Image: Vincent Starai was recently awarded over $1.5 million by the National Institutes of Health to investigate the mechanism by which Legionella pneumophila, the causative agent of Legionnaires’ disease, avoids host defense systems. Legionnaires’ disease begins with flu-like symptoms, but within days patients may experience severe chest pain and bloody coughing. Up to 30 percent of hospitalized cases can be fatal, and survivors usually take a long time to recover. Legionella exist naturally in the environment but can proliferate in still, warm water contained in poorly-maintained ventilation and water systems, and is transmitted when humans inhale mist, steam or other fine droplets from contaminated water. Foreign particles that enter the lungs are attacked by phagocytes which normally “eat” such invading particles by engulfing them with cellular membranes, and breaking them into smaller fragments within a specialized compartment called the lysosome. Legionella bacteria prevent the fusion of the bacteria-containing membrane vesicles with the host lysosome, and are thus able to survive and grow within the phagocyte. Once the phagocyte dies, it releases the Legionella which are ready to infect more phagocytes. “Legionella pneumophila produces and secretes a number of proteins that alter or inhibit membrane fusion,” said Dr. Starai. “Our goals are to study the mechanisms through which the bacteria change the host cell environment for its own survival.”
