Identification of sialic acid on Photobacterium damsela subspecies pisicida– possible role in cell adhesion and survival in the fish host

Carbohydrates associated with a number of mammalian bacterial pathogens are known to play a role in the pathogenesis of the organism. Sialic acid, present on the surface of bacteria, has been shown to inhibit the complement cascade of the host and to protect bacteria from host antibodies. However, the importance of carbohydrates in the pathogenesis of fish pathogens remains to be clarified. acid was identified and compared between different strains of Photobacterium damsela subspecies piscicida (Ph.d.p), formerly named Pasteurella piscicda, isolated from a variety of fish species from different geographical regions. Japanese isolates contained sialic acid with a molecular weight of 22 kDa, as did the Photobacterium damsela type strains. Sialic acid from Mediterranean region isolates was identified at 26 kDa, with the exception of two isolates where it was found to be 38 kDa. Isolates representing the different sialic acid groups were all affected by mild acid treatment, however, they showed different susceptibilities to treatment withVibrio cholerae Type 11 sialidase. erence test, based on a modified enzyme linked immunosorbent assay (ELISA) was developed to assess the attachment of Ph.d.p to fish cell lines. The influence of oligosaccharides on attachment was also investigated using seven lectins, including N-acetylmuraminic acid (sialic acid). Significant differences were observed in the levels of adhesion of Ph.d.p, isolated from different geographical regions, to Chinook salmon (Oncorhynchus tshawytscha), CHSE-214 cells. Representative isolates, from Italy and Japan, exhibited differences in binding to the CHSE cells after lectin treatment. These results will be discussed with reference to the role of sialic acid in cell adhesion and survival within the host.