Detection Of Integron And Antibiotic Resistance Analysis In A Lab-scale Quinoline Degrading Microbial Community

Antibiotic-resistant bacteria prevail in contaminated environment. Some of them have multi-resistance which is related to the environmental pressures. In the aquatic environment, hospital effluence is the main source of bacteria's antibiotic-resistance, followed by municipal sewage. Resistant bacteria are abundant in the activated sludge of hospital wastewater and sewage treatment plants. However, there are few reports about antibiotic resistances in the industrial wasterwater treatment environment.The integron-gene cassette system plays an important role in the horizontal gene transferring process of resistant genes. The integron, which was found in bacterial genome, is a mobile gene element that includes a site-specific recombination system capable of integrating and expressing exogenous gene cassettes. A lab-scale denitrifying bioreactor, with quinoline as sole carbon source, has been established and able to efficiently remove quinoline and nitrate from the synthetic wastewater. In this study, PCR technique and clone library method were used to analyze the composition and potential functions of integrons in the ecosystem of quinoline-degrading bioreactor. The results showed that the integrons carry various of gene cassettes with size of between 200bp and 1000bp. Some of them, belonging to aminoglycoside resistence genes, such as aadA gene, might encode antibotic-resistance protein. Others which are similar with the sequences of integrons previously obtained in industrial wastewater or tar pond, such as FldF gene, might be related to degradation of aromatic compounds. Some gene cassettes could not find any significant similarity sequence. Their functions are unkown yet.Since types of antibiotic-resistant gene cassettes were the majority among the gene cassettes detected in the wastewater treament bioreactor, it is of interest to understand the antibiotic resistence property of the microorganisms. Thus, we analyzed the antibiotic resistance pattern, plasmid profile as well as broad-host-range plasmid characters of 35 functionally important strains, which were isolated from the studied quinoline-degrading bioreactor. The result showed that 42.9% of the isolates were resistant to antibiotics, and the incidence of multiple antibiotic resistances was 28.6%. The ratio of resistance to ampicillin, kanamycin, chloromycetin, streptomycin and rifampicin of the isolates were 28.6%, 22.9%, 20.0%, 22.9% and 0, respectively. There is no clear evidence showing the relationship between the plasmid profiles and resistance pattern. Moreover, the negative results from analysis of Inc-group-specific PCR amplification indicated that the broad-host-range plasmids might not play the main role in horizontal gene transfer in the bioreactor microbial community.There barely exists antibiotic pressure in the quinoline wastewater bioreactor, also the seed sludge came from a coking wastewater plant where hardly exists antibiotic component. However, the functionally important strains were generally resistant to antibiotic and many integrons in the community genome carried resistant gene cassettes. This phenomenon so far has not been reported and its mechanism needs further research.