The Prevalence of Integrons as the Carrier of Antibiotic Resistance Genes in Natural and Man-Made Environments

Class
1 integrase intI1 has been considered as a good proxy
for anthropogenic pollution because of being linked to genes conferring
resistance to antibiotics. The gene cassettes of class 1 integrons
could carry diverse antibiotic resistance genes (ARGs) and conduct
horizontal gene transfer among microorganisms. The present study applied
high-throughput sequencing technique combined with an intI1 database and genome assembly to quantify the abundance of intI1 in 64 environmental samples from 8 ecosystems, and
to investigate the diverse arrangements of ARG-carrying gene cassettes
(ACGCs) carried by class 1 integrons. The abundance of detected intI1 ranged from 3.83 × 10–4 to
4.26 × 10° intI1/cell. High correlation
(Pearson’s r = 0.852) between intI1 and ARG abundance indicated that intI1 could
be considered as an important indicator of ARGs in environments. Aminoglycoside
resistance genes were most frequently observed on gene cassettes,
carried by 57% assembled ACGCs, followed by trimethoprim and beta-lactam
resistance genes. This study established the pipeline for broad monitoring
of intI1 in various environmental samples and scanning
the ARGs carried by integrons. These findings supplemented our knowledge
on the distribution of class 1 integrons and ARGs carried on mobile
genetic elements, benefiting future studies on horizontal gene transfer
of ARGs.