Legionella is a type of bacteria commonly found in water, specifically from cooling towers, hot tubs, and plumbing systems. It causes Legionnaires’ disease, an acute type of pneumonia. Prevention of the growth of this bacterium in water systems is, therefore, very important to public health. This article intends to discuss the most effective biocides against Legionella along with their mechanisms of action and application methods to ensure comprehensive coverage.
What is Legionella?
The genus Legionella includes more than 60 species of bacteria. The most important, however, is Legionella pneumophila. They are aerobic, gram-negative bacillus multiplying in warm water, and thus the cooling towers, domestic hot water tanks, and larger plumbing systems provide an excellent environment for these bacteria. Legionella poses significant risks when it becomes aerosolized and, upon inhalation, can cause serious pathologies in the lower respiratory tract.
Importance of Controlling Legionella
Control of Legionella in the water system is critical to prevent outbreaks of Legionnaires’ disease. Elderly persons, smokers, and those with a weak immune system are at serious risk from this opportunistic infection. Effective control measures while maintaining safe water systems in hospitals, hotels, and public buildings are very important. This also includes the use of biocides against Legionella, which play a pivotal role in mitigating contamination risks.
Overview of Biocide Approaches Against Legionella
Biocides are chemical elements with the ability to inactivate or kill Legionella and other opportunistic pathogenic microorganisms. The real effectiveness of a biocide is dependent on its potential diffusivity through biofilms, which protect the bacteria from adverse environments. It is important to formulate biocides against Legionella. Here are some of the most effective biocide ingredients:
1. Chlorine-Based Biocides approaches against Legionella:
Mechanism
Chlorine-based biocides represent the largest portion of biocides used for the control of Legionella. It can be in the form of chlorine gas, sodium hypochlorite, and chlorine dioxide. The mechanism of action is based on the oxidation of bacterial cell walls, ultimately leading to cell death.
Application Environments
Chlorine-based biocides against Legionella are employed in various water systems, including cooling towers, swimming pools, and drinking water systems. However, this requires frequent monitoring and adjustment of the chlorine level to maintain its effectiveness.
2. Copper-Silver Ionization
Mechanism
Ions of copper/silver in water interfere with the outer membrane of bacteria and various other enzymes to cause cellular death. Such a mechanism is very effective for biofilm-associated Legionella.
Application Environments
Copper-silver ionization is most often used in hospital water systems and is used in cooling tower systems, and large plumbing systems .The good thing with this method is that it automatically provides protection without every day chemical feed. One of the strategies employed in formulating biocides against Legionella.
3. Monochloramine
Mechanism
Monochloramine is the product of the reaction of chlorine with ammonia, yielding an oxidant that is less aggressive than chlorine yet offers a more persistent effect in water. Monochloramine can penetrate biofilms and has the capacity to cause functional damage to bacterial cells. It is a persistent oxidant and is effective as biocides against Legionella.
Application Environments
Monochloramine is usually applied in the treatment of drinking water systems and large building water systems. It is applied preferably in water systems that have long retention times, ensuring better control of Legionella for longer durations. Monitoring should be practiced on a consistent and regular basis to sustain the optimal level of monochloramine.
4. Ozone
Mechanism
Ozone is a strong oxidant that imparts the destruction of the bacterial cell walls and interference with cellular functions. Generated on-site using ozone generators, it reaches beyond biofilms, proving to be one of the effective biocides against Legionella.
Application Environments
Ozone is used in cooling towers, swimming pools, and spa systems. It is also employed in water treatment plants. Ozone has the advantage that it decomposes into oxygen, so there are no residues. Its effectiveness can be affected by the quality of the water and the organic load.
5. Ultraviolet (UV) Light
Mechanism
UV light works by killing bacteria through damage of their DNA, effectively sterilizing them. It is, therefore, effective in attacking Legionella and other pathogenic bacteria found in water. UV systems are installed along paths of water flowing to ensure full exposure of bacteria to light, as a supplementary treatment to biocides against Legionella.
Application Environments
UV light is used not only in drinking water systems and aquaculture but also in industrial water systems. UV is used as a supplementary treatment to other biocides. Even though UV does not penetrate biofilms, it does so in other areas thus lessening the free-floating bacteria in water.
6. Thermal Treatment
Mechanism
In this process, the temperature of water is raised to a point that will destroy the bacteria. More specifically, at temperatures higher than 60°C (around 140°F), the bacterial cell membranes and proteins are destroyed, and therefore, the cells die.
Application Environments
It is applied in the domestic hot water systems in hospitals, hotels, and residential buildings. Thermal treatment, being a very effective way to control Legionella, requires quite intensive temperature control to avoid the risks of scalding.
7. Hydrogen Peroxide and Silver
Mechanism
The combination of hydrogen peroxide and silver ions acts in a synergistic way thus enhancing the biocidal activity. Hydrogen peroxide acts as an oxidizer when silver ions act to disrupt bacterial cell functions. It is this synergistic approach that enables the combination to penetrate biofilms act as one of the efficient biocides against Legionella.
Application Environments
This type of biocide approach is used in cooling towers, hospital water systems, and large plumbing systems. It protects continuously and is very convenient for application in systems where complications are caused by biofilm growth. The effectiveness of the treatment entails regular monitoring.
Combining Biocide Approaches
In most of the cases, a Legionella control strategy cannot effectively be based on a single biocide. Often,the combination of biocides against Legionella have a synergistic effect to enhance the overall effectiveness in eliminating Legionella. For instance, by using UV and chlorine-based biocides, not only the free-floating bacteria but also biofilm bacteria can be reduced.
Challenges and Considerations
1. Resistance Development
With time, Legionella becomes resistant to some biocides. This makes it very important to rotate or combine biocides to avoid the development of resistant microorganisms.
2. Biofilm Penetration
Biofilms offer a kind of shelter for Legionella, making it very difficult for biocides to reach the bacteria and kill them. Effective biocide must penetrate these biofilms to ensure complete eradication.
3. Environmental and Health Concerns
A few biocides can have impacts on the environment and human health. For example, chlorine can form harmful byproducts, and high ozone concentrations are toxic.
4. System Design and Maintenance
Key to Legionella control is proper water system design and maintenance to add to the effect of biocides. The proper system design includes eliminating dead ends and ensuring proper water movement to avoid stagnation.
An effective Legionella control program applied to water systems needs to be multi-faceted, with a biocide against Legionella as an integral part of the comprehensive solution. Chlorine-based biocides, copper-silver ionization, monochloramine, ozone, UV light, thermal treatment, and hydrogen peroxide with silver are the most effective biocide approaches against Legionella. The integration of these methods and the development of techniques to deal with obstacles to their effectiveness—especially poor biofilm penetration and developing resistance—make them more effective. Maintaining safe water systems is also a key to preventing Legionella outbreaks.
Role of MIS
MIS is a global testing laboratory specializing in testing antimicrobial products. With expertise in evaluating the bactericidal activity of chemical disinfectants and biocides against Legionella, MIS can help you ensure your water systems are safe and compliant with health standards. Contact MIS today for comprehensive testing and solutions to protect against Legionella.
