Lactobacillus are the useful bacteria present in our digestive tract, vaginal tract etc. Antibiotics taken may kill these useful bacteria along with the harmful bacteria. The killing of useful bacteria may result in the overgrowth of harmful bacteria in gut or vaginal tract that may produce toxins and cause diarrhoea or inflammation. Thus, inorder to maintain balance and optimum number of useful bacteria in the gut or vaginal tract and prevent conditions like diarrhoea or inflammation, most of the antibiotics are sold
with Lactobacillus these days