Salmonella does not infect according to Scheme F

Researchers discover new penetration mechanism of diarrhea

Electron micrograph of Salmonella. © Manfred Rohde / HZI
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Scientists have discovered a previously unknown infection mechanism, which Salmonella makes use of when penetrating into intestinal cells: they can be drawn into it via special fibers of the host cells, so to speak, by muscle power. The bacteria therefore have more complex infection strategies than previously thought.

According to the World Health Organization, not only the number of salmonella infections is increasing steadily, but also the severity of infections has been increasing for several years. One of the reasons for this could be their sophisticated infection strategies. This astonishing variety in the choice of infection mechanisms may be the reason why salmonella can infect many different types of human cells and, in addition to humans, even a number of other hosts.

Actin fibers as a gateway

"Salmonella not only infect their host cells according to Scheme F, " explains Theresia Stradal, who was recently appointed by the Braunschweig Helmholtz Center for Infection Research to the University of Münster. "But so far, one knew only one single mechanism of infection - and that too not in all details, " adds Klemens Rottner, professor at the University of Bonn. The Salmonella infection pathway targets the actin cell skeleton of the host cell. Actin forms fine, very dynamic fiber structures that support the cell while making it mobile. These filaments are constantly being built up and taken down.

The most important core element for the construction of actin fibers is the Arp2 / 3 complex. All cell follicles and cell membrane disruptions are met by actin fibers. In the previously known route of infection Salmonella use the Arp2 / 3 complex to penetrate into the host cell: they activate the complex and thus ensure that the cell forms Membranausstülpungen, so-called "Ruffles". The bacteria can be surrounded by these "Ruffles" and take up inside the cell.

In the current study, the Braunschweig experts have succeeded in describing a hitherto completely unknown infection mechanism, which is published in the current issue of "Cell Host & Microbe". Although Salmonella manipulate the actin cell skeleton of the host cell in this new infection pathway, this time not through new filaments, but through their interaction with the motor protein myosin II. Salmonella can thus enter the cell interior without "ruffling". display

Stress fibers of the epithelial cells attract Salmonella into the cell interior

The interaction between actin and myosin is well known from muscle cells. In a muscle that is actively contracting, myosin and actin bundles get stuck together, gliding past one another, thus shortening the muscle: it contracts. This is similar in epithelial cells. Actin and myosin form so-called stress fibers, which resemble the contractile fibers in muscle cells.

These stress fibers are linked to the surface of the membrane and probably simply pull the bacteria in during an infection. Also in this way the salmonella has reached its goal the cell interior. "This pathway is completely independent of the Arp2 / 3 complex - the central signaling molecule of the classical invasion mechanism, " emphasizes Jan H nisch, who is working on this project as a postdoctoral researcher Has. (Cell Host Microbe, 2011 Apr 21; 9 (4): 273-85)

(Helmholtz Center for Infection Research, 26.04.2011 - NPO)