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Quantification of Legionella pneumophila by qPCR and Culture in Tap Water with Different Concentrations of Residual Disinfectants and Heterotrophic Bacteria
Citation:
Donohue, M. Quantification of Legionella pneumophila by qPCR and Culture in Tap Water with Different Concentrations of Residual Disinfectants and Heterotrophic Bacteria. SCIENCE OF THE TOTAL ENVIRONMENT. Elsevier BV, AMSTERDAM, Netherlands, 774:145142, (2021). https://doi.org/10.1016/j.scitotenv.2021.145142
Impact/Purpose:
Legionellosis prevalence is increasing in the United States. This disease is caused primarily by the bacterium Legionella pneumophila that is 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 PCR (qPCR) was tested for its use in monitoring L. pneumophila, tap-water samples (n=358) from across the US. All samples were tested for L. pneumophila by culture and qPCR and for other bacteria by heterotrophic plate counts (HPC). Residual disinfectant concentrations, free chlorine or monochloramine, were measured in all samples. Legionella pneumophila was found at the highest prevalence and in the highest concentrations in chlorinated water with a residual disinfectant of less than 0.2 mg/L water. About 24% of the samples (87/358) were positive for L. pneumophila by qPCR and 3% of the samples (11/358) were positive by culture. Legionella pneumophila was culture recovered from two chloramine-treated water samples whose residual was >1 mg/L. Quantitative PCR detection of L. pneumophila in chloramine-treated water occurred in water that had a high residual concentration. These detections, despite the present of a residual, also had a large viable bacteria population. Both culture and qPCR methods have limitations in predicting the risk associated with finding 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 that is 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 PCR (qPCR) was tested for its use in monitoring L. pneumophila, tap-water samples (n=358) from across the US. All samples were tested for L. pneumophila by culture and qPCR and for other bacteria by heterotrophic plate counts (HPC). Residual disinfectant concentrations, free chlorine or monochloramine, were measured in all samples. Legionella pneumophila was found at the highest prevalence and in the highest concentrations in chlorinated water with a residual disinfectant of less than 0.2 mg/L water. About 24% of the samples (87/358) were positive for L. pneumophila by qPCR and 3% of the samples (11/358) were positive by culture. Legionella pneumophila was culture recovered from two chloramine-treated water samples whose residual was >1 mg/L. Quantitative PCR detection of L. pneumophila in chloramine-treated water occurred in water that had a high residual concentration. These detections, despite the present of a residual, also had a large viable bacteria population. Both culture and qPCR methods have limitations in predicting the risk associated with finding Legionella in tap water. Measuring disinfectant residuals and quantifying HPC in water samples should help improve these risk assessments.
URLs/Downloads:
DOI: Quantification of Legionella pneumophila by qPCR and Culture in Tap Water with Different Concentrations of Residual Disinfectants and Heterotrophic Bacteria
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