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Sci Total Environ. 2012 Jan 1;414:608-13. doi: 10.1016/j.scitotenv.2011.10.005. Epub 2011 Nov 21.

Quantification of Legionella pneumophila by real-time quantitative PCR from samples with humic acid and ferric ion.

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Institute of Environmental Health, College of Public Health, National Taiwan University, Taipei City 100, Taiwan.


This study determined and overcame the influences of humic acid (HA) and/or ferric ion (Fe) on quantification of Legionella pneumophila by real-time quantitative PCR (qPCR). Four commonly used DNA isolation methods, QiAamp DNA Mini Kit (Q), Q with Sepharose 4B gel column (Q/G), freeze-thaw/phenol-chloroform lysis (FT-PC), and FT-PC/G, were adopted to isolate L. pneumophila DNA from samples containing Fe alone (0-30 mg l(-1)) or Fe/HA (0/0-3/100 mg l(-1)). Among the four DNA isolation methods, Q removed HA effectively and obtained the greatest DNA yield regardless of Fe and HA concentration (P<0.05). For samples containing Fe (0.3-3 mg l(-1)) or Fe/HA (0.3/10-3/100 mg l(-1)), qPCR inhibition was found in all isolated DNA, especially in those obtained by Q/G and FT-PC/G. DNA dilution at either 10 or 100 folds reduced qPCR inhibition and increased cell recovery (P<0.05). Under 10-fold dilution, Q acquired the highest concentrations of L. pneumophila determined by qPCR. Consequently, Q with post 10-fold dilution is suggested prior to qPCR for quantifying L. pneumophila from water containing Fe (≤ 3 mg l(-1)) or Fe/HA (≤ 3/100 mg l(-1)).

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