Practicals

• What is the focus of the microbiology practical exam?

  Microscopic examination of bacteria
• What are the types of slide preparations for microscopic examination?

  • Native (wet mount) slides
  • Dry (permanent, stained) slides
• What does a wet mount slide contain?

  Sample suspended in water or saline
• What is the purpose of the hanging drop procedure?

  To observe live culture motility
• How does the hanging drop procedure distinguish true motility from Brownian motion?

  By observing movement patterns of organisms
• What are the steps in smear preparation for staining?

  1. Smear preparation
  2. Drying
  3. Fixation (physical, chemical)
  4. Staining
• What is the purpose of simple staining methods?

  To see shapes and sizes of bacteria
• What is the Loeffler’s Methylene blue method used for?

  To stain bacteria blue for observation
• What color do bacteria appear after Fuchsin staining?

  Red
• What is the purpose of differential staining methods?

  • To differentiate bacteria based on cell wall properties
  • Examples include Gram staining and Ziehl-Neelsen staining
• What is the main principle of Gram staining?

  Based on different structure of cell wall
• How do Gram-positive and Gram-negative bacteria differ in Gram staining?

  Gram-positive retains crystal violet, Gram-negative does not
• What is the role of iodine in Gram staining?

  To form a stable complex with crystal violet
• What is the effect of prolonged decolorization in Gram staining?

  Causes gram-variable appearance
• What are the steps in Gram staining?

  1. Prepare smear
  2. Heat-fix the smear
  3. Apply crystal violet
  4. Add iodine
  5. Decolorize with alcohol or acetone
  6. Rinse with water
  7. Counterstain with safranin or fuchsin
• What is the Ziehl-Neelsen staining method used for?

  To stain acid-fast bacteria
• What is the main component of the cell wall in acid-fast bacteria?

  Mycolic layer
• What is the purpose of Neisser’s Method?

  To identify volutin granules
• What are the steps in Neisser’s Method?

  1. Prepare a smear
  2. Air dry
  3. Heat-fix the slide
  4. Flood with Neisser 1 dye
  5. Flood with Neisser 2 dye
  6. Wash with water
• What color does the cytoplasm appear in Neisser’s Method?

  Light brown and granular blue-black
• What is the purpose of Moeller’s method?

  • To observe spore formation
  • Involves heat-fixing and staining with carbol fuchsin
• What is the purpose of Pshkov’s method?

  • To observe blue spores and red cells
  • Involves heat-fixing and staining with methylene blue
• What is the Klett method used for?

  • To observe capsule formation
  • Involves heat-fixing and staining with methylene blue
• What is Gins method for capsules?

  • Uses Indian ink for negative staining
  • Observes capsules surrounding bacterial cells
• What are the types of artificial growth media?

  • Liquid
  • Solid
  • Semisolid
• What are the types of media regarding purpose?

  • Minimal essential media
  • Enriched media
  • Selective media
  • Differential media
• What is the composition of minimal essential media?

  Primary precursors for growth
• What is blood agar used for?

  • To isolate fastidious organisms
  • Detects hemolytic activity
• What is the function of MacConkey agar?

  • Differentiates lactose fermenting from non-fermenting bacteria
  • Lactose fermenters appear pink
• What is the purpose of selective media?

  • To recover specific organisms from mixtures
  • Inhibitors suppress unwanted organisms
• What is the function of differential media?

  • Allows identification of organisms in mixtures
  • Specific ingredients added for biochemical reactions
• What are the culture properties of bacteria in liquid media?

  1. Whole broth becomes dull
  2. Sediment at the bottom
  3. Film on the surface
  4. Staining of the whole specimen
• What are the culture properties of bacteria in solid media?

  1. Colony formation within 24h
  2. Differences in color, size, form, structure
• What is anaerobic cultivation?

  Growth of microorganisms in absence of oxygen
• What is the role of CO2 in anaerobic cultivation?

  Creates an environment unfavorable for aerobic organisms
• What is the purpose of antimicrobial susceptibility testing?

  • To assess effectiveness of antibiotics against bacteria
  • Assists in selecting treatment options
• What is the method for determining minimal inhibitory concentration?

  • Involves preparing a series of dilutions
  • Tests effectiveness of antibiotics
• What percentage of CO2 is typically used in anaerobic environments?

  5-10%
• How does CO2 affect aerobic organisms?

  It creates an environment un-favorable for them
• What role does CO2 play in anaerobic cultivation?

  It prevents oxygen entry into the medium