Magazine article Science News

Pathogen Preference: Infected Amoebas Flourish in Cooling Towers

Magazine article Science News

Pathogen Preference: Infected Amoebas Flourish in Cooling Towers

Article excerpt

Cooling towers on buildings harbor amoebas infected with both known and unknown types of bacteria. New research raises the possibility that such towers are more effective than natural waters at fostering novel bacterial species that cause illnesses in people.

Scientists suspect that many microbial species responsible for human illnesses first preyed upon amoebas, unicellular organisms found in aquatic environments. Though microscopic, amoebas normally are shaped like "a piece of chewing gum that's been chewed," says Sharon G. Berk of Tennessee Technological University in Cookeville. But after they've been infected by bacteria, they become spherical. Finally, they burst and release the bacteria, she says.

Well known among those pathogens are Legionella pneumophila bacteria, which cause Legionnaires' disease. Cooling towers--structures that cool water streams for air conditioning, power generation, or other purposes--are a source of Legionella-infected amoebas. These towers cool water by exposing it to outside air and then blowing out warm air. That airflow carries fine water droplets, which can release bacteria.

Berk and her colleagues wondered whether infected amoebas would be more prevalent in cooling towers than in natural water environments. They took samples from cooling towers on hospitals and industrial buildings and also from rivers and lakes.

The researchers found infected amoebas in 22 of 40 cooling tower samples but in only 3 of 40 natural samples. …

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