Legionella pneumophila: comparison of isolation from water specimens by centrifugation and filtration

A comparison was made between membrane filtration and centrifugation for the isolation of Legionella pneumophila from seeded water samples. Using samples of varying concentration, the optimum speed and time of centrifugation were determined and the relationship between the number of organisms present in the water and the proportion recovered was examined. Following this, sequential routine environmental waters were filtered and centrifuged in parallel. Centrifugation and filtration using nitrocellulose filters were found to be comparable. The optimum speed and time of centrifugation was approximately 6000 g for 10 min. There was a constant proportion of viable organisms recovered irrespective of the concentration in the unspun samples.