Preventive and therapeutic effects of auxotrophic Edwardsiella tarda mutant harboring CpG 1668 motif-enriched plasmids against scuticociliatosis in olive flounder (Paralichthys olivaceus)

Previously generated two auxotrophic genes knockout Edwardsiella tarda (Δalr Δasd E. tarda) was used as a delivery vehicle for CpG 1668 motif-enriched plasmids (pL-CpG30), and potential of the Δalr Δasd E. tarda-mediated delivery of CpG motifs in both prevention and therapeutic treatment of scuticociliatosis caused by Miamiensis avidus in olive flounder (Paralichthys olivaceus) was investigated. The auxotrophic E. tarda mutant with pL-CpG30 plasmids elicited evidently higher survival rates and delayed both onset of mortality and time-to-death of olive flounder against M. avidus challenge. Furthermore, administration of E. tarda mutant that contains plasmids enriched in CpG 1668 motif elicited clearly higher survival rates of fish that were already infected with M. avidus. These results indicate that CpG 1668 plasmids-harboring E. tarda mutant may provide not only preventive measure but also therapeutic approach against scuticociliatosis in olive flounder.