Orally ingested probiotic micro-organisms do not exert health effects exclusively in the intestine. Some strains can alleviate or prevent bacterial, fungal or viral infections in other organs by stimulation of the immune system. By preservation or improvement of the barrier function of the intestinal mucosa, they may inhibit translocation of potential pathogens and thus prevent infections of the blood stream and other tissues and organs. Modulation of the intestinal microflora can affect the local microflora of the urogenital tract and possibly of the oral cavity. Finally, some strains of orally ingested bacteria reach target organs like the urogenital tract in a viable state; alternatively they can be applied locally.

Despite the infection-preventing properties of probiotic bacteria, lactic acid bacteria have rarely been identified in infections of the blood stream, heart valves and other organs, usually only in patients with severe disease. It is the general opinion that in most cases the source of infection was the commensal microflora of the intestine or the oral cavity. Until now only one case of infection associated with administration of a probiotic strain has been published.

The most promising health-promoting effects have been seen in vaginosis, urinary tract infections, Helicobacter pylori gastritis and infections of the respiratory tract in children. More controlled clinical trials with sufficient numbers of participants are needed to determine the scientific basis for the use of probiotic bacteria in infections in locations of the body other than the intestine.