Detection of antibiotic resistance determinants in bacteria isolated from fish

Introduction: For decades antibiotic therapy was the most efficient treatment of infectious diseases. However, microbes reacted to antimicrobial agents by developing antibiotics resistance (AR). Spreading of multidrug-resistant bacteria is a worldwide problem. The clinically relevant bacterial AR genes are constantly spreading to the environment from human and animal sources. Specific DNA elements integrons enable the spreading of AR genes between different bacterial species. Aim: The aim of this study was to examine the prevalence of genetic determinants responsible for antibiotic resistance in bacteria isolated from wild and farmed fish. Materials and methods: A total of 115 bacterial isolates from fish obtained from fish farming (95) and natural waters (20) were examined for the genes conferring resistance to clinically important antibiotics (aminoglycosides, β-lactams, fluoroquinolones, chloramphenicol, tetracyclines, macrolides, glycopeptides), biocides and for the carriage of class 1 and 2 integrons. Detection has been performed using PCR with specific primers, integron structure was accessed by DNA sequencing and bioinformatic analysis. Results: Genes conferring resistance to aminoglycosides (aph (6) Id, ant (3 ‚‘) Ib, aac (3) IIa), β-lactams including 3th generation of cephalosporins (oxa1, ctx-M), fluoroquinolones (qnrS) and biocides (qacE) were found. Bacterial isolates from fish obtained in natural water pond and river were distinguished by multiple antibiotic resistance profile, whereas bacteria isolated from fish obtained in breeding farms and supermarkets harbored genes responsible for biocide resistance. Integrons were rare and most of them carried no gene cassettes. Class 1 integron with integrated gene cassettes was found in two bacterial isolates from wild fish (Nemunas river). Integrons carried aminoglycoside adenylyltransferase aadA2 gene and dihydrofolate reductase dfrA12 gene responsible f