A reader asked:
“Could you tell me what you know about streptococcus thermophilus? I am Th2 overactive and have read on numerous websites that this strain should be avoided if Th2 dominant. Do you if there is any studies to show this is true?”
First, I want to know what we know about it in general. Because it is used in yogurt, a lot of studies are for it in combination with other probiotics. This means finding studies of it alone are actually rare.
- “Streptococcus thermophilus is one of the most widely used lactic acid bacteria in the dairy industry, in particular in yoghurt manufacture, where it is associated with Lactobacillus delbrueckii subsp. bulgaricus…. One of the most unpredicted results was a significant decrease of most of the transcripts and enzymes involved in purine biosynthesis. Interestingly, the expression of nearly all genes potentially encoding iron transporters of S. thermophilus decreased, … suggesting a reduction in the intracellular iron concentration, probably in response to H(2)O(2) production by L. bulgaricus.” 
- So yogurt does not help with iron absorption….
- However, no significant change in the number of fecal bifidobacteria was observed in the other groups (yogurt fermented with Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus for 2 weeks, ) throughout the ingestion period. 
- Streptococcus thermophilus.. no increase in the feces of the probiotic therapy group 
- Streptococcus salivarius ssp. thermophilus improved flatulence 
- a significantly higher density of LAB and C. perfringens and a significant decrease in the density of Bacteroides was observed after consumption of both types of yogurt. 
- ” In contrast, in the stool samples there was a higher relative abundance of Bacteroidetes and lower abundance of Firmicutes observed in ME/CFS patients compared to healthy controls.”  – so yogurt appears to help the microbiome of CFS patients.
- “The results showed that the test groups (III and IV) receiving folate-rich fermented milks prepared using high-folate producing S. thermophilus strains (RD 102 and RD 104) showed a significant increase in hemoglobin level compared with the control groups (I and II).” 
- So two specific strains does help with iron absorption (assumed to be without the typical yogurt probiotics)….
- “S. thermophilus did not influence the balance Th1/Th2.” 
- “Streptococcus thermophilus AHU1838 (FERM AP-21009), and Lactobacillus paracasei subsp. casei AHU1839 (FERM AP-21010) enhanced the secretion of Th1 cytokines such as interferon-gamma (IFN-gamma) and interleukin-12 (IL-12).” 
- “S. thermophilus was able to induce IL-12 production (Th2), while the production of IL-12 induced by other bacteria remained at a low level.”
- “Oral administration of Streptococcus thermophilus CCFM218 (ST218) treatment revealed a strong suppressive effect on airway inflammation characterized by reduced inflammatory cell infiltration and levels of Th2 cytokines in lung tissues,” 
- “Of ten LAB extracts, four (from L. acidophilus, L. bulgaricus, L. casei, and S. thermophiles) promoted both cell proliferating and TH1 cytokine production.”
It appears that whether S. thermophilus increases or decreases or has no effect on TH1 or TH2 depends on the specific strains. It appears that S. thermophilus by itself has no impact on the microbiome. In yogurt (with other probiotics), it appears to have to shift the microbiome in a favorable way — but I need to explicitly research this and will post when this is done. Yogurt may decrease iron (and thus hemoglobin, resulting in less oxygen delivery to tissue).