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Microbiology RR > General Microbiology > Flashcards

General Microbiology Flashcards

1
Q

Who invented the Polymerase Chain Reaction (PCR) and what does it detect?

A

• Inventor: Kary B. Mullis
• Purpose: Detects genes (Molecular technique).

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2
Q

Who developed the Enzyme-Linked Immunosorbent Assay (ELISA) and what does it detect?

A

• Inventors: Eva Engvall and Peter Perlman
• Purpose: Detects antigens (Ag) and antibodies (Ab) (Immunological technique).

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3
Q

What is the primary purpose of microscopy in microbiology?

A

• Purpose: Detection of organisms
• Morphology: Staining (Killed organisms)
• Motility: Hanging drop (Live organisms)

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4
Q

Which microscopes are commonly used to visualize motility?

A
  1. Bright field microscope (Light)
    1. Darkfield microscope
    2. Phase contrast microscope
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5
Q

What is the most commonly used microscope for visualizing motility?

A

Bright field

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6
Q

What is the characteristic feature of the following microscopes?
1. Brightfield microscope
2. Darkfield microscope
3. Phase contrast microscope

A
  1. Brightfield: Bright organism with bright background.
    1. Darkfield: Bright organism with dark background.
    2. Phase contrast: Dark organism with bright background.
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7
Q

What type of organisms’ motility can be observed using different microscopes?

A
  1. Brightfield microscope: Motility observed for all except thin organisms.
    1. Darkfield microscope: Motility observed for all organisms, especially spirochetes (corkscrew motility).
    2. Phase contrast microscope: Motility observed for thin organisms, including spirochetes.
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8
Q

What are the features of the darkfield and phase contrast microscopes?

A
  1. Darkfield microscope: Contains a dark field condenser.
    1. Phase contrast microscope: Contains a phase plate.
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9
Q

What is the first step in Gram staining?

A

• Primary staining:
• Reagents: Crystal violet, Gentian violet, or Methyl violet
• Duration: 1 minute
• Result: Organisms stain violet.

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10
Q

What is the purpose of adding Gram’s iodine in the Gram stain procedure?

A

• Mordant step:
• Reagent: Gram’s Iodine
• Duration: 1 minute
• Result: Organisms remain violet.

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11
Q

What is the critical step in the Gram stain procedure?

A

• Decolorization:
• Reagents: Acetone (2-3 seconds) or Alcohol (20-30 seconds)
• Outcome:
• Decolorize -: Retain violet stain.
• Decolorize +: Organism becomes colorless.

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12
Q

What is the final step in Gram staining and its purpose?

A

• Counterstaining:
• Reagents: Saffranin or Dilute carbol fuchsin
• Duration: 1 minute
• Result:
• Violet: Gram Positive (Thick cell wall)
• Pink: Gram Negative (Thin cell wall)

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13
Q

What is the sequence of steps in the Gram staining procedure?

A
  1. Primary Staining: Apply Crystal violet, Gentian violet, or Methyl violet for 1 minute (Organisms turn violet).
    1. Mordant: Add Gram’s Iodine for 1 minute (Organisms remain violet).
    2. Decolorization: Apply Acetone (2-3 seconds) or Alcohol (20-30 seconds).
      • Decolorize -: Organisms retain violet stain.
      • Decolorize +: Organisms become colorless.
    3. Counterstaining: Apply Saffranin or Dilute carbol fuchsin for 1 minute.
      • Violet: Gram Positive (Thick cell wall).
      • Pink: Gram Negative (Thin cell wall).
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14
Q

What are the different concentrations of H₂SO₄ used for various organisms in the Acid-Fast Stain?

A
  1. 20% H₂SO₄: Mycobacterium tuberculosis (M. Tb).
    1. 5% H₂SO₄: Mycobacterium leprae (M. leprae).
    2. 1% H₂SO₄: Nocardia & Parasites.
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15
Q

What is the final step in the Acid-Fast Staining procedure?

A

• Counter Staining:
• Reagent: Methylene blue.
• Result:
• Acid-fast organisms: Stay pink.
• Non-acid-fast organisms: Appear blue.

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16
Q

What is the critical step in the Acid-Fast Staining procedure?

A

• Decolorization:
• Reagent: 20% H₂SO₄ for 1 minute.
• Outcome:
• Decolorize -: Organisms remain pink.
• Decolorize +: Organisms become colorless.

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17
Q

What is the first step in the Acid-Fast Staining procedure?

A

• Primary Staining + Mordant:
• Reagent: Concentrated Carbol fuchsin (Pink)
• Duration: 5 minutes with intermittent heating.

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18
Q

What does the blue background indicate in the Acid-Fast Stain?

A

• Blue background: This is the counterstain (Methylene blue), which highlights the non-acid-fast organisms.

