Identification of Salmonella typhimurium invasiveness loci

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.

The fliA gene encoding sigma 28 in Yersinia enterocolitica

“…Jones et al (28) have shown that the ability of a nonmotile S. typhimurium isolate to enter Peyer's patches in vivo is reduced 10-fold compared with that of the wild type. In agreement with this observation, motility seems to be required for S. typhimurium invasion of epithelial cells in vitro (6,30). In C. jejuni, flagella also play a role in penetration of cultured cells of human intestinal epithelial origin, but they are not involved in adhesion to epithelial cells (22).…”

Pathogenesis of Human Enterovirulent Bacteria: Lessons from Cultured, Fully Differentiated Human Colon Cancer Cell Lines

“…In addition, it has been observed that flagella of S. enterica serovar Enteritidis are involved in the association with and invasion of fully differentiated cells (382)(383)(384). Using three of the four classes of mutants that remain virulent in mice, Betts and Finlay (375) observed that S. Typhimurium invasiveness requires intact motility and at least six distinct genetic loci. CorA, the primary or "housekeeping" Mg 2ϩ channel, appears to be involved in the expression of several S. Typhimurium virulence factors, since a corA mutant strain loses swimming motility and expresses lower levels of InvH and SipC, accompanied by a decreased ability to invade fully differentiated Caco-2 cells (385).…”

“…Following the disruption of the cell membrane, S. Typhimurium penetrated the cells and appeared in the basolateral medium of the fully differentiated Caco-2 cell monolayer. F-actin filament rearrangement and morphological changes at the apical domain of Caco-2 cells are essential for the entry of S. Typhimurium (374)(375)(376)(377). The T3SS-1 effector SipA, which directly binds F actin, thus modulating actin dynamics and facilitating bacterial entry, has been found to be preferentially associated with peripheral cortical F-actin filaments but not with stress fibers in infected fully differentiated Caco-2 cells (390).…”

The Actin-Polymerizing Activity of SipA Is Not Essential for Salmonella enterica Serovar Typhimurium-Induced Mucosal Inflammation

“…S. Typhimurium has the ability to enter nonphagocytic eukaryotic cells and to exist as intracellular parasites inside Salmonella-containing vacuoles (SCVs) (3)(4)(5). Several studies have identified genes that are required for Salmonella pathogenesis, in particular, for Salmonella invasion of nonphagocytic cells (6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17). Many of these virulence genes and operons are located in large genetic elements of the Salmonella chromosome.…”