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Legionnaires' Disease Discovery Could Lead to New Treatments


The bacteria that cause Legionnaires’ disease are very resourceful and capable of getting the nourishment they need to grow and flourish, according to University of Louisville scientists. This discovery could help researchers develop new treatments, including antibiotics and vaccines, for Legionnaires’ disease as well as other illnesses.

Legionnaires’ disease affects thousands of people each year

Back in 1976, an infection swept through a population of individuals who had attended an American Legion convention in Philadelphia. Although the cause of the lung condition remained unknown at the time, Dr. Joseph McDade identified the causative bacterium in 1977, and it was named Legionella.

Currently, treatment for Legionnaires’ disease is antibiotics, and healthy individuals usually recover from the infection. However, the disease can cause death in up to 30% of patients.

In the new study, investigators examined Legionella for two years and identified how they manipulate cells to get the food they need. Basically, the bacteria, which exist in amoebae in water, utilize the amoeba’s cellular process to target proteins and cause them to break down into amino acids. The bacteria then use the amino acids for their food supply.

When the bacteria infect people, the process is similar, but instead of the bacteria doing the dirty work, they trick the person’s body into targeting the proteins to break down. Using mouse models, the scientists discovered that if they inactivated the factor that tricked the body’s cells into degrading proteins, they could prevent Legionnaires’ disease in the animals.

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Yousef Abu Kwaik, PhD, the Bumgardner Endowed Professor in Molecular Pathogenesis of Microbial Infections at the University of Louisville, and his team, explained the importance of these discoveries. “It is possible that the process we have identified presents a great target for new research in antibiotic and vaccine candidates, not only for Legionnaires’ disease but in other bacteria that cause illness.”

In addition, Abu Kwaik noted that prior to their discovery, no one had understood how bacteria produced enough nourishment from their host to grow and reproduce. “Our work is the first to identify this process for any bacteria that cause disease,” explained Abu Kwaik.

Between 8,000 and 18,000 people are hospitalized with Legionnaires’ disease in the United States each year, although the actual number may be higher because many infections are not diagnosed or reported. Because symptoms of the disease are similar to those of other forms of pneumonia (e.g., high fever, chills, cough, headache), Legionnaires’ disease can be difficult to diagnose at first, until the bacteria are identified.

Legionnaires’ disease is contracted by breathing in droplets of water in the air that have been contaminated with the bacteria. These bacteria can be found in air conditioning units, whirlpools, and other water systems accessed by a large number of people. The disease is not contagious.

The new discovery about Legionnaires’ disease “is not a process that is well understood yet,” noted Abu Kwaik, “but by first discovering how an organism gets nutrients by tricking the host into degrading proteins, and then interfering with that process, we can, in effect, starve it to death and prevent or treat the disease.”

Centers for Disease Control and Prevention
University of Louisville

Picture credit: Wikimedia Commons