BIOS242 Lab Practical SG-3 Fundamentals of Microbiology with Lab - Chamberlain

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Lab Practical Study Guide Know and understand the experiments you conducted this term and the equipment involved (petri dishes, inoculating needle, various stains, etc) Obvious Understand the resul... ts of the experiments (i.e. what does the sugar test look for, products of carbohydrate fermentation, hydrogen peroxide test, Catalase Test What is the purpose of the test? The purpose is to see if the microbe has catalase, a protective enzyme capable of destroying the dangerous chemical hydrogen peroxide. How is catalase activity determined? Growth from an overnight culture of the microbe is smeared on a microscope slide. A drop of 3% hydrogen peroxide is added. If copious bubbles are observed, the microbe is positive for catalase. What medium is used? The medium for growth can be most any general purpose medium. Care should be taken to avoid using blood agar, as blood cells contain catalase and trace contamination of medium can lead to false positive results. Removal of cells from an isolated colony on a streak plate is recommended. OF Glucose Test What is the purpose of this test? The pathways used to metabolize a sugar under aerobic conditions differ from those used under anaerobic conditions. When oxygen is present, the process is called oxidation, and when oxygen is absent it is called fermentation. This test provides insight into the ability of the bacterium to use glucose by both methods. Two tubes of OF glucose medium are used, one of which is covered with a layer of sterile mineral oil as an oxygen barrier. If glucose is metabolized in either tube, acidic end products accumulate and the pH drops. A pH indicator in the medium changes color to indicate acid production. Acid from Glucose What is the purpose of the test? The purpose is to see if the microbe can ferment the carbohydrate (sugar) glucose (also known as dextrose) as a carbon source. How is glucose ( dextrose) fermentation determined? If glucose ( dextrose) is fermented to produce acid end products, the pH of the medium will drop. A pH indicator in the medium changes color to indicate acid production. What medium is used? Several media are available for this. Most commonly used is phenol red glucose (dextrose) broth. The medium is a nutrient broth to which 0.5-1.0% glucose ( dextrose) is added. The pH indicator phenol red is red at neutral pH but turns yellow at pH <6.8. It also changes to magenta or hot pink at pH >8.4. Additionally, this medium contains a Durham tube, a smaller inverted tube which can serve as a trap for gas bubbles generated during fermentation of sugars. Gas from Glucose What is the purpose of the test? The purpose is to see if the microbe can ferment the carbohydrate (sugar) glucose (also known as dextrose) as a carbon source, and to see if the fermentation products include gases. How is gas production from glucose determined? When many microbes ferment glucose ( dextrose), they produce gases, mainly carbon dioxide and hydrogen. These gases bubble up through the medium and escape into the atmosphere. Tubes of broth media can be made with inverted tubes called Durham tubes which are filled with medium after sterilization. Gas-producing microbes generate enough gas to force the medium from the tube, filling it with bubbles. Lactose Fermentation Test What is the purpose of the test? The purpose is to see if the microbe can ferment the carbohydrate (sugar) lactose as a carbon source. How is lactose fermentation determined? If lactose is fermented to produce acid end products, the pH of the medium will drop. A pH indicator in the medium changes color to indicate acid production. what are blood agar plates used for? BAPs are enriched, differential media used to isolate fastidious organisms and detect hemolytic activity. What are MSA plates, used for? This medium is important in medical laboratories by distinguishing pathogenic microbes in a short period of time by It encourages the growth of a group of certain bacteria while inhibiting the growth of others. This is a selective medium that favors the growth of staphylococci and for differentiation between pathogenic and non-pathogenic types [Show More]

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