No abstract

Legionella pneumophila, a bacterium that replicates within aquatic amoebae and persists in the environment as a free-living microbe, is the causative agent of Legionnaires' disease. Among the many Legionella species described, L. pneumophila is associated with 90% of human disease, and within the 15 serogroups (Sg), L. pneumophila Sg1 causes more than 84% of Legionnaires' disease worldwide. Thus, rapid and specific identification of L. pneumophila Sg1 is of the utmost importance for evaluation of the contamination of collective water systems and the risk posed. Previously we had shown that about 20 kb of the 33-kb locus carrying the genes coding for the proteins involved in lipopolysaccharide biosynthesis (LPS gene cluster) by L. pneumophila was highly specific for Sg1 strains and that three genes (lpp0831, wzm, and wzt) may serve as genetic markers. Here we report the sequencing and comparative analyses of this specific region of the LPS gene cluster in L. pneumophila Sg6, -10, -12, -13, and -14. Indeed, the wzm and wzt genes were present only in the Sg1 LPS gene cluster, which showed a very specific gene content with respect to the other five serogroups investigated. Based on this observation, we designed primers and developed a classical and a real-time PCR method for the detection and simultaneous identification of L. pneumophila Sg1 in clinical and environmental isolates. Evaluation of the selected primers with 454 Legionella and 38 non-Legionella strains demonstrated 100% specificity. Sensitivity, specificity, and predictive values were further evaluated with 209 DNA extracts from water samples of hospital water supply systems and with 96 respiratory specimens. The results showed that the newly developed quantitative Sg1-specific PCR method is a highly specific and efficient tool for the surveillance and rapid detection of high-risk L. pneumophila Sg1 in water and clinical samples.Legionella pneumophila is ubiquitous in natural, aqueous environments, where it parasitizes aquatic protozoa (1). From these environments Legionella can contaminate artificial water circuits and then grow and proliferate to high numbers, in particular in hot water systems, including aerosol-producing devices such as air conditioning systems or cooling towers (18,19,37). Upon aerosol formation via man-made water systems, Legionella can enter the human lung and cause a severe form of pneumonia. Since transmission of Legionella from person to person has never been observed, prevention needs to concentrate on the elimination of this pathogen from water and aerosol-producing systems. Thus, rapid and precise detection of Legionella in water systems is of the utmost importance for risk prediction and the elimination of Legionella from possible infection sources.Water contamination by Legionella is currently monitored by culture-based methods approved by the International Organization for Standardization (29) and the French organization for standardization (2). The alert and action thresholds defined by the national authorities that obli...