Simultaneous occurrence of Vibrio salmonicida and antibiotic-resistant bacteria in sediments at abandoned aquaculture sites

Abstract. The present authors have examined the survival of the fish pathogenic bacterium Vibrio salmonidda and the occurrence of antibiotic resistant bacteria in sediments from abandoned aquaculture sites. Survival of V. salmonidda was determined by fluorescent monoclonal antibody labelling combined with 4',6-diamidino-2-phenylindole (DAPI) staining. Using this method, the authors were able to detect V. salmonidda in sediment samples from six out of 12 abandoned fish farm locations. One out of the six positive stations was abandoned in 1982. Vibrio salmonidda was not detected at the three stations not affected by aquaculture (control locations) or in sediment samples taken 200–250m away from aqua-culture sites. When applying high-performance liquid chromatography, oxytctracyclinc or furazolidonc residues were not detected in sediment samples from control or abandoned aquaculture sites. Nevertheless, the percentage of bacteria resistant to oxytctracycline was higher in aquaculture sediments, as compared to control sediments. The simultaneous occurrence of fish pathogens and high levels of resistant bacteria in sediments increases the risk of transfer of resistance to the pathogens.