“…69 Whether it is a traditional probiotic or a new live biologic, mainstream clinical use has chosen to use probiotics after antibiotics, and there may be multiple reasons for such a combination order (Fig. 1): (1) the subsequent addition of probiotics can effectively occupy these ecological sites, thus competing to exclude the more resistant C. difficile strains, vegetative cells and spores; 9 (2) the addition of probiotics competes with the remaining C. difficile strains and their vegetative cells for nutrients essential for growth such as carbohydrates and amino acids, thus inhibiting the normal growth and metabolism of C. difficile; 19 (3) probiotics are able to secrete organic acids after colonization and affect the level of intestinal bile acid metabolism, especially enhancing the level of secondary bile acids, thus altering the intestinal growth environment to the detriment of C. difficile; 49,50 (4) after colonization, probiotics can secrete antimicrobial peptides, bacteriocins, extracellular polysaccharides and other types of antimicrobial substances, which have a direct killing effect on C. difficile strains; 64,[70][71][72] (5) probiotics can activate the intestinal immune system and enhance the related immune response to clear C. difficile; 73 and (6) probiotics can indirectly promote the growth of low-abundance beneficial microbes in the gut by "cross-feeding", thus co-antagonizing C. difficile. 74 Fig.…”