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Unexpected Bacterial Similarities May Lead to Vaccine

Unexpected Bacterial Similarities May Lead to Vaccine

In the March 31 issue of Science, researchers from MIT and the Louisiana State University Health Sciences Center report finding surprising similarities between two bacteria with widely differing lifestyles in how they establish chronic infections in mammals and plants. Upon first glance, agriculturally important bacterium Rhizobium meliloti and pathogen Brucella abortus have no features in common. However, Graham Walker, professor of biology at MIT, reports that both bacteria interact with their hosts similarly.

While all organisms require nitrogen, plants cannot utilize it until it has been converted into ammonia. This conversion is accomplished by leguminous plants with the help of rhizobia, bacteria residing in the soil. The bacteria invade the nodules on the roots of the plants and are then taken up by the plants. “You can look at it as a chronic infection of the plant, although unlike other infections, this is beneficial to the organism,” Walker said. “The plant allows itself to be invaded by the bacteria. In this way the plant gets ammonia and the bacteria gets carbon.”

On the other hand, Brucella abortus infects mammals by being ingested in the form of infected milk or animal tissue, resulting in brucellosis, a debilitating disease accompanied by symptoms that include fever, malaise, and weight loss. The disease is difficult to eradicate because the bacteria reside inside human cells. According to MIT postdoctoral fellow Kristin Levier, the bacterial gene bacA is crucial to both the rhizobia and the mammalian pathogen Brucella abortus. “The bacA function seems to be necessary for the bacteria to overcome the defense response of the host that would otherwise prevent a chronic infection,” said Walker, as removal of the bacA gene made it impossible for the bacteria to infect its host.

Thus, this scenario, which involves removing the bacA gene from the bacteria to allow the human immune system to recognize and kill the intruder, is a perfect starting point for the development of a vaccine against brucellosis.

-- Georgia Panagiotakos

Information released by MIT News Office.