Salmonella can hijack immune cells and use them to spread around the body. Experiments in mouse cells suggest the bacteria do this by disrupting electrical signals in the gut.
Our intestines have small electric fields, caused by charged ions, such as potassium and chloride, flowing in and out of intestinal cells. Salmonella infections, such as food poisoning, disrupt these electric fields as they damage the cells, which alerts the body’s immune cells to come and clean up the mess.
Usually, the immune system is good at limiting the infection to the gut. But sometimes Salmonella escapes by riding inside macrophages, a type of immune cell that don’t normally leave the gut, to other organs like the liver and spleen.
To investigate the process, Yaohui Sun at the University of California, Davis and his colleagues placed gut membrane cells from mice in an electric field to mimic an infected gut.
The team found without the presence of salmonella, nearly all macrophages moved towards the positively charged end of the field, corresponding to the interior of the intestines.
However, after engulfing Salmonella enteritidis, the most common species associated with food poisoning, about 41 per cent of macrophages reversed direction, moving towards the negatively charged end, corresponding to leaving of the gut.
We knew that salmonella has proteins that help them survive within macrophages, but It’s unclear how it flips the electric charge macrophages are attracted to, says Sun. It’s possible that bacteria release enzymes that damage the charge-sensing sugar structures on the macrophages’ surface, he says.
The finding can help develop treatments for diseases, says Sarah Fankhauser at Emory University at Georgia. This mechanism may be more common than just salmonella. For example, the bacterium that causes tuberculosis, also spreads using macrophages, and thus may use a similar strategy, she says.
Journal reference: PLOS Biology, DOI: 10.1371/journal.pbio.3000044
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