Antibiotics destroy or inhibit the growth of bacteria that can cause infection. And while these medicines are necessary to kill the "bad" bacteria that cause such illnesses as strep throat, urinary tract infections, sinus infection and wound and skin infections, in the treatment process, they often also kill the "good" bacteria in the large intestine, leading to problems like diarrhea and upset stomach. In fact, bouts of diarrhea can be so upsetting to people taking antibiotics, up to one in five people on antibiotics stop taking their full course of therapy, according to researchers at Albert Einstein College of Medicine of Yeshiva