Occurrence ofPlasmids inDanish Isolates ofVibrio anguillarum Serovars 01and02andAssociation ofPlasmids with Phenotypic Characteristics

-Twohundred andtwenty-eight isolates ofVibrio anguillarum serovar 01(125isolates) andserovar 02(103 isolates) havebeencharacterized withregard toplasmid contents, biochemical properties, andinvitro hemagglutination andhydrophobic properties. Among74V.anguillarum isolates fromdiseased fish, 63carried onlya67-kbplasmid (pJMl), 9carried anadditional 98-kbplasmid, and1isolate carried onlythe98-kb plasmid. Onlyoneisolate waswithout plasmids. InV.anguillarum serovar 01fromnondiseased fish (mucus andgills), plasmids ofthesamesizes werepresent in29isolates (58%), whereas 21isolates (42%) wereplasmid free. Basedonhemagglutination andbiochemical properties, V.anguillarum serovar 01isolates weredivided into eight biovars. Theplasmid-carrying strains (102isolates) allfell within biovars 1and2,whereas the23 strains ofbiovars 3to8werewithout plasmids. Itwastentatively concluded there aretwopopulations ofV. anguillarum serovar 01.Onepopulation contains plasmid(s), ishemagglutination negative andtrehalose negative, anddoesnotformpellicles inbrothcultures, whereas theother population isplasmid freeandhas theopposite characteristics. Theformer groupistheonerelated todisease infish. All20V.anguillarum serovar 02isolates fromtheenvironment werewithout plasmids, whereas 54(65%)oftheisolates fromfish (trout and cod)carried plasmids. Thebiochemical diversity within serovar 02waspronounced; 13different biovars were demonstrated. Nocorrelation between thepresence ofplasmids andbiochemical properties wasobserved. Vibrio anguillarum isthemostimportant agent ofhemor- rhagic septicemias amongmarine fish. V.anguillarum iso- lates canbesubdivided into 10groups basedon0 antigens; mostisolates fromdiseased fish areclassified asserovar 01 or02(22). Intheir analysis ofhighly virulent strains ofV.anguil- larum, Crosaetal.(6)consistently demonstrated a50-MDa plasmid, designated pJM1,thatwasnotpresent inweakly virulent strains. Curing ofthepJM1plasmid wascorrelated withdecreased virulence (5). pJM1encodes averyefficient iron-sequestering