Homology of Vibrio anguillarum strains causing epizootics in turbot, salmon and trout reared on the Atlantic coast of Spain

Abstract

In this paper we report the physiological, biochemical, serological, and molecular properties of pathogenic Vibrio anguillarum strains isolated from turbot, salmon and trout reared at several seawater hatcheries on the Galician coast (N.W. Spain). These characteristics were compared with reference strains isolated from different fish or in other geographic areas. The role of extracellular virulence factors in the pathogenesis of vibriosis was also investigated. Agglutination reactions and LPS patterns revealed that most of our isolates belonged to serotype 1, and only the strain responsible for a turbot epizootic in 1985 belonged to serotype 2. The main differential phenotypic traits between these pathogenic vibrios were indol reaction, growth at 37°C and acid production from arabinose, galactose and sorbitol. All the isolates displayed strong protease, amylase, and phospholipase activities, and produced haemolysins against human, sheep and trout erythrocytes. In addition, these strains exhibited similar drug resistance patterns, being sensitive to nitrofuranes, flumequine, oxolinic acid, oxytetracycline and chloramphenicol, and highly resistant to ampicillin. Although the extracellular products from our Vibrio isolates displayed strong cytotoxic activity on the five fish cell lines tested, a non-pathogenic reference strain also showed a positive toxic effect, which indicates that a relationship between fish virulence and cytotoxicity cannot be established for all V. anguillarum strains. Whereas the Northwest Spain isolates belonging to serotype 1 shared one plasmid (47 Md) similar to the virulence plasmid pJM1, in the pathogenic vibrios assigned to serotype 2, no plasmids were detected and, hence, their virulence properties are chromosome-coded.