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19
Q

What is the result of the Acid-Fast Stain for Non-Acid-Fast organisms?

A

• Non-Acid-Fast organisms: Blue
• Reason: These organisms do not retain the pink stain and appear blue against the blue background.

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20
Q

What is the result of the Acid-Fast Stain for Acid-Fast organisms?

A

• Acid-Fast organisms: Pink
• Reason: Mycolic acid in the cell wall.

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21
Q

What is Differential Media and give an example?

A

• Definition: Media designed to distinguish between different organisms based on their metabolic characteristics.
• Examples:
1. McConkey agar: Selects for Gram-negative organisms.
2. CLED (Cystine-lactose-electrolyte deficient) agar: Allows growth of Gram-negative, Gram-positive organisms, and Candida.

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22
Q

What are the exceptions to the appearance of colonies on Blood agar?

A
  1. α-hemolysis (Partial): Greenish-grey zone around the colony.
    • Example: Pneumococcus.
    1. β-hemolysis (Complete): Clear zone around the colony.
      • Example: Streptococcus pyogenes.
    2. Double zone/Target hemolysis: Complete followed by partial hemolysis.
      • Example: Clostridium perfringens.
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23
Q

What is Enriched Media and give an example?

A

• Definition: Media that contains additional nutrients to support the growth of more fastidious organisms.
• Example: Blood agar.
• Normal Appearance: No zone surrounding colonies.

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24
Q

What are the exceptions to the appearance of colonies on Nutrient agar?

A

• Golden yellow pigment: Staphylococcus aureus.
• Bluish-green pigment: Pseudomonas aeruginosa.
• White-grey colonies: General appearance.

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25
Q

What is a Simple/Basal Culture Media and give an example?

A

• Definition: A basic medium used to grow non-specialized organisms.
• Example: Nutrient agar (straw-colored).
• Appearance: White-grey colonies.

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26
Q

How can you differentiate Lactose Fermenters (LF) and Non-Lactose Fermenters (NLF) on McConkey agar?

A

• Lactose Fermenters (LF):
• Pink colonies (e.g., E. coli, Klebsiella).
• Non-Lactose Fermenters (NLF):
• Pale colonies (e.g., Salmonella, Shigella).

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27
Q

How can you differentiate Lactose Fermenters (LF) and Non-Lactose Fermenters (NLF) on CLED agar?

A

• Lactose Fermenters (LF):
• Yellow colonies (e.g., E. coli, Klebsiella).
• Non-Lactose Fermenters (NLF):
• Blue colonies

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28
Q

What are the features of the Thioglycollate broth?

A

• Thioglycollate broth: Supports both aerobic and anaerobic growth.
• Aerobic growth: Top layer.
• Anaerobic growth: Bottom layer.

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29
Q

What is the best Anaerobic Culture Media?

A

• Best Anaerobic media: Robertson cooked meat (RCM).
• Purpose: Supports only anaerobic growth, with meat particles present.

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30
Q

What transport media is used for stool samples, excluding Vibrio and Campylobacter?

A

• Buffered glycerol saline: For all stool pathogens except Vibrio and Campylobacter.

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31
Q

What is the best transport media for stool samples?

A

• Best transport media for stool pathogens: Cary Blair media.

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32
Q

What is the NALC-NaOH method and what does it do?

A

• NALC-NaOH method: Used to inhibit commensals in sputum samples.
• N-Acetyl-L-cysteine (NALC): Liquefies sputum.
• NaOH: Inhibits commensals.

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33
Q

What pathogens are associated with each type of Enrichment Culture Media?

A
  1. Selenite F broth, Tetrathionate broth: Salmonella, Shigella.
    1. Alkaline peptone water: Vibrio.
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34
Q

Name some types of Enrichment Culture Media and their colors.

A
  1. Selenite F broth: Light brown.
    1. Tetrathionate broth: Bluish-green.
    2. Alkaline peptone water: Straw-colored.
35
Q

What is the purpose of Enrichment Culture Media?

A

• Purpose: Inhibit commensals in stool samples to allow the growth of pathogens.

36
Q

What are the features of the Catalase test?

A

• Positive: Bubbles
• Negative: No bubbles

37
Q

What are the features of the Oxidase test?

A

• Positive: Blue color
• Negative: No blue color

38
Q

What are the features of the Urease test?

A

• Positive: Pink color
• Negative: No pink color

39
Q

What organisms are associated with the following tests?
1. Catalase
2. Oxidase
3. Urease

A
  1. Catalase -ve:
    • Examples: Streptococcus, Pneumococcus, Enterococcus.
    1. Oxidase +ve:
      • Examples: Vibrio, Pseudomonas, Campylobacter, Helicobacter.
    2. Urease +ve:
      • Examples: Helicobacter, Proteus.
40
Q

What is the first step in the PCR process?

