Comparison of microbial profiles between hospital wastewater and river water

This study aimed to compare the microbial profiles between hospital wastewater and river water to assess the dissemination of clinical isolates into the environment. Two types of water samples were collected from sampling sites which were geographically close (wastewater from the University Hospital of Larissa and river water from the Pineios River). Gram-negative bacteria isolated from both sample types were identified using MALDI-TOF. Furthermore, the minimum inhibitory concentration (MIC) of antibiotics were evaluated. A total of 54 Gram-negative isolates, belonging to diverse species, were collected from wastewater sample and river sample. All isolates were classified as MDR, exhibiting resistance to at least one agent from more than three different antibiotic classes. Based on species identification and susceptibility profiles, 27 isolates (19 from wastewater and 8 from river-water) were selected to be further characterized by whole-genome sequencing (WGS). Analysis of WGS data, revealed the presence of different STs, even in isolates belonging to the same bacterial species. Additionally, WGS data showed that carbapenemase-encoding genes were identified in the majority of isolates. PlasmidFinder identified a huge variety of plasmid replicons among the isolates studied. In conclusion, both hospital wastewater and river water contained isolates carrying clinically relevant resistance determinants, such as carbapenemase-encoding genes. The presence of these pathogenic bacteria in the river poses a significant public health concern. Although we could not identify the origin of MDR bacteria in the river sample, these findings highlight the growing threat of antimicrobial resistance in the environment and underscore the urgent need for improved treatment methods and stricter surveillance to control its spread.