Carbapenemase and extended-spectrum β-lactamase producing bacteria isolated from municipal wastewater treatment plant and urban river in Nepal

Municipal wastewater treatment plants (WWTPs) and rivers receiving sewage are known hotspots for antibiotic-resistant bacteria (ARB), harboring a wide variety of antibiotic resistance genes (ARGs) and mobile genetic elements. However, the specific distribution of ARB carrying multiple resistance genes in municipal WWTPs and their receiving rivers in Kathmandu remains unclear. Therefore, this study investigated the proportion of antibiotic-resistant bacterial populations and the presence of various ARGs and integrons in carbapenemase- and extended-spectrum β-lactamase (ESBL)-producing bacteria isolated from municipal wastewater and river water. The improvement in water's physicochemical characteristics and a significant reduction in ARB and antibiotic resistance determinants were observed in treated municipal wastewater compared to untreated wastewater. Among 232 bacterial isolates from these samples, 34.82 % were identified as carbapenemase producers, while 42.50 % were confirmed as ESBL producers. <i>E. coli</i> and <i>K. pneumoniae</i> were the predominant carbapenemase- and ESBL-producing bacteria, with their highest abundance in untreated municipal wastewater. Among carbapenemase-producing bacteria, <i>bla</i> _NDM and <i>bla</i> _OXA genes were more prevalent, whereas <i>bla</i> _TEM and <i>bla</i> _CTX-M genes were commonly detected in ESBL-producing bacteria. Nearly half of these bacterial isolates carried the <i>intI1</i> gene, indicating its role in the dissemination of ARGs. These findings underscore the critical role of WWTPs in the removal of chemical and biological pollutants, highlighting their significance in urban ecosystem-based adaptation. However, the simultaneous presence of multiple resistance genes and integrons in ARB contributes to the rising antimicrobial resistance in the environment, emphasizing the need for targeted efforts to manage and mitigate the spread of resistance factors.