Submitted to: American Society for Microbiology Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: February 20, 2009
Publication Date: May 17, 2009
Citation: Russo, R., Shoemaker, C.A., Panangala, V.S., Klesius, P.H. 2009. An Attenuated Strain of Edwardsiella ictaluri is Killed by Channel Catfish (Ictalurus punctatus) Macrophages and Confers Protection in Few Days. American Society for Microbiology Annual Meeting. p. 210. Technical Abstract: Background: Edwardsiella ictaluri is able to survive inside macrophages. Several studies have demonstrated that in channel catfish protective immunity against E. ictaluri is mediated by a cellular immune response. Methods: A virulent strain and an attenuated strain (used as a modified live vaccine) of E. ictaluri were transformed with plasmids encoding either a green fluorescent (pZsGreen) or a red florescent (pDsRed2) protein. In the first part of the study, channel catfish macrophages were exposed to either the fluorescent virulent or avirulent strain of E. ictaluri or to both strains simultaneously. Macrophage killing efficiency, ROS and nitric oxide production were determined. In the second part of the study, adult fish were intraperitoneally (IP) injected with fluorescent virulent or avirulent E. ictaluri to determine the localization of the bacterium in the body in the first 48 hours. In the third part of the study, adult fish were IP injected with the avirulent strain of E. ictaluri 3, 2, 1 day before, or at the same time of the challenge with the virulent strain of E. ictaluri. Results: The virulent strain of E. ictaluri survived and replicated inside macrophages, meanwhile the avirulent strain was killed. If macrophages were exposed simultaneously to both strains they were able to kill the bacteria. Fluorescent virulent bacteria were observed in all organs of the fish with the exception of the brain. Avirulent E. ictaluri were observed only in lymphoid organs. Injection of the avirulent strain of E. ictaluri at least 1 day prior to challenge conferred protection (survival from 83 to 100 % in dependant of the trial). Conclusion: Macrophages of channel catfish are able to kill the avirulent strain of E. ictaluri and the immune system is able to control the dispersion of this strain in the body. The protection conferred by the E. ictaluri avirulent strain highlights the possibility to use this strain as “therapeutic” during disease outbreak.