What Does Legionella Need to Survive?

Legionella bacteria thrive in specific environmental conditions, which enable them to survive and multiply. Understanding these conditions is essential for managing the risks associated with Legionella in water systems. Below are factors that contribute to the survival and proliferation of Legionella – factors that should kept in mind during a Legionella risk assessment and Legionella remediation.

Water

Primary Habitat: Legionella bacteria are aquatic organisms, naturally found in various water environments, including lakes, rivers, and even man-made water systems like cooling towers, hot tubs, and plumbing systems. Water is a fundamental requirement for their survival, as they cannot persist in dry conditions.

Moisture: Without moisture, Legionella cannot thrive, making water a non-negotiable element for their growth and proliferation.

Temperature

Optimal Growth Range: Legionella bacteria grow best in warm water, typically between 20°C to 45°C (68°F to 113°F). This temperature range is often found in systems such as hot tubs, water heaters, cooling towers, and other warm water systems.

Ideal Temperature: The bacteria are particularly prolific at temperatures between 32°C and 42°C (90°F to 108°F), where growth rates are highest.

Survival at Cooler Temperatures: While Legionella cannot grow in cooler water, they can survive in temperatures as low as 0°C. However, growth resumes once they re-enter the warmer, more favorable conditions.

Heat Resistance: At temperatures above 60°C (140°F), Legionella bacteria are typically killed, which is why hot water systems that reach and maintain these temperatures are less susceptible to Legionella colonization.

Nutrients

Biofilm Formation: Legionella frequently live within biofilms, which are slimy layers of microorganisms attached to surfaces within water systems. These biofilms protect the bacteria from disinfectants and provide access to nutrients.

Organic Matter: The bacteria feed on organic matter such as algae, amoebae, and other microbes that reside in the water system. The presence of these nutrients allows Legionella to thrive and multiply.

pH Levels

Survival Range: Legionella can survive within a wide pH range, from 5.0 to 8.5. However, they prefer slightly neutral conditions, with an optimal pH range between 6.0 and 7.0.

Protection from Disinfection

Resistance Mechanisms: Within biofilms, Legionella are shielded from common Legionella disinfectants like chlorine. Sediment, scale, and rust deposits in water systems can further protect the bacteria from direct exposure to disinfectants.

Amoebae Hosts: In addition to biofilms, Legionella can live inside amoebae, single-celled organisms found in water. This relationship provides the bacteria with protection from environmental stressors and disinfection efforts.

Stagnant Water

Stagnation: Legionella proliferates in stagnant or slow-moving water. Areas such as unused taps, stagnant pipes, and water systems that are not frequently flushed create an ideal environment for Legionella growth. Stagnation limits water circulation, which can lead to localized warming, increased biofilm formation, and reduced disinfectannt effectiveness.

Oxygen

Aerobic Requirement: Legionella bacteria are obligate aerobes, meaning they require oxygen to survive. They rely on oxygen for their metabolic processes, which is why they thrive in water systems that are exposed to air, such as cooling towers and hot tubs. Even within biofilms, oxygen diffusion allows the bacteria to continue their growth and reproduction.

Biofilm Environment: Although biofilms can create areas with lower oxygen levels, Legionella survives due to microenvironments where oxygen is still present. This combination of oxygen availability and protection makes biofilms a critical habitat for the bacteria.

Key Takeaways for Legionella Survival

For Legionella to survive and thrive, it needs a combination of key environmental factors, including water, the right temperature range, nutrients from organic matter, protection from disinfection, and oxygen. In water systems that meet these conditions, Legionella can grow rapidly, posing a risk to human health. Proper water management plans (WMP) for water systems, including regular cleaning, disinfection, and temperature control, are essential to prevent the growth of Legionella and reduce the risk of Legionnaires’ disease. To learn more about your facility’s liability for Legionella, testing for Legionella, and Legionella mitigation, contact the Legionella experts at Legionella Control Systems.