Environmental Transmission Of High-Risk Antibiotic Resistance Genes Carried By Integrons

With the extensive use and abuse of antibiotics in human production and life,it’s gradually found that antibiotics can induce the appearance and enrichment of antibiotic resistance genes(ARGs)and antibiotic resistant bacteria,resulting in environmental pollution and the failure of antibiotics.Mobile genetic elements can carry ARGs to transfer horizontally between microorganisms to promote their environmental spread and proliferation.Integrons are typical mobile genetic elements that can be loaded by other mobile genetic elements(such as plasmids and transposons)for horizontal gene transfer between bacteria,and they play an important role in horizontal gene transfer of ARGs.Therefore,a comprehensive analysis of the ARGs carried by integrons and their development rules are important for us to understand the environmental risks of ARGs,based on which to develop control strategies.In this study,we first investigated the literature related to integrons and antibiotic resistance genes in the past 40 years,counted the diversity of ARGs reported to be carried by integrons,and reviewed the potential high-risk ARGs carried by integrons in combination with their environmental distributions,bacterial hosts and gene cassette arrangements.Two antibiotics(kanamycin and ampicillin)corresponding to the most common ARGs carried by integrons showed by the investigation results were used as the experimental antibiotics,and the effect of antibiotic selection pressure on the carrying of class 1 integrons by environmental microorganisms was investigated by using the combination of molecular methods and third-generation sequencing.Finally,for a comprehensive profile of potential high-risk ARGs,a mobile ARG database was established by summarizing ARG information carried by mobile genetic elements(integrons,plasmids and transposon).The establishment of the mobile antibiotic resistance genes database provides an important reference database for future research,which can be used to identify potential high-risk mobile ARGs.The main conclusions are as follows:(1)507 ARG subtypes were found carried by integrons.Aminoglycoside resistance genes,β-lactam resistance genes and trimethoprim resistance genes were the most common ARGs carried by integrons.Escherichia coli,Pseudomonas aeruginosa and Klebsiella pneumoniae are the most common bacterial hosts of integrons,and ARGs-containing integrons have been frequently detected in various environments(pollution source environments,natural environments and human-related environments).(2)5 mg/L kanamycin can effectively enrich integron-ARGs carrying microorganisms,especially Aeromonas.After exposure of 16 days under 5 mg/L kanamycin,61.2% of bacterium carrying ARGs-containing integrons were identified as Aeromonas rivipollensis,followed by Aeromonas Media(18.3%),and Aeromonas caviae(10.2%).Aac(6’)-I,aac(6’)-Ib-cr,aad A16,aad A2,ant(3’’)-Ih-aac(6’)-IId,bla VIM-1,cat B3,arr2,dfr A12 and dfr A17 were detected in variable regions of integrons carried by these culturable bacterium.(3)Identification of variable regions of class 1 integrons in systems showed that the variable regions of class 1 integrons changed significantly under the selective pressure of 50 mg/L kanamycin.After its exposure of 16 days,the number of resistance gene cassettes carried by total microbes accounted for 38.4% of the detected number of class 1 integron gene cassettes,which was 2.2 times higher than that in the control group.Meanwhile,the diversity of ARG subtypes carried by integrons was in the highest among all groups that 54 ARG subtypes were detected and encoded resistance to 7 antibiotics.Compared with the control group,the selective pressure induced an increase of 17 ARG subtypes to be observed.Thus,50mg/L kanamycin could significantly promote microbial enrichment of resistance gene cassettes in the environment.(4)A database referring potential mobile antibiotic resistance genes of 537 ARG subtypes and 25,267 gene sequences was established.β-lactam resistance genes accounted for 39.9% of the total number of mobile ARGs,followed by aminoglycoside resistance genes(126 subtypes,23.5%)and trimethoprim resistance genes(45 subtypes,8.4%).