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SECTION 1: MICROSCOPY
1. Parts of a Microscope and Their Functions
Part Function
Eyepiece (Ocular Lens) Magnifies the image (usually 10x or 15x)
Objective Lenses Provide different levels of magnification (4x, 10x, 40x, 100x)
Stage Holds the slide for viewing
Stage Clips Secure the slide in place
Coarse Adjustment Knob Moves the stage up and down for initial focusing
Fine Adjustment Knob Sharpens the image under high magnification
Condenser Focuses light onto the specimen
Diaphragm (Iris Diaphragm) Controls the amount of light passing through the specimen
Light Source Illuminates the specimen
Base Provides stability and support
Arm Connects the base to the body and supports the microscope
2. Magnification and Resolution
● Total Magnification Formula:Total Magnification=Eyepiece Magnification×Objective Lens MagnificationTotal Magnification=Eyepiece Magnification×Objective Lens Magnification Example: ○ Eyepiece (10x) × Objective Lens (40x) = 400x total magnification ● Resolution: The ability to distinguish two close objects as separate.
3. Types of Microscopy
Type Purpose
Brightfield Microscopy Commonly used for stained specimens
Darkfield Microscopy Enhances contrast in unstained, live specimens
Phase-Contrast Microscopy Used for unstained, living cells
Fluorescence Microscopy Uses fluorescent dyes to detect specific structures
Electron Microscopy Provides high magnification and resolution (TEM for internal structures, SEM for surface structures)
4. Oil Immersion Technique (100x Objective Lens)
● Used to observe bacteria and small microorganisms. ● Why use oil? ○ Oil reduces light refraction and improves clarity. ○ Without oil, the image will appear blurry.
5. Common Errors in Microscopy and How to Fix Them
Problem Solution
Image is too dark Increase the light intensity or open the diaphragm
Image is blurry Adjust the fine focus knob
Cannot see specimen at 100x Add immersion oil
Image moves out of view Center the specimen before switching magnification
SECTION 2: CULTURE MEDIA
1. Types of Culture Media
Type Definition & Example
Enriched Media Contains extra nutrients to grow fastidious bacteria (e.g., Blood Agar, Chocolate Agar)
Bacteria Type Color After Staining
Gram-positive Purple
Gram-negative Pink
2. Acid-Fast Staining (Ziehl-Neelsen Method)
Used to detect Mycobacterium tuberculosis and Mycobacterium leprae.
Steps in Acid-Fast Staining
- Primary Stain: Carbol Fuchsin (Stains bacteria red)
- Heat Fixation: Helps stain penetrate mycolic acid in the cell wall
- Decolorizer: Acid-Alcohol (Removes stain from non-acid-fast bacteria)
- Counterstain: Methylene Blue
Bacteria Type Color After Staining
Acid-fast bacteria Red/pink
Non-acid-fast bacteria Blue
SECTION 4: MEDICAL & SURGICAL ASEPSIS
1. Difference Between Medical & Surgical Asepsis
Type Definition
Medical Asepsis Reducing microbes (e.g., handwashing, disinfecting surfaces)
Surgical Asepsis Eliminating all microbes (e.g., sterilization, autoclaving)
2. Hand Hygiene Guidelines
● Handwashing: At least 20 seconds with soap and water. ● Alcohol-Based Hand Rub: At least 60% alcohol content. ● When to Wash Hands: ○ Before and after patient contact ○ After contact with body fluids ○ Before an aseptic procedure
3. Personal Protective Equipment (PPE) Order
Donning (Putting On PPE):
- Gown
- Mask
- Goggles/Face Shield
- Gloves
Doffing (Removing PPE):
- Gloves
- Goggles/Face Shield
- Gown
- Mask
4. Sterile Field Guidelines
● 1-inch border around the sterile field is contaminated. ● Keep hands above waist level to maintain sterility. ● Never reach over a sterile field.
5. Isolation Precautions
Precaution Type Example Disease PPE Needed
Contact Precautions MRSA, C. difficile Gloves, gown
Droplet Precautions Influenza, Meningitis Mask
Airborne Precautions Tuberculosis, Measles, Varicella
N95 mask, negative pressure room
