamental role in virulence since it enables intracellular proliferation and dissemination and affects the innate immune response. An essential requirement for the intracellular replication of S. Typhimurium is the need to regenerate ATP. The metabolic route used to fulfil this requirement is the subject of the present study. For infection models we used human and murine epithelial and macrophage cell lines. The epithelial cell lines were mICc12, a transimmortalised murine colon enterocyte cell line that shows many of the characteristics of a primary epithelial cell line, and HeLa cells. The model macrophage cell lines were THP-1A human monocyte/macrophages and RAW 264.7 murine macrophages. Using a mutational approach combined with an exometabolomic analysis, we showed that neither fermentative metabolism nor anaerobic respiration play major roles in energy generation in any of the cell lines studied. Rather, we identified overflow metabolism to acetate and lactate as the foremost route by which S. Typhimurium fulfils its energy requirements.

Highlights

Salmonella is an enteric pathogen responsible for a variety of disease outcomes in humans and animals ranging from self-limited gastroenteritis to lethal typhoid fever
Typhimurium within the macrophage and epithelial cell lines used in this study suggested hexose sugar(s) were a major catabolic substrate
Typhimurium ΔpflBΔldhA strain for its ability to replicate in the epithelial and macrophage cell lines used in this study, we found that there was no significant difference compared to the parent strain for any of the cell lines (Fig 3B), implying that fermentative metabolism is not necessary for intracellular replication

Summary

Introduction

Salmonella is an enteric pathogen responsible for a variety of disease outcomes in humans and animals ranging from self-limited gastroenteritis to lethal typhoid fever. It is estimated that worldwide, typhoidal and non-typhoidal Salmonella infections result in an estimated 20 and 98.3 million human cases each year, of which 200,000 and 155,000 result in death respectively [1, 2]. Salmonella invades epithelial cells lining the small intestine, mediated by Salmonella Pathogenicity Island 1 (SPI1) which encodes a type 3 secretion system (T3SS) which injects effector proteins into the host cell to facilitate uptake of bacteria (invasion) [3]. Intracellular Salmonella deploy a second T3SS encoded within SPI2, which modifies the initial membrane-bound compartment or phagosome to form the ‘Salmonella. Salmonella passes through the gut wall and is phagocytosed by macrophages which can carry the pathogen to systemic sites within the host. Typhimurium within certain organs, at least within the murine infection model [5]

Methods

Results

Conclusion