There are two possible dangers of probiotics: invasive infection, resistance to antibiotics Invasive Infection occurs by taking probiotics which then translocate into the blood stream. Probiotics, according to the WHO are "live microorganisms". The reported cases where invasive infection occurs after taking probiotics are low but they exist: *Transpl Infect Dis. 2010 Oct 7. doi: 10.1111/j.1399-3062.2010.00580.x. [Epub ahead of print] Lactobacillus probiotic use in cardiothoracic transplant recipients: a link to invasive Lactobacillus infection? *http://chemistry-today.teknoscienze.com/pdf/HIBBERD AGRO4-08.pdf CONCLUSIONS Overall, we conclude that use of probiotics by most people is safe, based on a comparison of to the large number of people who have consumed them, and the small number of people in whom serious adverse events have been reported. However, probiotics can cause invasive infection and, based on laboratory and animal studies, there is a possibility of translocation from the gut. Based on these data and available case reports, we recommend that probiotics be used with caution in individuals who have an abnormal gastrointestinal mucosal barrier, and should be avoided in children with short gut syndrome. Probiotics should also be avoided or used with care in patients with central venous catheters, particularly when lyophilized formulations are being handled prior to administration. We also recommend against use of probiotics in severely immunocompromised patients and critically ill patients in intensive care units. Similarly, patients with co morbid conditions that place them at increased risk of invasive infection should avoid probiotics. We also conclude that there is a theoretical risk of transfer of antibiotic resistance plasmids from some but not all probiotic organisms. However the risk appears to be very low. Probiotics do not appear to cause adverse immunologic, toxic or metabolic effects in the gastrointestinal tract or systemically. http://books.google.de/books?id=nIn...nepage&q=probiotic invasive infection&f=false Page 875: All 14 people, where invasive infection was attributed to probiotics, were immune compromised. http://books.google.de/books?id=M4R...onepage&q=probiotic invasive infection&f=true Page 259: Saccharomyces infection is clinically indistinguishable from invasive candidasis. Page 260: Saccharomyces boulardii administration is contraindicated for patients of fragile health. As a conclusion we maybe can say that probiotics do harm in only very few cases who all seem to have immune dysfunction/suppression. But if they do, they should be stopped immediately.