ORLANDO – A microbiologist has uncovered an unknown mechanism that helps a deadly food-borne bacterium subvert healthy cells.

Listeria monocytogenes is a bacterium that can cause pregnant women to lose their foetuses and can trigger meningitis fatalities among the elderly or people with compromised immune systems.

The bacterium has been linked to outbreaks traced to food processing plants in the US and Canada. Those cases in eight states were linked to people eating contaminated sliced turkey meat.

Scientists have long known that Listeria spreads from one human cell to another. Bacteria growing in one cell move fast enough to create a finger-like structure that protrudes from the cell and pushes into an adjacent cell. The bacteria then infects the adjacent cell.

Keith Ireton, microbiology professor at the University of Central Florida (UCF) and his team have discovered a previously unknown second process that gradually overwhelms the second cell’s ability to defend itself from infection.

The plasma membrane, or outer layer, of healthy human cells normally exhibits tension. Such tension might be expected to prevent Listeria from spreading to adjacent uninfected cells.

However, Ireton’s lab found that a Listeria protein called InlC appears to relieve tension at the plasma membrane in infected cells, making it easier for moving bacteria to deform the membrane and then spread into adjacent, healthy cells.

“Our discovery could have relevance for bacterial pathogens that cause Shigellosis or Rocky Mountain spotted fever, as these bacteria resemble Listeria in their ability to move inside the host cell and spread,” Ireton says.

The report features in Nature Cell Biology.