Term
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Definition
| Selective and differential medium |
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Term
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Definition
| Bile salt that inhibits growth of gram + organisms |
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Term
| Xylose, Lactose and Sucrose |
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Definition
| Sugars provided for fermentation in XLD Agar |
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Term
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Definition
| An amino acid provided for decarboxylation |
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Term
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Definition
| Provides oxidized sulfur for organisms capable of reducing it to H2S |
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Term
| What indicators are used in XLD agar? |
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Definition
Ferric ammonium citrate:
Releases ferric ions into the medium that will react with H2S and form FeS, a black precipitate.
Phenol red:
yellow when acidic and red or pink when alkaline |
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Term
| What do yellow colonies in XLD agar represent? |
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Definition
| Organisms that ferment xylose and cause an acidic medium |
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Term
| How are red colonies formed in XLD agar? |
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Definition
| Organisms capable of decarboxylation of lysine will release CO2 and raise the pH. |
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Term
| How are black colonies formed in XLD agar? |
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Definition
| Organisms able to reduce sulfur will produce H2S, which will precipitate with Fe3+ |
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Term
| What do Shigella and Providencia species do in XLD agar? |
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Definition
| Form red colonies because they do not ferment xylose, but do decarboxylate lysine |
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Term
| What does Salmonella species do in XLD agar? |
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Definition
| Reduce sulfur, ferment xylose, and decarboxylate lysine. The colonies will be red with black centers. |
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Term
| How are yellow colonies formed? |
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Definition
| Enterics such as Escherichia, Klebsiella, Enterobacter |
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Term
| What is the purpose of XLD agar? |
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Definition
| It is a selective and differential medium used to isolate and identify shigella and providencia from stool samples. |
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Term
| What is the purpose of the oxidation-fermentation test? |
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Definition
| Used to differentiate bacteria on the ability to oxidize or ferment specific sugars. It allows presumptive separation of the fermentative enterobacteriaceae from the oxidative Pseudomonas and Bordetella and the nonreactive Alcaligenes and Moraxella |
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Term
| in the O-F test, which acidify the medium more? |
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Definition
| Fermenters because acids are a product of fermentation. |
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Term
| In the O-F test, how do you ensure that alkaline products from peptone utilization will neutralize weak acids? |
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Definition
| A high sugar to peptone ratio prevents that. |
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Term
| What dye is added to the O-F test as an indicator? |
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Definition
| Bromothymol blue dye which is yellow at pH 6.0 and green at pH 7.1 |
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Term
| How do you prepare the 2 mediums? |
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Definition
| One is sealed with mineral oil to promote anaerobic growth and fermentation, the other is left open to allow aerobic growth and oxidation |
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Term
| What does a yellow medium in the O-F test mean? |
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Definition
| Organisms are able to ferment,or ferment and oxidize sealed and unsealed media. |
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Term
| In the O-F test, if the sealed media is green and unsealed is green what does it mean? |
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Definition
| Organisms are only able to oxidize |
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Term
| Result of slow or weak fermenters in O-F test? |
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Definition
| Both tubes slightly yellow at the top |
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Term
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Definition
| A differential test medium. Used to differentiate members of Enterobacteriaceae and to distinguish them from other gram - rods |
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Term
| What is included in phenol red broth? |
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Definition
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Term
| What are the pH indicator colors of phenol red? |
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Definition
Yellow below 6.8
Pink to Magenta above 7.4
Red between these two |
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Term
| In phenol red broth, what lowers the pH? |
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Definition
| Acid production from fermentation of the carbohydrate |
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Term
| In phenol red broth, what lowers the pH? |
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Definition
| Acid production from fermentation of the carbohydrate |
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Term
| In phenol red broth, what raises the pH? |
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Definition
| Deamination of peptone amino acids produces ammonia which raises the pH |
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Term
| What else is included in phenol red broth test to test for gas production? |
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Definition
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Term
| Methyl Red and Voges-Proskauer Tests |
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Definition
| Component of the IMViC battery of tests used to distinguish between members of the family Enterobacteriaceae and differentiate them from other Gram- rods. |
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Term
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Definition
| Peptone, glucose, phosphate buffer |
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Term
| What do peptone and glucose proved in the MR-VP media? |
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Definition
| Protein and fermentable carbohydrate |
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Term
| Purpose of potassium phosphate in MR-VP media? |
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Definition
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Term
| What is the MR test designed to do? |
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Definition
| Detect organisms capable of performing mixed acid fermentation, which overcomes the phosphate buffer in the medium and lowers the pH. |
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Term
| How is mixed acid fermentation verified in MR tets? |
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Definition
| Methy red dye is added as an indicator following incubation. Red color veriefies the positive result. |
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Term
| What color is methyl red at the various pH's? |
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Definition
Below 4.4-RED
at 6.2 YELLOW
Between 4.4 and 6.2 ORANGE |
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Term
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Definition
| Designed for organisms that are able to ferment glucose, but quickly convert their acid products to acetoin and 2,3-butanediol. |
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Term
| What is a positive VP result? |
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Definition
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Term
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Definition
| Converts H2O2 into H20 and O2. |
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Term
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Definition
| Catalyzes conversion of superoxide radicals to H202 |
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Term
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Definition
| Carrier molecule in the ETC that can bypass the next carrier molecule in the chain and transfer electrons directly to oxygen. Produces 2 highly potent cellular toxins- H202 and O2-(superoxide radical) |
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Term
| What happens when hydrogen peroxide is added to a catalase positive culture? |
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Definition
| Oxygen gas bubbles form immediately |
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Term
| What is the catalase test used for? |
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Definition
| To differentiate members of catalase-positive Micrococcaceae from catalase-negative Streptococcaceae. |
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