Direct Detection of Legionellae in Respiratory Tract Specimens by Using Fluorescence In Situ Hybridization

In this chapter the authors report the application of fluorescence in situ hybridization (FISH) for the direct detection and identification of Legionella spp. and L. pneumophila from respiratory tract specimens of patients with pneumonia using published 16S rRNA-based probes specific for the genus Legionella (Leg705) and for L. pneumophila (LegPne1). To evaluate the usefulness of FISH as a clinical diagnostic method, the authors analyzed 160 respiratory samples (bronchoalvealar lavage (BAL), pleural fluid, sputum, and tissue) from patients suspected of having pneumonia caused by Legionella spp. Probes Leg705 and LegPne1, one labeled with fluorescein and the other labeled with Cy3, were added simultaneously to each well, except for the negative-control well, where hybridization buffer alone was added. Almost two-thirds of Legionella pneumonia cases identified were caused by either L. longbeachae or L. micdadei. Given this background, development of a series of probes specific for the predominant species may be of value for identification and epidemiologic purposes.