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Quantification of Legionella pneumophila by qPCR and Culture in Tap Water
Citation:
Donohue, M. Quantification of Legionella pneumophila by qPCR and Culture in Tap Water. Presented at WQTC, Cincinnati, OH, November 13 - 17, 2022.
Impact/Purpose:
Legionellosis prevalence is increasing in the United States. This disease is caused primarily by the bacterium Legionella pneumophila found in water and transmitted by the inhalation of aerosols. This pathogen has a slow growth rate and can “hide” in amoeba, making it difficult to monitor in water by the traditional method of culturing on selective media. Therefore, quantitative polymerase chain reaction (qPCR) was used to monitor L. pneumophila in tap-water samples (n=358) from across the United States. All samples were tested for L. pneumophila by culture and qPCR and other bacteria by heterotrophic plate counts (HPC). Residual disinfectant concentrations, free chlorine or monochloramine, were measured in all samples. Twenty-four percent of the samples (87/358) were positive for L. pneumophila by qPCR, and 3% of the samples (11/358) were positive by culture. In chlorine treated water, 80% (45/56) of the positive detection by either qPCR or culture were in water whose free-chlorine residual was < 0.2 mg Cl2/mL. Culture concentrations ranged in chlorine treated water from 0.5 to 11 CFU/mL, age 2.5 CFU/mL. Quantitative PCR concentrations in chlorine treated water ranged from 0.03 to 1.9 x 103 cell equivalence (CE)/mL, avg 7.9 x102 CE/mL. Legionella pneumophila was recovered by culture in two chloramine-treated water samples whose residual was >1 mg/, concentrations were 2 and 2.5 CUF/mL. Legionella. pneumophila was qPCR detected in chloramine-treated water with high amounts of monochloramine disinfectant, avg 3.45 mg of Cl2/L range (0.1-8 mg Cl2/L). Despite the presence of residual, a large viable bacteria population was also detected avg HPC concentration 2.8 x103 CFU/mL. Quantitative PCR concentrations of L. pneumophila in chloramine treated water ranged from 0.02 to 1.4 x102 CE/mL, avg 5 CE/mL. Both culture and qPCR methods have limitations when predicting the risk associated with Legionella in tap water. Measuring disinfectant residuals and quantifying HPC in water samples should help improve these risk assessments.
Description:
Legionellosis prevalence is increasing in the United States. This disease is caused primarily by the bacterium Legionella pneumophila found in water and transmitted by the inhalation of aerosols. This pathogen has a slow growth rate and can “hide” in amoeba, making it difficult to monitor in water by the traditional method of culturing on selective media. Therefore, quantitative polymerase chain reaction (qPCR) was used to monitor L. pneumophila in tap-water samples (n=358) from across the United States. All samples were tested for L. pneumophila by culture and qPCR and other bacteria by heterotrophic plate counts (HPC). Residual disinfectant concentrations, free chlorine or monochloramine, were measured in all samples. Twenty-four percent of the samples (87/358) were positive for L. pneumophila by qPCR, and 3% of the samples (11/358) were positive by culture. In chlorine treated water, 80% (45/56) of the positive detection by either qPCR or culture were in water whose free-chlorine residual was < 0.2 mg Cl2/mL. Culture concentrations ranged in chlorine treated water from 0.5 to 11 CFU/mL, age 2.5 CFU/mL. Quantitative PCR concentrations in chlorine treated water ranged from 0.03 to 1.9 x 103 cell equivalence (CE)/mL, avg 7.9 x102 CE/mL. Legionella pneumophila was recovered by culture in two chloramine-treated water samples whose residual was >1 mg/, concentrations were 2 and 2.5 CUF/mL. Legionella. pneumophila was qPCR detected in chloramine-treated water with high amounts of monochloramine disinfectant, avg 3.45 mg of Cl2/L range (0.1-8 mg Cl2/L). Despite the presence of residual, a large viable bacteria population was also detected avg HPC concentration 2.8 x103 CFU/mL. Quantitative PCR concentrations of L. pneumophila in chloramine treated water ranged from 0.02 to 1.4 x102 CE/mL, avg 5 CE/mL. Both culture and qPCR methods have limitations when predicting the risk associated with Legionella in tap water. Measuring disinfectant residuals and quantifying HPC in water samples should help improve these risk assessments.