Gut instinct: Salmonella bacteria's molecular tactics to cau...( Hundreds of trillions of bacteria ma...),Health

Hundreds of trillions of bacteria make their home in the vertebrate gut. Though many of these microbes perform helpful duties for their host, othersthe pathogensare unwelcome visitors, causing disease.

Salmonella typhimurium is one such pathogenic bacterium. It has evolved sophisticated means of growth, replication, transport and survival within the forbidding environment of the body, where it is responsible for most cases of food-borne illness. Yixin Shi, a researcher at Arizona State University's Biodesign Institute, has taken a keen interest in the regulatory mechanisms that allow Salmonella bacteria to overcome their surroundings and continuously modify both their own and their host's responses in order to stay alive.

By cooperating with the Dr. Roy Curtiss' lab in the Biodesign Institute, Shi's research, which appears in the Proceedings of the National Academy of Sciences, (PNAS) unveils a key survival circuit, which activates a signaling cascade, switching on or off a suite of genes necessary to circumvent the body's multiple defense mechanisms.

The bacteria are tenacious, surviving acidic pH conditions, digestive enzymes, bile salts, antimicrobial peptides, and other hazards as they pass through the stomach and intestine, and invade the mucosa of the small intestine. Once they make contact with the intestinal lumen, their goal is to secure a safe havenwithin the cells of the intestinal epithelium.

To reach this sanctuary, Salmonella first invite themselves in by secreting specific protein factors derived from a region of DNA known as the Salmonella Pathogenicity Island 1 or SPI-1. These factors trick the body, inducing the reorganization of the host cell's cytoskeleton. Epithelial cells respond to the Salmonella secretions by surrounding the bacterial cell in a membrane-bound balloonthe Salmonella Containing Vacuole or SCV.
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