quiz 2 practice test

  1. What does a color change from pink to yellow in Mannitol Salt Agar (MSA) indicate?

    • This change indicates that the bacterium has metabolized mannitol, leading to acid production which drops the pH below 6.8.

  2. What happens to bacteria that do not metabolize mannitol on MSA?

    • These bacteria still grow on MSA but do not cause a color change, as the medium remains pink.

  3. What is the objective of the EMV medium?

    • The EMV medium is used to assess whether bacteria can metabolize lactose.

  4. What does a green metallic sheen on EMV indicate?

    • This sheen indicates effective lactose metabolism, particularly observed with E. coli.

  5. What happens to the appearance of the green sheen over time?

    • It may fade, resulting in dark purple growth, which still signifies strong lactose metabolism.

  6. What are the characteristics of Spirit Blue Medium?

    • Spirit Blue Medium is non-selective but differential; it supports both Gram positive and Gram negative bacteria and tests for lipase enzyme presence.

  7. What does clearing around bacterial growth in Spirit Blue Medium signify?

    • The halo effect indicates the presence of lipase, which breaks down lipids.

  8. What is the function of glucose in TSI (Triple Sugar Iron) Medium?

    • Glucose serves as a limited carbon source to encourage testing for lactose and sucrose metabolism when glucose is exhausted.

  9. What occurs in TSI Medium when glucose and/or other sugars are metabolized?

    • The medium turns yellow due to acidic byproducts from fermentation.

  10. What does it mean if TSI Medium remains red?

    • A red color indicates that only peptone is metabolized, resulting in a basic condition due to ammonia production.

  11. How does peptone affect the pH of TSI Medium?

    • Metabolizing peptone raises the pH, turning the medium red.

  12. What role does Sodium Thiosulfate play in TSI Medium?

    • It releases elemental sulfur in acidic conditions, which bacteria can reduce to hydrogen sulfide (H2S).

  13. What indicates hydrogen sulfide production in TSI Medium?

    • A black precipitate forms when ferric ammonium citrate binds with hydrogen sulfide, indicating sulfur as a terminal electron acceptor in the electron transport chain.

  14. What are the two pathways for carbon metabolism mentioned?

    • Glycolysis for sugar breakdown and the Krebs cycle for decarboxylation processes.

  15. What is the purpose of the stab and streak method for TSI?

    • To create aerobic and anaerobic environments for better observation of bacterial growth.

  16. How does the Bile Esculin Test indicate successful esculin hydrolysis?

    • A dark brown/black coloration indicates that esculin has been metabolized in the presence of ferric citrate.

  17. What indicates positive results in the MIO test for indole production?

    • A red ring appears after adding Kovac's reagent, indicating tryptophanase enzyme presence.

  18. What does the presence of putrescine in the MIO test signify?

    • The production of putrescine from ornithine decarboxylation raises the pH, changing the medium from yellow to purple.

  19. What precautions should be taken when handling Pseudomonas?

    • Always change gloves due to its increased virulence compared to other bacteria.

  20. What is the medical significance of hemolysis observed on Blood Agar Plates?

    • The degree of hemolysis correlates with pathogenicity; for example, beta-hemolytic strep can cause serious infections.

  21. How does the Snyder Test Agar detect lactobacilli?

    • It detects them by observing color change from green to yellow due to lactic acid production, which lowers the pH.

  22. What environment does an anaerobic chamber create for bacteria?

    • It removes oxygen and introduces nitrogen or carbon dioxide, allowing anaerobic bacteria to grow.

  23. How does gas production manifest in TSI Medium?

    • It is indicated by cracks or bubbles in the medium.

  24. What safety measure is crucial in the lab when working with potentially virulent bacteria?

    • The importance of proper inoculation techniques to avoid contamination while ensuring active growth.

  25. What does the presence of ferric citrate in Bile Esculin Test indicate?

    • Ferric citrate is crucial for detecting the reaction product esculetin, which binds to form a coloration.

  26. What kind of bacteria does the Snyder Test target specifically?

    • This agar is designed to detect lactobacilli, related to dental caries risk.

  27. What happens if triglycerides are broken down in Spirit Blue Medium?

    • The blue color diminishes, indicating lipase activity.

  28. Why is it important not to cover the surface of Spirit Blue Medium entirely during inoculation?

    • To observe the halo effect clearly around the bacterial growth.

  29. What specific appearance suggests beta-hemolysis on Blood Agar Plates?

    • Clear zones surrounding the growth indicate complete breakdown of red blood cells.

  30. What is the importance of using specific fermentation tests like TSI and Bile Esculin?

    • They help discern metabolic capabilities of bacteria, including sugar fermentation and enzyme production, aiding in identification.