In Vivo Study of the Survival of Lactobacillus delbruecki subsp. bulgaricus CECT 4005T and Streptococcus thermophilus CECT 801 by DVC-FISH after Consumption of Fermented Milk

Abstract

An in vivo study of the lactic acid bacteria (LAB) from traditional yogurt has been performed in order to study their survival through the gastrointestinal tract. DVC-FISH technique has been used. Direct Viable Count method (DVC), has been developed for L. delbrueckii subsp. bulgaricus and S. thermophilus in recent studies. DVC procedure has been combined with fluorescent in situ hybridization (FISH) for the specific detection of viable cells of both bacteria. This method has been used to determine in vitro viability of these LAB with a simulation of gastrointestinal juices. In vitro resistance of L. delbrueckii subsp. bulgaricus and S. thermophilus to gastric and pancreatic juices has been 26.2% and 9.2%, respectively. On the other hand, an in vivo study has been carried out with the application of the DVC-FISH technique for the detection of these LAB in human feces in a viable state, after the consumption of fermented milk. Cells of L. delbrueckii subsp. bulgaricus were not detected in any of the fecal samples, whereas viable cells of S. thermophilus were detected in a number higher than 103 cells g-1 in a 30% of the samples after four weeks of yogurt consumption. DVC-FISH procedure was successfully applied to determine the viability of these LAB to gastrointestinal tract both in vitro and in vivo. DVC-FISH procedure is a quick and culture-independent useful method which has been applied for the first time in an in vivo survival study of LAB.