Shigella flexneri can do what E. coli cannot.

• Position: Food-Borne Illness

A pathogen annually blamed for an estimated 50,000,000 cases of food-borne illness defeats a host's immune response by using a fat-snipping enzyme to cut off cellular communication, report researchers at the University of Texas Southwestern Medical Center, Dallas.

"Our findings provide insight into severe bacterial infectious diseases, as well as some forms of cancer, in which the attachment of fat molecules to proteins is an essential feature of the disease process," explains Neal Alto, assistant professor of microbiology.

The research group discovered a scissor-like enzyme that specifically cuts off functionally essential fatty acids from proteins. "The one we studied in particular--a 14-carbon saturated fatty acid called myristic acid--has received a lot of attention due to its crucial role in the transformation of normal cells to cancer cells and for promoting cancer cell growth."

Because of the fat's importance in human disease, researchers have tried for years to identify effective methods to remove them from proteins.

"To our amazement, bacteria have invented the precise tool for the job," Alto marvels.

The bacteria used in this study, Shigella flexneri, are able to cross the intestinal wall and infect immune cells. Other intestinal bacteria, such as E. coli, are unable to do this. Once Shigella encounters immune system cells, including white blood cells such as macrophages, the bacteria use a needle-like complex to...