Legionella pneumophila: Properties of the Bacteria

Legionella pneumophila

L. pneumophila is the causative agent of Legionnaire’s disease, aswell as of Pontiac fever.

Properties of the Bacteria

◗ Morphology

pneumophila shows following features:

·           L. pneumophila is a small, slender, pleomorphic, Gram-negative bacillus.

·           L. pneumophila organisms in clinical specimens stain poorlywith Gram staining. They can by stained better by silver impregnation method using Dieterle silver stain.

·           It measures 0.3–0.9 3 2–5 mm with pointed ends and tendency to form filaments in culture on solid media.

·           It is motile by means of one or more polar or subpolar flagella.

·           It is nonsporing and non–acid fast.

◗ Culture

L. pneumophila is a strict aerobe, grows at an optimum temper-ature of 35°C and an optimum pH of 6.9. It is nutritionally fastidious and grows on the medium supplemented with iron salts and L-cysteine.

Buffered charcoal yeast extract (BCYE) agar: The agarcontaining buffered charcoal, yeast extract, and cysteine is a useful medium for growth of L. pneumophila. It is a slow-growing bacterium and may take 3–5 days to produce visible colonies. The colonies on BCYE agar are circular, gray, or gray-blue and low convex with a slightly irregular margin. Under the microscope, the colonies typically have a ground glass appearance.

◗ Biochemical reactions

L. pneumophila shows following biochemical properties:

·           It is mostly nonfermenter and derives its energy from the metabolism of amino acids.

·           It does not ferment any sugars and is urease and nitrate test negative.

·           It is catalase positive, oxidase variable, and liquefies gelatin.

·           It hydrolyzes starch and hippurate.

◗ Other properties

Susceptibility to physical and chemical agents: L. pneumoph-ila is readily killed by 70% ethyl alcohol, 2% glutaraldehyde,and 1% formaldehyde. It is also killed by residual chlorine (5 ppm of chlorine) in chlorinated water in 1 minute, by 1.25 ppm of chlorine in 15 minutes, and by 0.65 ppm of chlorine in 1 hour.