Detection of legionellae in hospital water samples by quantitative real-time LightCycler PCR.
Contamination of hospital water systems with legionellae is a well-known cause of nosocomial legionellosis. We describe a new real-time LightCycler PCR assay for quantitative determination of legionellae in potable water samples. Primers that amplify both a 386-bp fragment of the 16S rRNA gene from Legionella spp. and a specifically cloned fragment of the phage lambda, added to each sample as an internal inhibitor control, were used. The amplified products were detected by use of a dual-color hybridization probe assay design and quantified with external standards composed of Legionella pneumophila genomic DNA. The PCR assay had a sensitivity of 1 fg of Legionella DNA (i.e., less than one Legionella organism) per assay and detected 44 Legionella species and serogroups. Seventy-seven water samples from three hospitals were investigated by PCR and culture. The rates of detection of legionellae were 98.7% (76 of 77) by the PCR assay and 70.1% (54 of 77) by culture; PCR inhibitors were detected in one sample. The amounts of legionellae calculated from the PCR results were associated with the CFU detected by culture (r = 0.57; P < 0.001), but PCR results were mostly higher than the culture results. Since L. pneumophila is the main cause of legionellosis, we further developed a quantitative L. pneumophila-specific PCR assay targeting the macrophage infectivity potentiator (mip) gene, which codes for an immunophilin of the FK506 binding protein family. All but one of the 16S rRNA gene PCR-positive water samples were also positive in the mip gene PCR, and the results of the two PCR assays were correlated. In conclusion, the newly developed Legionella genus-specific and L. pneumophila species-specific PCR assays proved to be valuable tools for investigation of Legionella contamination in potable water systems.
Wellinghausen
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Department of Medical Microbiology and Hygiene, University of Ulm, D-89081 Ulm, Germany. nele.wellinghausen@medizin.uni-ulm.de
Frost
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C
Marre
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R
D001426:Bacterial Proteins; D015169:Colony Count, Microbial; D003470:Culture Media; D020459:Genes, rRNA; D006761:Hospitals; D020104:Immunophilins / Q000235:genetics; D007875:Legionella / Q000235:genetics / Q000302:isolation & purification*; D016952:Legionella pneumophila / Q000235:genetics / Q000302:isolation & purification; D008565:Membrane Proteins / Q000235:genetics; D019696:Peptidylprolyl Isomerase; D016133:Polymerase Chain Reaction / Q000379:methods*; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D012680:Sensitivity and Specificity; D014871:Water Microbiology; D014881:Water Supply
D001426:Bacterial Proteins; D003470:Culture Media; D008565:Membrane Proteins; D012336:RNA, Ribosomal, 16S; D020104:Immunophilins; C512922:Mip protein, Legionella pneumophila; D019696:Peptidylprolyl Isomerase