Classification, Antibiotics Resistance And Resistant Genes Detection Of The Bacterial Strains Isolated From Mariculture Diseased Fishes

Diseases caused by bacterial pathogens have been major harm to mariculture fishculture in China. Simutaneously, occurrence of antibiotics resistant strains has been agreat potential hazard to environment and aquatic food product. To get acomprehensive understanding of the species and the antibiotics resistance of thebacteria, we carried out a study to investigate the classification and the antibiotictisresistance of the bacterial strains isolated from diseased fishes from fish farm ofShandong, Jiangsu, Hebei, Tianjin between1999and2012.1. Classification of the bacterial strains. A total of124sequences of16S rRNA genewere obtained and comparied with the GenBank data with Blast, the results showedthat all strains were belonged to genus of Vibrio (83strains), Aeromonas (11stains),Edwardsiella (4strains), Pseudomonas (3stains) and Pseudoaltermonas (3strains),and the other15genera (20strains). The following phylogenetic analyse was able toclassified77strains into to18species，with dominated species as V. alginolyticus, V.harveyi, V. anguillarum, A. salmonicida and E. tarda. The presented results providesignificant data to ascertain the bacterial pathogens of mariculture fishes, which isimportant for making strategy to monitor and control the bacterial diseases.2. Antibiotics sensitivity assay of the bacterial strains. A total of230bacterialstrains were tested for thier susceptibility to6antibiotics (ampicillin, chloramphenicol,ciprofloxacin, furazolidone, rifampin and tetracycline) by K-B method. Among ofthese,149were ampicillin resistant strains, accounting for64.8%,29werechloramphenicol resistant strains(12.3%;),20were ciprofloxacin resistant(8.5%),110were furazolidone resistant (47.8%),8were rifampin resistant(3.4%),24weretetracycline resistant(10.2%). Multi-antibiotics resistance was found in108(47.0%) strains. Among of thesestrains,77(33.5%) strains were resistant to two,21(9.1%) strains to three,10(4.3%)strains to four antibiotics.3. Antibiotic resistant genes detection. Multi-PCR method was used to characterizethe chloramphenicol resistant genes (cat genes) and tetracycline resistant genes (tetgenes). In29chloramphenicol resistant strains, the catI were contained in12strains,catII in11strains, catIII in4strains, and none strain contains catIV. In24tetracyclineresistant strains, we found three mains genotype tetB(75%), tetC(16.7%) andtetE(8.3%). One strain was found to carry two diffrernt kind tet genes, tetC and tetD.Integron is the main cause of bacterial multi-drug resistance. We further carried outthe detection of class1and calss2integron in the tested230strains. There were sixstrains harbor class1integron and one of them had both class1and class2integron.Four strains had more than one diferent clones of class1integron. Sequences analysisof variable region of the integrons showed that antibiotic-, transporters-andpermease-associated genes were identified.