LEGIONELLA PNEUMOPHILA ENVIRONMENTAL GENOTYPES DIFFER SIGNIFICANTLY IN THEIR ECOPHYSIOLOGICAL BEHAVIORS AND VIRULENCE POTENTIAL

Yehonatan Sharaby 1 Sarah Rodríguez-Martínez 1 Olga Oks 1 Inbar Marom 1 Rotem Friedler 1 Marina Pecellin 2 Ingrid Brettar 2 Manfred Hofle 2 Malka Halpern 1
1Evolutionary and Environmental Biology, University of Haifa, Haifa, Israel
2Vaccinology and Applied Microbiology, Helmholtz Center for Infection Research, Braunschweig, Germany

Legionella pneumophila (L.p) is a gram-negative bacterium that causes Legionnaires` disease, a potentially fatal type of pneumonia. Human infections occur via inhalation of contaminated water aerosol droplets. Our previous studies demonstrated that specific L.p MLVA8 genotypes (Gt4, Gt6 and Gt15), colonized different parts of a Drinking Water Distribution System (DWDS) in Israel. In order to better understand the environmental parameters that influence L.p genotypes establishment and successful proliferation in the drinking water system, we studied three physiological traits related with the bacterial life cycle and virulence; growth traits (λ, µm, A), pore forming activity (hemolysis) and amoebae infectivity rates. Mathematical modeling of the bacterial growth at five different temperatures revealed significant differences between the growth traits of the three L.p genotypes. Gt4 strains exhibited superior growth and adaptation to lower temperatures (25-30ºC) while Gt15 appeared to be best adapted to relatively higher temperatures (42-45ºC). Only Gt15 strains were able to proliferate at 45ºC. In addition, significant differences in the virulence traits were observed between the genotypes. Gt15 strains showed a significantly higher hemolytic activity. In contrast, Gt4 and Gt6 strains were more infective for Acanthamoeba castellanii. We showed, for the first time, that different L.p genotypes possess different physiological traits. These traits may influence their colonization at specific ecological niches within the DWDS. Moreover, the differences in their virulence traits suggest that different genotypes have different pathogenicity potential. Our findings highlight the importance of understanding the ecophysiology and virulence of different L.p. genotypes. These findings may be used for better assessment of public health risks as well as for the improvement of currently used methods for L.p monitoring in DWDSs.









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