Etude du potentiel probiotique des microorganismes de diverses matrices biologiques pour des applications en alimentation animale

Abstract

Probiotics are microorganisms of varied origins, capable of positively impacting intestinal flora. The probiotic potential of microbial strains isolated from biological matrices from Morocco was studied based on several criteria. This included antibiotic resistance, the ability to adhere to solvents, the ability to produce antimicrobial substances, and the ability to colonize the gastrointestinal tract. Molecular (16S DNA) and analytical (MALDI-ToF-MS) techniques have been used to identify several microorganisms. The probiotic properties of five of them (Lactobacillus plantarum from sourdough, Leuconostoc pseudomesenteroides and Leuconostoc mesenteroides isolated from fresh goat's cheese, Enterococcus durans and Lactobacillus casei isolated from fermented milk) were characterized including their growth in MRS broth, their viability at pH 2.5 and 6.5 in the presence of bile salts (1%), their surface hydrophobicity, their ability to autoaggregate, their thermogravimetric decomposition pattern and their ability to express antagonistic activity towards certain pathogens. The results of antagonism tests showed that isolated Lactobacillus plantarum and Leuconostoc mesenteroides strains inhibited the growth of Bacillus cereus, Staphylococcus epidermidis and Escherichia coli pathogens, while Enterococcus durans and Lactobacillus casei strains were effective against B. cereus and E. coli. Antibiotic susceptibility results were satisfactory for most strains, except for Enterococcus durans, which showed resistance to each of the antibiotics tested. This strain was, however, the only one to grow at pH 2.5 in the presence of 1% bile salts, giving it the ability to survive in gastrointestinal conditions. The ability of strains to produce emulsifying substances was studied by determining the emulsion index (expressed as a percentage) of culture supernatants mixed within toluene. The results showed that Leuconostoc pseudomesenteroides culture supernatants had the highest emulsion-forming capacity (81.72%). However, the supernatant of Leuconostoc mesenteroides showed the best emulsifying stability which only went from 8.7% at 0h to 8.6% after 24h. Overall, all the bacteria used have a good autoaggregation capacity (over 90%). The surface hydrophobicity properties expressed as a percentage represent the ability of the bacterial cells studied to grow on an immiscible substrate. These percentages vary from species to species and are 36.82%, 28.18%, 39.23%, and 26.72% respectively for Lactobacillus plantarum, Leuconostoc pseudomesenteroides, Enterococcus durans, and Lactobacillus casei. These last two parameters were the main surface properties evaluated in this study. All these observations clearly show that the matrices analyzed obviously contain potential probiotic candidates.