ANTIGENIC CHARACTERIZATION OF ENTEROCOCCUS STRAINS PATHOGENIC FOR TURBOT AND THEIR RELATIONSHIP WITH OTHER GRAM-POSITIVE BACTERIA

We describe here the serological and antigenic characterization of a g roup of highly virulent Enterococcus strains that, since 1993, have ca used heavy economic losses in turbot Scophthalmus maximus reared in no rthern and northwestern Spain, Reference Gram-positive strains and the corresponding polyclonal antisera raised against some species of lact ic acid bacteria as well as Corynebacterium aquaticum and Renibacteriu m salmoninarum were included. Agglutination assays demonstrated that r egardless of the farm and year of isolation, all strains from turbot w ere serologically homogeneous. However, a number of cross-reactions oc curred among the various groups of bacteria (mainly among Enterococcus , Carnobacterium and Lactobacillus species). Analysis of the surface p roteins and western blot assays supported the antigenic homogeneity of the Enterococcus strains isolated from turbot because they all yielde d an essentially identical protein pattern (major common bands were 40 , 45, and 50 kDa) and reacted similarly with antisera raised against r epresentative strains of this group (there were at least 7 common band s of 20, 25, 30, 40, 45, 57 and 80 kDa). This serological homogeneity suggests that the development of vaccines to control enterococcosis in turbot should be feasible. Irrespective of the source of the polyclon al antisera employed, common immunoreactive proteins were present in a ll the Gram-positive bacilli and cocci tested. This, together with the cross-agglutination reactions noted among the various bacterial taxa tested, suggests that serological identification of the turbot Enteroc occus using polyclonal antisera could be problematical.