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Micro Lab Quiz 3

11-14

QuestionAnswer
Lab11 Question 1: What is a Contaminant? Unwanted microorganisms
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.
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.
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.
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.
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.
Lab 12 Conclusion 3: Which medium is selective? EMB and mannitol salt agar are both selective.
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.
Lab 12 Question 2: What is the purpose of the agar in the media? It is a solidifying agent.
Lab12 CT 1: What ingredient makes mannitol salt selective? The high concentration of NaCl.
Lab 13 Question 2: How can you tell amylase is an exoenzyme and not an endoenzyme? Starch is hydrolyzed outside of the bacterial cells.
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.
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.
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.
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.
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.
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.
Contamination The presence of unwanted microorganisms.
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"
Spread Plate Technique A small amount of a previously diluted specimen is spread over the surface of a solid medium using a spreading rod.
Pour Plate Technique A small amount of diluted sample is mixed with melted agar and poured into empty, sterile Petri dishes.
Selective Media Contains chemicals that prevent the growth of unwanted bacteria without inhibiting the growth of the desired organism.
Enrichment Media Usually liquid media. Contains chemicals that enhance the growth of certain bacteria. Chemical composition is known.
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.
Catabolism Chemical reactions that release energy from the decomposition of complex organic molecules.
Carbohydrates Organic molecules that contain carbon, hydrogen, and oxygen in the ratio of (CH2O)n. They're classified by size - monosaccharides, oligosaccharides, polysaccharides.
Monosaccharide Simple sugars containing 3-7 carbon atoms.
Oligosaccharides Composed of 2-about 20 monosaccharide molecules. Disaccharides are the most common of these type.
Polysaccharides Consist of 20 or more monosaccharide molecules.
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.
Oxidative Catabolism Requires the presence of molecular oxygen.
Fermentative Catabolism Does not require oxygen but may occur in its presence.
OF Medium A nutrient semisolid agar deep containing a high concentration of carbohydrate and a low concentration of peptone.
Fermentation Tube Used to detect acid and gas production from carbohydrates. (tube with the glass tube inside)
MRVP Test Used to distinguish organisms that produce large amounts of acid from glucose and organisms that produce the neutral product acetoin.
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.
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.
Created by: Lproctor on 2012-02-22



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