Q. Can probiotics prevent me from getting sick?

A. Believe it or not, some bacteria are actually good for you. Beneficial bacteria and yeasts known as probiotics assist in balancing the levels of microorganisms in the human body.

Some yogurts and acidophilus milk contain probiotics. They are also available as supplements in capsules, tablets, beverages or powders.

Typically, our intestines contain over 400 species of bacteria. Some of these bacteria are good for us, while others are not. Illness or antibiotic treatment can disturb the normal balance of these bacteria. Probiotics work by repopulating the small intestine with friendly bacteria while crowding out disease-causing bacteria. They produce substances that stimulate the body's own immune system. They also help keep our intestines acidic, making them inhospitable to unwanted germs.

Some of the best researched and commonly used probiotic bacteria include lactobacillus and bifidobacterium. These bacteria can prevent diarrhea caused by antibiotics in adults or by infections in infants and young children. They also may be useful in treating H. pylori infection, which can cause stomach ulcers.

Recent studies have found benefits of these same probiotic bacteria in combination with a streptococcus species in treating symptoms of irritable bowel syndrome. They reduce the pain, gas and bloating associated with this condition.

Additional species of probiotic bacteria are being studied and show promise in areas such as preventing respiratory infections, improving constipation in Crohn's disease and enhancing immune system activity.

Probiotics may even be useful in reducing digestive problems caused by some chemotherapy treatments. More research is still needed in these areas.

ConsumerLab.com independently tests supplements for purity and quality. Recently they evaluated 19 probiotic supplements. Most products passed; however, four supplements failed because they contained less than 1 billion active probiotic bacteria per daily serving. This is the minimum amount of live organisms needed for effectiveness. These products were: Advocare Probiotic Restore, DDS Acidophilus with FOS, Nature's Secret Ultimate Probiotic, and Rite Aid Acidophilus. Another supplement, Florasource, contained less probiotic bacteria than the label stated. To see which products were tested, visit www.ConsumerLab.com.

An advantage of using yogurts or acidophilus milk rather than supplements is that you get calcium, protein and vitamins in addition to the probiotics. Yogurts and dairy products that contain probiotics will say "contains live cultures" or "active cultures" on the label. Yoplait, Alta Denta, and Dannon Activa are some brands with active cultures.