Proliferation of Legionella pneumophila as an intracellular parasite of the ciliated protozoan Tetrahymena pyriformis

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Abstract
L. pneumophila proliferated as an intracellular parasite of the ciliated holotrich T. pyriformis in sterile tap water at 35.degree. C. After 7 days of incubation, serpentine chains of .apprx. 103 L. pneumophila cells were observed throughout the cytoplasm of the protozoan infected initially with 1-30 L. pneumophila cells. The overall L. pneumophila population increased from .apprx. 1.0 .times. 102 to .apprx. 5.0 .times. 104 cells/ml in the coculture within this time frame. The interactions between the protozoan and the bacterium appear to depend on their concentrations and on temperature of incubation. L. pneumophila did not multiply in sterile tap water alone, in suspensions of lysed T. pyriformis or in cell-free filtrates of a T. pyriformis culture. In addition to establishing an ecological model, addition of T. pyriformis to environmental (water) specimens served as an enrichment method that improved isolation of legionellae from the specimens.