A

• Nucleic acid extraction:
• Method: Enzyme method (e.g., Add Lysozyme).
• Purpose: To isolate the nucleic acids (DNA/RNA).

41
Q

Uses of PCR?

A

• Diagnostic test : Detects gene.

• Prognostic test : To monitor Rx response.

  • Gives organism load.
  • If PCR + : If ↑CT (Cycle Threshold) value ↓Organism↑Prognosis.
42
Q

Modifications in PCR?

A

• Conventional PCR : Detects only DNA.

• Real-time RT (Reverse Transcriptase) PCR - Detects DNA & RNA.

  • Semiautomated.

• Automated Realtime RT-PCR : CBNAAT (Cartridge based) & TruNAT (Chip based).

• Multiplex Realtime RT-PCR : Detects multiple organisms.

43
Q

Nucleic acid amplification?

A

In thermocycler
Steps are following

Denaturation (95°C) : ds to 2 single strands.
Annealing (55°C) : Primer attachment.
Extension (72°C) : Primer extension.

44
Q

Steps of PCR?

A

Nucleic acid extraction

Nucleic acid amplification

Nucleic acid detection by Gel electrophoresis/Fluorescent method

45
Q

What is the E-strip method in AST?

A

• Method: E-strip method on Mueller Hinton Agar (MHA).
• Outcome: MIC of the antibiotic is obtained.
• Interpretation:
• Zone of inhibition: Indicates antibiotic sensitivity.
• MIC: The lowest concentration of the antibiotic that inhibits bacterial growth.

46
Q

How do you interpret the zone of inhibition in the Kirby Bauer disk diffusion method?

A

• Zone of inhibition present: Antibiotic is effective (sensitive organism).
• Zone of inhibition absent: Antibiotic is ineffective (resistant organism).
• Note: Minimum Inhibitory Concentration (MIC) of the antibiotic is not determined by this method.

47
Q

What is used as the medium in the Kirby Bauer disk diffusion test?

A

• Medium used: Mueller Hinton Agar (MHA).

48
Q

What is the most common phenotypic method used for AST?

A

• Most common method: Kirby Bauer disk diffusion method.

49
Q

What is the phenotypic method for antimicrobial susceptibility testing (AST)?

A

• Phenotypic method: Culture-based testing to evaluate the effectiveness of antibiotics.

50
Q

What is the significance of the rpo-B gene in M. tuberculosis?

A

• rpo-B gene: Indicates resistance to Rifampicin if present.
• Presence of rpo-B gene: Rifampicin resistance.
• Absence of rpo-B gene: Rifampicin sensitivity.

51
Q

What is the genotypic method for antimicrobial susceptibility testing?

A

• Genotypic method: Molecular testing, such as PCR, to detect resistant genes.

52
Q

How is the antimicrobial susceptibility interpreted in the broth dilution method?

A

• Clear (No turbidity): The organism is sensitive to the antibiotic.
• Turbid broth: The organism is resistant to the antibiotic.

53
Q

What is used as the medium in the broth dilution method for AST?

A

• Medium used: Mueller Hinton Broth (MHB).

54
Q

What is the gold standard method for antimicrobial susceptibility testing (AST)?

A

• Gold standard method: Broth dilution.

55
Q

What are the two methods of hand hygiene?

A

• Hand washing
• Uses soap and water.
• Essential if hands are visibly soiled.
• Hand rubbing
• Preferred method.
• Uses disinfectant (e.g., alcohol-based solution).
• Not suitable if hands are visibly soiled.

56
Q

What are the steps for proper hand rubbing?

A
  1. Rub hands palm to palm.
    1. Rub the back of each hand with the opposite palm, fingers interlaced.
    2. Rub palm to palm, fingers interlaced.
    3. Rub the backs of fingers to opposing palms with fingers clasped.
    4. Rub the tips of fingers in a circular motion on the opposite palm.
    5. Rub each thumb in a rotational motion.
    6. Rub each wrist in a circular motion.
57
Q

What are the “5 Moments for Hand Hygiene”?

A
  1. Before touching a patient.
    1. Before aseptic procedures.
    2. After body fluid exposure risk.
    3. After touching a patient.
    4. After touching patient surroundings.
58
Q

What are the essential components of PPE?

A
  1. Gown.
    1. Gloves.
    2. Mask.
    3. Goggles.
    4. Face shield.
59
Q

What is the sequence for donning (putting on) PPE?

A
  1. Gown.
    1. Mask.
    2. Goggles or face shield.
    3. Gloves.
60
Q

What is the sequence for doffing (removing) PPE?

A
  1. Gloves.
    1. Goggles or face shield.
    2. Gown.
    3. Mask.
61
Q

What types of waste are disposed of in the yellow bag, and how are they treated?

A

• Type of Waste:
• Cotton and linen.
• Tissues and culture media.
• Chemicals and medicines.
Blood bags
• Disposal Method:
• Incineration.

