Virulence traits of environmental and clinical Legionella pneumophila multilocus variable-number tandem-repeat analysis (MLVA) genotypes

Legionella pneumophila causes water-based infections resulting in severe pneumonia. Recently, we showed that different MLVA-8 (multilocus variablenumber tandem-repeat analysis using 8 loci) genotypes dominated different sites of a drinking-water distribution system. Each genotype displayed a unique temperaturedependent growth behavior. Here we compared the pathogenicity potentials of different MLVA-8 genotypes of environmental and clinical strains. The virulence traits studied were hemolytic activity and cytotoxicity toward amoebae and macrophages. Clinical strains were significantly more hemolytic than environmental strains, while their cytotoxicity toward amoebae was significantly lower at 30°C. No significant differences were detected between clinical and environmental strains in cytotoxicity toward macrophages. Significant differences in virulence were observed between the environmental genotypes (Gt). Gt15 strains showed a significantly higher hemolytic activity. In contrast, Gt4 and Gt6 strains were more infective toward Acanthamoeba castellanii. Moreover, Gt4 strains exhibited increased cytotoxicity toward macrophages and demonstrated a broader temperature range of amoebal lysis than Gt6 and Gt15 strains. Understanding the virulence traits of Legionella genotypes may improve the assessment of public health risks of Legionella in drinking water.