Development of an effective in vitro epithelial cell infection model to study Edwardsiella tarda infections

Abstract

Edwardsiella tarda is an enteric pathogen that infects both warm‐water fish and humans. While it is known that E. tarda utilizes syringe‐like secretion systems to deliver bacterially‐derived pathogenic proteins into macrophages during infection, little is known about E. tarda pathogenesis in epithelial cells. To enable the investigation of E. tarda infection mechanisms, we hypothesized that an effective and reliable E. tarda infection model could be developed by utilizing epithelial cells that originate from organs that are targeted during in vivo infections. To develop this in vitro model, isolates of E. tarda from various locations around the world were used to infect 4 different epithelial cell lines derived from fish, using various bacterial loads and durations of the infections. We found that E. tarda infected 10–15% of BF‐2 (Bluegill fry caudal trunk cells) when used at a multiplicity of infection of 10 for three hours at 30°C. The E. tarda infection rate was measured by counting infected cells per slide after fixation and visualization by fluorescence microscopy. Our results constitute the most effective E. tarda infection model ever developed and provides us the foundation to elucidate the strategies E. tarda utilize to cause disease.Grant Funding Source: Natural Sciences and Engineering Research Council