Environmental sampling (wastewater) could be an efficient surveillance strategy to capture global emerging trends in the spread of antibiotic resistance. Long-read DNA sequencing can resolve the genetic context of antibiotic resistance genes (ARGs) and is a promising tool for non-culture-based monitoring of antibiotic-resistant pathogens and ARGs in environmental samples, but has not been rigorously validated against conventional methods. We tested long-read sequencing using the portable Nanopore MinION for surveying pathogens, ARGs, and antibiotic-resistant pathogens in municipal wastewater, hospital wastewater, and surface water collected from Boston, USA and Vellore, India. We compared detection of enteric pathogens by assembly of long reads, with and without short-read polishing, and unassembled raw long reads for ARGs to multiplex real-time PCR. Using real-time PCR as a benchmark, long-read metagenomics was 49% sensitive and 75% specific at pathogen detection in assembled contigs, and 16% sensitive and 100% specific at detecting 28 clinically relevant resistance genes in raw long reads. Short-read polishing did not substantially improve pathogen identification or impact ARG identification in the assembled contigs, demonstrating that short-read polishing is not required, which greatly reduces costs. The high specificity of ARG detection supports portable long-read sequencing as a valuable tool to profile ARGs and antibiotic-resistant pathogens for environmental surveillance programs.
Background Low- and middle-income countries (LMICs) bear the largest mortality burden due to antimicrobial-resistant infections. Small-scale animal production and free-roaming domestic animals are common in many LMICs, yet data on zoonotic exchange of gut bacteria and antimicrobial resistance genes (ARGs) in low-income communities are sparse. Differences between rural and urban communities in population density, antibiotic use, and cohabitation with animals likely influence the frequency of transmission of gut bacterial communities and ARGs between humans and animals. Here, we determined the similarity in gut microbiomes, using 16S rRNA gene amplicon sequencing, and resistomes, using long-read metagenomics, between humans, chickens, and goats in rural compared to urban Bangladesh. Results Gut microbiomes were more similar between humans and chickens in rural (where cohabitation is more common) compared to urban areas, but there was no difference for humans and goats. Urbanicity did not impact the similarity of human and animal resistomes; however, ARG abundance was higher in urban animals compared to rural animals. We identified substantial overlap of ARG alleles in humans and animals in both settings. Humans and chickens had more overlapping ARG alleles than humans and goats. All fecal hosts carried ARGs on contigs classified as potentially pathogenic bacteria, including Escherichia coli, Campylobacter jejuni, Clostridiodes difficile, and Klebsiella pneumoniae. Conclusions While the development of antimicrobial resistance in animal gut microbiomes and subsequent transmission to humans has been demonstrated in intensive farming environments and high-income countries, evidence of zoonotic exchange of antimicrobial resistance in LMIC communities is lacking. This research provides genomic evidence of overlap of antimicrobial resistance genes between humans and animals, especially in urban communities, and highlights chickens as important reservoirs of antimicrobial resistance. Chicken and human gut microbiomes were more similar in rural Bangladesh, where cohabitation is more common. Incorporation of long-read metagenomics enabled characterization of bacterial hosts of resistance genes, which has not been possible in previous culture-independent studies using only short-read sequencing. These findings highlight the importance of developing strategies for combatting antimicrobial resistance that account for chickens being reservoirs of ARGs in community environments, especially in urban areas.
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