Which bacterium causes Legionnaires’ disease and grows inside amoebae in natural water systems?

Legionella pneumophila causes Legionnaires’ disease and can multiply inside amoebae in natural and engineered water systems.

This Gram-negative bacterium is associated with freshwater environments, where it survives within protozoa such as amoebae. The intracellular lifestyle can protect Legionella from environmental stresses and may help it adapt to man-made water systems. People usually become infected by inhaling contaminated aerosols or aspirating contaminated water; ordinary person-to-person spread is uncommon.

Legionnaires’ disease is a severe form of pneumonia that may include fever, cough, muscle aches, headache, and gastrointestinal symptoms. A milder illness caused by the same species is called Pontiac fever. Outbreaks have been linked to cooling towers, plumbing systems, whirlpool spas, fountains, and hospital water supplies. Controlling water temperatures, reducing stagnation, cleaning systems, and managing biofilms are important prevention measures. The bacterium’s ability to manipulate host-cell processes makes it a significant subject in cell biology as well as public health.