Effects of Cage Farming on Antimicrobial and Heavy Metal Resistance of Escherichia coli, Enterococcus faecium, and Lactococcus garvieae

Objective: To characterize antibiotic resistance genes (ARGs) and heavy metal resistance genes (HMRGs) of Escherichia coli and Enterococcus faecium isolated from the sediment and Lactococcus garvieae isolated from fish. Materials and Methods: The isolated bacteria were identified by sequencing 16S rRNA genes. After identification of the bacteria, tetracycline ( tet A , tet B , tet D), erythromycin ( ere A, ere B), sulfonamides ( sul I , sul II), trimethoprim ( dhfr A1), β-lactam ( bla TEM , bla CTX , amp C), florfenicol ( flo R), and class 1 integron ( Int 1) resistance gene were then determined. The presence of HMRGs, including copper ( cop A), mercury ( mer ), cadmium, zinc, cobalt ( czc ), and nickel, cobalt cadmium ( ncc ), was also analyzed by PCR. All strains were checked for the presence of ARGs and/or HMRGs on the plasmid. Results: The frequency of the β-lactam resistance gene was highest and ranged from 49.7% to 62.3%, followed by sulfonamides, tetracyclines, phenicols, and macrolide resistance genes. The cage culture fish farming practice showed significant effects on ARG frequency of bacteria isolated from the sediment, whereas it had no effect on the frequency of HMRGs. The most prevalent HMRG was determined as mercury-resistant mer gene in all bacteria. All four of the HMRGs were located on plasmids with frequency ranging from 1.20% to 32.53%. The presence of ARGs on plasmids ranged between 2.2% ( Dhfr 1) and 75% ( Amp C, blactx, tetB), and plasmids did not contain tetD and ereB genes. Conclusion: The results of this study indicate that fish farming can significantly influence the antimicrobial resistance properties of bacteria isolated from sediment samples.