To evaluate the threat of the environmental dissemination
of antibiotic
resistance associated with wastewater treatment plants (WWTPs), the
removal efficiency of antibiotic resistance genes (ARGs) during wastewater
treatment needs to be assessed. The sample collection strategy is
one factor that is often overlooked in study design and most studies
on ARGs in wastewater perform grab sampling. Here, we hypothesized
that wastewater sampling (i.e., grab and composite sampling) influences
the observed ARG concentrations and calculated removal rates across
WWTPs. We compared the removal rates calculated based on the two different
sampling methods for several genes, including some clinically relevant
ARGs (blaNDM-1, blaOXA-1, MCR-1,
MCR-5, MCR-10, and qnrA). We conducted summer and
winter 24 h sampling campaigns where grab samples were collected every
2 h from the influent, secondary effluent, and final effluent. The
snapshot removal rate of each target gene calculated based on the
12 grab samples fluctuated by 0.5–1.6 log in the winter and
0.9–2.7 log in the summer, indicating diurnal variation. Overall,
for each target gene, the removal rates calculated based on 24 h composite
samples were approximately equal to the median of the 12 snapshot
removal rates. Our study confirms the importance of using composite
samples to monitor ARGs in wastewater.