Temporal dynamics of class 1 and class 3 integron pools in treated wastewater

Area of Science:

• Environmental microbiology
• Molecular biology
• Public health

Background:

• Wastewater environments are significant reservoirs for antimicrobial resistance (AMR) gene dissemination.
• Integrons play a crucial role in the spread of AMR, but their diversity in wastewater remains underexplored.

Purpose of the Study:

• To characterize the integron pool in secondary-treated municipal wastewater over a year.
• To identify clinically relevant antimicrobial resistance gene cassettes (ARGCs) and assess associated risks.

Main Methods:

• Weekly collection of 52 wastewater samples over one year.
• PacBio long-read sequencing of integron arrays from pooled monthly samples.
• Analysis of 283,579 integron reads to identify gene cassettes (GCs) and functions.

Main Results:

• Identified diverse class 1 and class 3 integrons, with AMR being a prevalent function in class 1.
• Most ARGCs conferred resistance to aminoglycosides and beta-lactams, including carbapenemases (e.g., blaGES-5).
• Observed seasonal variations in integron arrays and GC abundance, including macrolide and phenicol resistance.

Conclusions:

• Secondary-treated wastewater serves as a reservoir for diverse and clinically relevant resistance integrons.
• Class 1 and class 3 integrons are significant reservoirs for beta-lactamase-encoding GCs, including carbapenemases.
• Seasonal fluctuations in ARGCs suggest dynamic AMR evolution and spread within wastewater ecosystems.