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 (Tapes philippinarum ) 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 incubated in the genus Vibrio and further divided into 6 physiological groups. 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 P1. 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.