The BISSELL Pet Formulas have an added ingredient; enzyme producing bacteria. Enzyme producing bacteria remove urine, feces, and vomit from the cleaning surface completely and permanently by consuming the food source. By removing the urine, feces, and vomit, bacteria have nothing left to feed on. Bacteria simply die off. If you didn’t remove the urine, feces, or vomit, new bacteria will eventually start feeding again with the addition of moisture.