MOLECULAR CHARACTERIZATION OF MULTIPLE ANTIBIOTIC RESISTANCE IN Edwardsiella ictaluri AND Aeromonas hydrophila ISOLATES FROM DISEASED STRIPED CATFISH (Pangasianodon hypophthalmus) CULTURED IN THE MEKONG DELTA, VIETNAM  

The aim of this study was to examine the molecular multi-antibiotic resistance characteristics in E. ictaluri and A. hydrophila isolated from the intensive striped catfish farms of the Mekong Delta, Vietnam. A total of 141 E. ictaluri and A. hydrophila isolates were collected from 2013 to 2014. The percentage of multiple drug resistance (resistant to at least 3 antibiotics) of E. ictaluri and A. hydrophila isolates were 100% and 98.65%, respectively. The multiple antibiotic resistance (MAR) index mean values of E. ictaluri and A. hydrophila isolates were 0.54 and 0.28, respectively. The results indicated that these isolates were exposed to high risk sources of contamination where antibiotics were commonly used. Approximately 42% of E. ictaluri and 37% of A. hydrophila isolates from catfish contained class 1 integrons, but no class 2 and class 3 integrons were detected in both bacterial species. In the study, the genes found in gene cassettes regions associated with the class 1 integrons included those for dihydrofolate reductases (dfrA1), aminoglycoside adenyltransferases (aacA4, aadB), rifampin ADP-ribosyl transferase (aar2), metallo-betalactamase (blaVIM-1) and hypothetical proteins (orfC). The study also found genes resistant to sulfonamide (sul1 and sul2 harbored in 3'-CS region (conserved segment) of class 1 integron. In addition, other genes were responsible for resistance to tetracycline (tetA) and florfenicol resistant gene (floR) were detected in these class 1 integron-positive bacterial isolates. To our knowledge, this is the first report on molecular characterization of multiple antibiotic resistance of bacteria isolated from striped catfish farms in Vietnam.