Screening of virulence traits in Legionella pneumophila and analysis of the host susceptibility to infection by using the Dictyostelium host model system.

The social soil amoeba Dictyostelium discoideum has been established as a host model for several human pathogens including Legionella pneumophila. The complete genome sequence, the genetic tractability, and the phagocytic characteristics of Dictyostelium generate many opportunities for the study of host-pathogen interactions. Important applications of this haploid model organism are (i) the use of Dictyostelium cells as a screening system for bacterial virulence, (ii) the use of Dictyostelium mutant cells to identify genetic host determinants of susceptibility and resistance to infection, and (iii) experiments that allow the dissection of the complex cross-talk with infectious agents. Accordingly, this chapter describes a plaque assay to identify attenuated pathogens, an infection assay for the analysis of host cell mutants and pathogens, and a screening method for the isolation of Legionella mutants that are defective in the reprogramming of the phagolysosomal maturation of the host.