Lactobacillus reuteri

Lactobacillus reuteri is a lactic acid bacterium of the gut microbiota, commonly regarded as a beneficial probiotic species. Lactobacillus species have an established connection to host tryptophan metabolism.

Its biological effects in cancer appear to be strongly context-dependent rather than uniformly protective: L. reuteri and Lactobacillus-derived metabolites have been reported to promote adverse tumor outcomes, to regulate tumor-associated macrophage immunosuppression through tryptophan metabolism, and to contribute to treatment-related intestinal injury in particular settings. Tumor niche, microbial metabolic output, and host immune-metabolic state all appear to shape which direction the effect takes.