CHARACTERIZATION OF STRAINS RELATED TO BROWN RING DISEASE OUTBREAKS IN SOUTHWESTERN SPAIN

Several characteristics, including biochemical, serological, drug resistance and plasmid profiles, of strains isolated from clams in southwestern Spain affected with brown ring disease have been comparatively studied. On the basis of 36 standard physiological and biochemical tests, all strains isolated were included in the genus Vibrio and further divided into 6 groups. The groups were differentiated on the basis of only 8 phenotypic traits: growth at 35-degrees-C, arginine dihydrolase, gelatinase production, Voges-Proskauer and ONPG tests, and acid production from sucrose, amygdalin and mannitol. Applying these characteristics, the strains resembled Vibrio pelagius and V. splendidus species. However, the isolates of each group showed no cross-reactions with the antisera raised against several reference strains of different species of Vibrio, including V. anguillarum, V tubiashii, V damsela, V. pelagius, V splendidus and the unclassified Vibrio Pl. Although only 57.7 % of the strains tested harbored one or more plasmids, the majority of the plasmid-containing strains (93.3 %) carried a large plasmid band of 34.4 MDa. A high number of isolates, regardless of their taxonomic group, were resistant to ampicillin and erythromycin. However, all the Vibrio strains were sensitive to chloramphenicol, tetracycline, gentamicin, nitrofurantoin, nalidixic acid and trimethoprim sulphamethoxazole. No correlation between plasmid content and drug resistance was observed.