This Standard Process product is a probiotic.  It contains lactobacillus acidophilus and bifidobacterium longum.  These are the 2 main bacteria found in the normal gut flora.  Once in the small intestine, these two bacteria create lactic acid, hydrogen peroxide and acetic acid to increase the acidity of the intestine to stop the production of harmful bacteria in the gut.

Probiotics are important in recolonizing the gut after an infection or after antibiotic use.  Research has shown using a probiotic after a course of antibiotics has been completed can prevent 50 percent of post-antibiotic infections.  Long-term use of probiotics consistently resupplies your gut with good bacteria, but once you quit taking the supplement, your gut will return to its normal flora.