From the bacterial point of view, the human intestine is the promised land. The gut is warm, moist, and full of good food. It’s also extremely crowded. A cubic centimeter of prime real estate in the colon can hold 100 billion bacteria — nearly 20 times the entire human population of earth. A few hundred billion bacteria may seem like plenty, but some people might benefit from even more. Probiotics, remedies containing many millions of live “good” bacteria, have become hot sellers in health food stores across the country. Some people get their bacteria in capsules; others prefer live-culture yogurts. The basic goal is the same: In with the good bugs, out with the bad. Should you be taking regular doses of bacteria? The answer isn’t quite as simple as marketers would like you to believe. Probiotics clearly have potential. Recent studies suggest they may help fight antibiotic-induced diarrhea and …