Detection of <it>Legionella </it>by quantitative-polymerase chain reaction (qPCR) for monitoring and risk assessment

• Main Authors: Krøjgaard Louise H, Krogfelt Karen A, Albrechtsen Hans-Jørgen, Uldum Søren A
• Format: Article
• Language: English
• Published: BMC 2011-11-01
• Series: BMC Microbiology
• Online Access: http://www.biomedcentral.com/1471-2180/11/254

<p>Abstract</p> <p>Background</p> <p>Culture and quantitative polymerase chain reaction (qPCR) assays for the detection of <it>Legionella </it>were compared on samples from a residential area before and after two interventions. A total of 84 samples were collected from shower hoses and taps as first flush samples and at constant temperature. Samples were grouped according to the origin of the sample, a) circulation water b) water from empty apartments c) water from shower hoses. The aims were to investigate the usefulness of qPCR compared to culture for monitoring remedial actions for elimination of <it>Legionella </it>bacteria and as a tool for risk assessment.</p> <p>Results</p> <p>In water collected from the apartments <it>Legionella </it>spp were detected by qPCR in the concentration range from LOQ to 9.6*10⁵GU/L while <it>L. pneumophila </it>were detected in a range from LOQ to 6.8*10⁵GU/L. By culturing, the legionellae were detected in the range from below detection limit (> 10 CFU/L) to 1.6*10⁶CFU/L. In circulating water and in first flush water from shower hoses, culture and qPCR showed the same tendencies. The overall correlation between the bacteria number detected by culture and the two developed qPCR assays (<it>L</it>. spp and <it>L. pneumophila</it>) was relatively poor (r²= 0.31 for culture and <it>Legionella </it>spp. assay, r²= 0.20 for culture and <it>L. pneumophila </it>assay).</p> <p>Conclusion</p> <p>Detection by qPCR was suitable for monitoring changes in the concentration of <it>Legionella </it>but the precise determination of bacteria is difficult. Risk assessment by qPCR only on samples without any background information regarding treatment, timing, etc is dubious. However, the rapid detection by qPCR of high concentrations of <it>Legionella </it>- especially <it>Legionella pneumophila </it>- is valuable as an indicator of risk, although it may be false positive compared to culture results. On the other hand, the detection of a low number of bacteria by qPCR is a strong indication for the absence of risk.</p>