Streptococcus macedonicus strains isolated from traditional fermented milks: resistance to gastrointestinal...

Area of Science:

• Microbiology
• Food Science
• Probiotics

Background:

• Traditional fermented milks are sources of potentially probiotic microorganisms.
• Streptococcus macedonicus (S. macedonicus) is found in fermented dairy products.
• Probiotic candidates require specific physiological characteristics for efficacy.

Purpose of the Study:

• To identify and characterize S. macedonicus strains from Algerian fermented milks (Lben and Rayeb).
• To evaluate the probiotic potential of these strains based on acid and bile tolerance and cell adhesion.
• To genetically differentiate the identified S. macedonicus strains.

Main Methods:

• Phenotypic characterization included growth on Bile Esculin Azide medium (BEA), high salt (6.5% NaCl), and alkaline (pH 9.6) conditions.
• Genotypic identification involved 16S rRNA, ITS gene sequencing, and Multi-Locus Sequence Typing (MLST).
• In vitro assays assessed survival at low pH, tolerance to bile salts (10 mM), and adhesion to Caco-2 TC7 and HT29-MTX cell lines.

Main Results:

• Four distinct S. macedonicus strains were identified, genetically separate from other known strains.
• These strains demonstrated robust survival at pH 3 and high tolerance to bile salts (10 mM), outperforming reference strains Streptococcus thermophilus LMD-9 and Lactobacillus rhamnosus GG (LGG).
• The S. macedonicus strains showed comparable adhesion to LGG and superior adhesion to LMD-9 on both Caco-2 TC7 and HT29-MTX cell models.

Conclusions:

• The identified S. macedonicus strains possess key characteristics suitable for probiotic applications.
• Their demonstrated acid tolerance, bile salt resistance, and epithelial cell adhesion warrant further investigation for in vivo probiotic effects.
• This study highlights S. macedonicus as a promising candidate for functional food development.