PhD thesis of Aurélie HENNEBIQUE from TIMC TREE team will take place on september the 28th at 2pm:
" Cellular models for investigation of Francisella tularensis epidemiology and pathogenicity "
- Place : Bâtiment Jean Roget (salle visio 2), Faculté de Médecine et de Pharmacie de Grenoble, 23 Avenue Maquis du Grésivaudan, 38700 La Tronche.
- Max MAURIN, Professeur des Universités - Praticien Hospitalier, CHU Grenoble Alpes, Université Grenoble Alpes, laboratoire TIMC UMR 5525, Director
- Sandrine BOISSET, Maîtresse de conférence des Universités - Praticienne Hospitalière, Université Grenoble Alpes, Co-director
- Claire PONSART, Docteure en Sciences, Agence Nationale de Sécurité Sanitaire de l'Alimentation, de l'Environnement et du Travail, Reporter
- Anne VIANNEY, Maîtresse de conférence, Université Lyon, Reporter
- Pierre-Edouard FOURNIER, Professeur des Universités - Praticien Hospitalier, Aix Marseille Université, Examiner
- Muriel CORNET, Professeure des Universités - Praticienne Hospitalière, Université Grenoble Alpes, Examiner
tularemia, Francisella tularensis, Francisella sp., aquatic environment, amoebae, ecology
Francisella tularensis is the bacterium responsible for tularemia. Human contamination can occur through contact with an infected animal, arthropod bite, after contact with the hydro-telluric environment or after ingestion of contaminated water or food. However, the ways of human contamination from hydro-telluric environment as well as the mechanisms of survival in this environment are poorly characterised. Thus, it is mandatory to improve knowledge about these topics, especially because F. tularensis is classified as a potential agent for bioterrorism.
The first part of this work was to performed a literature review about F. tularensis and aquatic environment. This allowed to highlight that water-born tularemia can occur after consumption or use of contaminated water, after bite of in infected mosquito, or after recreational aquatic activities. The mechanisms of F. tularensis survival in water may include survival in a planktonic form in water with the possible transition to a viable but nonculturable (VBNC) state, the formation of biofilms, infection of mosquito larvae, and interaction with free-living amoebae. However, few studies about these mechanisms are available and some of them present conflicting results.
Indeed, the second part of this work aimed to deeply investigate the interactions between F. tularensis and amoebae, in comparison to F. novicida and F. philomiragia which are aquatic bacteria of low virulence. In amoeba plate screening tests (APT), all the Francisella species tested resisted the attack by amoebae. In infection model in poor culture medium, all the Francisella species tested did not displayed intra-amoebic growth. In co-culture models, the amoebae favoured survival of the three Francisella species over 16 days. This enhanced survival was likely dependent on amoeba-excreted compounds for F. novicida and for F. tularensis and on direct contact between bacteria and amoebae for F. novicida. Overall, our results demonstrate that amoebae likely promote Francisella survival in aquatic environments, including F. tularensis.
A third step of this work aimed to assess prevalence of F. tularensis DNA in the natural aquatic environment in a French region where tularemia indigence increased. In this aim, 87 water samples were collected during two sampling campaigns and were analysed using a combination of real-time PCR assays. Among 57 water samples of the first campaign, 15 (26.3%) were positive for Francisella sp., nine (15.8%) for F. tularensis and/or F. novicida, and four (7.0%) for F. tularensis subsp. holarctica. The ratios were 25/30 (83.3%), 24/30 (80.0%), and 4/30 (13.3%) for the second campaign. Thus, these results revealed a high prevalence of F. tularensis DNA in the studied aquatic environment. This aquatic environment could therefore be involved in the maintenance of F. tularensis and possibly in the endemicity of tularemia in this region.
Altogether, these works have shown that the aquatic environment is central to the ecology of F. tularensis.
Finally, two more applied works were performed. One described the first human case of F. salimarina infection, a species initially isolated from the aquatic environment. Another evaluated the performances of the Biotoxis kit, a commercial qPCR kit for the detection of F. tularensis in clinical and environmental samples.