ISCR2-Mediated Multidrug-resistance In Recirculating Aquaculature System

Since mid-20 th century, the aquaculture industry developing rapidly and which has became the fastest growing industries in food field around the world. However, in the process of aquaculture, frequent broken out of bacterial diseases have became the main factors affecting the quality of aquatic products. To control the disease, a large number of antibiotics are used, which causes the development of bacterial resistance. Therefore, studying the dissemination mechanisms of bacterial resistance is essential.This paper aimed at the popular recirculating aquaculture system and this project focus on ISCR2 element. We tried to reveal the role of ISCR2 in the dissemination of antibiotic resistance through analysising the distribution of ISCR2 and the regular pattern of it between environmental bacterias and pathogens.The object for this study is the aquaculture recirculatingsystem in which broken outskin fester disease.It failed tocontrol the diseaseafter using florfenicol and norfloxacin, which meansthe pathogens also had the resistance. It was found that floR mediatedthe florfenicol resistance. Genome sequencing showed that floR is located on a ISCR2 element. The result of MIC showed that the proportion of resistant strains is higher in isolates which contained ISCR2. Database statistics showed that 90% strains which contained ISCR2 had find sul2 in the downstream. We found ISCR2 connected withstrB, str A, sul2, tetA, tet31, mph-like and mef,and formed five different structures. Beside, these five structures could been found in the database, and most of the strains were pathogens. QPCR results showed that the abundance offloR, strB, str A, sul2, tetA and tet31 were correlated with ISCR2.Through the above results, we get the following conclusions: 1) ISCR2 gene is widely distributed in many species of bacteria, both in pathogens and environmental bacterias. 2) ISCR2 element carrying multiple resistance genes and form a variety of structures, the same kind of structure have been found in different species of bacteria. Sometimes, both in pathogens and environmental bacterias. 3) The downstream of ISCR2 always connected with sul2.Conclusions can be drawn from the above surmise: 1) ISCR2 elements may be involved in mediating horizontal gene transfer. 2) ISCR2 and sul2 may form a mobile unit to mediate the HGT of multiple resistance genes. 3) ISCR2 element were widely distributed in many species of bacterias, and are found both in human pathogens and environmental bacteria. It may become a bridge between human pathogens and environmental antibiotic resistant genes’ library.Through the above results, we get the following conclusions:1) ISCR2 element carrying multiple resistance genes and form a variety of structures, the same kind of structure have been found in different species of bacteria. Sometimes, both in pathogens and environmental bacterias. Which means ISCR2 elements may be involved in mediating horizontal gene transfer.2) In this recirculating aquaculture system, ISCR2 element mediates the dissemination of variety antibiotic resistance genes, leding to the development of bacterial resistance, which can seriously affecting the prevention and treatment of disease.3) The downstream of ISCR2 always connected with sul2. ISCR2 and sul2 may form a mobile unit to mediate the HGT of multiple resistance genes.4) ISCR2 gene is widely distributed in many species of bacteria, both in pathogens and environmental bacterias. It may become a bridge between human pathogens and environmental antibiotic resistant genes’ library.