Evaluation of the conditions and mechanisms of environmental survival of Francisella tularensis and countermeasures – TULAMIBE

The main objective of the TULAMIBE project is to define, in experimental and natural models, the conditions and mechanisms of prolonged survival of Francisella tularensis in the hydro-telluric environment. This bacterium, which is highly infectious and virulent in humans and many animals, is responsible for tularemia, a zoonosis present in the northern hemisphere. This disease has major public health and economic consequences in countries of high endemicity. In addition to the animal reservoir, an environmental reservoir of F. tularensis is strongly suggested by: 1 / the frequency of human infections from hydro-telluric sources; 2 / the occurrence of epidemics in countries where transmission of the diseases is linked to the consumption of contaminated water or to mosquito vectors, their larvae becoming contaminated in aquatic environments; And 3 / the occasional detection of this pathogen in the environment. However, the role of the environment as a long-term reservoir of F. tularensis and the life cycle of this bacterium in this environment remain unknown. F. tularensis is a potential biological threat agent categorized in the class A of the CDC. The deliberate dispersal of this pathogen may lead to numerous infections in humans and animals, either immediate or delayed after contact with the contaminated environment. It is important to better define the characteristics and factors of F. tularensis persistence in the environment.
Our strategy will be to evaluate the optimal conditions for survival of F. tularensis in various experimental or natural hydro-telluric environments. The species F. novicida and F. philomiragia will be studied in parallel because of their main environmental reservoir. The project will be divided into 4 tasks. In Task 1, soil and water samples will be artificially infected or collected in a natural tularemia endemic area. Our goal is to define Francisella's persistence capacity in samples, in the absence of any eukaryotic cells, under experimental or natural conditions. Task 2 will explore the capacity of formation of biofilms by Francisella, the composition of these biofilms and their mechanisms of formation. It is a question of characterizing the potential impact of these biofilms on the persistence of these bacteria in the environment. The task 3 will exhaustively study the interactions between Francisella and free amoebae of the environment, which are natural reservoirs of many intracellular bacteria. The Francisella multiply in the amoeba Acanthamoeba castellanii in vitro. We will characterize the population of amoebae, infected or not by Francisella, in the natural zone studied. We will then study the ability of Francisella species to multiply and persist in various species of amoebae. We will characterize the virulence factors of Francisella in these protozoa as compared to human macrophages. Task 4 will be devoted to the development of countermeasures to eradicate F. tularensis in a contaminated environment. We will test physical or chemical methods on this bacterium in its planktonic, biofilm or intra-amoebic forms. Our project potentially presents major positive civilian and military spin-offs, and the results could be valued in the form of publications and possibly patents.