Lab Quiz 2

  1. Describe the procedure for heat fixation
    • an air dried smear of the organisms is passed held in front of the opening of a microincinerator for 10 seconds
    • the heat coagulates the organisms' proteins causing the bacteria to stick to the slide
  2. Describe the procedure for methanol fixation
    • an air-dried smear of the organism is covered with a few drops of 95% methanol
    • after 2 min the methanol is washed off and the slide is left to air dry
    • this causes less damage and distortion to the bacteria
  3. Define: acidic dye
    • the color portion of the dye resides in the negative ion
    • ex. nigrosin, congo red
  4. Define: basic dye
    • the color portion of the dye resides in the positive ion
    • ex. methylene blue, crystal violet, safranin
  5. Define: direct stain
    the color stains the organism directly
  6. Define: indirect stain
    the color forms a deposit around the organism, leaving the organism colorless
  7. State in chemical and physical terms the principle behind direct staining
    when using a basic dye, the positively charged color portion of the stain combines with the neg. charged bacterial cytoplasm and the organism becomes directly stained
  8. State in chemical and physical terms the principle between indirect staining
    when using an acidic dye, the color portion of the dye is on the negative ion, so it will not readily combine with neg. charged bacterial cytoplasm and it forms a deposit around the organism, leaving the organism itself colorless
  9. Why is the gram stain said to be a differential stain
    because it differentiates between gram-positive and gram-negative bacteria
  10. Describe the differences between a gram-positive and a gram-negative cell wall
    • positive - thick, dense wall 20-80nm thick, various layers of peptidoglycan, interwoven w teichoic acids
    • negative - only 2-3 layers of peptidoglycan, surrounded by an outer membrane + LPS
  11. describe a theory as to why gram-positive bacteria retain the crystal violet-iodine complex while gram-negatives become decolorized
    in gram-neg, the single thin layer of peptidoglycan is unable to retain the dye bc the outer and inner membranes get dissolved but in gram-positive it can retain the larger molecule complex
  12. Describe three conditions that may result in a gram-positive organism staining gram-negatively
    • method & technique used - overheating during fixation or over decolorizing or using too much water in washes
    • ages of the culture - over 24 hrs old cannot retain crystal violet-iodine complex as well
    • the organism itself - some are better at retaining than others
  13. State the chemical nature and major functions of bacterial capsules
    • a slimy, viscous covering
    • help bacteria resist phagocytosis
    • in soil/water, prevent bacteria from being engulfed by protozoans
    • help bacteria adhere to surfaces & resist flushing
  14. Name two endospore-producing genera of bacteria
    • Bacillus
    • Clostridium
  15. State the function of bacterial endospores
    serves as resistant, dominant survival form of the organism
  16. What is a monotrichous flagellar arrangement
    single flagellum at one pole
  17. What is a lophotrichous flagellar arrangement
    two or more flagella at one or both poles
  18. What is an amphitrichous flagellar arrangement
    single flagella at both poles
  19. What is a peritrichous flagellar arrangement
    completely surrounded by flagella
  20. What are axial filaments
    internal flagella, usually in spirochetes
  21. State the function of bacterial flagella
    the organelles of locomotion
  22. Desribe three methods of testing for bacterial motility and indicate how to interpret the results
    • direct observation of motility using special-purpose microscopes (phase-contrast microscopy vs dark-field microscopy)
    • motility test medium (nonmotile - growth only along line of inoculation, motile - growth throughout the tube, cloudy-like)
    • flagella staining - used indirectly to denote motility
  23. State the chemical nature and function of enzymes
    speed of chemical reactions without being consumed
  24. Define endoenzyme
    enzymes located within the bacterium
  25. Define exoenzyme
    secreted by bacteria into the surrounding environment in order to break down larger nutrient molecules so they can enter the bacterium
  26. Describe a method of testing for starch hydrolysis
    When iodine is added to starch, the iodine-starch complex that forms gives a characteristic dark brown or deep purple color reaction. If the starch has been hydrolyzed into glucose molecules by the diastase exoenzyme, it no longer gives this reaction.
  27. How to interpret the results for starch hydrolysis
    • clear zone surrounds bacterial growth - starch is hydrolyzed
    • agar turns dark brown/blue - starch is not hydrolyzed
  28. Describe a method of testing for casein hydrolysis
    The protein casein exists as a colloidal suspension in milk and gives milk its characteristic white, opaque appearance. If the casein in the milk is hydrolyzed into peptides and amino acids, it will lose its opaqueness.
  29. How to interpret the results for casein hydrolysis?
    • clear zone around bacterial growth - casein is hydrolyzed
    • skim milk agar is still white/opaque - casein is not hydrolyzed
  30. Name the general end products which may be formed as a result of bacterial fermentation
    • acid end products
    • acid & gas end products
  31. Yellow/clear phenol indicator + gas bubble in durham tube indicates what?
    • carbohydrate fermentation
    • acid and gas products
  32. Yellow/clear phenol indicator + no gas bubble in durham tube indicates what?
    • carbohydrate fermentation
    • acid but no gas products
  33. Red/orange phenol indicator + no gas bubble in durham tube indicates what?
    • no carbohydrate fermentation
    • no acid or gas
  34. State the pathway for the breakdown of tryptophan to indole
    tryptophan --> indole + pyruvic acid + ammonia
  35. What is indole production useful for?
    identification of E. coli
  36. State the pathway for the detection of sulfur reduction in SIM medium
    • To test for hydrogen sulfide production, a medium with a sulfur-containing compound and iron salts is inoculated and incubated
    • If the sulfur is reduced and hydrogen sulfide is produced, it will combine with the iron salt to form a visible black ferric sulfide (FeS) in the tube
  37. State three reactions that may be tested for in SIM medium
    • Proteus mirabilis
    • Escherichia coli
    • Enterobacter cloacae
  38. how to interpret the results for sulfur in SIM medium
    • if tube turns black - sulfur was reduced
    • if tube remains yellow - sulfur was not reduced
Author
st2478
ID
332242
Card Set
Lab Quiz 2
Description
Lab Quiz 2 (labs 5-8)
Updated