Virulence traits of environmental and clinicalLegionella pneumophilaMLVA genotypes.

Abstract

Legionella pneumophila causes water-based infections resulting in severe pneumonia. Recently, we showed that different variable numbers of tandem repeat analysis (MLVA-8) genotypes dominated different sites of a drinking-water distribution system, with a genotype-related temperature and abundance regime. Here we compare the pathogenicity potential of different MLVA-8 genotypes of environmental and clinical strains. The virulence traits studied were hemolytic activity and cytotoxicity towards amoebae and macrophages. Clinical strains were significantly more hemolytic than environmental strains, while their cytotoxicity towards amoebae was significantly lower at 30°C. No significant differences were detected between clinical and environmental strains in cytotoxicity towards macrophages. Significant differences in virulence were observed between the environmental genotypes (Gt). Gt15 strain showed a significantly higher hemolytic activity. In contrast, Gt4 and Gt6 strains were more infective towardsAcanthamoeba castellaniiMoreover, Gt4 strain exhibited increased cytotoxicity towards macrophages and demonstrated a broader temperature range of amoebal lysis compared to Gt6 and Gt15. Understanding the virulence traits ofLegionellagenotypes may improve the assessment of public health risks ofLegionellain drinking water.ImportanceLegionella pneumophilais the causative agent of a severe form of pneumonia. Here we demonstrate that clinical strains were significantly more cytotoxic towards red blood cells compared to environmental strains, while their cytotoxicity towards macrophages was similar. Genotype 4 (Gt4) strains were highly cytotoxic towards amoebae, macrophages, and lysed amoebae in a broader temperature range, compared to the other studied genotypes. The results can explain the Gt4 relatively high success in the environment and in clinical samples; thus Gt4 strains should be considered as a main factor for the assessment of public health risks ofLegionellain drinking water. Our findings shed light on the ecology, virulence, and pathogenicity potential of differentL. pneumophilagenotypes that can be a valuable parameter for future modelling and Quantitative Microbial Risk Assessment ofLegionellain drinking water systems.