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  • Lisamarie Lamb

Legionella and Biofilm: Understanding the Connection for Effective Control

When it comes to waterborne pathogens, legionella stands out as a particularly concerning threat to public health. Legionnaires' disease, a severe form of pneumonia caused by inhaling legionella bacteria, can lead to hospitalisation and, in some cases, fatalities. One critical aspect of legionella control that often goes underappreciated is its relationship with biofilm, and in this article, we'll look at the connection between legionella and biofilm - read on to find out more.

What is Legionella?

Legionella is a genus of bacteria found naturally in freshwater environments, such as rivers and lakes. However, it becomes a concern when it proliferates in human-made water systems, such as cooling towers, hot water tanks, and plumbing systems. When conditions are favourable, legionella can multiply rapidly, increasing the risk of exposure and subsequent infection.

A beautiful lake that probably has legionella bacteria in it

The Role of Biofilm

Biofilm is a slimy layer formed by microorganisms, including bacteria, on surfaces submerged in water and it provides an ideal environment for legionella to thrive and multiply. The complex matrix of biofilm offers protection to legionella from disinfectants and other control measures, making eradication challenging.

Understanding the Connection

Legionella's association with biofilm is multifaceted. Firstly, legionella bacteria can attach to the surfaces within biofilm, allowing them to colonise and form reservoirs. Once established, legionella can persist within biofilm even when water conditions are unfavorable, posing a continuous risk of exposure. Secondly, biofilm provides a nutrient-rich environment for legionella, facilitating its growth and survival. Lastly, biofilm can act as a protective barrier, shielding legionella from chemical disinfectants and physical cleaning methods.

A dirty cold water storage tank with biofilm over the water

UK Legislation and Guidance

In the United Kingdom, legislation and guidance are in place to mitigate the risk of legionella contamination and ensure water safety. The Health and Safety Executive (HSE) provides comprehensive guidance through documents such as the Approved Code of Practice (ACOP) L8 and the HSG274 series. These documents outline the legal requirements for controlling legionella in various water systems, emphasising the importance of risk assessment, monitoring, and effective control measures.

Effective Control Strategies

Given the close association between legionella and biofilm, effective control strategies must target both elements. Regular cleaning and disinfection of water systems are essential for removing biofilm and reducing legionella levels. Additionally, implementing measures to prevent biofilm formation, such as maintaining appropriate water temperatures and minimising stagnation, can help mitigate the risk of legionella proliferation.


In conclusion, understanding the intricate connection between legionella and biofilm is crucial for implementing effective control measures. By addressing biofilm formation and persistence, alongside traditional legionella control methods, water systems can be safeguarded against contamination, protecting public health in accordance with UK legislation and guidance.

Remember, vigilance and proactive management are key to ensuring water safety and mitigating the risk of legionella-related illnesses in the UK. Contact Assured Water today to find out more.

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