Vaccination: Increasing Your Shot at a Long, Healthy Life

Vaccinations save lives. It doesn’t get much simpler than that. Today, vaccinations exist for a variety of diseases, including measles, tetanus, and everyone’s least favorite wintertime malady, influenza (i.e., the flu). But how are these vaccines developed? More important, are they safe?


A number of illnesses and diseases can be prevented through vaccination. (Photo credit: Richard Shock/Corbis)

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Delivering Vaccines Through Reengineered Food Poisoning Microbes

Researchers based at the Monash Institute of Pharmaceutical Sciences located at Monash University in Melbourne, Australia have discovered a way to deliver a vaccine orally with the help of a genetically engineered harmless version of the dangerous bacteria Listeria monocytogenes.

L. monocytogenes lives in soil and water. Foods such as fruits or vegetables may become contaminated with Listeria from the soil. Food from animal sources, such as meat or dairy products, may become contaminated from infected animals (which often show no symptoms of infection). If present, the Listeria bacterium is normally killed during the pasteurization process or cooking. However, improper food handling following processing can result in L. monocytogenes contamination.

Contamination by L. monocytogenes results in the food-borne illness called listeriosis. Symptoms of listeriosis include fever, muscle aches, and gastrointestinal conditions such as nausea or diarrhea. Listeriosis can also spread into the nervous system, leading to headaches, confusion, stiff neck, loss of balance, or convulsions. Those most susceptible to Listeria infections include pregnant women, infants, the elderly, and those with compromised immune systems.

Listeria is effective because it is able to survive the harsh, acidic conditions of the stomach and, using a protein called invasin, is able to penetrate epithelial host cells in the gastrointestinal tract. Colin Pouton and his colleagues at Monash University exploited this characteristic in developing their oral vaccine using a modified L. monocytogenes as the carrier. Oral vaccines are typically not effective because they are destroyed by stomach acid; since this is not a problem for the Listeria bacterium, this quality makes Listeria an excellent way to transport a vaccine.

In their research, the scientists created a new strain of L. monocytogenes that rendered the bacteria harmless and could instead by packed full of medicine or a vaccine. The thought was that the modified Listeria bacterium could be used to infect the recipient with a beneficial vaccine. The scientists also made the new strain of L. monocytogenes suicidal, meaning that the bacteria burst and die after entering the host cells.

In a trial run using intestinal cells grown in the lab, the scientists showed that the modified Listeria strain was able to successfully infiltrate the cells, deliver the intended protein, and then die, causing no harm to the intestinal cells themselves. Though encouraged by these early findings, more research will be necessary before this oral vaccination can be used in human subjects.

The results of the scientists research were published in the journal Molecular Pharmaceutics. Scientists who contributed to this research include Cheng-Yi Kuo, Shubhra Sinha, Jalal A. Jazayeri, and Colin W. Pouton.

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