*Article* **Mitigation of Expression of Virulence Genes in** *Legionella pneumophila* **Internalized in the Free-Living Amoeba** *Willaertia magna* **C2c Maky**

#### **Rayane Mouh Mameri 1, Jacques Bodennec 2, Laurent Bezin 2 and Sandrine Demanèche 1,\***


Received: 14 May 2020; Accepted: 3 June 2020; Published: 5 June 2020

**Abstract:** *Legionella pneumophila* is a human pathogen responsible for a severe form of pneumonia named Legionnaire disease. Its natural habitat is aquatic environments, being in a free state or intracellular parasites of free-living amoebae, such as *Acanthamoeba castellanii*. This pathogen is able to replicate within some amoebae. *Willaertia magna* C2c Maky, a non-pathogenic amoeba, was previously demonstrated to resist to *L. pneumophila* and even to be able to eliminate the *L. pneumophila* strains Philadelphia, Lens, and Paris. Here, we studied the induction of seven virulence genes of three *L. pneumophila* strains (Paris, Philadelphia, and Lens) within *W. magna* C2c Maky in comparison within *A. castellanii* and with the gene expression level of *L. pneumophila* strains alone used as controls. We defined a gene expression-based virulence index to compare easily and without bias the transcript levels in di fferent conditions and demonstrated that *W. magna* C2c Maky did not increase the virulence of *L. pneumophila* strains in contrast to *A. castellanii*. These results confirmed the non-permissiveness of *W. magna* C2c Maky toward *L. pneumophila* strains.

**Keywords:** free-living amoebae (FLA); *Legionella pneumophila*; virulence genes; *Willaertia magna* C2c Maky
