Potentially probiotic lactic acid bacteria isolated from unpasteurized milk

Some Lactic Acid Bacteria (LAB), when ingested in adequate quantities, are able to positively impact the host, being considered probiotics. To be used, these bacteria must have their identity known and show specific characteristics. In this study, LAB were isolated from unpasteurized milk samples and characterized in vitro for probiotic potential. After isolation, the colonies were analyzed by Gram stain and catalase test; total DNA was extracted, and the 16S rDNA was amplified and sequenced. Phylogenetic analysis was performed to reconstruct the evolutionary history of the isolates. The isolates were evaluated regarding the resistance to acidic pH and the presence of bile salts. The antagonistic activity of the isolated bacteria was evaluated by the overlay test and the antimicrobial susceptibility profile was performed by the disc diffusion method. Of the 13 isolated bacteria, three were characterized as Gram positive and catalase negative rods, showing 99% of identity with Lactobacillus casei, Lactobacillus paracasei, and Weisella paramesenteroides. The isolates showed in vitro resistance to acidic stress and to the presence of bile salts; showed similar antimicrobial resistance profile and ability to inhibit the growth of potentially pathogenic bacteria, such as Staphylococcus saprophitycus, Escherichia coli, Staphylococcus aureus, Enterococcus faecalis, and Enterococcus faecium. In view of the proven characteristics, the lactic acid bacteria isolated in this work have probiotic potential.