This bacteria aids digestion, extracting vitamins from the food we eat. Without it we would die. Candida also lives in the colon. The amount of Candida in a healthy person is quite small. The amount of bacteria is normally quite large.
Candida has no known benefits, but in small amounts it is harmless.
When a person takes antibiotics, they kill not only the harmful bacteria in the body, but also the friendly bacteria in the colon. Antibiotics do not affect Candida, which is both a yeast and a fungus. This allows the Candida to grow wild in the colon. While small amounts of Candida are harmless, larger amounts are not. Some harmful bacteria are also immune to some antibiotics.