Probiotics are defined by Drugs.com as "substances secreted by one micro-organism which stimulates the growth of another." The "American Journal of Clinical Nutrition," or AJCN, describes probiotics as live bacteria that cause a health benefit a person when ingested in adequate amounts. Probiotics are most commonly used for gastro-intestinal problems, such as inflammatory diseases and diarrhea, and for yeast and urinary tract infections. Probiotics are considered relatively safe, but they have some side effects, including infection, immune system problems and antibiotic resistance.
The risk of infection or sepsis is the most important area of concern with probiotic use, according to the AJCN. Some probiotics have been designed to have good adherence to the intestinal wall, which may increase bacterial trasnlocation and virulence, causing infection. The ACJN reports that the most potent probiotics may increase pathogenicit;y, or tendency to cause infection. Medline Plus states that people with severely weakened immune systems may develop serious infections or bacteria in the bloodstream from taking probiotics. The "British Medical Journal" cites cases of infection from Lactobacillus, a common probiotic. One 74-year-old woman developed liver abscesses after four months on a probiotic; a 67-year-old man who regularly took probiotic capsules developed an infection after a tooth extraction. Most reported infection cases occur in the elderly or in infants.
Immune and Metabolic Effects
The AJCN says that long-term alterations of "healthy" intestinal bacteria may have adverse effects on immune development. They explain that studies show that normal intestinal microbes are important in stimulating healthy immune development , such as in the abdominal lymphoid tissues. Ingesting probiotics may alter this crucial microbiota, with detrimental effects on immunity. This is especially true for neonates and pregnant women. The intestinal microbiota also play an important role in metabloic activities such as glucose regulation, lipid metabolism and complex carbohydrate digestion. There is a risk of adverse metabolic effects from the manipulation of intestinal flora with the use of probiotics.
Drugs.com states that antibiotic resistance has been reported for the probiotic Lactobacillus in Europe. "Clinical Infectious Diseases" reports that many strains of lactobacilli are naturally resistant to the antibiotic vancomycin. This can occasionally render the probiotic untreatable in rare cases of infection. "Biomedical and Environmental Sciences" cites a study that found that antibiotic resistance is present in different species of probiotic strains. Most strains were resistant to the antibiotics ciprofoxacin, amkacin and gentamycin. It states that this poses a threat to food safety and that probiotic use should be directed by guidelines and regulations.
Other Side Effects
Other side effects from probiotics include abdominal discomfort or gas, drug interactions and rare neurological effects. Endocarditis, an infection in the inner lining of the heart has been reported from infection in the bloodstream caused by probiotic use.