2‘FL and LNnT exert antipathogenic effects against C. difficile ATCC 9689 in vitro, coinciding with increased levels of bifidobacteriaceae and/or secondary bile acids

Clostridioides difficile (formerly Clostridium difficile) infection (CDI) is one of the most common hospital-acquired infections, which is often triggered by a dysbiosed indigenous gut microbiota (e.g., upon antibiotic therapy). Symptoms can be as severe as life-threatening colitis. The current study assessed the antipathogenic potential of human milk oligosaccharides (HMOs), i.e., 2'-O-fucosyllactose (2‘FL), lacto-N-neotetraose (LNnT), and a combination thereof (MIX), against C. difficile ATCC 9689 using in vitro gut models that allowed the evaluation of both direct and, upon microbiota modulation, indirect effects. During a first 48 h fecal batch study, dysbiosis and CDI were induced by dilution of the fecal inoculum. For each of the three donors tested, C. difficile levels strongly decreased (with >4 log CFU/mL) upon treatment with 2‘FL, LNnT and MIX versus untreated blanks, coinciding with increased acetate/Bifidobacteriaceae levels. Interindividual differences among donors at an intermediate time point suggested that the antimicrobial effect was microbiota-mediated rather than being a direct effect of the HMOs. During a subsequent 11 week study with the PathogutTM model (specific application of the Simulator of the Human Intestinal Microbial Ecosystem (SHIME®)), dysbiosis and CDI were induced by clindamycin (CLI) treatment. Vancomycin (VNC) treatment cured CDI, but the further dysbiosis of the indigenous microbiota likely contributed to CDI recurrence. Upon co-supplementation with VNC, both 2‘FL and MIX boosted microbial activity (acetate and to lesser extent propionate/butyrate). Moreover, 2‘FL avoided CDI recurrence, potentially because of increased secondary bile acid production. Overall, while not elucidating the exact antipathogenic mechanisms-of-action, the current study highlights the potential of HMOs to combat CDI recurrence, help the gut microbial community recover after antibiotic treatment, and hence counteract the adverse effects of antibiotic therapies.