Microbiologists have discovered how two bacterial species move through the human body by “hitching a ride” on immune cells. The organisms in question are: Francisella tularensis, which causes the infection tularemia, and Salmonella enterica, a common cause of foodborne illness.
Tularemia is known as rabbit fever or deer fever. It is named after Tulare County, California. Like Lyme disease, the disease is spread by tick bites. Symptoms vary depending on the route of infection. The most common condition is the formation of ulcers at the site of infection. This can be accompanied by fever and muscle pain. The tularemia disease is highly virulent, only ten bacterial cells are sufficient to trigger an infection, with symptoms apparent within several hours.
Symptoms of Salmonella infection, as Karen Graham has reported, include diarrhoea, stomach cramps and sometimes vomiting and fever.
The investigation into the bacteria that cause these diseases has focused on macrophages. Macrophages are types of immune cells which engulf infectious agents. Both species of bacteria are adept at avoiding being swallowed by macrophages, and instead attach to the outside of the immune cells and use the cells are a mechanism for reaching other parts of the human body.
Moreover, if a macrophage became damaged or died, the bacteria appear to be able to move from macrophage to macrophage. This happens when cells collide with each other.
The bumping of cells into each other is a natural process called trogocytosis. Here cells collide in order to exchange surface proteins, after which they separate. At this stage, the bacteria use the opportunity to switch from one immune cell to another.
It is hoped the knowledge will provide a new means with which to fight certain bacterial infections.
The research was conducted at the UNC School of Medicine. The findings are published in the journal eLife, in a study headed “Trogocytosis-associated cell to cell spread of intracellular bacterial pathogens.”
