Legionella Testing

Legionella is a genus of pathogenic gram-negative bacteria including 50 species and 70 serogroups and it is an intracellular pathogen of macrophages.

Figure 1. Electron micrograph of Legionella and related contaminated water

Legionella is very common in many environments such as freshwater and soil systems. The bacteria are usually not transmitted between humans and most people who are exposed to the bacteria do not get infection. Most outbreaks of Legionella are associated with poorly maintained cooling towers primarily due to the risk for widespread circulation. It can be also found in swimming pools, showers, domestic water systems, and ice-making machines. The number of cases of Legionella outbreaks reported has been increasing since 2000. The contaminated water source is one of the major causes for Legionella infection. The bacteria can become a health concern when it grows and spreads in human building water system where temperatures are between 20℃ and 50℃. People usually get infected by inhalation of water droplets containing the bacteria from a contaminated source. The transmission from the aspiration of drinking water from a contaminated source is generally less common. The prevention of Legionella contamination depends on how well possible sources are maintained.

Legionella can cause illness called legionellosis including a serious type of lung infection (Legionnaires' disease) and a mild flu-like illness (Pontiac fever). Legionnaires' disease requires treatment with antibiotics. But some people may continue to have problems after treatment. The elderly, smokers, and people with weakened immune systems are particularly susceptible to Legionnaires' disease. Legionnaires' disease usually needs an incubation period between 2 and 10 days.

There is a Maximum Contaminant Level Goal (MCLG) established by the United States Environmental Protection Agency (EPA) for Legionella and zero organisms can be present in drinking water. The presence of Legionella in cooling tower with more than 10³ CFU/mL generally indicates an unacceptable level of contamination.

Legionella Testing of Food at Alfa Chemistry

The standard methods (EN/ISO) that have been widely used to quantify Legionella are culture-based methods after the isolation of Legionella from water by filtration. Common laboratory procedures for the detection of Legionella in water first filtrate water sample through a 0.22 mm membrane to concentrate the bacteria. Acid or heat treatments are often used to reduce the interference from other microbes in the sample. Then Legionella is detected by incubation on non-selective buffered charcoal yeast extract (BCYE) agar. Its growth requires the presence of iron and cysteine. Then the bacteria is inoculated onto the selective medium to suppress the growth of other flora in the sample. The suspect Legionella colonies need to grow on the selective medium for up to 10 days after incubation. It is followed by the plate counting technique to determine the level of Legionella in samples. The species and/or serogroups of Legionella in the sample can be determined by immunological techniques.

Alfa Chemistry offer accurate and validated testing platforms for the enumeration and confirmation of Legionella in water samples to meet customers' needs. We also have experience working on different standards and regulations.

Platform: Plate counting technique after preconcentration by filtration

Limit of detection: < 1 CFU/mL

Sample type: Liquid water samples

Sample size: 100 mL