Does environmental water support the survival of Francisella tularensis, the etiological agent of tularemia?

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Hennebique, Aurélie | Brunet, Camille | Peyroux, Julien | Knezevic, Masa | Santic, Marina | Pelloux, Isabelle | Caspar, Yvan | Boisset, Sandrine | Maurin, Max

Edité par CCSD -

International audience. BackgroundTularemia is a zoonosis caused by the intracellular facultative bacterium Francisella tularensis. Human contamination mainly occurs through contact with wildlife animals or arthropod bites. Tularemia can also be a water-borne disease. However, F. tularensis mechanisms of survival in aquatic environments are poorly characterized.MethodsFirstly, using in vitro models, we investigated interactions of F. tularensis subsp. holarctica (the tularemia agent found in the northern hemisphere), and the aquatic species F. novicida and F. philomiragia with amoebae of the Acanthamoeba species. Secondly, we conducted an environmental study by collecting surface water samples in a tularemia endemic region in France. We investigated the presence of F. tularensis and other Francisella species in water using a set of qPCRs.ResultsIn amoeba plate screening tests, all the Francisella species tested resisted the attack by amoebae. In infection model, focusing on strictly intra-amoebic growth, none of the Francisella species tested displayed any intra-amoebic multiplication. In co-culture models, focusing both on intra and extra-amoebic bacterial multiplication, the amoebae favoured Francisella survival over 16 days and preserved bacterial morphology.Two sampling campaigns were conducted in West of France, in July 2019 and January 2020, allowing the collection of 87 water samples. Among 57 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 percentages were 83.3%, 80.0%, and 13.3% for the 30 samples of the second campaign. ConclusionsOur in vitro experiments suggest that amoebae promote Francisella sp. survival in aquatic environments, including the tularemia agent F. tularensis.Our environmental study reveals a high prevalence of Francisella sp., including F. tularensis, in the studied aquatic environment. Altogether, our results suggest that the aquatic environment can be a natural reservoir of F. tularensis

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