| Streptococcus thermophilus | |
|---|---|
| Scientific classification | |
| Kingdom: | Bacteria |
| Phylum: | Firmicutes |
| Class: | Cocci |
| Order: | Lactobacillales |
| Family: | Streptococcaceae |
| Genus: | Streptococcus |
| Species: | S. salivarius |
| Subspecies: | S. salivarius subsp. thermophilus |
| Binomial name | |
| Streptococcus salivarius subsp. thermophilus (ex Orla-Jensen 1919) Schleifer et al. 1995 |
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Streptococcus salivarius subsp. thermophilus (previous name Streptococcus thermophilus) is a Gram-positive bacteria and a homofermentative facultative anaerobe, of the viridans group.[1] It tests negative for cytochrome, oxidase and catalase, and positive for alpha-hemolytic activity.[1] It is non-motile and does not form endospores.[1]
It is also classified as a lactic acid bacterium.[2] S. thermophilus is found in fermented milk products. It is not a probiotic (it does not survive the stomach in healthy humans) and is generally used in the production of yogurt,[3] alongside Lactobacillus delbrueckii subsp. bulgaricus. The two species are synergistic, and S.s. thermophilus probably provides L.d. bulgaricus with folic acid and formic acid which it uses for purine synthesis.[4]
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S.s. thermophilus is one of the most widely used bacteria in the dairy industry. USDA statistics from 1998 showed that more than 1.02 billion kilograms of mozzarella cheese and 621 million kilograms of yogurt were produced from S.s. thermophilus.[5] Although its genus, Streptococcus, includes some pathogenic species, food industries consider S.s. thermophilus a safer bacterium than many other Streptococcus species. In fact, yogurt and cheese that contain live cultures of S.s. thermophilus are thought to be beneficial to health.[6] Live cultures of S.s. thermophilus make it easier for people who are lactose-intolerant to digest dairy products. The bacteria break down lactose, the sugar in milk that lactose-intolerants find difficult to digest.
As long ago as the early 1900s, S.s. thermophilus has been used to make yogurt. Many of the yogurts sold in grocery stores today do not contain many live cultures of S.s. thermophilus because pasteurization destroys these beneficial organisms. Nonetheless, S.s. thermophilus is required by law to be present in yogurt. Its purpose is to turn lactose, the sugar in milk, into lactic acid. The increase in lactic acid turns milk into the gel-like structure characteristic of yogurt.[7]
Streptococcus derives from a Greek term meaning "twisted berry" and refers to the way the bacterium is grouped in chains that resemble a string of beads.[8] "Thermophilus" derives from the Greek term thermotita meaning "heat". It refers to an organism's ability to thrive at high temperatures.[9]
The genus Streptococcus includes several pathogenic species, such as S. pneumoniae and S. pyogenes, but food industries consider S.s. thermophilus non-pathogenic. S.s. thermophilus is believed to have developed separately from pathogenic Streptococcus species for at least 3000 years. Research teams have sequenced the genome of two strains of S.s. thermophilus, CNRZ1066 and LMG13811, and stated that the bacteria are not dangerous.[10]
When the S.s. thermophilus species diverged from its pathogenic relatives, it lost most of the genes acknowledged as being responsible for virulence. The species may have lost these genes because it adapted to a new, dairy-producing, environment in which it did not need these genes anymore.
Genome analysis has also shown that by adapting to dairy production, the species has acquired genes that its pathogenic cousins do not have. For example, S.s. thermophilus can use the energy in lactose to help itself grow.
S.s. thermophilus helps make reduced-fat cheese with similar characteristics to regular, full-fat cheese. In the experiment, two different strains of bacteria are used to make reduced-fat cheddar cheese: a strain of Lactococcus lactis and a strain of S.a. thermophilus. These bacteria are chosen because they produce exopolysaccharide (EPS) which give reduced-fat cheese a similar texture and flavor as regular cheese. However, cheese made from L. lactis yielded a different type of cheese from S.a. thermophilus.
L. lactis produced cheese with higher moisture levels compared to other reduced-fat cheeses. On the other hand, S.s. thermophilus produced low moisture cheese and decreased the bitterness of cheese. It had been concluded that applying both L. lactis and S.s. thermophilus strains create higher quality reduced-fat cheese with similar characteristics to regular cheese.[11]
Chemotherapy often causes mucositis, severe inflammation of primarily the small intestines. Currently, there is no treatment to alleviate the symptoms of mucositis caused by chemotherapy. When rats were inflicted with mucositis by chemotherapy drugs, cells in the infected areas functioned more healthily and the tissue was less distressed.[12] In her nutrition book, Jean Carper describes an experiment by Dr Joseph A Scimeca, in which commercially-available yogurt containing S.s. thermophilus and L.d. bulgaricus was fed to mice. After these mice were injected with cancer cells, the incidence of lung cancer in the yogurt-fed mice was one-third less than expected.[13]
S.s. thermophilus supplements have maintained a stable growth rate in children. Children who received S.s. thermophilus supplements had better growth during a 6-month period than children who did not receive the supplement.[14]
Strains of S.s. thermophilus have also reduced risks of AAD (antibiotic-associated diarrhea), an issue that results from taking antibiotics. Antibiotics can have the adverse effect of destroying beneficial bacteria and causing harmful bacteria to multiply, which invokes diarrhea. Adults who ate yogurt containing S.s. thermophilus while being treated with antibiotics had lower rates of diarrhea than the control group (12.4% vs. 23.7%).[15]