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Expression of the Salmonella virulence plasmid gene spvB in cultured macrophages and nonphagocytic cells
1Department of Veterans Affairs Medical Center, San Diego, California 92161.
Abstract:
Certain serotypes of salmonellae carry virulence plasmids that greatly enhance the pathogenicity of these bacteria in experimentally infected mice. This phenotype is largely attributable to the 8-kb spv regulon. However, spv genes are not expressed while bacteria grow in vitro. We now show that spvB, which is required for virulence, is expressed rapidly after Salmonella dublin is ingested by cultured J774 and murine peritoneal macrophages and that expression is not affected by the alkalinization of intracellular vesicles. The level of induction of spvB is reduced when macrophages are pretreated with gamma interferon. spvB is also expressed in human and canine epithelial cell lines and a human hepatoma cell line. In all cases, spvB expression is dependent on the spvR gene, just as it is in stationary-phase cultures in vitro. These data suggest that spv virulence genes are expressed by intracellular salmonellae in vivo in response to a signal that is common to the intracellular compartments of cells that are invaded by salmonellae.
Insights
Salmonella virulence (spv) genes are expressed inside host cells, not in lab cultures. This rapid spvB gene expression in macrophages and epithelial cells indicates an in vivo response to intracellular signals.
Area of Science:
- Microbiology
- Bacterial Pathogenesis
- Molecular Biology
Background:
- Salmonella virulence plasmids enhance pathogenicity.
- The 8-kb spv regulon is a key factor in Salmonella pathogenicity.
- spv genes are typically not expressed during in vitro bacterial growth.
Purpose of the Study:
- To investigate the expression of spvB, a crucial virulence gene, in Salmonella Dublin within host cells.
- To determine the conditions affecting spvB expression inside macrophages and epithelial cells.
- To identify the regulatory mechanism controlling spvB expression in an intracellular environment.
Main Methods:
- Monitoring spvB gene expression in Salmonella Dublin after ingestion by J774 and murine peritoneal macrophages.
- Assessing the impact of intracellular vesicle alkalinization on spvB expression.
- Evaluating the effect of gamma interferon pretreatment on macrophage spvB induction.
- Examining spvB expression in human and canine epithelial cell lines and a human hepatoma cell line.
- Investigating the role of the spvR gene in regulating spvB expression.
Main Results:
- spvB is rapidly expressed by Salmonella Dublin within cultured macrophages and various human/canine cell lines.
- Intracellular vesicle alkalinization does not affect spvB expression.
- Gamma interferon pretreatment reduces spvB induction levels in macrophages.
- spvB expression is consistently dependent on the spvR gene, mirroring in vitro conditions.
Conclusions:
- Salmonella spv virulence genes are expressed intracellularly in vivo.
- Expression is triggered by a common signal present in intracellular compartments of invaded host cells.
- The spvR gene is essential for spvB expression in both intracellular and in vitro settings.