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55 Cards in this Set
- Front
- Back
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What is the oxidative-fermentative test (O/F test) used for? |
It is used to determine bacteria that metabolize carbohydrates oxidatively, by fermentation, or are nonsacchrolytic |
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What does nonsacchrolytic mean? |
That the bacteria have no ability to use the carbohydrate in the media |
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Certain nonfermenting bacteria metabolize glucose using oxidation/aerobic respiration and therefore produce what? |
Only a small amount of weak acids during the Krebs cycle and glycolysis |
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When there is an increase in glucose concentration during the O/F test, what happens? |
It enhances the production of the weak acids and will turn the bromthymol blue indicator in OF media from green to yellow |
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How is the anaerobic process induced during the O/F test? |
It is induced by adding an oil overlay on the top of the medium |
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During the anaerobic process of fermentation, what happens? |
Pyruvate is converted to a variety of mixed acids depending on the type of fermentation. |
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The high concentration of acid produced during fermentation does what? |
It turns the bromthymol blue indicator in the OF media from green to yellow in the presence or absence of oxygen. |
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Nonsacchrolytic bacteria give what type of OF result? |
Negative |
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What is a negative result indicated by in an OF test and why is this? |
Indicated by no color or blue/green color in the bromthymol blue due to the increase in pH; this is due to amine production by bacteria that break down the peptone (protein) in the medium |
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If an oxidation reaction occurs, what will all three results be? |
Tube without oil will be yellow on top of tube; tube with oil with have no yellow; a negative result will be blue or green |
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If OX/Fermentation reaction occurs, what will all three possible results be? |
Tube without oil will be yellow; tube with oil overlay will be yellow; a negative result will be green |
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If Nonsacchrolytic reaction occurs, what will all three possible results be? |
The tube without oil will be green; the tube with oil with be blue/green; and a negative result will be green |
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How many OF tubes did you grab for the test? |
2 |
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When bacteria ferments sugar, what happens? |
An acid will build up which will then reduce the pH and change the color of phenol red. |
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Sugars undergo fermentation when? |
When it acts as an electron donor, such as in glycolysis |
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what end products does the fermentation reaction generate? |
acids, ethanol, hydrogen gas, carbon dioxide gas, and other organic compounds |
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What happens in the glucose, lactose, and mannitol broths when there is fermentation with only acid production? |
The media changes from red to yellow |
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What happens in the glucose, lactose, and mannitol broths when there is organic acid and gas production? |
medium changes from red to yellow and a gas bubble is visible in the inverted tube |
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What happens in the glucose, lactose, and mannitol broths when there is absence of fermentation? |
The broth will retain the red color because it can not utilize the carbohydrate |
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What does MRVP contain? |
Glucose, peptone, and phosphate buffer |
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How can enteric organisms overcome the buffering capacity of a media? |
By producing large quantities of stable acid end products, which lowers the pH |
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How is acid production detected in an MRVP broth? |
By using the pH indicator methyl red |
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What is the methyl red test used to identify? |
it is used to identify mixed acid fermenting bacteria that yield a stable acid end product |
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The Voges-Poskauer tests is used to identify what? |
used to identify bacteria capable of 2,3 butanediol fermentation following mixed-acid fermentation |
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The reagents in the VP test test for what? |
It tests for the precursor acetoin rather than the 2,3 butanediol |
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A positive MR test shows what? |
A stable red color on the surface of the medium after the addition of methyl red |
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A negative MR test shows what? |
It shows a yellow color on the surface of the medium |
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A positive VP test shows what? |
Pink-red color on the surface of the medium 15 minutes to one hour after the addition of the reagents |
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A negative VP test shows what? |
It shows a yellow/brown color on the surface of the medium |
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What did we do for the citrate test? |
Drew the bacteria up the slant in a zig zag motion and then stabbed the needle through the middle |
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What does bacteria require to utilize citrates? |
it requires citrate transport proteins |
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Oxaloacetate is metabolized to what? |
pyruvate and carbon dioxide |
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What does pyruvate and carbon dioxide react with and what does that produce ? |
Water and socium ion in the medium to produce sodium carbonate, which raise pH |
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When is ammonium hydroxide produced in the citrate test? |
When the ammonium salts in the medium are used as the sole nitrogen source by the bacteria |
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What does it mean when the citrate was utilized in the citrate test? |
That it was a positive result so it turned blue |
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What does it mean when the citrate was not utilized in the citrate test? |
That it was a negative result and turned green |
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What does the oxidase test detect? |
The presence of the enzyme cytochrome C oxidase. |
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What does cytochrome C oxidase do? |
it takes part in the final stage of bacterial respiration (involves the electron transport chain) |
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What is the indication when the enzyme cytochrome C oxidase is absent? |
the reagent will remain yellow |
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what is the indication when the enzyme cytochrome C oxidase is present? |
reagent turns blue/purple |
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What does the enzyme catalase do? |
It degrades ht hydrogen peroxide in the cell before it can do any cell damage; it also splits the hydrogen peroxide to free oxygen bubbles and water |
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What is the positive test reaction for a catalase test? |
It is very fast and obvious bubbles are visible with the addition of hydrogen peroxide on to the cells |
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Enteric bacteria that reduce nitrate usually produce what? |
Nitrite |
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There are other bacteria that reduce nitrate as well, what do they produce? |
ammonia, nitric oxide, nitrogen gas and nitrous oxide |
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The first product of reduction to look for before any reagents are added is what? |
reduction to nitrogen gas (denitrification) within the durham tube |
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How is the broth tests for reduction of nitrate to nitrite? |
By adding sulfanilic acid reagent and alpha-naphtylamine |
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What will happen when the broth is tested for the reduction of nitrate and nitrite? |
A color change to red will indicate a positive nitrate reduction. |
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When can you stop in a nitrate reduction test? |
when you get a red color |
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If the medium does not turn red in a nitrate reduction test, what does it mean? |
That the organism was unable to reduce the nitrate or the organism was able to denitrify the nitrate or nitrite to produce ammonia or molecular nitrogen |
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What do you do if a nitrate reduction test does not turn red? |
Add a small amount of powdered zing |
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If the tube turns red after the addition of zinc in a nitrate reduction test, what does it mean? |
That the unreduced nitrate was present and it produced a negative result |
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When nitrate changes to nitrite: is there nitrogen gas?, what is the color after adding reagents?, and what is the color after adding zinc? |
No nitrogen gas produced; red color after adding reagents; and zinc was not added |
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When nitrate changes to nitrogen gas, is there nitrogen gas present?, what is the color after adding reagents?, and what is the color after adding zinc? |
Nitrogen gas is produced; no color after adding reagents; zinc was not added |
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When nitrate changes to ammonia, is nitrogen gas produced?, what is the color after adding reagents?, and what is the color after adding zinc? |
No nitrogen gas is produced; no color after adding reagents; no color after adding zinc |
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If there is no reaction in a nitrate reduction test, will there be nitrogen gas produced?, what will the color be after adding reagents?, and what is the color after adding zinc? |
Nitrogen gas is not produced, no color is shown after adding reagents, and it will be pink-red after adding zinc. |
