BIO221 Lab Material Review: Microbiology Laboratory Fundamentals

Lab Safety, Equipment, and Biohazard Awareness

Personal Protective Equipment (PPE) and Lab Safety

Proper safety practices are essential in the microbiology laboratory to prevent contamination and ensure personal safety.

• Correct PPE: Lab coat, gloves, and safety goggles are standard PPE for microbiology labs.

• Discard Procedures: Contaminated materials (e.g., gloves, pipette tips) must be disposed of in designated biohazard containers.

• Glove Disposal: Used gloves are discarded in biohazard waste bins, not in regular trash.

• Emergency Protocols: The first action in any emergency is to alert the instructor and follow institutional procedures (e.g., evacuate, use safety showers).

• Biohazard Levels: Laboratories are classified from Biosafety Level 1 (BSL-1) to BSL-4, with increasing containment and safety requirements.

• HazCom Symbols: Hazard Communication symbols indicate risks such as biohazard, chemical, or radiation hazards.

• Common Equipment: Includes microscopes, Bunsen burners, pipettes, incubators, and autoclaves.

Example: A BSL-2 lab requires lab coats, gloves, and eye protection, and restricts access to trained personnel only.

Microscopy and Wet Mount Preparation

Microscope Parts and Usage

Microscopes are essential for observing microorganisms. Understanding their parts and proper handling is crucial.

• Microscope Parts: Ocular lens (eyepiece), objective lenses, stage, coarse and fine focus knobs, light source, condenser, arm, and base.

• Importance of Each Part: Objective lenses provide magnification; the stage holds the slide; focus knobs adjust clarity.

• Carrying/Storage: Always carry with two hands (one on the arm, one under the base). Store with the lowest objective in place and cover the microscope.

Example: The 100x oil immersion lens is used for observing bacterial morphology.

Wet Mounts and Cell Types

Wet mounts allow observation of living microorganisms and their motility.

• Purpose: To observe live cells, motility, and natural arrangements.

• Prokaryotes vs. Eukaryotes: Prokaryotes (e.g., Bacteria, Archaea) lack a nucleus; eukaryotes (e.g., Fungi, Protozoa, Algae) have a nucleus and organelles.

• Groups: Prokaryotes: Bacteria, Archaea. Eukaryotes: Protists, Fungi, Plants, Animals.

• Preparation: Place a drop of sample on a slide, cover with a coverslip, and observe under the microscope.

Example: Observing Paramecium movement in a wet mount.

Aseptic Technique and Bacterial Growth

Aseptic Technique

Aseptic technique prevents contamination of cultures and the environment.

• Importance: Maintains pure cultures and protects the experimenter.

• Maintaining Sterility: Disinfect work surfaces, flame sterilize tools, minimize exposure of sterile media.

• Sterilizing Tools: Use a Bunsen burner to flame inoculating loops and needles before and after use.

Example: Flaming the mouth of a test tube before transferring cultures.

Liquid Media Bacterial Growth Terminology

• Turbidity: Cloudiness indicating bacterial growth throughout the medium.

• Sediment: Cells settled at the bottom.

• Pellicle: Growth at the surface.

• Flocculent: Clumpy or flaky growth.

Bacterial Staining and Morphology

Types of Bacterial Staining

Staining enhances contrast to visualize bacteria under the microscope.

• Simple Stain: Uses one dye to color all cells.

• Differential Stain: Distinguishes between types (e.g., Gram stain, Acid-fast stain).

• Special Stains: Highlight specific structures (e.g., capsule, endospore stains).

Bacterial Morphologies

• Shapes: Cocci (spherical), Bacilli (rod-shaped), Spirilla (spiral).

• Arrangements: Chains (strepto-), clusters (staphylo-), pairs (diplo-).

Gram Stain Procedure and Problems

• Steps: Crystal violet, iodine, alcohol decolorization, safranin counterstain.

• Common Problems: Over-decolorization (false Gram-negative), under-decolorization (false Gram-positive), thick smears.

