Persistent Risks in the Effluents of Wastewater Treatment Plants: Mobile Genetic Elements and Viral-Mediated Dissemination of Pathogenic Antibiotic-Resistant Bacteria

Wastewater treatment plants (WWTPs) are recognized as
reservoirs
of pathogenic antibiotic-resistant bacteria (PARB), yet their genomic
risk dynamics remain unclear. This study recovered PARB genomes from
102 influent and effluent metagenomes from six countries; their activity
and risk potential were then experimentally validated with metatranscriptomics
on samples from a Shanghai WWTP. A total of 44 PARB genomes were reconstructed,
which carried both antibiotic resistance genes (ARGs) and virulence
factor genes (VFGs), and they persisted in the effluent. Mobile genetic
elements might mediate ARG transfer in 13 PARB genomes. Moreover,
bacteriophages infecting PARB harbored and were transcribing ARGs/VFGs,
and antiviral defense systems of PARB correlated with horizontal gene
transfer (HGT). Evolutionary analyses indicated that influent PARB
maintained high microdiversity via homologous recombination, while
effluent populations underwent purifying selection, suggesting that
wastewater treatment reduced the genetic diversity of PARB through
purifying selection. However, the persistent accumulation of PARB
as well as HGT might maintain the dissemination of ARGs. This study
emphasized the necessity of selecting the PARB genomes for wastewater
monitoring, thereby optimizing treatment strategies and mitigating
the potential health risks posed by pathogenic bacteria.