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Study sheds light on how food bugs infect cells

Research shows how some gut bacteria with long corkscrew-like structures stick to cells and help cause disease.

Illustration of bacterial flagella sticking to cell
Contrary to previous experiments, rotating flagella can play a role in cell membrane disruption. Image credit: Eliza Wolfson

Long corkscrew-like structures on Salmonella and E. coli bacteria, which are common causes of food poisoning, may play an additional role in how they infect cells, a study has shown.

Scientists found that the structures, called flagella, interact with the surface of cells, deforming the cell membrane, which may help the bacteria attach to host cells.

Flagella taken from these bacteria were also able to enhance the function of key proteins involved in host cell shape, the scientists observed, which may help bacterial attachment and invasion.

The findings will inform further investigations looking at interactions between bacteria with flagella and their host cells, which may aid strategies to prevent bacterial disease.

Crossing the cell surface

The study, led by researchers from the Roslin Institute and the University of Bristol, focused on bacterial flagella – long, corkscrew-shaped filaments that rotate to allow bacteria to swim  ̶  because these are known to help bacteria stick to host cells, an important early step in infection.

Scientists used fluorescence and electron microscopes to look at interactions between bacterial flagella and host cells from cattle and pigs, the natural reservoirs of E. coli and Salmonella.

They observed flagella apparently inside host cells, but this was difficult to confirm with a fluorescence microscope. Using an electron microscope, they were able to see deformed cell membranes around and next to flagella, suggesting that rotating flagella might be warping them.

Data from haemolysis  ̶  rupturing of red blood cells  ̶  indicated that, contrary to previous experiments, rotating flagella can play a role in cell membrane disruption.

We saw what looked like very close interactions of bacterial flagella with host cells, but it was challenging to explore just how close, because both flagella and host cell membranes are extremely thin and move about. A lot of big questions are raised by the possibility that flagella may disrupt cell membranes.

Dr Eliza Wolfson, Scientific Illustrator, formerly of the Roslin Institute and University of Bristol

These results give us a clearer picture of the first steps of infection by food poisoning bacteria. We hope that further study will give us a better understanding of exactly what role flagella play, and that this will help in the development of control strategies.

Professor David Gally, Roslin Institute

The study is published in the journal Microbiology and was funded by the Biotechnology and Biological Sciences Research Council, part of UK Research and Innovation.

** The Roslin Institute is part of the University of Edinburgh’s Royal (Dick) School of Veterinary Studies. **

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