Constant use of antibiotic has resulted in emergence of resistant bacteria of it, and there are several issues increasing social concerns on public health internationally;
raised issues are including difficulty on infection treatment, safety issues with residue of antibiotic, and transmission of resistant bacteria to human body. Therefore, this study determined resistant rate of fish pathogenic bacteria isolated
from cultured flounder on tetracycline, typical antibiotic sed in aquaculture, and analyzed the type of resistance genes distributed in resistant strain through PCR method. In this study, we isolated and utilized 160 Streptococcus prauberis isolates, 1 Streptococcus iniae isolate, 66 Edwardsiella tarda isolates, 56 Vibrio sp. isolates, and 23 of unidentified isolates (in total 306 isolates) from presumed infected olive
flounder in Jeju island from march 2016 to October 2017.
Antibiotic resistance pattern of each strains is examined on 21 different antibiotics including ampicillin, nalidixic acid, erythromycin, kanamycin, tetracycline, and sulfadiasine. The result shows that S. parauberis isolates are highly resistant to quinolone type, tetracycline type, and sulfadiazine. Vibrio sp. isolates are highly resistant to penicillin type containing ampicillin, amoxicillin. Similar to Vibrio sp. isolates, E. tarda isolates are highly resistant to various antibiotics including penicillin type. In addition, most strains used in the test were multi-resistance that are resistant to more than 2 types of antibiotics. Investigation on antibiotic resistance pattern and resistant bacteria through antibiotic susceptibility test of isolated strains from Jeju requires continuous study to restrain increase of resistance on antibiotic and selection of proper treatment. This study will be basis data of resistance study by strains.
Isolated strains are generally resistant to tetracycline type antibiotic. Thus, this study analyzed resistance genes in resistant strains to tetracycline and oxytetracycline. Out
of 306 isolated strains, tetracycline resistant strains are 83 S. parauberis isolates, 49 E. tarda isolates, and 15 Vibrio sp. isolates (in total 147 strains). We conducted PCR and multiplex PCR to check resistance determination in resistant strains. The result of multiplex PCR to detect tet (A-G) from gram negative bacteria shows that tet (D) was found in most E. tarda isolates. And other genes are not found in it. The presence of tet (B), tet (D), tet (M), tet (B&M) in Vibrio sp. was found in isolates, and we confirmed various tet gene were distributed in Vibrio sp.
The result of single PCR to detect tet (M), tet (O), tet (S), and so on from gram positive bacteria shows that S. parauberis isolates contain tet (M), tet (S), and tet (M&S), and tet (S) is most dominant gene since 76 isolates contain it.