How Salmonella Gets a Foothold in the Body

Researchers have discovered that once Salmonella enters the body, it works to hide its presence from the body's immune system. This trick gives the salmonell infection crucial time to multiply and spread before the body reacts. "That's bad news for the body," says Professor of Gastroenterology and Hepatology at The University of Rochester Medical Center, Dr. Jun Sun. "Salmonella is trickier than we imagined."

Leading a team of researchers, Sun found that Salmonella is equipped with a special protein that prevents inflammation during the initial infection. Inflammation is one of the early warning systems the body uses to rally its defenses. By preventing inflammation, the salmonella infection makes sure the body's immune system remains unaware of the infection for a much longer period of time. If the immune system detects invading germs earlier, it has a better chance of resisting the salmonella infection since there are fewer germs to destroy. Dr. Sun theorizes "It may be that Salmonella is especially equipped with tools to allow it to evade the immune system early on, growing quietly and then really making the host quite ill."

Perhaps this is why Salmonella can take up to three days to present symptoms once the victim is infected. The amount of time between the initial exposure and the first symptoms also complicates the effort of health authorities to quickly identify the source of the contamination.

Dr. Sun's research was funded by the National Institute of Diabetes and Digestive and Kidney Diseases. Her team included include Anne Liao, Yun Zhao, and Yinglin Xia of the University of Rochester; Elaine Petrof of Queen's University in Kingston, Ontario; and Erika Claud of the University of Chicago. According to Dr. Sun, "It's a surprising finding, which is why we've repeated our studies many times and done tests in different experimental models,"

Dr. Sun says that this biological stealth technology is present in 4 out of 5 types of Salmonella including Salmonella serotype Saintpaul, as well as the two most common strains: Salmonella enteritidis and Salmonella Typhimurium which cause more than 50% of diagnosed cases in humans.
The mechanism used by these types of Salmonella reduces the activity of an inflammatory molecule known as NF-Kappa B is much like some modern anti-arthritis medications. It also bears a striking similarity to a protein used for the same purpose by the micro organism Yersinia, which better known as the germ responsible for the Black Plague. This new finding reminds us, as Dr. Sun says, "Bacteria have been evolving for millions of years. That gives them some tricks that perhaps we don't understand yet."

Source: University of Rochester Medical Center . Salmonella: Trickier Than We Imagined. http://www.urmc.rochester.edu/pr/news/story.cfm?id=2036