62
Q

What types of waste are disposed of in the red bag, and how are they treated?

A

• Type of Waste:
• Plastic items (e.g., urine bags).
• Rubber.
• Disposal Method:
• Autoclaving followed by recycling.

63
Q

What types of waste are disposed of in the white bag, and how are they treated?

A

• Type of Waste:
• Metallic sharps (e.g., needles, scalpels).
• Disposal Method:
• Treated with sodium hypochlorite.
• Shredded or packed in puncture-proof containers and buried.

64
Q

What types of waste are disposed of in the blue bag, and how are they treated?

A

• Type of Waste:
• Metals.
• Glass.
• Disposal Method:
• Treated with sodium hypochlorite.
• Recycling.

65
Q

What is sterilization, and how does it differ from disinfection?

A

• Sterilization: Complete killing of all forms of microorganisms, including spores.
• Disinfection: Eliminates most microorganisms but does not kill spores.

66
Q

What are the conditions for sterilization by moist heat, and what is its biological indicator?

A

• Method: Autoclave.
• Conditions: 121°C for 15 minutes under 15 lbs pressure.
• Biological Indicator: Bacillus stearothermophilus.

67
Q

What are the conditions for sterilization by dry heat, and what are its biological indicators?

A

• Method: Hot air oven.
• Conditions: 160°C for 2 hours.
• Biological Indicators:
1. Bacillus subtilis.
2. Bacillus atrophaeus.
3. Clostridium tetani.

68
Q

What is the biological indicator for H2O2/Plasma sterilization?

A

Bacillus stearothermophilus

69
Q

What is ethylene oxide (ETO), and its biological indicators?

A

• Biological Indicators:
1. Bacillus subtilis.
2. Bacillus atrophaeus.
3. Clostridium tetani.

70
Q

What is the sterilization method for surgical instruments (except sharps)?

A

• Materials: Linen, sutures without needles.
• Method: Autoclave > H2O2 > Ethylene oxide (ETO).

71
Q

What is the sterilization method for plastic and rubber materials (e.g., syringes, gloves)?

A

• Materials: Plastic and rubber items.
• Method: Autoclave > H2O2 > Ethylene oxide (ETO).

72
Q

What is the sterilization method for glass and sharps (e.g., flasks, scalpels)?

A

• Materials: Glass and sharps.
• Method: Autoclave > Hot air oven.

73
Q

What is the sterilization method for culture media (CM)?

A

• Materials: All culture media.
• Method: Autoclave, except for special cases.

74
Q

What are the exceptions for sterilization of culture media (CM), and their methods?

A

Inspissation > Tyndallization

• Serum-based CM (e.g., Loeffler’s serum slope)
• Egg-based CM (e.g., Lowenstein-Jensen medium)

75
Q

What is the sterilization method for oily and powdery materials (e.g., liquid paraffin, glove dust powder)?

A

• Materials: Oily and powdery substances.
• Method: Hot air oven.

76
Q

What disinfectant should be used for thermometers and hand rubs?

A

Alcohol

77
Q

What disinfectant should be used for blood spills?

A

1% Sodium hypochlorite

78
Q

What is the recommended disinfectant for endoscopes?

A

• Aldehyde (Glutaraldehyde > Orthophthalaldehyde).
• Alternatives: H2O2, Ethylene oxide (ETO).

79
Q

What tests are used to assess the efficacy of disinfectants?

A
  1. Chick Martin Test: Tests efficacy.(best)
    1. Rideal Walker Test: Tests efficacy.
    2. Kelsey Sykes Test: Tests capacity.
    3. Maurer’s In-use Test: Tests contamination.
80
Q

What are the types of disinfectants and their characteristics?

A

• High-level disinfectants (HLD):
• Example: Aldehyde (e.g., Glutaraldehyde).
• Function: Kills some spores.
• Intermediate-level disinfectants (ILD):
• Example: 1% Sodium hypochlorite.
• Low-level disinfectants (LLD):
• Example: Alcohol.

81
Q

What is the level of disinfection required for non-critical devices?

A

• Non-critical Devices:
• Contact: Intact skin.
• Examples: Stethoscopes, sphygmomanometers.
• Required Disinfection Level: Intermediate-level disinfection (ILD) or low-level disinfection (LLD).

82
Q

What is the level of disinfection required for semi-critical devices?

A

• Semi-critical Devices:
• Contact: Mucous membranes.
• Examples: Endoscopes.
• Required Disinfection Level: High-level disinfection (HLD).

83
Q

What is the level of disinfection required for critical devices?

A

• Critical Devices:
• Contact: Enter sterile sites.
• Examples: Surgical instruments, implants.
• Required Disinfection Level: High-level disinfection (HLD).

Microbiology RR (2 decks)

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