Some bacterium ferment different sugar this test tests for this and pH from phenol red, Red is neutral, deep read is a pH of 8.5 or above (alkaline) and a yellow pH is 6.9 or below making it acidic
Mixed acid fermentation (MR Test)
To see when the bacteria produce mixed acid from sugars, You add methyl red so when you put it in the tube it turns red if it's acidic (4.4) saying that it is a acid maker or it will turn yellow with a pH of 6.2 or higher meaning that it doesn't
Tests for butanediol fermentation, they actually test for acetoin a precursor
A postive will turn red instantly if it;s postive for butanediol
Some bacteria use nitrate as there terminal electron acceptor instead of O2
Once you had the reagant and it turns red right away that means it turns nitrate into nitrite.
If you add zinc (and xinc turns nitrate to nitrite) and it turns red and means its negative because it doesnt break down nitrate at all
If it turns DOESN"T turn red even after zinc and the reagants this is a positive reaction because it means that it used but all the nitrate and converted into ammonia gas
Some bacteria use citrate as their sole source of carbon. it also has a pH indicator, yellow at 6. or lower and blue at a pH of 7.6 or more
It's positive if their is growth and a color change of blue (so it does use citrate for carbon and alkaline)
If there is growth and red color ( a indicator of respiration) than that means it moved throughout the medium
TSI (triple sugar iron) test
We found out if its able to ferment glucose lactose and if it reduces sulfur to hydrogen sulfide.
If it's red then the peptones are utilized and converted to NH3, which increases pH.
Yellow on the slant means that lactose are utilized if it's found in the butt glucose is utilized
If it's black then sulfur us reduced producing H2S