JUST DEFINITIONS

Q: What are the parts of the microscope?
A: Objective lens, ocular lens (eyepiece), stage, coarse and fine focus knobs, diaphragm, light source.

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Q: What are the steps of the Gram Stain Procedure and the purpose of each step?
A:

  1. Primary Stain (Crystal Violet): Stains all cells purple.

  2. Mordant (Iodine): Fixes the crystal violet to the cell walls.

  3. Decolorizer (Alcohol): Removes stain from Gram-negative cells.

  4. Counterstain (Safranin): Stains Gram-negative cells pink.

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Q: What is the difference between differential staining and simple staining?
A: Differential staining distinguishes between types of bacteria (e.g., Gram stain), while simple staining colors all cells the same for basic visualization.

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Q: How can you recognize Gram-positive vs. Gram-negative cells under the microscope?
A: Gram-positive cells appear purple, and Gram-negative cells appear pink/red after staining.

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Q: What are common cell shapes and arrangements?
A:

  • Shapes: Coccus (spherical), Bacillus (rod-shaped).

  • Arrangements: Staphylo- (clusters), Strepto- (chains).

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Q: What is the purpose of autoclaving media and supplies, and what conditions are required?
A: Autoclaving sterilizes by using high pressure and temperature (typically 121°C for 15-20 minutes), killing all microbes and spores.

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Q: What is the difference between an antiseptic and a disinfectant?
A: Antiseptics are used on living tissue to reduce microbes; disinfectants are used on inanimate objects to kill microbes.

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Q: Describe broth culture, agar plate, slant, and deep, and why each is used.
A:

  • Broth Culture: For growing bacteria in liquid.

  • Agar Plate: Solid medium for isolating colonies.

  • Slant: Solidified at an angle, provides larger surface area.

  • Deep: Used to grow anaerobic bacteria.

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Q: What types of media have been used in lab, and are they selective, differential, enriched, or complex?
A:

  • TSA (Trypticase Soy Agar): Complex, non-selective.

  • MSA (Mannitol Salt Agar): Selective for Staphylococcus spp., differential for mannitol fermentation.

  • Blood Agar: Enriched, differential (hemolysis).

  • MacConkey Agar: Selective for Gram-negative, differential for lactose fermentation.

  • PEA (Phenylethyl Alcohol Agar): Selective for Gram-positive bacteria.

  • BEA (Bile Esculin Agar): Selective for enteric bacteria, differential for esculin hydrolysis.

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Q: How is MacConkey Agar used to identify Enterobacteriaceae?
A: Selects for Gram-negative bacteria and differentiates based on lactose fermentation.

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Q: How are carbohydrates classified, and how are they broken down?
A: Classified by size; glycosidic bonds link them, and specific enzymes break them down during metabolism.

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Q: What does the Phenol Red broth test detect, and how is it interpreted?
A: Detects carbohydrate fermentation; a color change to yellow indicates acid production (fermentation).

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Q: What Gram-positive tests should be understood, and how are they used?
A:

  • MSA: Selective for Staphylococcus, differential for mannitol fermentation.

  • BAP (Blood Agar Plate): Used for hemolysis (α, β, γ).

  • Coagulase Test: Differentiates S. aureus from other staph by coagulase positivity.

  • Catalase Test: Differentiates Staphylococcus (catalase-positive) from Streptococcus (catalase-negative).

  • Bacitracin and Optochin Sensitivity: Used to identify specific Gram-positive bacteria.

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Q: What are the types of hemolysis seen on blood agar?
A:

  • Alpha (α) Hemolysis: Partial clearing, greenish.

  • Beta (β) Hemolysis: Complete clearing.

  • Gamma (γ) Hemolysis: No clearing.

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Q: How is the CAMP test used, and which bacteria test positive?
A: Differentiates Group B Streptococci, which show enhanced hemolysis near S. aureus.

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Q: What is the difference between halotolerant organisms and halophiles?
A: Halotolerant organisms can survive high salt concentrations, while halophiles require high salt for growth.

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Q: How do you calculate the dilution factor in a serial dilution?
A: Dilution factor = Volume of sample / (Volume of sample + Volume of diluent).

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Q: How is the Kirby-Bauer test interpreted?
A: Measure the zone of inhibition around antibiotic disks; refer to charts to determine sensitivity or resistance.

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Q: What are common bacterial structures related to motility, survival, and protection?
A:

  • Flagella: Used for motility.

  • Spores: Allow survival under adverse conditions.

  • Capsules: Provide protection against host immune response.

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Q: Describe key differences between media types: Selective, Differential, Enriched, and Complex.
A:

  • Selective: Supports growth of certain microbes, inhibits others.

  • Differential: Differentiates organisms based on metabolic traits.

  • Enriched: Contains nutrients to support fastidious organisms.

  • Complex: Contains unknown quantities of nutrients.