Garzetti, D. | Search bioRxiv

bioRxiv2026

Gut microbiota within-host evolution enforces colonization resistance against enteric infection

Limited resource availability in the gut promotes competitive interactions between bacteria, which drive adaptive within-host evolution (1-3). While adaptive evolution of bacterial communities has been increasingly studied in the recent years (4-7), its functional implications for host physiology remain unknown. Here, we show that within-host evolution of the human commensal Enterococcus faecalis boosts colonization resistance to enteric Salmonella enterica serovar Typhimurium (S. Typhimurium) infection. During gut colonization, E. faecalis evolves the ability to metabolize fructoselysine, an abundant Amadori rearrangement product generated by thermal food processing. The depletion of this diet-derived nutrient prevents S. Typhimurium colonization by restricting an essential resource. This protective mechanism was conserved across independent mouse colonies and arises via diverse evolutionary trajectories, including nucleotide polymorphisms, gene amplifications, and a horizontal gene transfer event. Additionally, analysis of E. faecalis isolates from human infants revealed that adaptation to fructoselysine availability occurs in a diet-dependent manner. Isolates from infants fed with fructoselysine-rich formula were able to utilize fructoselysine, whereas those from infants fed with fructoselysine-poor breast milk were not. Conclusively, our results identify an inherent microbiome-driven self-healing mechanism, wherein bacterial evolution restores colonization resistance against enteric pathogens through evolved nutrient depletion. Understanding these evolutionary dynamics will inform microbiome-targeted approaches to prevent and treat infectious diseases by harnessing adaptive bacterial metabolism.

microbiology↗

bioRxiv2023

Contribution of bacterial and host factors to pathogen "blooming" in a gnotobiotic mouse model for Salmonella enterica serovar Typhimurium-induced enterocolitis

Inflammation has a pronounced impact on the intestinal ecosystem by driving an expansion of facultative anaerobic bacteria at the cost of obligate anaerobic microbiota. This pathogen "blooming" is also a hallmark of enteric Salmonella enterica serovar Typhimurium (S. Tm) infection. Here, we analyzed the contribution of bacterial and host factors to S. Tm "blooming" in a gnotobiotic mouse model for S. Tm-induced enterocolitis. Mice colonized with the Oligo-Mouse-Microbiota (OMM12), a minimal bacterial community, develop fulminant colitis by day 4 after oral infection with wild type S. Tm but not with an avirulent mutant. Inflammation leads to pronounced reduction in overall intestinal bacterial loads, distinct microbial community shifts and pathogen blooming (relative abundance >50%). S. Tm mutants attenuated in inducing gut inflammation generally elicit less pronounced microbiota shifts and reduction in total bacterial loads. In contrast, S. Tm mutants in nitrate respiration, salmochelin production and ethanolamine utilization induced strong inflammation and S. Tm "blooming". Therefore, individual Salmonella-specific inflammation-fitness factors seem to be of minor importance for competition against this minimal microbiota in the inflamed gut. Finally, we show that antibody-mediated neutrophil depletion normalized gut microbiota loads but not intestinal inflammation or microbiota shifts. This suggests that neutrophils equally reduce pathogen and commensal bacterial loads in the inflamed gut.

microbiology↗