BACTERIAL SPECIES OTHER THAN RENIBACTERIUM-SALMONINARUM CROSS-REACT WITH ANTISERA AGAINST R-SALMONINARUM BUT ARE NEGATIVE FOR THE P57 GENE OF R-SALMONINARUM AS DETECTED BY THE POLYMERASE CHAIN-REACTION (PCR)

Genomic DNA was extracted from 4 strains of Carnobacterium piscicola a nd 2 strains of Corynebacterium aquaticum that had previously been rep orted to produce a 57 kDa protein that reacted with polyclonal antiser um against Renibacterium salmoninarum. Genomic DNA was also extracted from a Gram-negative bacterium isolated from the kidney tissue of a ma ture female coho salmon Oncorhynchus kisutch. The bacterium, tentative ly identified as Pseudomonas maltophila, cross-reacts with 2 polyclona l antisera, one of which is used in an enzyme-linked immunosorbent ass ay and the other in a fluorescent antibody test to identify R. salmoni narum. The isolate of P. maltophila, and the Carnobacterium piscicola and Corynebacterium aquaticum strains, were negative by a polymerase c hain reaction (PCR) that was designed to amplify a segment of the gene encoding p57, a major protein of R. salmoninarum. These results sugge st that although antibodies directed against R. salmoninarum crossreac t with antigens of bacterial species other than R. salmoninarum, the c ross-reacting antigen(s) is clearly not the same protein, as the non-R . salmoninarum bacteria lacked the gene encoding p57. These findings h ighlight some of the shortcomings of immunodiagnostic tests for detect ing R. salmoninarum and indicate the high degree of specificity associ ated with a PCR-based diagnostic technique.