Question | Answer |
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. |