While several of Salmonella's proteins allow it to loosen up and punch through this latticework, Sun's team unexpectedly found that AvrA allows the bacteria to maintain these tight junctions. This ability reduces the body's inflammatory response and allows the bacteria to avoid detection by the immune system for some time, enabling the bacteria to survive in the host. The severe symptoms of infection, including nausea, vomiting, diarrhea, and abdominal cramps, typically hit anywhere from 8 to 72 hours after initial exposure to the bug.
"It's a surprising finding, which is why we've repeated our studies many times and done tests in different experimental models," said Sun, whose team studied the phenomenon in the laboratory, in mice, and in cultured human cells.
AvrA is one of several virulence proteins that Salmonella has at its disposal, using syringe-like molecular machinery to shoot toxins and proteins into cells just seconds after its first encounter with a cell in the small or large intestine. The protein is especially adept at functioning in low-acid locales like the gut and bears close resemblance to a virulence protein known as YopJ that is active in Yersinia the bug that caused the Black Plague.
Sun is one of several scientists who have shown that AvrA reduces inflammation in the body, acting to some degree like new arthritis medications by reducing the activity of an inflammatory molecule known as NF-Kappa B.
There are thousands of types of the bug. Sun studied Salmonella Typhimurium, one of the two most common types; that bacterium and Salmonella
|Contact: Tom Rickey|
University of Rochester Medical Center