Isolation of Legionella

Legionella species are Gram negative aerobic bacilli which stain poorly with most aniline dyes. They are non-sporing, and are usually motile by means of one or more subpolar flagella. Most Legionella species are short rods but some strains have filamentous forms. They do not grow on ordinary media but will grow on media supplemented with L-cysteine and ferric salts. Legionella was isolated from four different samples. The samples from which isolation occurred were called Legionella-positive samples. The most common habitats from which Legionella was isolated were cooling towers and water tanks. 20% of the water tanks/tap water and 60% of the cooling towers were Legionella-positive samples. The species, most commonly found in the isolates was Legionella pneumophila serogroup 1. Both the Legionella counts (DFA) and the microorganisms counts (FITC) were found to be statistically significant (p < 0.05) higher in Legionella- positive samples than in Legionella-negative samples. Other factors were found to affect the growth of Legionella including incubation, sedimentation, solar irradiation and the presence of Amoebae.