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R.K. Cooper

Publications and source records attributed to R.K. Cooper.

2 recordsLinked to original sources
USGS1993

Plasmid-mediated romet resistance of Edwardsiella ictaluri

Romet®, a potentiated sulfa drug composed of five parts sulfadimethoxine and one part ormetoprim, is used to treat channel catfish Ictalurus punctatus infected with Edwardsiella ictaluri , the causal agent of enteric septicemia of catfish (ESC). Recently, several Romet-resistant isolates of E. ictaluri were isolated from channel catfish that had died from ESC in Virginia and Mississippi. This antimicrobial resistance was determined to be plasmid-encoded, as shown by agarose gel electrophoresis of plasmid DNA, and by the fact that the plasmid and associated antimicrobial resistance could be transferred to a recipient by single-step conjugation. Size of the R plasmid was approximately 55 kilobase pairs. Plasmids also conferred resistance to tetracycline, oxytetracycline, streptomycin, trimethoprim, and SXT (another potentiated sulfonamide, composed of trimethoprim and sulfamethoxazole). Each Romet-resistant E. ictaluri isolate was mated with a plasmid recipient, the Romet-sensitive Escherichia coli isolate 1932. Transconjugates were selected by plating on Mueller-Hinton agar that contained antimicrobials, and the mean transfer frequency was 1.483 × 10 −3 transconjugates per donor cell in the mating mixture. Each E. coli transconjugate was then mated with 20 Romet-sensitive isolates of E. ictaluri to assess the propensity of these E. ictaluri isolates to accept the R plasmid. The average transfer frequency when E. ictaluri isolates of channel catfish origin (N = 14) were used as recipients was 1.197 × 10 −2 transconjugates per donor cell in the mating mixture; mean transfer frequency when E. ictaluri isolates not originating from channel catfish were used was 1.019 × 10 -3 transconjugates per donor cell, which was significantly less (P = 0.0002).

Journal of Aquatic Animal Health↗