5. What is the result of Staphylococcus epidermidis on MSA? Describe how you came to this conclusion. 6. What are the 2 types of hemolysis that these Gram+ bacteria show? Describe what the 2 types mean the bacteria can or cannot do. 7. What is the result of Staphylococcus epidermidis on blood agar? Describe how you came to this conclusion. 8. What is the result of Staphylococcus epidermidis in the catalase test? What does this mean the bacteria does or does not contain? 9. What is the result of Staphylococcus epidermidis in the coagulase test? What does this mean the bacteria does or does not contain? 10. Review the overall data for the 3 bacteria (Staphylococcus aureus, Staphylococcus epidermidis, Micrococcus luteus). If you just did a Gram stain on these bacteria, could you determine which bacteria you had? Why or why not?
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The result of Staphylococcus epidermidis on MSA (Mannitol Salt Agar) is **negative**. This means that Staphylococcus epidermidis does not ferment mannitol, and the agar remains pink or red. We can conclude this because MSA is selective for Staphylococcus species, Show more…
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Microbiology Pre-lab handout points: Fill out the table to predict the characteristics of the eight bacterial species (in bold) mentioned in the reading. Indicate whether each species occurs as a coccus or a rod, and whether it is gram-positive or gram-negative. Also, indicate the results of the catalase, oxidase, and coagulase tests. Table: Species Shape Gram Stain Catalase Oxidase Coagulase Djctcnium Rod Gram-positive Positive Negative Negative Bacillus Rod Gram-positive Positive Negative Negative Staphylococcus Coccus Gram-positive Positive Negative Negative Escherichia Rod Gram-negative Negative Negative Negative Pseudomonas Rod Gram-negative Negative Positive Negative Based on the table, the most helpful test for distinguishing between the two Gram-negative rods is the oxidase test. The unknown bacterium was cultured on nutrient agar. The bacterium turned purple when Gram stained. Under the compound microscope at 1000X magnification, the unknown appeared as individual and clustered rods, measuring approximately 1.0 um in width and length. Biochemical testing showed that the bacteria were able to hydrolyze hydrogen peroxide.
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Lab 15: Gram positive cocci 5. What are the oxygen requirements of Gram positive cocci, such as staphylococci and streptococci? Do they possess catalase? 6. What is the function of coagulase? 7. How do bacteria use coagulase to protect themselves against the host? 8. What medium do we use to test for coagulase? Can you replace this medium with TSA? 9. What type of medium is blood agar? a) What is hemolysis? b) Describe three types of hemolysis c) What type of hemolysis could be caused by normal flora bacteria? d) What type of hemolysis is associated with pathogenesis? 10. What is Novobiocin? How do we use Novobiocin to differentiate staphylococci? 11. What is capsule? What is the function of the capsule? 12. What kind of streptococci can form capsule? 13. What is the appearance of capsule in capsule staining?
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Questions: 1. What purpose does the Tryptic Soy Agar (TSA) plate serve? a. How does the TSA plate increase the validity of the test results? 2. Why is the streak plate method preferred over the zig-zag method of plate inoculation for this exercise? 3. With the diversity of microorganisms in the world, how can a single test, such as MSA, be used to confidently identify Staphylococcus aureus? 4. Phenylethyl Alcohol agar (PEA) contains only 0.25% phenylethyl alcohol because high concentrations inhibit both Gram-negative organisms and Gram-positive organisms. List some possible reasons why this is true. 5. For each media inoculated, write a paragraph to discuss the observations. The paragraph should include which organisms were inoculated onto the media, what results were observed, if the results were expected, and what the results reveal about the characteristics of the organism. 6. If any of the results were not expected, write a paragraph to trouble-shoot the problem. The paragraph should state the problem, how the observations were affected, and how the problem can be avoided in the future.
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