Isolation of Legionella pneumophila from water supplies: comparison of methods based on the guinea-pig and culture media.

The detection of Legionella pneumophila in water via guinea-pig intraperitoneal injection has been compared with direct isolation of these organisms on semiselective BCYE alpha media. Both techniques were of similar sensitivity, detecting as few as 10(2) L. pneumophila in 10 ml of water. However, at this concentration, detection using guinea-pig intraperitoneal injection was via the indirect parameters of antibody production and immunofluorescent microscopy. Isolation of L. pneumophila from guinea-pig tissue for further investigation required greater than 10(7) organisms injected and in this respect is relatively much less sensitive than direct isolation on semiselective BCYE alpha media. Since L. micdadei and L. longbeachae are inhibited by one of the selective supplements used, other supplements and techniques need to be developed in order to avoid possible inhibition of other Legionella species. This work is based on simulated water samples containing strains of L. pneumophila defined in terms of pneumonic Legionnaires' disease in the guinea-pig. As such, this work serves as a guide to technique and the need to test large numbers of naturally infected water samples in parallel by techniques outlined in this work is emphasized.