Quantitative real-time Legionella PCR for environmental water samples: data interpretation.
Quantitative Legionella PCRs targeting the 16S rRNA gene (specific for the genus Legionella) and the mip gene (specific for the species Legionella pneumophila) were applied to a total of 223 hot water system samples (131 in one laboratory and 92 in another laboratory) and 37 cooling tower samples (all in the same laboratory). The PCR results were compared with those of conventional culture. 16S rRNA gene PCR results were nonquantifiable for 2.8% of cooling tower samples and up to 39.1% of hot water system samples, and this was highly predictive of Legionella CFU counts below 250/liter. PCR cutoff values for identifying hot water system samples containing >10(3) CFU/liter legionellae were determined separately in each laboratory. The cutoffs differed widely between the laboratories and had sensitivities from 87.7 to 92.9% and specificities from 77.3 to 96.5%. The best specificity was obtained with mip PCR. PCR cutoffs could not be determined for cooling tower samples, as the results were highly variable and often high for culture-negative samples. Thus, quantitative Legionella PCR appears to be applicable to samples from hot water systems, but the positivity cutoff has to be determined in each laboratory.
Joly
Philippe
P
Centre National de Référence des Legionella, INSERM E-0230, Faculté de Médecine, IFR 62, 7 rue Guillaume-Paradin, 69372 Lyon Cedex 08, France.
Falconnet
Pierre-Alain
PA
André
Janine
J
Weill
Nicole
N
Reyrolle
Monique
M
Vandenesch
François
F
Maurin
Max
M
Etienne
Jerome
J
Jarraud
Sophie
S
D000389:Air Conditioning; D015169:Colony Count, Microbial; D003470:Culture Media; D004269:DNA, Bacterial / Q000032:analysis; D005618:Fresh Water / Q000382:microbiology*; D007753:Laboratories; D007875:Legionella / Q000302:isolation & purification*; D016952:Legionella pneumophila / Q000302:isolation & purification; D016133:Polymerase Chain Reaction / Q000379:methods*; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D012015:Reference Standards; D012680:Sensitivity and Specificity; D014881:Water Supply
D003470:Culture Media; D004269:DNA, Bacterial; D012336:RNA, Ribosomal, 16S