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Salmonella Science Unsettled

The words “settled” and “science” are two words that should never go together.

Science Daily yesterday taught us that lesson once again and this time the subject was Salmonella.

Salmonella is not the newest pathogen on the block.  Call it what you will, conventional wisdom or settled science, it was assumed that Salmonella bacteria invaded intestinal cells where there was a ruffle or distinctive membrane wave.

Now, according to Science Daily, come researchers from the Helmholtz Centre for Infection Research for Braunschweig, Germany who say the Salmonella bacteria can invade with or without ruffles.

The Helmholtz Centre for Infection Research is a member of the Helmholtz Association, Germany’s largest scientific organization.

It boasts a community of scientists from more than 40 countries and operates with an annual budget of €47 million. The federal government of Germany and the state of Lower Saxony support the center.

“Based on our data, the molecular mechanism of infection employed by Salmonella has to be revised,” Klemens Rottner, head of the HZI research group “Cytoskeleton Dynamics” told Science Daily.

The group’s results were recently published in the journal, Cellular Microbiology.

Salmonella causes more foodborne illnesses than any of the other nasty bacteria. It is very adaptive and can survive with or without oxygen, making it able to thrive in a human intestine.

Eggs, egg dishes like mayonnaise, raw milk, meat, and sausages are all possible ways for a person to ingest the Salmonella bacteria.  Severe diarrhea and fever are among the symptoms of Salmonella infection, and anyone with a compromised immune system is especially at risk.

Science Daily said Salmonella’s long history aside, its “mechanisms of infection are incompletely understood.”

“The bacteria inject a protein cocktail using ‘molecular syringe’ into host cells, leading to dramatic rearrangement of cytoskeleton filaments below the cell membrane. As a result, membrane waves are formed, which enclose the bacteria, and apparently facilitate their invasion. Those characteristic membrane waves are called “ruffles,” the process is known as “ruffling.” Until now, researchers regarded the formation of these ruffles as absolutely essential for bacterial entry.

In a collaborative effort, HZI research groups “Cytoskeleton dynamics” and “Signalling and Motility” have now succeeded in shedding new light on the infection strategy of Salmonella.

“We wanted to improve our mechanistic understanding of how Salmonella invade their host cells,” said Jan Hänisch, who performed most experiments in the course of his PhD-thesis.

Cells that were engineered to lack those membrane ruffles normally induced during Salmonella infection still engulfed the bacteria.

“We showed for the first time that membrane ruffles are not essential for the bacteria to penetrate the host cell membrane.” 

Since ruffling was used so far as the signature of successful host cell invasion by this pathogen, the usefulness of such methods has to be reconsidered.

Finally, the researchers discovered a new piece in the puzzle of Salmonella entry, called WASH.

Science Daily says this novel factor promotes bacterial invasion by contributing to the formation of host cell cytoskeleton filaments important for entry.

“Our results have significant impact on the molecular and mechanistic understanding of the infection strategy used by this pathogen,” says Rottner, “and on the development of novel strategies to screen for potential inhibitors of the entry process in the future.”

© Food Safety News