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Updated: Aug 9, 2026
An Allelotyping PCR for Identifying Salmonella enterica serovars Enteritidis, Hadar, Heidelberg, and Typhimurium
Published on: July 22, 2011
Identification of Salmonella typhimurium invasiveness loci
1Department of Biochemistry, University of British Columbia, Vancouver, Canada.
Abstract:
Salmonella typhimurium is capable of entering into (invading) nonphagocytic host cells. To systematically identify the bacterial genes necessary for this process, 15,000 Tn10dCm random transposon mutants of S. typhimurium were individually screened for invasiveness, using the human colonic epithelial Caco-2 cell line. Four hundred and eighty-eight mutants had decreased levels of invasiveness; most were nonmotile. However, five mutants, representing four loci, were completely motile. Further characterization of these five mutants showed that they were also unable to enter the dog kidney epithelial cell line MDCK and the mouse macrophage line J774.A1. In contrast to the parental strain, they were unable to disrupt the transepithelial resistance of polarized epithelial monolayers, nor were they able to penetrate across these epithelial barriers. Three of the four classes of mutants remained virulent in mice. The results confirm several aspects of S. typhimurium invasiveness: (i) intact motility enhances invasiveness of cultured cells; (ii) S. typhimurium invasiveness is multifactorial, and at least six distinct genetic loci are involved; and (iii) invasion loci involved in uptake into epithelial cells are also needed for uptake into cultured phagocytic cells. The results also emphasize that decreased levels of invasiveness eliminate bacterial penetration of polarized epithelial barriers and invasiveness loci mutants are not necessarily avirulent.
Insights
Salmonella typhimurium invasion requires specific bacterial genes. Motility enhances invasion, and multiple genetic loci are crucial for Salmonella to enter host cells and penetrate epithelial barriers.
Area of Science:
- Microbiology
- Cell Biology
- Genetics
Background:
- Salmonella typhimurium invades nonphagocytic host cells.
- Understanding the genetic basis of Salmonella invasion is crucial for controlling infections.
Purpose of the Study:
- To systematically identify bacterial genes essential for Salmonella typhimurium invasion.
- To investigate the role of motility in Salmonella invasiveness.
Main Methods:
- Screening of 15,000 random transposon mutants of S. typhimurium for invasiveness.
- Utilizing human colonic epithelial Caco-2 cell line for invasion assays.
- Characterizing mutant strains using epithelial cell lines (MDCK) and macrophage lines (J774.A1).
Main Results:
- Identified 488 mutants with decreased invasiveness; most were nonmotile.
- Five motile mutants, representing four loci, were unable to invade epithelial and phagocytic cells.
- Mutants were unable to disrupt transepithelial resistance or penetrate epithelial barriers.
- Three out of four mutant classes retained virulence in mice.
Conclusions:
- Intact motility enhances Salmonella typhimurium invasiveness.
- Salmonella invasion is a multifactorial process involving at least six genetic loci.
- Invasion loci are critical for both epithelial cell uptake and phagocytic cell entry.
- Reduced invasiveness impairs bacterial penetration of epithelial barriers, but does not always lead to avirulence.
