Catalase enzyme
The presence of catalase enzyme in the test isolate is detected using hydrogen peroxide. If the bacteria possess catalase (i.e., are catalase-positive), when a small amount of bacterial isolate is added to hydrogen peroxide, bubbles of oxygen are observed. It contains four porphyrin heme (iron) groups that allow the enzyme to react with the hydrogen peroxide. The optimum pH for human catalase is approximately 7, and has a fairly broad maximum (the rate of reaction does not change appreciably at pHs between 6.8 and 7.5). If sucrose or lactose is fermented, the reaction will be A/A (acid slant over acid butt). Because of the high concentration of these sugars, enough acid is produced by fermentation in the butt to lower the pH of both the butt and the slant, turning both yellow. Principle: TSI contains three sugars – glucose, sucrose, and lactose. Phenol Red is the indicator that turns yellow at an acid pH resulting from fermentation. The glucose concentration is 0.1% and the lactose and sucrose concentrations are 1%. The Triple Sugar Iron or TSI test is a microbiological test roughly named for its ability to test microorganism's ability to ferment sugars and to produce hydrogen sulfide. It is often used in the selective identification of enteric bacteria including but not limited to Salmonella and Shigella. These byproducts are usually acids, which will change the color of the red pH-sensitive dye (phenol red) to a yellow color. Position of the color change distinguishes the acid production associated with glucose fermentation from the acidic byproducts of lactose or sucrose fermentation. Triple Sugar Iron (TSI) Agar Purpose: Determine fermentation of glucose and lactose or sucrose and H 2 S production. Principle: TSI contains three sugars – glucose, sucrose, and lactose. Phenol Red is the indicator that turns yellow at an acid pH resulting from fermentation. The glucose concentration is 0.1% and the lactose and sucrose concentrations are 1%. The catalase test is used to differentiate staphylococci (catalase-positive) from streptococci (catalase-negative). The enzyme, catalase, is produced by bacteria that respire using oxygen, and protects them from the toxic by-products of oxygen metabolism.  Interpretation of Triple Sugar Iron Agar Test. 1  If lactose (or sucrose) is fermented, a large amount of acid is produced, which turns the phenol red indicator both in butt and in the slant. 2  Some organisms generate gases, which produces bubbles/cracks on the medium. So the expected results of TSI Agar test are: Triple Sugar Iron Agar Test Results. Image source: Clark College. 1  Alkaline slant/no change in butt (K/NC) i.e Red/Red = glucose, lactose and sucrose nonfermenter. The TSI slant is a test tube that contains agar, a pH-sensitive dye (phenol red), 1% lactose, 1% sucrose, 0.1% glucose, as well as sodium thiosulfate and ferrous sulfate or ferrous ammonium sulfate. All of these ingredients are mixed together and allowed to solidify in the test tube at a slanted angle. These byproducts are usually acids, which will change the color of the red pH-sensitive dye (phenol red) to a yellow color. Position of the color change distinguishes the acid production associated with glucose fermentation from the acidic byproducts of lactose or sucrose fermentation. What does a positive result look like in a TSI slant. Butt = yellow (acidic) = glucose fermented (should always happen) Slant = yellow (acidic) = Sucrose and lactose (if yellow one or the other fermented, or both) Thiosulfate added as sulfur, media contains Fe. What is the benefit to the organism to have a positive result to the EMB. having a positive result means that the organism can ferment lactose or sucrose, being able to ferment those carbs is beneficial because it gives the organism an another energy source. Catalase is a common enzyme found in nearly all living organisms exposed to oxygen (such as bacteria, plants, and animals). It catalyzes the decomposition of hydrogen peroxide to water and oxygen. It contains four porphyrin heme (iron) groups that allow the enzyme to react with the hydrogen peroxide. The optimum pH for human catalase is approximately 7, and has a fairly broad maximum (the rate of reaction does not change appreciably at pHs between 6.8 and 7.5). A bacterium that is a non-lactose fermenter and ferments glucose, initially causes a yellow slant/yellow bottom (acid/acid reaction) after 8 hours but then converts to a red slant/yellow bottom after 24 hours (alkali/acid reaction). These byproducts are usually acids, which will change the color of the red pH-sensitive dye (phenol red) to a yellow color. Position of the color change distinguishes the acid production associated with glucose fermentation from the acidic byproducts of lactose or sucrose fermentation.
https://en.wikipedia.org/wiki/Catalase http://www.chadguilliams.50webs.com/text/enterobacteriaceae%20biochemical%20test.pdf https://en.wikipedia.org/wiki/TSI_slant http://www.chadguilliams.50webs.com/text/enterobacteriaceae%20biochemical%20test.pdf http://learn.chm.msu.edu/vibl/content/catalase.html http://microbeonline.com/triple-sugar-iron-agar-tsi-principle-procedure-and-interpretation/ https://en.wikipedia.org/wiki/TSI_slant https://quizlet.com/3661310/biochemical-tests-flash-cards/ https://en.wikipedia.org/wiki/Catalase https://en.wikipedia.org/wiki/TSI_slant
what enzyme does a positive TSI test detect