Figure 1. Schematic model of the potential molecular mechanisms responsible for probiotic prevention of AAD.

Antibiotic treatment disrupts the composition of the GI tract microbiota, leading to increased growth of opportunistic pathogens, the accumulation of undigested carbohydrates, and reduced levels of SCFAs and modified bile acids. Probiotics might counter antibiotic-induced effects in the GI tract by directly impairing pathogen growth or by inducing other alterations to gut microbiota composition via SCFA synthesis, production of other secreted metabolites such as bacteriocins, or by reducing lumenal pH and O2 levels. Probiotics might also cause changes to bile acid composition as well as directly interact with the intestinal epithelium and immune system to result in increased gut barrier function and modulation of water and solute transport.