About Legionella

Species of the genus Legionella are Gram-negative, non-spore-forming, rod-shaped, aerobic bacteria. They contain branched-chain fatty acids, have a non-fermentative metabolism, and require L-cysteine and iron salts for growth.

They have been placed in the family Legionellaceae, which contains the single genus Legionella; of which there are at least 42 species. Some species of Legionella can be further differentiated into serotypes, of which there are at least 15 for L. pneumophila but so far no more than two for any other species.

Legionella are ubiquitous in natural aquatic environments, capable of existing in waters with varied temperatures, pH levels, and nutrient and oxygen contents.

They can be found in groundwater as well as fresh and marine surface waters. Their widespread survival in nature can be attributed to their relationships with other micro-organisms in the environment. Symbiotic existence with algae and other bacteria, particularly in biofilms, increases the availability of nutrients.

They are also able to infect protozoans and subsequently reproduce within these organisms. These relationships provide protection against adverse environmental conditions, including standard water disinfection techniques. Consequently, Legionella are also prevalent in anthropogenic waters such as potable water, cooling tower reservoirs, and whirlpool baths.

Legionella spp are generally associated with respiratory infections in humans and exposure to infectious aerosols (water droplets containing the bacterium) or droplet nuclei (particles left over after the water has evaporated), which is inhaled into the lungs (particularly into the alveoli), can result in a condition known as Legionellosis.