Isolation, molecular identification and determination of some properties of starter bacteria in traditional yoghurt

The fermentation process of starter cultures is one of the most important factors of chemical, physical and biological changes that occur during the transformation of milk into yoghurt. In this thesis, it was aimed to identify genotypic/proteomic and some characteristics of starter cultures, which will be used for production of high- nutritional-value functional foods with high economic and social benefits. For this purpose 39 local yoghurt samples produced by traditional methods in Bolu, Mersin, Amasya, Isparta and Kayseri regions, were collected and inoculated and into the agar media. After incubation period 283 Streptococcus salivarius subsp. thermophilus and 101 Lactobacillus delbrueckii subsp. bulgaricus suspected isolates have been isolated. These colonies were stored for further analysis but 153 S. thermophilus and 28 Lb. bulgaricus suspected isolates were reactivated. 53 S. thermophilus, 23 Lb. bulgaricus and 49 S. thermophilus, 22 Lb. bulgaricus strains were identified according to the results of MALDI-TOF MS and real-time PCR analyses, respectively. Strains identified by MALDI-TOF MS and real-time PCR were subjected to 16S rRNA sequence analysis and 1 S. thermophilus, 9 Lb. bulgaricus were confirmed. A total of 61 S. thermophilus and 21 Lb. bulgaricus strains identified by MALDI-TOF MS or/and real-time PCR were used in order to determine their sensivity to antibiotics such as streptomycin, gentamicin, penicillin G, chloramphenicol, linkomycin, chlortetracycline, tetracycline, ampicillin and roxithromycin with the minimal inhibitor concentration (MIC) by macro dilution tube method. The results showed that the highest sensitivity was found to be 98.4% and 81% of the strains of S.thermophilus and Lb. bulgaricus against ampicillin, respectively. All strains of S. thermophilus were resistant to gentamicin while Lb. bulgaricus strains were resistant to streptomycin and chloramphenicol. It was concluded that 26.2% of S. thermophilus and 42.9% of Lb. bulgaricus strains were sensitive to tetracycline. One S. thermophilus (St27) and 7 Lb. bulgaricus (Lb25, Lb29, Lb46, ML4-1, ML7-6, ML9-5 ve ML9-6) isolates which were identified with three methods, have been researched their effect on the natural immune system, allergic response and immune system cells. In the study using THP-1 macrophages and K562 (natural killer cells) cell lines; TNF-α, IL-8 and IL-10 cytokine responses were evaluated after stimulation of cells with selected LAB. Increase in TNF-α and IL-8 cytokine levels in the interaction of S. thermophilus isolate with K562 cell line and increase in IL-8 level and decrease in IL-10 cytokine level in interaction with THP-1 cell line were detected. The obtained data showed that the two study results are compatible with each other. Besides that, it has been determined that the selected LAB isolates are different from the responses they stimulate in both cell types and increase the proliferation of monocytes and natural killer cells. A decrease in the level of IL-8 cytokine was detected in some LABs, TNF-α cytokine levels in THP-1 monocytic cell lines and 2 LABs isolates in K562 natural killer cell line. The interaction of ML7-6 and ML4-1 isolates with the THP-1 cell line leads to an increase in IL-10 cytokine levels. The obtained results, which suggest that these four isolates have promoting effects of the immune system and suppress the allergic response.