Isolation and characterization of outer membrane proteins of Edwardsiella tarda and its application in immunoassays

Edwardsiella tarda is an important cause for hemorrhagic septicemia in fish and also for gastro intestinal infections in humans. Sodium lauryl sarcosinate extraction method was used for the isolation of outer membrane proteins (OMPs) from 16 isolates of E. tarda, recovered from snakeheads (Ophiocephalus punctatus). Sodium dodecyl sulphate polyacrylamide gel electrophoresis profiles of OMPs from E. tarda isolates had one major and common protein band of 44 kilodalton (kDa) and 9 other variable protein bands. Rabbit polyclonal antibodies (RPAbs) against OMPs of E. tarda ET-7 detected mainly one common 44 kDa protein in all isolates by western blotting. RPAbs strongly reacted with all isolates of E. tarda by indirect enzyme linked immunosorbent assay (ELISA). These polyclonal antibodies showed no cross reactivity with OMPs or whole cells of other selected aquatic bacteria, i.e., Escherichia coli, Pseudomonas fluorescens, Aeromonas hydrophila, Vibrio cholerae and Flavobacterium ferrugineum. This study indicated that RPAbs against OMPs is useful for detection of E. tarda by ELISA.