Frequent Occurrence of Drug Resistant Bacteria in Ayu (Plecoglossus altivelis) Culture

Abstract

Chloramphenicol (CM)- and tetracycline (TC)-resistant bacteria which could grow on Heart Infusion agar containing 6.2 mcg/ml of CM or TC, respectively, were isolated with high frequencies from the intestinal tracts of cultured Ayu (Plecoglossus altivelis) and the water of Ayu culturing ponds in Tokushima Pref. CM- and TC-resistant bacteria were not isolated from the intestinal tracts of wild Ayu collected from the river Nakagawa in Tokushima Pref. The principal drug resistant bacteria isolated from the intestinal tracts were Aeromonas hydrophila and Vibrio anguillarum. Drug resistant Pseudomonas, Enterobacter aerogenes, E. cloacae, Escherichia coli, Hafnia, Salmonella arizonae and other unidentified Enterobacteriaceae were occasionally found. Drug resistant bacteria isolated from the water of ponds were common to those from the intestinal tracts. However, drug resistant E. coli, Psudomonas and V. anguillarum were not isolated from the water. All drug resistant V. anguillarum strains carried R plasmids. R plasmids were detected in a part of the Hafnia, E. cloacae, A. hydrophila, unidentified Enterobacteriaceae and E. aerogenes strains. The drug resistance markers present in the R plasmid bearing strains were in most cases sulfonamides streptomycin CM and TC.