Lab Safety and Handwashing

Lab Safety Procedures

Microbiology laboratories require strict safety protocols to prevent contamination and ensure the safety of personnel and the environment.

• Personal Protective Equipment (PPE): Includes lab coats, gloves, goggles, and sometimes face shields, depending on the biosafety level.

• Biosafety Levels (BSLs): Laboratories are classified from BSL-1 (lowest risk) to BSL-4 (highest risk), each with specific safety requirements.

• General Safety: No eating, drinking, or applying cosmetics; proper disposal of biohazardous waste; immediate reporting of spills or accidents.

Importance: These procedures minimize the risk of exposure to potentially harmful microorganisms.

Handwashing

• Order and Timing: Wet hands, apply soap, scrub all surfaces (including between fingers and under nails) for at least 20 seconds, rinse, and dry with a disposable towel.

• When to Wash: Before and after lab work, after removing gloves, after contact with any potentially contaminated surface.

Bacterial and Fungal Ubiquity

Ubiquity of Microorganisms

Microorganisms are found everywhere in the environment, a concept known as ubiquity.

• Bacteria: Single-celled, prokaryotic organisms with diverse shapes and metabolic capabilities.

• Fungi: Eukaryotic organisms, including yeasts and molds, with chitinous cell walls.

• Colony Morphology: Bacterial colonies are usually smooth and moist, while fungal colonies are often fuzzy or powdery.

Agar: A gelatinous substance derived from seaweed, used as a solidifying agent in culture media because it is not degraded by most microbes and remains solid at incubation temperatures.

• Colony: A visible mass of microbial cells arising from a single cell or group of cells.

• Inoculate: To introduce microorganisms into a culture medium.

• Incubate: To maintain cultures under conditions suitable for growth.

Brightfield Microscopy

Microscope Structure and Function

Microscopes are essential tools for visualizing microorganisms.

• Parts: Ocular lens (eyepiece), objective lenses (scanning, low, high, oil immersion), stage, condenser, diaphragm, coarse and fine focus knobs.

• Magnification: Total magnification is calculated as:

• Principles: Parfocal (remains in focus when objectives are changed), refractive index (affects light bending), oil immersion (increases resolution), proper cleaning and handling.

• Resolving Power/Resolution: The ability to distinguish two points as separate.

• Working Distance: Distance between the objective lens and the specimen.

• Field of View: The visible area seen through the microscope.

Survey of Eukaryotic Microbes

Identification and Classification

Eukaryotic microbes include protozoa, algae, fungi, and helminths.

• Protozoa: Unicellular, often motile, may exist as trophozoites (active) or cysts (dormant).

• Helminths: Parasitic worms, often with complex life cycles; distinguishable by sex and developmental stage.

• Algae: Photosynthetic, aquatic organisms.

• Fungi: Yeasts (unicellular), molds (multicellular, with hyphae), may be dimorphic.

• Key Terms: Parasite, host, invertebrate, hyphae, yeast, pseudohyphae, spores, saprophyte, dimorphic, mycoses.

Example: Plasmodium (malaria parasite) is a protozoan; Ascaris lumbricoides is a helminth.

Aseptic Technique and Pure Culture

Aseptic Technique

Procedures designed to prevent contamination of cultures and the environment.

• Wash hands, disinfect work surfaces, flame sterilize tools, minimize exposure of sterile media.

• Use of broth, slants, and plates for culturing microbes.

Streak Plate and Pure Culture

• Streak Plate: Method to isolate individual colonies by spreading cells over the surface of an agar plate.

• Colony Morphology: Describes size, shape, color, margin, and elevation of colonies; useful for identification.

• Dilution Principle: Spreading cells reduces their density, allowing isolated colonies to form.

• Key Terms: Aseptic, contaminant, sterile, inoculate, inoculating loop/needle, petri plate, broth, turbid, pure culture, mixed culture, subculture, streak plate technique, dilution gradient, slant.

Subculture: Transferring a colony to fresh media to obtain a pure culture; select well-isolated colonies for subculturing.

Incubation: Plates are incubated inverted to prevent condensation from dripping onto the agar surface.

Smear Preparation and Simple Staining

Staining Techniques

• Simple Stain: Uses a single dye to color cells, revealing shape and arrangement.

• Direct Stain: Stains the cells themselves.

• Negative Stain: Stains the background, leaving cells unstained; useful for visualizing capsules.

• Differential Stain: Uses multiple dyes to distinguish cell types or structures.

• Basic Dyes: Positively charged, bind to negatively charged cell components.

• Acidic Dyes: Negatively charged, repelled by cells, stain the background.

Fixation: Process of attaching cells to the slide, often by heat; required for most stains except negative stains. Overheating can distort cells.

• Smear: Thin layer of cells on a slide.

• Heat Fixing: Kills cells and adheres them to the slide, but excessive heat can damage morphology.

Smear Thickness: Too thick smears hinder observation; smears from solid media require mixing with water, while liquid cultures can be spread directly.

Identification: Recognize bacterial shapes (cocci, bacilli, spirilla) and distinguish between staining methods.

Differential Staining

Gram Stain Procedure

• Steps: Primary stain (crystal violet), mordant (iodine), decolorizer (alcohol), counterstain (safranin).

• Purpose: Differentiates bacteria based on cell wall structure.

• Gram Positive: Thick peptidoglycan, retains crystal violet (purple).

• Gram Negative: Thin peptidoglycan, loses crystal violet, takes up safranin (pink/red).

Acid-Fast Stain

• Steps: Primary stain (carbol fuchsin), heat, decolorizer (acid-alcohol), counterstain (methylene blue).

• Acid-Fast Bacteria: Contain mycolic acid in cell walls, resist decolorization.

• Key Terms: Differential staining, primary stain, mordant, counterstain, decolorize, mycolic acid.

Gram Variable: Some bacteria may not stain consistently, often due to culture age.

Structural Staining

Capsule and Spore Staining

• Capsule: Gelatinous outer layer; increases virulence by protecting against phagocytosis.

• Capsule Stain: Uses negative staining; capsules do not take up most dyes.

• Endospore: Dormant, resistant structure formed by some bacteria.

• Spore Stain: Uses heat to drive malachite green into spores; counterstain colors vegetative cells.

• Structural Stains: Specialized stains to visualize specific cell structures.

Endospores are difficult to stain due to their tough outer coat; heat is required to facilitate dye penetration.

Identification: Distinguish endospores (green) from vegetative cells (red/pink) in spore stain; capsules appear as clear halos around cells.

Genetic Transformation

Plasmids and Transformation

• Plasmids: Small, circular DNA molecules used to introduce new genes into bacteria.

• GFP (Green Fluorescent Protein): A protein from Aequorea victoria jellyfish; used as a reporter gene.

• Expression Requirements: Presence of specific promoters and inducers (e.g., arabinose for GFP expression).

• Competent Cells: Bacteria treated to allow uptake of DNA, often by calcium chloride and heat shock.

Transformation Experiment

• Plates: Contain LB (nutrient broth), ampicillin (antibiotic), and/or arabinose (inducer).

• Controls: Plates without plasmid or without antibiotic.

• Expected Results: Only cells with plasmid grow on ampicillin; GFP expressed only with arabinose.

Transformation Efficiency: Calculated as:

• Key Terms: Gene, plasmid, chromosome, horizontal gene transfer, transformation, antibiotic resistance, competent cells, heat shock, transformation efficiency.