Long-Term Survival of Legionella pneumophila in the Viable But Nonculturable State After Monochloramine Treatment
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Legionella pneumophila, a facultative intracellular human pathogen, can persist for long periods in natural and artificial aquatic environments. Eradication of this bacterium from plumbing systems is often difficult. We tested L. pneumophila survival after monochloramine treatment. Survival was monitored using the BacLight Bacterial Viability Kit (Molecular Probes), ChemChrome V6 Kit (Chemunex), quantitative polymerase chain reaction and culturability on buffered charcoal–yeast extract agar. In nonculturable samples, regain of culturability was obtained after addition of the amoeba Acanthamoeba castellanii, and esterase activity and membrane integrity were observed after >4 months after treatment. These results demonstrate for the first time that L. pneumophila could persist for long periods in biofilms into the viable but nonculturable (VBNC) state. Monitoring L. pneumophila in water networks is generally done by enumeration on standard solid medium. This method does not take into account VBNC bacteria. VBNC L. pneumophila could persist for long periods and should be resuscitated by amoeba. These cells constitute potential sources of contamination and should be taken into account in monitoring water networks.
KeywordsTotal Organic Carbon Esterase Activity Plumbing System Dead Bacterium VBNC State
We are sincerely grateful to Michael Steinert for providing the A. castelanii strain. Many thanks to Yann Héchard for help in the amoeba experiments. Manilduth Ramnath is gratefully acknowledged for valuable review of the text. The research of L. Alleron has been made possible by a fellowship from the Région Poitou-Charentes (France).
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