Dynamics of class 1 integrons in aerobic biofilm reactors spiked with antibiotics

Jiaoqi Huyan, Zhe Tian, Yu Zhang*, Hong Zhang, Yanhong Shi, Michael R. Gillings, Min Yang

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    12 Citations (Scopus)
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    Class 1 integrons are strongly associated with the dissemination of antibiotic resistance in bacteria. However, little is known about whether the presence of antibiotics affects the abundance of integrons and antibiotic resistance genes during biological wastewater treatment. To explore the roles of class 1 integrons in spreading antibiotic resistance genes in environmental compartments, the dynamics of integrons were followed in biofilm reactors treating synthetic wastewater respectively spiked with streptomycin (STM) and oxytetracycline (OTC). The relative abundance of the integron-integrase gene (intI1) increased 12 or 29-fold respectively when treated with STM or OTC, under incrementally increasing dosage regimes from 0 to 50 mg L−1. Significant increases in intI1 abundance initially occurred at an antibiotic dose of 0.1 mg L−1. At the beginning of the experiment, 51% to 64% of integrons carried no gene cassettes. In STM and OTC spiked systems, there was a significant increase in the proportion of integrons that contained resistance gene cassettes, particularly at intermediate and higher antibiotic concentrations. Gene cassettes encoding resistance to aminoglycosides, trimethoprim, beta-lactam, erythromycin, and quaternary ammonium compounds were all detected in the treated systems. Three tetracycline resistance genes (tetA, tetC, tetG) were significantly correlated with the abundance of intI1 (p < 0.01), despite no tet resistance being present as a gene cassette. Genome sequencing of isolates showed synteny between the tet resistance genes and intI1, mediated through linkage to transposable elements including Tn3, IS26 and ISCR3. Class 1 integrons appeared to be under positive selection in the presence of antibiotics, and might have actively acquired new gene cassettes during the experiment.

    Original languageEnglish
    Article number105816
    Pages (from-to)1-9
    Number of pages9
    JournalEnvironment International
    Publication statusPublished - Jul 2020

    Bibliographical note

    Copyright the Author(s) 2020. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.


    • Antibiotic resistance
    • Lateral gene transfer
    • Mobilome
    • Pollution
    • Resistome


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