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Salmonella pathogenicity island 2-encoded type III secretion system mediates exclusion of NADPH oxidase assembly from
A Gallois1, J R Klein, L A Allen
1The Inflammation Program and Department of Medicine, University of Iowa and the Veterans' Affairs Medical Center, Iowa City, IA 52242, USA.
Abstract:
Salmonella typhimurium requires a type III secretion system encoded by pathogenicity island (SPI)-2 to survive and proliferate within macrophages. This survival implies that S. typhimurium avoids or withstands bactericidal events targeted to the microbe-containing vacuole, which include intraphagosomal production of reactive oxygen species (ROS), phagosomal acidification, and delivery of hydrolytic enzymes to the phagosome via fusion with lysosomes. Recent evidence suggests that S. typhimurium alters ROS production by murine macrophages in an SPI-2-dependent manner. To gain insights into the mechanism by which S. typhimurium inhibits intraphagosomal ROS production, we analyzed the subcellular distribution of NADPH oxidase components during infection of human monocyte-derived macrophages by wild-type (WT) or several SPI-2 mutant strains of S. typhimurium. We found that the membrane component of the NADPH oxidase, flavocytochrome b(558), was actively excluded or rapidly removed from the phagosomal membrane of WT-infected monocyte-derived macrophages, thereby preventing assembly of the NADPH oxidase complex and intraphagosomal production of superoxide anion. In contrast, the NADPH oxidase assembled on and generated ROS in phagosomes containing SPI-2 mutant S. typhimurium. Subversion of NADPH oxidase assembly by S. typhimurium was accompanied by increased bacterial replication relative to that of SPI-2 mutant strains, suggesting that the ability of WT S. typhimurium to prevent NADPH oxidase assembly at the phagosomal membrane represents an important virulence factor influencing its intracellular survival.
Insights
Salmonella typhimurium prevents macrophage killing by blocking the assembly of NADPH oxidase, an enzyme complex that produces reactive oxygen species (ROS). This SPI-2 dependent mechanism allows the bacteria to survive and multiply within host cells.
Area of Science:
- Microbiology
- Immunology
- Cell Biology
Background:
- Salmonella typhimurium uses the SPI-2 secretion system to survive inside macrophages.
- Intracellular survival involves evading macrophage bactericidal mechanisms like reactive oxygen species (ROS).
Purpose of the Study:
- To investigate how Salmonella typhimurium inhibits intraphagosomal ROS production.
- To elucidate the mechanism of SPI-2's role in subverting macrophage defenses.
Main Methods:
- Analyzing the subcellular localization of NADPH oxidase components in infected human macrophages.
- Comparing wild-type S. typhimurium with SPI-2 mutant strains.
Main Results:
- Flavocytochrome b(558), a key NADPH oxidase component, was excluded from phagosomal membranes in wild-type S. typhimurium infections.
- NADPH oxidase assembled and produced ROS in phagosomes with SPI-2 mutant strains.
- Exclusion of NADPH oxidase correlated with increased bacterial replication.
Conclusions:
- Salmonella typhimurium actively prevents NADPH oxidase assembly on phagosomal membranes via SPI-2.
- This evasion of ROS production is a crucial virulence factor for intracellular bacterial survival and proliferation.