Lactobacilli are normal inhabitants of the gastrointestinal tract of man and animals. L. acidophilus rods are considered to extert many benefits but also some side effects. These bacteria were found to reduce the incidence of Escherichia coli 0157:H7 in feedlot cattle.

There are many sites on the Internet which offer L. acidophilus in the form of supplements. In natural form, these bacteria are present in acidophilous milk or yogurt. However, in commercial yogurt the amount of Lactobacillus acidophilus cells does not currently appear on the labels because their concentrations cannot yet be accurately measured in the presence of other cultures, particularly Lactobacillus bulgaricus and Streptococcus thermophilus, which are the bacteria converting milk into yogurt.

Since oral antibiotics kill many intestinal bacteria, the healthy balance of bacteria should be re-created in the intestine after a course of medically prescribed antibiotic therapy. This may be achieved by consuming an acidophilus preparation for up to a month beyond the antibiotic treatment period.

Additional information about these "friendly", "probiotic" bacteria may be found in the Virtual museum of bacteria.