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Salmonella as a Cancer Fighter

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Salmonella as a Cancer Fighter
Salmonella Bacteria

Salmonella Bacteria (red)

Image: Rocky Mountain Laboratories, NIAID, NIH

Salmonella as a Cancer Fighter

In an interesting twist of events, researchers at the Yale Cancer Center are using Salmonella bacteria to fight cancer. The first phase of human trials has started and the Salmonella is currently being administered to patients. In the trials, the patients are administered a genetically altered form of Salmonella and initially monitored at a hospital. After administration and subsequent monitoring, the patients are discharged.

Salmonella is commonly known for its role in food poisoning and septic shock. It is responsible for millions of foodborne illnesses each year. Salmonellosis, an illness caused by Salmonella, can be contracted by eating contaminated food. Symptoms of Salmonella infection include nausea, vomiting, abdominal pain and diarrhea.

Once inside the body, Salmonella use several methods to avoid destruction by the immune system. These bacteria excrete a protein that hampers the body's ability to produce an inflammatory response. This helps the bacteria avoid detection by the immune system and gives them enough time to reproduce throughout the body. The protein affects epithelial cells in the wall of the intestines and stomach. Salmonella also excrete proteins that enable them to take in zinc and other metal ions in spite of the attempts of the immune system to reduce these vital substances needed for bacterial survival.

Under optimal conditions, bacteria can reproduce rapidly, doubling in population size in a matter of minutes. Most bacteria reproduce asexually through a process called binary fission. During binary fission, a single DNA molecule replicates and both copies attach to the bacterial cell membrane. The cell membrane begins to grow between the two DNA molecules. Once the bacterium just about doubles its original size, the cell membrane begins to pinch inward. A cell wall then forms between the two DNA molecules dividing the original cell into two bacterial cells that are genetically identical. While binary fission is an effective way for bacteria to reproduce, it does produce problems for the organism. Since the cells produced through this type of reproduction are identical, they are all susceptible to the same types of antibiotics.

In the study, scientists altered the "wild type" of Salmonella. It is genetically modified and stripped of its ability to cause illness. Once stripped, the bacteria have been successfully used to shrink solid tumors in animals. The modified form also inhibits the growth of the tumors as well. With its pathogenicity removed, the Salmonella can target cancer cells with little adverse effects. In the test animals, scientists were able to substantially increase the life span of the animals that had melanoma cancer.

Based on the results obtained in the animal trials, the researchers are optimistic about the expected results in humans. The human trials will consist of several phases designed to determine if the altered Salmonella can successfully inhibit and shrink tumors. The patients in the study thus far all have tumors that are in or beneath the skin.

Virus Cancer Fighters

Bacteria are not the only microbes being used to fight cancer. Scientists and researchers are also focusing on ways to use viruses to treat cancer. They are creating genetically modified viruses that specifically target cancer cells. Some of these viruses infect and replicate in cancer cells, causing the cells to stop growing or shrink. Other studies focus on using viruses to improve immune system response. Some of the potential cancer fighting viruses being studied are the human reovirus, the vesicular stomatitis virus, and the measles virus.

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