Abstract
Analysis of the plasmid deoxyribonucleic acid complement of high- and low- virulent strains of the fish pathogen Vibrio anguillarum showed a correlation between enhanced virulence and the presence of a 50-megadalton plasmid class. All 50-megadalton plasmids isolated from different high-virulent V. anguillarum strains were homologous as judged by the analysis of plasmid deoxyribonucleic acid-deoxyribonucleic acid hybridization. The 50-megadalton plasmid class did not have polynucleotide sequences in common with plasmids of different incompatibility groups.