THARA METHALE VELAKKATH PARAMBA, ARATHY VISWANATHAN, JAN-ULRICH KREFT, AND INDUMATHI MANIVANNAN NAMBI
Abstract
Antimicrobial resistance (AMR) in urban aquatic environments is an emerging public health concern, particularly in rapidly growing cities with inadequate wastewater and solid-waste management. This study assessed the occurrence, distribution and potential dissemination pathways of AMR across diverse water environments in Chennai, South India. Samples were collected from sewage treatment plants and associated upstream and downstream locations, an industrial wastewater detention tank, groundwater near a dumpsite, and community-managed water systems. Water-quality parameters, culturable bacterial populations, antibiotic-resistant bacteria and antibiotic resistance genes (ARGs) were analysed using culture-based methods, quantitative polymerase chain reaction and high-throughput Resistomap profiling. Bacterial abundance varied considerably among the sampling locations, with the highest counts recorded upstream of a sewage treatment plant (5.64 log CFU/ml) and in groundwater near the dumpsite (4.60 log CFU/ml). Industrial wastewater contained elevated total bacterial counts (4.56 log CFU/ml) and Escherichia coli (3.52 log CFU/ml), whereas the community-managed lake and swimming pool showed minimal E. coli contamination. The class 1 integron gene intI1 and the carbapenem resistance gene blaNDM reached maximum abundances of 10.90 and 10.24 log GC/ml, respectively. Other frequently detected resistance determinants included sul2, qnrS, aph32 and ermF. Industrial wastewater and dumpsite-affected waters were identified as major AMR hotspots, while centralized treatment systems achieved only partial removal of resistant bacteria and ARGs. Associations between heavy metals and several ARG classes further indicated the potential contribution of metal-driven co-selection. The findings demonstrate that treated effluents and diffuse urban pollution sources jointly promote environmental AMR dissemination. Integrated surveillance, improved wastewater treatment, industrial effluent control and effective landfill leachate management are therefore required to reduce AMR risks in urban aquatic ecosystems.