11-14
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| Lab11 Question 1: What is a Contaminant? | Unwanted microorganisms
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| Lab11 Question 2: How would you determine whether a colony was a contaminant on a streak plate? | A contaminant might appear different from the majority of colonies. A contaminant will often grow off the streak line.
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| Lab11 Question 2: How would you determine whether a colony was a contaminant on a POUR plate? | Contaminants aren't easily detected on a pour plate.
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| Lab 11 Critical Thinking 2: What is a disadvantage of the streak plate technique? | Since it is a dilution technique, only organisms in the majority will be isolated. The streak plate allows observation of colony morphology and selection of isolation colonies.
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| Lab 11 Critical Thinking 2: What is a disadvantage of the pour plate technique? | Since it is a dilution technique, only organisms in the majority will be isolated. The main advantage of the pour plate is for counting numbers of bacteria.
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| Lab 12 Conclusion 2: How did the results observed on the mannitol salt and EMB correlate to the Gram reaction of the bacteria? | (answers vary) The bacteria are identified by metabolic characteristics in the culture and cannot be identified from a Gram stain.
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| Lab 12 Conclusion 3: Which medium is selective? | EMB and mannitol salt agar are both selective.
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| Lab 12 Question 1: What is the purpose of peptone in the media? | Bacteria that cannot use the sugars in the media should be able to grow using peptone.
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| Lab 12 Question 2: What is the purpose of the agar in the media? | It is a solidifying agent.
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| Lab12 CT 1: What ingredient makes mannitol salt selective? | The high concentration of NaCl.
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| Lab 13 Question 2: How can you tell amylase is an exoenzyme and not an endoenzyme? | Starch is hydrolyzed outside of the bacterial cells.
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| Lab 13 Question 3: How can you tell from OF-glucose medium whether and organism uses glucose aerobically? | An organism that produces acid in the open tube only is using glucose aerobically.
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| Lab 13 Question 3: How can you tell from OF-glucose medium whether and organism ferments glucose? | A organism that produces acid in both tubes can ferment glucose.
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| Lab 13 Question 3: How can you tell from OF-glucose medium whether and organism doesn't use glucose? | Organisms that use the peptones instead of glucose will produce alkaline conditions in the OF tubes.
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| Lab14 Q #1: Why are fermentation tubes evaluated at 24 and 48 hours? | A: After exhausting the carbohydrate, the organism could use the amino acids. End products of amino acid catabolism are alkaline which would turn the indicator basic, giving a false negative reaction. Phenol red turns fushia at pH 8.4.
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| Lab 14 Q#3: Which of these media is selective? Why is it Selective? | Citrate agar; Because only bacteria that can usecitrate as their sole carbon source and NH4- as their nitrogen source can grow.
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| Lab 14 CT #1 Could an organism be a fermenter and also be both MR and V-P negative? Explain... | Yes, some fermenters could produce excess neutral products other than acetone, such as alcohol.
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| Contamination | The presence of unwanted microorganisms.
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| Streak Plate Technique | A loop is used to streak the mixed sample many times over the surface of a solid culture medium in a Petri plate. "Streaking for isolation"
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| Spread Plate Technique | A small amount of a previously diluted specimen is spread over the surface of a solid medium using a spreading rod.
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| Pour Plate Technique | A small amount of diluted sample is mixed with melted agar and poured into empty, sterile Petri dishes.
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| Selective Media | Contains chemicals that prevent the growth of unwanted bacteria without inhibiting the growth of the desired organism.
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| Enrichment Media | Usually liquid media. Contains chemicals that enhance the growth of certain bacteria. Chemical composition is known.
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| Differential Media | Chemical composition is unknown. These media contain various nutrients that allow the investigator to distinguish one bacterium from another with how they metabolize the media.
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| Catabolism | Chemical reactions that release energy from the decomposition of complex organic molecules.
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| Carbohydrates | Organic molecules that contain carbon, hydrogen, and oxygen in the ratio of (CH2O)n. They're classified by size - monosaccharides, oligosaccharides, polysaccharides.
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| Monosaccharide | Simple sugars containing 3-7 carbon atoms.
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| Oligosaccharides | Composed of 2-about 20 monosaccharide molecules. Disaccharides are the most common of these type.
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| Polysaccharides | Consist of 20 or more monosaccharide molecules.
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| Hydrolytic enzymes | Exoenzymes that leave the cell and break down, by the addition of water , large substrates into smaller components, which can then be transported into the cell.
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| Oxidative Catabolism | Requires the presence of molecular oxygen.
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| Fermentative Catabolism | Does not require oxygen but may occur in its presence.
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| OF Medium | A nutrient semisolid agar deep containing a high concentration of carbohydrate and a low concentration of peptone.
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| Fermentation Tube | Used to detect acid and gas production from carbohydrates. (tube with the glass tube inside)
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| MRVP Test | Used to distinguish organisms that produce large amounts of acid from glucose and organisms that produce the neutral product acetoin.
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| Methyl Red Test(MR) | MRVP medium is a glucose-supplemented nutrient broth used for this test. If an organism produces a large amount of organic acid from glucose, the medium will remain red when methyl red is added in a positive MR test, indicating that the pH is below 4.4.
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| Voges-Proskauer (V-P) Test | or VP is a test used to detect acetoin in a bacterial broth culture. A cherry red color indicates a positive result, while a yellow-brown color indicates a negative result.
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