Term
| Hektoen Enteric (HE) Agar |
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Definition
| Complex, moderately selective, and differential medium designed to isolate Salmonella and Shigella species from other enterics. |
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Term
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Definition
| Based on the ability to ferment lactose, sucrose, or salicin, and to reduce sulfur to H2S. |
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Term
| What is the source of oxidized sulfur in HE agar? |
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Definition
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Term
| What is the source of oxidized iron included to react with any sulfur? |
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Definition
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Term
| Why are bile salts included in HE agar? |
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Definition
| To prevent or inhibit growth of gram + organisms. Also have a moderate inhibitory effect on enterics, so high concentration of animal tissue and yeast extract must offset this. |
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Term
| What dyes are added to HE agar to indicate pH changes? |
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Definition
| Bomothymol blue and acid fuchsin dyes |
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Term
| What color will enterics that produce acid from fermentation produce? |
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Definition
| Yellow to salmon-pink colonies |
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Term
| What color do colonies of salmonella or shigella appear? |
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Definition
| They do not ferment any of the sugars, instead they break down the animal tissues which raises the pH, causing a blue-green color. |
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Term
| What doe Salmonella species do that Shigella do not? |
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Definition
| They reduce sulfur to H2S, so the colonies also contain FeS, which makes them partially or completely black, |
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Term
| What does anaerobic respiration involve? |
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Definition
| Reduction of an inorganic molecule other than oxygen. |
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Term
| What is nitrate reductase? |
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Definition
| An enzyme that many gram - organisms contain to reduce nitrate to nitrite. |
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Term
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Definition
| Multi-step process of enzymatic conversion of nitrate to molecular nitrogen. |
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Term
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Definition
| Undefined medium of beef extract, peptone, and potassium nitrate. No color indicators are included. |
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Term
| What is the reason for color change in nitrate broth? |
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Definition
| A result of reactions between metabolic products and reagents added after incubation. |
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Term
| How do you test to see if denitrification has occurred? |
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Definition
| Look for presence of gas in the durham tube. |
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Term
| Assimilatory nitrate reduction |
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Definition
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Term
| What forms in the medium if nitrate is reduced to nitrite? |
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Definition
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Term
| What is added to the medium when there is no visual evidence of denitrification? |
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Definition
| Sulfanilic acid and naphthylamine. If present, nitrite will form nitrous acid which reacts with reagents to produce red, water-soluble compound. |
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Term
| After addition of reagents to nitrate broth, what could the results mean? |
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Definition
| Color change to red indicates reduction of nitrate to nitrite. No color change indicates it was not reduced to nitrite. |
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Term
| What is the next step if there was no color change after adding reagents? |
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Definition
| A small amount of powdered zinc is added to the broth to catalyze reduction of any nitrate to nitrite. The medium will turn red. This color change indicates that the organism did not reduce the nitrate. No color change indicates that it was reduced by the organism. |
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Term
| What are coliforms used for? |
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Definition
| Used as the indicator species when testing water for fecal contamination because they are relatively abundant in feces and easy to detect. |
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Term
| What is the basic process of membrane filter? |
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Definition
| A water simple is drawn through a special porous membrane designed to trap microorganisms larger than 0.45 micrometers. After filtering, the paper is applied to the surface of plated endo agar and incubated for 24 hours. |
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Term
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Definition
| A selective medium that encourages gram- bacterial growth and inhibits gram + growth. Contains lactose for fermentation and a dye to indicate changes in pH. |
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Term
| What color do coliform colonies usually appear? |
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Definition
| Red and/or mucoid with a gold or green metallic sheen. |
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Term
| How do noncoliform bacteria appear? |
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Definition
| Pale pink, colorless, or the color of the medium. |
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Term
| What does a countable plate contain in the membrane filter technique? |
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Definition
| Between 20-80 coliform colonies with a total colony count no larger than 200. |
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Term
| How do you ensure the correct number of countable coliform colonies? |
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Definition
| Dilute heavily polluted samples |
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Term
| How is the membrane filter technique used/what is its importance? |
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Definition
| Commonly used to identify the presence of fecal coliforms in water. |
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