SIMULTANEOUS OCCURRENCE OF VIBRIO-SALMONICIDA AND ANTIBIOTIC-RESISTANT BACTERIA IN SEDIMENTS AT ABANDONED AQUACULTURE SITES

The present authors have examined the survival of the fish pathogenic bacterium Vibrio salmonicida and the occurrence of antibiotic resistant bacteria in sediments from abandoned aquaculture sites. Survival of V. salmonicida 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. salmonicida in sediment samples from six out of 12 abandoned fish farm locations. One out of the six positive stations was abandoned in 1982. Vibrio salmonicida was not detected at the three stations not affected by aquaculture (control locations) or in sediment samples taken 200-250 m away from aquaculture sites. When applying high-performance liquid chromatography, oxytetracycline or furazolidone residues were not detected in sediment samples from control or abandoned aquaculture sites. Nevertheless, the percentage of bacteria resistant to oxytetracycline 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.