CHARACTERIZATION AND INFECTIVITY OF 4 BACTERIAL STRAINS ISOLATED FROMBROWN RING DISEASE-AFFECTED CLAMS

Four bacterial strains isolated from carpet-shell clams (Ruditapes dec ussatus) and manila clams (R. philippinarum) exhibiting Brown Ring Dis ease (BRD) symptoms in Galicia (Northwest of Spain) were characterized using biochemical and serological techniques. Moreover their pathogen icity for clams and resistance against clam hemolymph were determined. AU of the Vibrio isolates exhibited biochemical characteristics typic al of the genus. Strains GR1703RP and GR6301RP, isolated from R. phili ppinarum showing signs of BRD, shared phenotypical and antigenic chara cteristics and bacterial extracellular products enzymatic activities w ith the Vibrio tapetis. Strains GR0705RD and GR0202RD, isolated from R . decussatus showing BRD signs, although biochemically similar to V. t apetis, did not show positive agglutination with V. tapetis antiserum. The virulence of the bacteria varied depending on the bacterial strai n and clam species assayed. Mortalities were recorded for a 30-day per iod, reaching values ranging from 6 to 80%, Strain GR0202RD was the mo st virulent for R. philippinarum with a cumulative mortality rate of 4 5%, while the strain GR0705RD induced the highest prevalence of BRD si gns, affecting 75% of the survivors. In the case of R. decussatus, the four bacterial strains produced a cumulative mortality rate higher th an 45%. In general, bacterial strains, showed resistance to clams hemo lymph. (C) 1998 Academic Press.