Gut Hi-C metagenomes of severe COVID-19 patients: bacteria and yeast involved in gut-lung axis.

Antimicrobial resistance (AMR) poses a critical threat to global health, particularly in intensive care units, where vulnerable patients are frequently exposed to multidrug-resistant microorganisms. The human gut microbiome serves as a key reservoir for AMR genes, which can disseminate to other body sites, including the lungs, especially during severe illness. We applied Hi-C metagenomics to stool samples from 11 critically ill COVID-19 patients and analyzed microbial isolates from their lungs to investigate intra-host transmission of AMR genes. Plasmid-resolved microbial interaction networks revealed AMR gene sharing across 13 bacterial genera, primarily from Firmicutes and Proteobacteria, with evidence of plasmid-mediated transfer across phylum boundaries and between gut and lung compartments. Notably, we identified genetically identical Klebsiella pneumoniae strains colonizing both the gut and lungs of a single patient, as well as shared plasmids carrying qnrS-1 and blaCTX-M-231 resistance genes between gut Escherichia coli and lung K. pneumoniae. In addition to bacterial pathogens, Candida yeast species isolated from both niches harbored resistance genes to multiple antifungal classes, including azoles. These findings underscore the dynamic, cross-compartmental nature of AMR dissemination within the human body and highlight the importance of integrative surveillance strategies to control resistance in clinical settings.IMPORTANCEWhile COVID-19 itself caused severe illness, many deaths were ultimately due to secondary microbial infections-often worsened by antibiotic resistance. Plasmids, which shuttle resistance genes between bacterial species, are key players in their spread, yet their roles in transmission, especially across body sites such as the gut and lungs, are to be elucidated. The use of Hi-C metagenomics allowed us to map bacterium-plasmid links in the guts of severe COVID-19 patients and reconstruct high-quality genomes of opportunistic fungi. Comparing these with lung-derived isolate genomes, we gained insight into possible intra-host dissemination routes of resistance genes. Preparing for future pandemics will require not only rapid pathogen detection but also tools to monitor microbiome health and resistance dynamics, and understanding how treatments and microbial imbalances shape infection risks.