Medical Uses | Mechanisms of Action

Safety of Probiotics

The majority of probiotics are lactic acid bacteria which are used to make fermented dairy products. Through the extensive and long history of human consumption of these bacteria there has been very few instances of infections or other side effects. Surveillance studies have indicated that approximately 0.094% to 0.23% of blood cultures shown to be bacterially positive contain lactic acid bacteria" [1], [2], [3]. In general the clinical isolates, although often from the same species as probiotics, do not resemble the organisms used as probiotics [2]. The reviews by Gasser and by Aguirre and Collins provide an extensive list of disease conditions in which lactic acid bacteria have been found [3], [4]. The most common conditions are endocarditis and bacteremia and others include fistula, abscess, and empyema. Approximately 70% of the isolates were pure cultures and a significant percentage of patients with lactic acid bacteria isolates had underlying diseases or risk factors, such as coronary heart disease, congenital heart disease, diabetes, drug abuse, cancer, hepatic cirrhosis, and post surgical infections. Less than 10% of cases were described as in good health.

In summary, infections which are either caused by or are coinfected with lactic acid bacteria are rare and cases involving probiotics are extremely rare. Certainly there is a potential for side effects from probiotics, however, this extremely rare event would most likely occur with new probiotics and in individuals who have serious underlying diseases.