Identification of in vitro upregulated genes in a modified live vaccine strain of Edwardsiella ictaluri compared to a virulent parent strain

Using PCR-select subtractive cDNA hybridization technique, 41 in vitro expressed sequence tags (ESTs) were isolated from a modified live vaccine strain (AQUAVAC-ESC®, formerly RE-33) vs a virulent parent strain (EILO) of Edwardsiella ictaluri. Transcriptional levels of the 41 in vitro ESTs in the vaccine strain and the virulent strain were then evaluated by quantitative PCR (qPCR). The qPCR results revealed that 33 ESTs were consistently upregulated at least 3-fold in the modified live vaccine strain compared to the virulent parent strain. Of the 33 upregulated ESTs, 11 were upregulated greater than 5-fold. The 41 ESTs were found to be homologues of genes involved in protective immunity (22%), adhesion (7%), cell growth and survival (20%), signaling (7%), metabolism (5%), and transcriptional regulation (5%). However, putative functions of 20% of the genes identified are currently unknown. Putative roles of some of the in vitro upregulated genes in protective immunity induced by the vaccine strain are discussed.