Résistance de souches bactériennes isolées de lait d’ânesse aux hostilités digestives simulées in vitro.

Abstract

The aim of this work was to characterize lactic strains isolated from donkey milk by identifying them and testing their growth potential (at different salt concentrations and different temperatures) and their ability to withstand in vitro simulated digestive hostilities as a criterion for eligibility for "probiotic" status. The results obtained showed that the nine lactic strains isolated from the donkey milk used in this work keep growing at 10, 45 or 63.5 °C and in the presence of 2.4 and 6.5% (w / v) NaCl. They also display a differential resistance capacity depending on the strain type under the conditions of the digestive tract simulated by salivary α-amylase, acidity and gastric secretion, bile salts, lysozyme and pancreatic enzymes (pancreatin, lipase, amylase and proteases). Thus, the strains are initially sensitive to salivary α-amylase but recover growth again after the first 30 minutes of exposure. All strains are slowed in their growth by simulated gastric acidity at levels between 25 and more than 40%. There were 2 strains (S1 and S2) out of 9 tested whose bile salt and lysozyme survival was significantly (p <0.05) reduced by 35%. Exposure of lactic acid strains for 5 hours to pancreatic enzymes did not significantly alter their survival, the lowest (around 80%) was recorded for strains S1, S3 and S7 whereas other strains kept growing giving rise to more than 100% of survival. It is the S8 strain that has the most resistance to proteases. S5 and S8 strains were the most resistant strains to the digestive tract conditions, and therefore were selected for molecular identification by MALDI TOF, which revealed that they belong to the genus Enterococcus. Analysis of the MALDI TOF mass spectra have shown that the two strains (S5 and S8) belong to the same species which is the species faecium with scores of 2.40 for S5 and 2.36 for S8.