Lactic acid production by Lactobacillus delbrueckii in a dual reactor system using packed bed biofilm reactor.

AIMS: An integrated dual reactor system for continuous production of lactic acid by Lactobacillus delbrueckii using biofilms developed on reticulated polyurethane foam (PUF) is demonstrated. METHODS AND RESULTS: Lactobacillus delbrueckii was immobilized on PUF, packed in a bioreactor and used in lactic acid fermentation. The rate of lactic acid production was significantly high with a volumetric productivity of 5 g l(-1) h(-1) over extended period of time. When coupled to a bioreactor, the system could be operated as dual reactor for over 1000 h continuously without augmentation of inoculum and no compromise on productivity. CONCLUSIONS: Polyurethane foams offer an excellent support for biofilm formation. SIGNIFICANCE AND IMPACT OF THE STUDY: The system was very robust and could be operated for prolonged period at a volumetric productivity of 4-6 g l(-1) h(-1).

Role of viability of probiotic strains in their persistence in the gut and in mucosal immune stimulation.

AIMS: To determine how probiotic bacteria contact with intestinal epithelial and immune cells and the conditions to induce a good mucosal immune stimulation. METHODS AND RESULTS: Lactobacillus casei was studied by transmission electron microscopy (TEM) to determine its interaction with the gut. We compared the influence of viable and nonviable lactic acid bacteria on the intestinal mucosal immune system (IMIS) and their persistence in the gut of mice. TEM showed whole Lact. casei adhered to the villi; the bacterial antigen was found in the cytoplasm of the enterocytes. Viable bacteria stimulated the IMIS to a greater extent than nonviable bacteria with the exception of Lact. delbrueckii subsp. bulgaricus. For all the strains assayed at 72 h no antigenic particles were found in the intestine. CONCLUSION: Antigenic particles but not the whole bacteria can enter to epithelial cells and contact with the immune cells. Bacterial viability is a condition for a better stimulation of the IMIS. SIGNIFICANCE AND IMPACT OF THE STUDY: We demonstrated that only antigenic particle interact with the immune cells and their fast clearance from the gut agrees with those described for the particulate antigens. The regular consumption of probiotics should not adversely affect the host.