The plasmid profile of Edwardsiellaictaluri *

Abstract. The plasmid content of 18 isolates of Edwardsiella ictaluri found in channel catfish was analysed by agarose gel electrophoresis. Each isolate contained an identical set of plasmids. This set consisted of two prominent plasmids of 5.2 and 4.4 kilobase pairs, and three smaller and less apparent plasmids. One plasmid (the 5.2 kilobase plasmid) was radiolabelled and used to probe a blot of DNA from all isolates. All plasmids were hybridized but no chromosomal DNA was labelled. These plasmids must share some homologous regions. DNAs from other bacteria, including the related Edwardsiella tarda , were also probed and no hybridization was seen. It is suggested that a plasmid probe may be a sensitive, specific probe for detection of E. ictaluri in channel catfish