Abstract
Legionella pneumophila, the causative agent of Legionnaire's disease, is well characterized as a bacteria surviving and developing, almost exclusively, as intracellular parasite within freshwater protozoa. Several species of protozoa and ciliae have been shown to support the growth of the pathogenic bacteria. In the present study, we report for the first time the behaviour of the protozoan Willaertia magna towards L. pneumophila and compared it with Acanthamoeba castellanii and Hartmannella vermiformis, two known L. pneumophila permissive protozoa. The results show that Willaertia amoebas displayed the ability to internalize the pathogenic bacteria but at a different extent when compared to other species. Surprisingly, and at the opposite of the other two amoebic species, coculture experiments showed that Willaertia magna inhibited the growth and the development of L. pneumophila and that it was resistant to bacterial induced cytotoxicity. Electron microscopy demonstrated that the formation of replicative phagosomes observed within Acanthamoeba sp. and Hartmannella sp. is deficient in Willaertia sp. These observations describing for the first time the occurrence of a protozoan species that display resistance towards the bacteria L. pneumophila, shed new light on a cellular model that may provide useful information on the mechanisms underlying bacterial infection and show that among free-living amoebas, the different species are not equally permissive to L. pneumophila