Prevalence of vancomycin resistance genes in Polish hospital wastewater

Resistance to vancomycin in bacteria (VRB) is primarily mediated by van genes (VRGs), among which the vanA and vanB phenotypes have the greatest clinical significance. They can be transferred between microbial cells via mobile genetic elements, which determines the high epidemic potential of these strains, creating even more dangerous "superbugs". Hospital wastewater (HW) discharged to wastewater treatment plants (WWTPs) is the main anthropogenic source of VRB and VRGs in municipal wastewater, which are finally released into the environment. Therefore, the main goal of this study was to assess the concentration of VRGs in hospital wastewater collected from the whole territory of Poland.

In this study, HW samples were collected in winter and summer seasons from 64 hospitals located in various provinces of Poland. Environmental DNA wasextracted from HW using the FastDNA™ Spin Kit for Feces (MP Biomedicals). The concentration of VRGs was analysed by high-throughput long-read sequencing based on nanopore technology.

In both sampling seasons (winter and summer, 2024), qualitative and quantitative analyses of VRGs revealed considerable differences in gene counts between seasons and regions of HW sample collection. The abundance of VRGs ranged from 0 to 6.55x10² gene copies/Gb and was highest in HW collected in winter from central-eastern Poland. Among ARGs responsible for resistance to vancomycin, vanA and vanB genes presented most frequently and the most common hosts of VRGs were Enterococcus faecium and Staphylococcus aureus.

The results of this study prove that untreated HW is a hotspot for VRGs and VRB to enter the environment. This research can be used to clarify the requirements for hospitals regarding the disinfection of wastewater, as well as the requirements for microbiological quality of wastewater entering WWTPs.