Comparison of four methods to detect Legionella in pipe water samples collected from Shanghai port

Objective To evaluate the sensitivities of 4 methods to detect Legionella in pipe water samples. Methods A total of 132 pipe water samples were collected from Shanghai port in 2010. Traditional culture, polymerase chain reaction (PCR), real-time fluorescence quantitative PCR (real-time PCR) and Ethidium monoazide-real-time PCR (EMA-real-time PCR) were conducted simultaneously for qualitative and quantitative analysis of Legionella in pipe water samples. Results The positive rate of Legionella was 18.9% for traditional culture, 20.5% for PCR, 24.2% for real-time PCR and 24.2% for EMA-real-time PCR, respectively. The amount of Legionella in each positive samples were 50-1320 CFU/L, 20-13 085 GU/L and 10-4480 GU/L by traditional culture, real-time PCR and EMA-real-time PCR, respectively. The mean Legionella concentration of 32 positive pipe water samples detected by traditional culture, real-time PCR, and EMA-real-time PCR were 415.2 CFU/L, 2036.6GU/L and 629.9GU/L, respectively. Significant differences were found in Legionella concentration detected by different methods (2=193.6, P0.01), the concentration of Legionella detected by real-time PCR was highest and that by traditional culture was lowest. Conclusion Real-time PCR and EMA-real-time PCR have higher sensitivities than traditional culture. EMA-real-time PCR can be used as a routine surveillance tool to detect Legionella in pipe water.