Production of the 57 kDa major surface antigen by a non-agglutinating strain of the fish pathogen Renibacterium salmoninarum

Abstract

ABSTRACT:The major surface antigen of Renibacterium salmoninarum, p57, is associated with cell autoagglutination and imphcated as a virulence factor in fish infections. An autoagglutinating strain, JD24, caused 92% mortality when 2 X lo7 cells were injected intraperitoneally into rainbow trout Oncorhynchus mykiss, while a non-agglutinating strain, MT 239, produced only 7 % mortality after 100 d. The p57 antigen was present in the supernates of broth cultures of both strains when examined by western immunoblotting, and the gene for p57 was detected in both strains by PCR. Electron microscopy of cryopreserved thin sections showed an amorphous layer associated with the cell surface of JD24 which was not seen with MT 239. While p57 from JD24 could reassociate with cells of both strains, p57 from MT 239 failed to restore haemagglutination activity to either strain. Biotinylation of bacterial surfaces demonstrated the presence of a carbohydrate component of p57 from JD24 which was absent from the p57 produced by MT 239. The higher virulence of JD24 may depend not only on the production of p57, but also its direct association with the bacterial cell surface.

Mortality and kidney histopathology of chinook salmon Oncorhynchus tshawytscha exposed to virulent and attenuated Renibacterium salmoninarum strains

“…Fish exposed to the strain MT 239 had the lowest mortality (8%), and the reduced virulence reported with this strain in rainbow trout was also observed in a later study by Senson & Stevenson (1999). The MT 239 strain produces a 57 kDa protein (p57) that has been associated with autoagglutination and virulence (Bruno 1988(Bruno , 1990), but it differs from the virulent strains, including the type strain 33209 of the American Type Culture Collection (33209), in having no detectable p57 associated with its cell surface (Bruno 1990, Daly & Stevenson 1990, Wood et al 1995.…”

“…It is also the first study in which fish were challenged with a virulent and an attenuated strain of R. salmoninarum via 2 exposure routes and analyzed for the presence of gross and histopathological changes. The attenuated virulence observed with chinook salmon corresponds with the reduced virulence previously reported in rainbow trout (Bruno 1988, Senson & Stevenson 1999. Therefore, the attenuated virulence of MT 239 occurs in at least 2 salmonid species: O. tshawytscha, which is highly susceptible to BKD, and O. mykiss, which is more resistant (Sanders et al 1978, Bell 1987.…”

“…In addition, analysis of MT 239 by electron microscopy has failed to demonstrate the amorphous layer surrounding the bacterium (Senson & Stevenson 1999) that is observed with virulent, agglutinating strains and is believed to partially consist of p57 (Dubreuil et al 1990, Senson & Stevenson 1999. Recently, it was shown that low levels of p57 are associated with whole cell preparations of strain MT 239, but these levels are much lower compared to virulent strains (O'Farrell & Strom 1999, Senson & Stevenson 1999. In contrast, comparable levels of p57 are found in the culture supernatants (O'Farrell & Strom 1999, Senson & Stevenson 1999.…”

“…Recently, it was shown that low levels of p57 are associated with whole cell preparations of strain MT 239, but these levels are much lower compared to virulent strains (O'Farrell & Strom 1999, Senson & Stevenson 1999. In contrast, comparable levels of p57 are found in the culture supernatants (O'Farrell & Strom 1999, Senson & Stevenson 1999. Genetic analysis revealed that the sequence of msa in MT 239 is identical to the msa sequence in 33209, and the expression of msa is nearly equivalent in the 2 strains (O'Farrell & Strom 1999).…”

“…The MT 239 strain produces a 57 kDa protein (p57) that has been associated with autoagglutination and virulence (Bruno 1988(Bruno , 1990), but it differs from the virulent strains, including the type strain 33209 of the American Type Culture Collection (33209), in having no detectable p57 associated with its cell surface (Bruno 1990, Daly & Stevenson 1990, Wood et al 1995. In addition, analysis of MT 239 by electron microscopy has failed to demonstrate the amorphous layer surrounding the bacterium (Senson & Stevenson 1999) that is observed with virulent, agglutinating strains and is believed to partially consist of p57 (Dubreuil et al 1990, Senson & Stevenson 1999. Recently, it was shown that low levels of p57 are associated with whole cell preparations of strain MT 239, but these levels are much lower compared to virulent strains (O'Farrell & Strom 1999, Senson & Stevenson 1999.…”