Legionella & Pseudomonas Awareness

Legionella & Pseudomonas can both forms of bacteria which be dangerous if found in your water system.

Pseudomonas is similar to Legionella in the sense it thrives in relatively nutrient-poor water environments, and they will produce biofilm on surfaces, making them extremely tough to remove. Although similar they are still very different – Pseudomonas is a much more complex bacteria as it can grow at low temperatures. It also grows more rapidly than legionella and the pass level is not detected in 250 ml which is extremely exacting.

In this blog we will take a closer look these bacteria.


Legionella enters a building’s water systems in low numbers, but it is when they start to grow and multiply that they become a health risk.

If the legionella gets the chance to grow it will then spread via droplets small enough for people to breathe in. People can get Legionnaires’ disease or Pontiac fever when they breathe in small droplets of water in the air that contain these bacteria.

The three key elements contribute to Legionella risk:

  • Intrusion (introduces Legionella into the system)
  • Growth (occurs when Legionella increases within the system)
  • Transmission (happens when aerosols, or small water droplets, containing Legionella are inhaled)

You must manage your water systems effectively; to minimise the risks and prevent growth.

The key to preventing Legionnaires’ disease is to prevent Legionella growth.Legionella bacteria will grow best between 20°C and 45°C, it will rapidly be killed at temperatures above 60°C, and do not multiply at temperatures above 50°C. They will not multiply at temperatures below 20°C either but can remain alive until the temperature rise to a level allowing multiplication to occur.

If you find a small amount of Legionella bacteria in one of your building water system, it   does not mean it is the source of an outbreak.

It means a more thorough investigation is needed to figure out how the bacteria got there and where else in the building and surrounding area it could still potentially be found.

The water used in virtually all building water systems comes from the drinking water supply, in some systems it is refreshed regularly and is sometimes treated by water management professionals on behalf of building owners. If incoming water contains bacteria, it can enter a sub-system and in most cases the water management practices consistent with “Best Practices” will neutralize it.


Pseudomonas is a species of bacteria which can be found in your water supply, while the majority of pseudomonas species are not harmful to humans, when in a healthcare setting the specific form, pseudomonas aeruginosa, they can cause serious infections and illnesses in immunosuppressed patients.

Biofilms will be found on plumbing materials in the water system and in most cases, P.aeruginosa will be concentrated within 2 metres of the point of water delivery at the outlet, i.e. tap / shower heads.

If it is found in the water supply it has the potential to cause infections in almost any organ or tissue, especially in patients compromised by underlying disease, age or immune deficiency.

The first thing that should be considered when preventing the growth of pseudomonas in water systems is that in many cases pseudomonas growth is also directly related to legionella growth, and similar treatment regimens should be used for the control of both.

A significant difference between legionella bacteria and pseudomonas bacteria is the route of infection. As mentioned, inhalation of very small droplets of water is the single root cause for the development of Legionnelosis (Legionnaires Disease), whereas Pseudomonas infection can be transferred from person-to-person, or surfaces etc. which means that standard good hygiene practises, to prevent cross contamination within a healthcare setting, are essential in preventing pseudomonas infections.

In healthcare settings, it is spread through improper hygiene, such as from the unclean hands of healthcare workers, or via contaminated medical equipment that wasn’t fully sterilized. When hospitalized, you have a higher risk for a serious, life-threatening Pseudomonas infection if you have surgical wounds or are being treated with a breathing machine, such as a ventilator, or other medical devices, such as urinary or intravenous catheters.


One of the main differences between legionella and pseudomonas species is the temperature range of growth.

Legionella species grow very slowly, if at all, when the temperature is below 20°c and are killed at elevated temperatures above 50°c. Unlike Pseudomonas, where this species will grow down to 5°c, their growth in cold water systems can therefore be more of a problem.

Due to the nature of this specific type of bacteria it is important that your water is monitored, and the risks are kept to a minimal. A risk assessment should be undertaken to identify actions to mitigate risks and ensure appropriate sampling, monitoring and clinical surveillance arrangements are being implemented and adhered to.


As you can see, both Legionella & Pseudomonas can be very dangerous if they are given the chance to grow and spread. While they have similar properties they have very different characteristics and separate tests & risk assessment should be carried out to ensure the risk is kept to a minimum.