The Invasion of HeLa Cells by Salmonella typhimurium: Reversible and Irreversible Bacterial Attachment and the Role of Bacterial Motility

Abstract

The interactions which brought about the invasion of HeLa cells by Salmonella typhimurium consisted of a sequence of three phases. Initially, the motility of the bacteria facilitated their contact with the HeLa cells whereupon the bacteria became attached in a reversible manner (i.e. the bacteria could be removed readily by washing the HeLa cell monolayers with Hanks' Balanced Salt solution). The binding forces responsible for reversible attachment were probably the weak long-range forces of the secondary minimum level of attractive interactions between the bacterium and the HeLa cell. Reversible attachment was a necessary interlude before the bacteria became irreversibly attached to the surfaces of the HeLa cells (i.e. the bacteria were no longer removed by the washing procedure that removed the reversibly attached salmonellae). Irreversible attachment was prevented in solutions of low ionic strength; the forces responsible were probably those of the primary minimum generated between the HeLa cell and a bacterial adhesin which was capable of acting over only short distances between the reversibly attached bacterium and the HeLa cell (i.e. probably less than 15 nm). Only irreversibly attached bacteria proceeded to the third phase and were internalized by the HeLa cells.

Effect of measles-virus infection and interferon treatment on invasiveness of Shigella flexneri in HEp2-cell cultures

“…Earlier studies by Jones et al (1981) have shown that bacterial invasion in cell cultures may be divided into three phases: reversible adhesion, irreversible adhesion and invasion, each influenced by virus infection. One possibility is a change of electrical potential in the medium or the solution surrounding the cells.…”

Motility fractionation of bacteria by centrifugation

“…Modulating flagellar activity in response to a variety of chemical and physical stimuli, single-celled micro-organisms can effectively search for optimal environmental conditions 1 . Flagellar motility also plays an important role in medicine, being a major contributing factor to pathogenicity and colonization in bacteria like Vibrio cholerae [2][3][4] . More recently, the possibility of exploiting swimming micro-organisms as actuators for microstructures has extended the interest for flagellar motility to the physical domain of micro-engineering applications [5][6][7][8][9][10][11] .…”

The ability of Salmonella to enter mammalian cells is affected by bacterial growth state.

“…This entry process resembles phagocytosis and results in intracellular bacteria enclosed within membrane-bound vacuoles. To study the molecular details of the initial entry process, in vitro assays have been developed for quantitating the ability of Salmonella to adhere to and enter cultured mammalian cells (7)(8)(9)(10)(11)(12)(13). Recent studies (14)(15)(16) have examined the interaction of Salmonella with epithelial cells that have formed polarized monolayers in vitro (17).…”