Incidence of antibiotic and metal resistance and plasmid Carriage in Aeromonas isolated from brown bullhead (latalurus nebulosus)

G.W. PETTIBONE, J.P. MEAR AND B.M. SAMPSELL. 1996. Seventy-four strains of Aeromonas were isolated from skin, intestine, kidney and liver of 16 brown bullhead ( Ictalurus nebulosus ). All strains demonstrated multiple antibiotic resistance (MAR) with most strains resistant to rifampin (97%), novobiocin (96%) and vancomycin (85%). The minimum inhibitory concentration of eight metals to selected strains of Aeromonas revealed an apparent toxicity of chromium > copper > cadmium > nickel > mercury > zinc > cobalt > lead, based on the percentage of isolates sensitive to each concentration of metal. Plasmid DNA was found in 36% (27) of the isolates and most plasmid-containing strains had multiple plasmids less than 12 kilobase pairs (kbp) in size. No relationship between plasmid content and antibiotic or metal resistance was found. Plasmid incidence in bacteria isolated from five fish indicated that plasmids were more likely to occur in strains isolated from kidney and liver than in strains isolated from skin and intestine.