Comparing various epithelial cell lines as in vitro models for Francisella tularensis non‐phagocytic infections

The potential bioterrorism agent Francisella tularensis subspecies tularensis ( F. tularensis ) causes the disease tularemia; if untreated the disease can result in up to 60% mortality. As an intracellular bacterium, F. tularensis invades and occupies non‐phagocytic epithelial cells of its host – a process critical to the development of disease. To study epithelial infections, many cell culture models have been developed; yet choosing a suitable model from the literature is challenging due to varied infection parameters and inaccurate assessments of intracellular bacterial loads. In our lab, we have developed an epithelial cell model using a murine surrogate of F. tularensis Francisella tularensis subspecies novicida ( F. novicida ) and the cultured hepatocyte cell line BNL CL.2. Since our model emulates the murine model of tularemia, we hypothesize BNL CL.2 cells will be more susceptible to F. novicida infection compared to other models currently present in the literature. We assessed 8 different models with the same parameters using antibiotic survival assays and an immunofluorescence strategy to label intracellular vs extracellular bacteria. We found that while COS‐7, CMT‐93, and HEK‐293 cell lines may be suitable for studying specific aspects of infection such as invasion or replication; overall, BNL CL.2 cells were the most appropriate cell line to study F. tularensis epithelial infections in vitro . Grant Funding Source : NSERC and CIHR