Plasmid-profile in pathogenic edwardsiella ictaluri isolated from infected catfish

ABSTRACT

Thirteen strains of catfish pathogen, Edwardsiella ictaluri, were isolated from infected catfish over a period of four years from different geographic areas. All the strains were found to be susceptible to aminoglycosides, cephalosporins, penicillins, quinolones, tetracyclines, chloramphenicol, nitrofurantoin and sulfonamides. The isolated strains were examined for their plasmid contents. The plasmid profile in the channel catfish isolates of E. ictaluri consisted of one to four species of plasmids. Fewer plasmid species were observed in the strains which were isolated in earlier years and the number was progressing in the strains isolated in later years. In the non-channel catfish isolates of E. ictaluri, variable patterns of plasmid profiles were observed in the E. ictaluri strains. Such profiles were dependent on the host fish species, but at least one or two of the plasmid species were common among some of these strains. There was no detectable antibiotic resistance in any of the strains which excluded the evolvement of any of the plasmids in antibiotic resistance. Plasmid curing was studied to investigate some of the functions of these plasmids. Curing was performed by treatment with a curing agent [acridine orange, ethidium bromide, nalidixic acid] or by incubation at elevated temperature. Plasmids in E. ictaluri appeared to have virulence related functions that contribute to the pathogenicity against catfish