Bacteria in your food are a bad thing, usually: Think of E. coli or other harmful bugs.
But a whole other world of "friendly" bacteria lurks out there.
Called "probiotics" and found in such products as yogurt and yogurt drinks, they provide health benefits beyond the regular live cultures found in those foods.
Probiotics are among the fastest-growing category of functional foods, according to the market research firm Mintel, which cites a 140 percent increase last year in the launch of new probiotic-fortified products.
So far, the strongest evidence on probiotics has focused on digestive-tract problems such as lactose intolerance and diarrhea -- including infectious diarrhea among children and the type that develops after a person has taken antiobiotics.
Additional studies suggest probiotics may help decrease the risk of colon cancer and ease symptoms of irritable bowel syndrome and the more serious inflammatory bowel disease, which includes Crohn's disease and ulcerative colitis.
Researchers also are beginning to see signs that probiotics may help lower blood pressure and blood cholesterol levels.
Some foods may be made with microbes -- everything from sourdough bread to pickles, sauerkraut, kim chi, miso and fermented meats like salami.
But it doesn't mean all the "good bugs" survived the processing or that the strains used provide actual health benefits, which is required before it would qualify as a probiotic, Sanders said.
If you want a yogurt with the gut-healthy, friendly bugs, you need to scour the label to see if the manufacturer supplemented the standard strains with probiotic bacteria.
The two most common are Lactobacillus acidophilus and bifidobacteria (or bifidus).
These bacteria (and their probiotic cousins L. casei, L. reuteri and others) also are being added to fermented milks like acidophilus milk, kefir and soy beverages.