An Introduction to Legionella Bacteria

Disclaimer
Please note this article is for general interest and research purposes only and does not purport to give professional advice. This article should not be considered as training material or used for any other purpose.

(Left: A magnified picture of the harmful legionella pneumophila; approximate length 2µm.)

Legionella are water borne bacteria and often found in natural water supplies, typically sausage shaped and usually has a thin flagellum attached (tail-like appendage) which can give it mobility in an aquatic environment.

The organism can multiply rapidly in water temperatures between 20°C and 45°C. As the temperature rises above 60°C the majority of legionella will be killed within 5 minutes. Maintaining water temperatures above 50°C and below 20°C is therefore the main method of controlling legionella in domestic water systems as described by the Health & Safety Commission (L8) and others.

There are at least 40 different species of legionella with Legionella pneumophila being the most pathogenic. The greater the number of legionella present in a water system the more likelihood there is of contracting the disease. This is why all the available guidance on the control of Legionnaires’ disease stresses the importance of maintaining controls that reduce the numbers of legionella in water systems.

Organic nutrients required by legionella for growth may be supplied by other bacteria, algae, and protozoa which are found in most water systems.

Amoebae

Amoebae are free living protozoa, which engulf and subsequently digest bacteria they find in aquatic biolfilms (a thin slime found on the internal aspects of pipe work and fittings). Some legionella have acquired the ability to inactivate the amoebas digestive process. These legionella can then begin to multiply within the amoeba, using their new host as a source of nutrients for growth, and supported in a micro-environment free of other competitive microorganisms.

Eventually the amoeba will rupture, releasing large numbers of legionella in a more virulent form into the aquatic system, where the process can be repeated many times. Amoeba can also protect legionella from harmful external factors including biocides and raised temperatures.

Domestic Water Systems

Man-made environments, and especially domestic water systems, are associated with the majority of legionella infections. It would be prudent to always assume legionella are present, even when legionella cannot be detected as they may be harbouring elsewhere in the system or about to enter the system from the municipal water supply. It is important to ensure a working-balance between central system and peripheral system controls; always:

• Maintain recommended water temperatures;
• Make sure outlets are in regular weekly use and not simply assumed in use, or:
  • Ensure outlets are manually flushed at least weekly (see L8, para 165), with records kept;
  • Alternatively, fit self-purging outlets (see L8, para 166);
• Maintain and monitor water systems in compliance with L8;
• If low levels of legionella cannot be maintained always seek immediate professional advice and take corrective measures where necessary.

Microorganisms often develop resistance to many of the methods intended to eradicate them, it would prudent to remain vigilant for developing resistance and to never underestimate the value of the simple engineering solutions.

Article by:
Legionella Control Journal - www.lcj-online.co.uk