Interaction of Francisella noatunensis subsp. orientalis with Oreochromis mossambicus bulbus arteriosus cell line
Francisella noatunensis subsp. orientalis ( Fno ) (syn. F. asiatica ) is an emergent warmwater fish pathogen and the causative agent of piscine francisellosis. Although Fno causes septicemia and can live extracellularly in infected tilapia ( Oreochromis spp.), the early interaction of Fno with vasculature endothelium is unknown. In the present study, we examined the interaction of wild-type Fno (WT) and two Fno knockout [intracellular growth loci C (Δ iglC ) and pathogenicity determinant protein A (Δ pdpA )] strains with the endothelial O. mossambicus bulbus arteriosus cell line (TmB) at 25 °C and 30 °C. Similar amounts of WT, Δ iglC, and Δ pdpA attached and were detected intracellularly after 5 h of incubation at both temperatures; however temperature affected attachment and uptake. While significantly greater amounts of Fno (WT, Δ iglC, and Δ pdpA ) were detected intracellularly when TmB cells were incubated at 30 °C, bacteria attached to TmBs at greater levels at 25 °C. Only WT Fno was able to replicate intracellularly at 25 °C, which resulted in Fno mediated cytotoxicity and apoptosis at 24 and 72 h post-infection. WT Fno incubated at 30 °C as well as Δ iglC, and Δ pdpA incubated at 25 °C and 30 °C were all defective for survival, replication, and the ability to cause cytotoxicity in TmB. Taken together, these results demonstrate that temperature plays a vital role for Fno intracellular survival, persistence and cytotoxicity.