Identification of a 19.3-kDa protein in MRHA-positive Edwardsiella tarda: putative fimbrial major subunit.

The hemagglutinating properties of Edwardsiella tarda isolated from fish were investigated. Hemagglutination of E. tarda was not inhibited by D-mannose but was strongly inhibited by fetuin and N-acetylneuraminic acid. Extraction of hemagglutinating activity from bacterial cells was achieved using n-octyl-beta-D-thioglucoside (NOTG), and the NOTG extracts were fractionated by sucrose density gradient ultracentrifugation. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of the fractions revealed that a 19.3-kDa protein band appeared in the fractions exhibiting highest hemagglutinating activity. In an immunoblot analysis of NOTG extracts from 18 strains of E. tarda, the 19.3-kDa protein was detected only in the extracts possessing hemagglutinating activity. The predicted amino acid sequence of a 534-bp gene encoding the 19.3-kDa protein was identical to fimbrial subunit (FimA) of E. tarda by FASTA homology search. These findings suggest that fimbriae are implicated in the hemagglutination of E. tarda.