Enterobacterale strains like E. coli, Klebsiella pneumoniae, and Enterobacter spp. pose a serious epidemiological threat due to their potential as pathogenic organisms. Furthermore, bacteria belonging to the order Enterobacterales frequently exhibit resistance to carbapenem antibiotics and are capable of producing extended-spectrum β-lactamases (ESBLs). Consequently, they have been designated as critical priority pathogens by the World Health Organization (WHO, 2024).
Therefore, this study aimed to determine the impact of treated wastewater discharge on bacterial biodiversity within the order Enterobacterales and the presence of carbapenem resistance genes (CRGs) in river water samples at the catchment level.
River water was sampled at eight points from the upper Pilica River to its confluence with the Vistula (Poland). A total of 32 samples in four seasons were collected. Metagenomic DNA was extracted from the samples, and single-read Illumina sequencing was carried out. The number of CRGs in the samples was established through digital PCR. Physico-chemical parameters were studied in accordance with standard methods.
In the current study, the prevalence of Enterobacterales was lower than that of the other identified taxa. Enterobacterales accounted for about 1% of all amplicon sequence variants (ASVs), including Escherichia-Shigella (65.97% of Enterobacterales ASVs), Yersinia spp. (10.63%), Klebsiella spp. (9.69%), Enterobacter spp. (7.17%), Serratia spp. (4.21%) and others. All studied CRGs were present in the analysed samples. The most prevalent genes in river samples were blaVIM and blaOXA, while other studied genes (blaIMP, blaNDM, and blaKPC) occurred at lower concentrations. The research confirmed a relationship between selected Enterobacterales ASVs and CRG concentrations in the analysed samples. Moreover, we observed a statistically significant relationship between the studied micropollutants and temperature, as well as BOD5, COD, total phosphorus and nitrogen.
Concentrations of all studied micropollutants, including CRGs, Enterobacterales ASVs, and physico-chemical parameters, were sensitive indicators of anthropogenic influence in river water.
