Determination of probiotic properties and biological activities of lactic acid bacteria isolated from kefir

Probiotic microorganisms have been used for years to prevent and treat diseases. Especially the bacteriocins and exopolysaccharides produced by these microorganisms have an important place in the microbiota. Kefir, which is a fermented milk product, has become an increasing product due to its richness in probiotic microorganisms. For this reason, in this study, it was aimed to determine the probiotic properties and biological activities of lactic acid bacteria isolated from kefir. For this purpose, a total of 15 kefir samples, 12 commercial and 3 homemade, were collected. Firstly, kefir samples were analyzed in terms of physicochemical parameters such as pH, total acidity, dry matter and ash analysis. Although the results obtained in terms of pH, dry matter and ash analyzes are compatible with the literature, it has been observed that these results may vary according to the kefir production parameters and the raw material used. Phenotypic tests were applied to confirm the lactic acid bacteria obtained from the samples by conventional methods at the species level. As a result of phenotypic tests, 142 isolates were determined as suspicious lactic acid bacteria. The suspected isolates were identified genotypically by 16S rRNA PCR analysis and it was observed that 37 isolates gave bands in 1500 bp region. Afterwards, bacteriocin was obtained from the bacteria for which phenotypic and genotypic tests were performed, and its antimicrobial effects on four Gram positive and four Gram negative bacteria were determined by the well diffusion method. According to the well diffusion results, 3 isolates were positive for bacteriocin on S. mutans. 16S rRNA sequence analyzes of bacteriocin positive isolates were performed. The quality of the reads obtained as a result of sequencing was combined with the BioEdit program and the most closely related species was determined in the Genbank using the NCBI Nuclotide BLAST program. As a result of the sequence analysis, 1 isolate was determined as Leuconostoc mesenteroides. The cytotoxic activity at 24, 48 and 72 hours on DLD-1 (human colon adenocarcinoma) and CCD-18Co (normal colon) cell lines obtained from exopolysaccharide obtained from phenotypically and genotypically confirmed lactic acid bacteria was analyzed by MTT method. As a result of the MTT test, the cytotoxic activity of exopolysaccharin on the DLD-1 cell line was determined as 2500 µg/mL for 24 hours, and it was determined that it did not show any cytotoxic activity on the CCD-18Co cell line. This shows that exopolysaccharin will have a selective toxic effect on colon cancer cells without harming healthy colon cells. With this study, the positive effect of kefir on the microbiota was emphasized once again.