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The intestine is the primary colonisation site for carbapenem-resistant Enterobacteriaceae (CRE) and serves as a reservoir of CRE that cause invasive infections (e.g. bloodstream infections). Broad-spectrum antibiotics disrupt colonisation resistance mediated by the gut microbiota, promoting the expansion of CRE within the intestine. Here, we show that antibiotic-induced reduction of gut microbial populations leads to an enrichment of nutrients and depletion of inhibitory metabolites, which enhances CRE growth. Antibiotics decrease the abundance of gut commensals (including Bifidobacteriaceae and Bacteroidales ) in ex vivo cultures of human faecal microbiota; this is accompanied by depletion of microbial metabolites and enrichment of nutrients. We measure the nutrient utilisation abilities, nutrient preferences, and metabolite inhibition susceptibilities of several CRE strains. We find that CRE can use the nutrients (enriched after antibiotic treatment) as carbon and nitrogen sources for growth. These nutrients also increase in faeces from antibiotic-treated mice and decrease following intestinal colonisation with carbapenem-resistant Escherichia coli . Furthermore, certain microbial metabolites (depleted upon antibiotic treatment) inhibit CRE growth. Our results show that killing gut commensals with antibiotics facilitates CRE colonisation by enriching nutrients and depleting inhibitory microbial metabolites. Broad-spectrum antibiotics can kill harmless bacteria in our intestine, thus facilitating invasion by antibiotic-resistant bacteria such as carbapenem-resistant Enterobacteriaceae (CRE). Here, Yip et al. show that killing gut bacteria with antibiotics leads to enrichment of nutrients and depletion of inhibitory microbial metabolites, which overall potentiates CRE growth.

The intestine is the primary colonisation site for carbapenem-resistant Enterobacteriaceae (CRE) and serves as a reservoir of CRE that cause invasive infections (e.g. bloodstream infections). Antibiotics disrupt colonisation resistance mediated by the gut microbiota, promoting the expansion of CRE within the intestine. We used ex vivo faecal cultures to measure the impact of antibiotics (that promote CRE intestinal colonisation) on the faecal microbiota from healthy human donors. We demonstrated that antibiotics decreased the abundance of gut commensals (including Bifidobacteriaceae and Bacteroidales) in human faecal microbiota, resulting in an enrichment of nutrients and a depletion of microbial metabolites. We measured the nutrient utilisation abilities, nutrient preferences, and metabolite inhibition susceptibilities of several carbapenem-resistant Enterobacteriaceae strains, including Escherichia coli, Klebsiella pneumoniae, and Enterobacter hormaechei. Nutrients (which were elevated with antibiotics) acted as carbon and nitrogen sources to support CRE growth, where CRE strains showed an ordered preference for specific nutrients. These nutrients were also increased in faeces from antibiotic-treated mice but decreased following intestinal colonisation with carbapenem-resistant E. coli. Microbial metabolites (which decreased with antibiotics) were inhibitory towards CRE growth in vitro. Carbapenem-resistant E. coli growth was decreased in faecal samples from mice treated with a mixture of inhibitory metabolites compared with PBS-treated mice. These findings demonstrated that killing gut commensals with antibiotics disrupts colonisation resistance by enriching nutrients that support CRE growth and depleting metabolites that inhibit CRE growth. These results support the development of new microbiome therapeutics to prevent CRE intestinal colonisation, which would also prevent the subsequent development of invasive CRE infections.