THE PLASMID PROFILES OF FISH PATHOGENIC ISOLATES OF AEROMONAS-SALMONICIDA, VIBRIO-ANGUILLARUM, AND VIBRIO-ORDALII FROM THE ATLANTIC AND PACIFIC COASTS OF CANADA

The plasmid profiles of oxytetracycline- and streptomycin-resistant is olates of Aeromonas salmonicida, Vibrio anguillarum, and Vibrio ordali i were examined by agarose gel electrophoresis. Bacterial isolates wer e from disease outbreaks in fish on the Atlantic and Pacific coasts. R esistant isolates were examined when grown in the presence and absence of antibiotic. Alkaline lysis methods were used for plasmid isolation . Vibrio spp. were predominantly plasmidless, except for a 47-kilobase (kb) plasmid. Atlantic coast isolates of A. salmonicida possessed fou r or six plasmids, with four smaller plasmids ranging in size from 4.3 to 8.1 kb being consistently observed. The plasmid profiles of antibi otic-sensitive ATCC strains were identical. The plasmid profiles of th e Pacific coast isolates of A. salmonicida varied slightly from those of the Atlantic coast isolates with six plasmids observed, ranging in size from 4.2 to 8.9 kb. Resistance to the antibiotics was not altered following plasmid curing experiments and resistance was not transfera ble to Escherichia coli. Thus, resistance to oxytetracycline and strep tomycin did not appear to be plasmid mediated.