type III secretion system-dependent repression of NF-κB activation to the intracellular growth of Edwardsiella tarda in human epithelial cells

Edwardsiella tarda is a pathogen with a broad host range infecting animals and humans. We have reported recently that the type III secretion system (TTSS) is essential for intracellular replication of the bacterium in murine macrophages. The present study shows that the TTSS is also needed for intracellular growth of the bacterium in human epithelial cells (HEp-2). However, different from the previous microarray analyses on murine macrophages, upregulation of the mRNA expression level of NF-κB target genes was not detected in the infected HEp-2 cells. The wild-type E. tarda, but not its TTSS mutant, actually repressed the tumor necrosis factor α-dependent NF-κB activation in an NF-κB reporter gene assay. These results suggest TTSS-dependent repression of the NF-κB activation in HEp-2 cells infected with E. tarda.