Good bacteria from foods are microorganisms that can survive the digestive process and live alongside naturally occurring bacteria in your intestinal tract, where they help promote good health. Foods that promote good bacteria include: probiotics, such as cultured buttermilk, that actually contain active microorganisms; prebiotics, such as bananas, which feed the microorganisms and encourage their growth; and synbiotics, such as yogurt, that are both probiotic and prebiotic.
Probiotic bacteria are similar to the good bacteria that already live in your digestive tract. When you eat a probiotic food, you are enhancing your body's supply of these "friendly" bacteria and boosting their ability to create an environment in your intestine that encourages good health. Foods that contain natural or added probiotic bacteria include yogurt, cultured buttermilk, cultured cheeses, fresh (unpasteurized) sauerkraut and pickles, Korean kimchee or kimchi (fermented cabbage), fermented soy products such as miso and tempeh, soy beverages, the fermented milk beverage kefir, kombucha drinks and some juice and smoothie products. Probiotics have also been added to ready-to-eat cereals, granola bars and baby formulas.
Prebiotic foods promote good bacteria by "feeding" specific types of probiotic bacteria and stimulating their growth and activity. Wheat, barley, rye, asparagus, artichokes, onions, garlic, leeks, bananas and honey contain various prebiotics. Some of the the most common prebiotics in these and other foods are fructooligosaccharides (FOS), inulin, lactulose and raffinose. Prebiotic foods undergo fermentation in the digestive tract, and in the process, feed specific probiotic bacteria that reside naturally in the body or are consumed in food. Some prebiotics are extracted from these foods or synthesized for use in supplemental products such as powdered drink mixes and are also added to some brands of cookies and snack foods.
Synbiotic foods promote good bacteria because they contain combinations of probiotics and prebiotics. Many symbiotic food products are in the developmental stage, but commercially available examples include yogurt and smoothie-style yogurt drinks that contain the same probiotic cultures as other yogurts but also contain the prebiotic fiber inulin, extracted from chicory root.
Source - http://livestrong.com/