Legionella bacteria are studied from various water samples, such as hot domestic water, drinking water, cooling and humidification water, spa water, and wastewater. Solid samples such as sludge, soil, and compost are also analysed.
The culture method is based on standard SFS-EN ISO 11731:2017, and the sample’s dirtiness determines the matrix used:
- Matrix A: clean waters (e.g., drinking water, swimming and whirlpools, humidification water, natural waters). Plates: BCYE, BCYE+AB, GVPC.
- Matrix B: moderately dirty waters (e.g., cooling and process water). Plates: BCYE, GVPC.
Unlike other environmental samples, cooling water samples are also analysed for aerobic microbial concentration. This is done by surface culture on TH media, incubated for 2 days at 30 °C. This method is not accredited. - Matrix C: dirty samples (e.g., wastewater, sludge, soil, compost). Plates: GVPC.
Incubation is carried out at 36 °C for 10–12 days. Samples are concentrated, and growth of other microbes is restricted by antibiotics, heat treatment, and acid treatment.
Legionella analysis also includes, at no extra cost, determination of heterotrophic bacteria by culture (R2A medium, 14 days), as this provides background information on general growth conditions in the water system.
Results are reported as
- Water samples: CFU/l (colony-forming units per liter)
- Solid samples: CFU/g (colony-forming units per gram)