New insights into Lactobacillus and functional intestinal disorders.

Intestinal microflora can be considered as a ''dynamic system'' that actively interacts with the intestinal epithelium and the local immune system. It synthesizes antimicrobial substances (bacteriocins), vitamins (PP, B1, B6, B12), it produces a major intestinal nutrient (butyric acid) and interacts in a competitive fashion with the pathogens. Lactobacilli concentration (Gram+, Gram variable, facultative anaerobes) is generally decreased in irritable bowel syndrome (IBS) patients. This syndrome has, until recently been considered to be ''functional'', whereas, in fact, it may result from previous enteritis (in up to 31% of patients), featuring a persistent low-grade intestinal inflammation and a reduction in interleukin-10 (IL-10) concentration. Some Lactobacilli strains (e.g. L. paracasei subsp. paracasei) in vitro lead to normalisation of the hypercontractility of the smooth muscle cells. A growing body of clinical findings indicates that some ''genetically stable'' strains of Lactobacilli may be useful in the treatment, even long term, of IBS, and reduce the postoperative infection rate, especially in critically ill patients (orthotopic liver transplant, severe pancreatitis). However, some Lactobacilli, ''not genetically stable'', used in the treatment of neutropenic patients during chemotherapy and in pediatric patients submitted to gastrojejunostomy, have been reported to lead to bacteremia and endocarditis. These effects may be due to transfer of bacteria and genetic material. Therefore, the confirmed genetic stability and the fact that no antibiotic resistance occurs are fundamental requisites for the use of Lactobacilli in certain disorders of the gastrointestinal tract, such as, for instance, IBS. In conclusion, ''genetically stable'' Lactobacilli (L. paracasei subsp. Paracasei F19) have recently become available, representing an exiting new field in clinical studies and for treatment purposes, offering guarantees of safety also for long-term use. Careful personalized evaluation, as always in medical practice, is necessary in order to gain further insight into, and to validate with additional studies, the role of ''genetically stable'' Lactobacilli in the treatment of IBS.