Eha, a regulator of Edwardsiella tarda, required for resistance to oxidative stress in macrophages

Edwardsiella tarda is distributed widely in a variety of hosts. Eha is its virulence regulator just found. In order to explore the mechanism of its regulation, we investigated the survival rates of wild type ET13, its eha mutant and complemented strains in RAW264.7 macrophages under light microscopic observation as well as by counting bacterial CFUs on the plates. All kinds of the strains could live within macrophage, however, the intracellular numbers of wild type were significantly higher than the mutant when the incubation time extended 4 h or 6h ( P < 0.05). Furthermore, more ROS was produced by the mutant-infected cells, indicating that Eha may enhance the ET13's capacity to detoxify ROS. Consistently, we found that the mutant exhibited more sensitivity and less survival ability to H2O2 by disk inhibitory assay and H2O2 treatment. We further demonstrated that the bacterial antioxidant enzymes SodC and KatG were regulated by Eha with qRT-PCR and β -Galactosidase assay. Collectively, our data show Eha is required for E. tarda toresist the oxidative stress from macrophages.