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Applied and Environmental Microbiology, November 1999, p. 4881-4886, Vol. 65, No. 11
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Survival, Physiology, and Lysis of Lactococcus lactis in the Digestive Tract

Sophie Drouault,1 Gérard Corthier,2 S. Dusko Ehrlich,1 and Pierre Renault1,*

Unité de Génétique Microbienne1 and Unité d'Ecologie et de Physiologie du Système Digestif,2 Institut National de la Recherche Agronomique, 78352 Jouy en Josas cedex, France

Received 28 June 1999/Accepted 25 August 1999

The survival and the physiology of lactococcal cells in the different compartments of the digestive tracts of rats were studied in order to know better the fate of ingested lactic acid bacteria after oral administration. For this purpose, we used strains marked with reporter genes, the luxA-luxB gene of Vibrio harveyi and the gfp gene of Aequora victoria, that allowed us to differentiate the inoculated bacteria from food and the other intestinal bacteria. Luciferase was chosen to measure the metabolic activity of Lactococcus lactis in the digestive tract because it requires NADH, which is available only in metabolically active cells. The green fluorescent protein was used to assess the bacterial lysis independently of death. We report not only that specific factors affect the cell viability and integrity in some digestive tract compartments but also that the way bacteria are administrated has a dramatic impact. Lactococci which transit with the diet are quite resistant to gastric acidity (90 to 98% survival). In contrast, only 10 to 30% of bacteria survive in the duodenum. Viable cells are metabolically active in each compartment of the digestive tract, whereas most dead cells appear to be subject to rapid lysis. This property suggests that lactococci could be used as a vector to deliver specifically into the duodenum the proteins produced in the cytoplasm. This type of delivery vector would be particularly appropriate for targeting digestive enzymes such as lipase to treat pancreatic deficiencies.

* Corresponding author. Mailing address: Unité de Génétique Microbienne, Institut National de la Recherche Agronomique, 78352 Jouy en Josas cedex, France. Phone: 33-1 34 65 25 27. Fax: 33-1 34 65 25 21. E-mail: renault{at}biotec.jouy.inra.fr.

Applied and Environmental Microbiology, November 1999, p. 4881-4886, Vol. 65, No. 11
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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