Example: Staphylococcus aureus appears purple (Gram-positive cocci), Escherichia coli appears pink (Gram-negative rods).

Colony Isolation and Morphology

Petri Plate Labeling and Storage

• Labeling: Write on the bottom (agar side) of the Petri plate.

• Storage: Store plates inverted (agar side up) to prevent condensation on the agar surface.

Colony Morphologies

• Characteristics: Shape (circular, irregular), margin (entire, undulate), elevation (flat, raised), color, and texture.

Colony Isolation Techniques

• Purpose: To obtain pure cultures from mixed populations.

• T-streak: A streaking method dividing the plate into three sections to dilute cells and isolate colonies.

• Describing Colonies: Use morphology characteristics to identify and differentiate colonies.

Enumerating Bacteria

Counting Techniques

• Techniques: Spread plate, pour plate, serial dilution, direct microscopic count.

• Lab Method: Serial dilution and spread plate are commonly used to count colony-forming units (CFUs).

• Pipette Use: Use pipettes accurately to transfer specific volumes during dilutions.

• Calculating Dilutions: Use the formula:

$\text{CFU/mL} = \frac{\text{Number of Colonies} \times \text{Dilution Factor}}{\text{Volume Plated (mL)}}$

Selective and Differential Media

Types and Examples

• Selective Media: Inhibits growth of some organisms while allowing others (e.g., MacConkey agar selects for Gram-negative bacteria).

• Differential Media: Distinguishes organisms based on metabolic properties (e.g., color change).

• Examples: MacConkey agar (lactose fermentation), Mannitol Salt agar (mannitol fermentation), Snyder agar (acid production).

• Special Features: MacConkey agar contains bile salts and crystal violet; Snyder agar uses bromcresol green as a pH indicator.

Example: Escherichia coli ferments lactose on MacConkey agar, producing pink colonies.

Oxygen and Carbon Growth Requirements

Oxygen Requirements

• Indicator Dyes: Resazurin or methylene blue indicate oxygen presence by color change.

• Classification: Obligate aerobes, obligate anaerobes, facultative anaerobes, microaerophiles, aerotolerant anaerobes.

• Inoculation: Use aseptic technique to inoculate media such as fluid thioglycollate broth.

• Electron Transport Chains: Aerobic bacteria use oxygen as the final electron acceptor; anaerobic bacteria use alternative acceptors.

Carbon and Fermentation Tests

• Gas Production: Indicates fermentation; detected by Durham tubes.

• Sugar Fermentation Tubes: Contain a sugar, pH indicator, and Durham tube to trap gas.

• Citrate Slant: Tests for citrate utilization; color change from green to blue indicates positive result.

• MR-VP Tubes: Methyl Red and Voges-Proskauer tests for mixed acid and butanediol fermentation.

Enzymatic and Blood Agar Tests

Enzymatic Tests

• Tryptophanase Test: Uses SIM medium; indole production detected with Kovac's reagent (red color = positive).

• Phenylalanine Deaminase Test: Uses phenylalanine agar; green color after adding ferric chloride indicates positive result.

Blood Agar and Hemolysis

• Hemolysins: Enzymes that lyse red blood cells.

• Types of Hemolysis:

  • Alpha (α): Partial hemolysis, greenish discoloration.

  • Beta (β): Complete hemolysis, clear zone.

  • Gamma (γ): No hemolysis.

• Coagulase Test: Detects ability to clot plasma, used to identify Staphylococcus aureus.

Example: Streptococcus pyogenes shows beta-hemolysis on blood agar.

Test	Medium	Positive Result	Purpose
Indole (Tryptophanase)	SIM	Red ring after Kovac's	Detects indole production
Phenylalanine Deaminase	Phenylalanine agar	Green color after FeCl3	Detects deamination of phenylalanine
Citrate Utilization	Simmons citrate slant	Blue color	Detects citrate as sole carbon source
MR-VP	MR-VP broth	Red (MR), Red (VP)	Detects mixed acid or butanediol fermentation
Hemolysis	Blood agar	Alpha, Beta, Gamma	Classifies hemolytic activity