Wastewater-based surveillance reveals distinct resistome profiles in younger and older populations

Antimicrobial resistance (AMR) poses serious health risks, especially to the older population. In this study, differences in antibiotic resistance genes (ARGs) between younger and older populations were investigated using wastewater-based surveillance. Wastewater samples were collected from four nursing homes, three high schools, and two residential areas in Changshu, China. Metagenomics was used to analyze the diversity and abundance of ARGs and their host characteristics, with a focus on pathogen-related ARGs. The age representativeness of the wastewater samples was verified by examining the expression levels of senescence-related genes and species composition. The results showed that the diversity of ARGs in wastewater samples from the nursing homes was higher than that from schools and residential buildings, with 1264, 986, and 1002 subtypes, respectively. Besides, ARG abundance was also higher in the samples from nursing homes, particularly for those clinically relevant β-lactam resistance genes (e.g., bla_VEB, bla_TEM, and bla_CTX-M families). Pathogen-related ARGs also had similarly higher diversity and coverage in the samples from nursing homes. Key pathogens (e.g., Escherichia coli and Klebsiella pneumoniae) had more complex resistance profiles in nursing home samples. These observations unequivocally indicate that the older population has a higher overall resistance level than the younger population. This study also demonstrates that wastewater-based surveillance can effectively assess the level of ARG carriage in specific subgroups, providing an important basis for supplementing clinical surveillance and developing targeted prevention and control strategies.