The study aimed to analyze the correlation between heavy metals, metal resistance genes (MRGs), carbapenem resistance genes (CRGs), and mobile genetic element (MGE) in wastewater and determine their spread into river water. The q-PCR analysis was performed to investigate the occurrence and distribution of two CRGs (blaKPC and blaNDM), one MGE (intl1), and six MRGs across all the sampling sites. The absolute abundance of bacteria was generally higher in river sites impacted by wastewater discharge compared to upstream locations, with urban wastewater showing the most significant bacterial loads. This pattern suggests that untreated wastewater has a significant impact on both the overall bacterial frequency and the prevalence of resistance genes in the river water. The absolute and relative abundance of blaKPC (2.25 × 107 copy ml−1 and 2.05 × 10−4 copy 16S rRNA−1) and blaNDM (2.84 × 106 copy ml−1 and 6.74 × 10−6 copy 16S rRNA−1) was highest at K4, which is close to the direct discharging site of K2 and K3, suggesting that the wastewater played an essential role in the distribution of CRGs. Most genes were found K5 at a lower abundance, possibly due to a dilution effect. The presence of the intl1 gene was observed in all samples, indicating the possible risk of horizontal transfer of these genes. The CRGs and MRGs had a positive correlation with intl1, indicating that these genes tend to co-occur in the same bacterium or have identical sources of pollution. Network analysis provided additional evidence for the co-occurrence of CRGs with MRGs and MGE. These results indicated that untreated wastewater is the main contributor to ARGs in the river water.
Sahoo et al. (Fri,) studied this question.