Introduction to Microbiology

Historical Timeline and Development of Microbiology

Microbiology developed as a science through key discoveries and technological advances. The timeline below highlights major contributors and their findings:

• 1600s – Robert Hooke: First to publish descriptions of cells using a microscope.

• 1632–1723 – Antonie van Leeuwenhoek: First to observe bacteria and protozoa, calling them “animalcules.”

• 1840s – Ignaz Semmelweis: Introduced handwashing in hospitals to prevent infections.

• 1860s – Joseph Lister: Developed antiseptic surgery using carbolic acid.

• 1822–1895 – Louis Pasteur: Supported biogenesis, invented pasteurization, and developed vaccines for rabies and anthrax.

• 1843–1910 – Robert Koch: Established germ theory, formulated Koch’s postulates, and identified disease-causing microbes.

• 1850–1920 – Golden Age of Microbiology: Major discoveries in culturing and identifying pathogens.

Key findings: Microorganisms cause disease, produce food, make medications, break down hazards, and inhabit nearly every environment on Earth.

Theories of Spontaneous Generation and Biogenesis

• Spontaneous generation: The belief that life arises from nonliving matter (e.g., maggots from meat).

• Biogenesis: Life arises only from existing life.

• Evidence against spontaneous generation: Redi’s covered meat jars (no maggots) and Pasteur’s swan-neck flask (no microbial growth unless exposed to air).

Major Contributors to Microbiology

• Louis Pasteur: Disproved spontaneous generation, developed pasteurization, and created vaccines.

• Robert Koch: Developed germ theory, Koch’s postulates, and improved staining/culturing methods.

• Joseph Lister: Introduced antiseptic surgery and sterilization techniques.

• Ignaz Semmelweis: Advocated hand hygiene, reducing childbed fever.

• Robert Hooke: First to describe cells under a microscope.

• Antonie van Leeuwenhoek: First to observe living bacteria and protozoa.

• Florence Nightingale: Established aseptic nursing techniques and modern nursing.

Characteristics and Classification of Microorganisms

Features of Living Things and Non-Cellular Microbes

• Viruses: Acellular, nonliving, composed of genetic material (DNA or RNA) and a protein coat (capsid); some have a lipid envelope. Require a host cell to replicate.

Distinguishing Features of Microbial Groups

• Algae: Photosynthetic protists with chlorophyll, found in aquatic environments.

• Bacteria: Unicellular prokaryotes lacking a nucleus.

• Fungi: Eukaryotes (yeasts, molds) with chitin cell walls.

• Protozoans: Unicellular eukaryotes, classified by movement.

• Viruses: Acellular infectious particles.

• Helminths: Parasitic worms (roundworms and flatworms).

Classification of Bacteria and Fungi; Mycosis

• Bacteria: Classified by shape, size, arrangement, Gram stain, and metabolism.

• Fungi: Classified by yeast/mold form, hyphae structure, and spore formation.

• Mycosis: Fungal infection or disease.

Bacterial Endospores vs. Fungal Spores

• Bacterial endospore: Dormant survival structure (e.g., Bacillus, Clostridium); highly resistant to heat, chemicals, and radiation.

• Fungal spore: Reproductive structure for growth and spread.

• Healthcare challenge: Endospores are difficult to kill and may persist on medical equipment, increasing infection risk.

Classification of Protozoans and Helminths

• Protozoans: Classified by motility (amoeboid, flagellated, ciliated, spore-forming).

• Helminths: Two main groups: roundworms (nematodes) and flatworms (platyhelminths); classified by body shape.

Microscopy and Staining Techniques

Types of Microscopes and Techniques

• Light microscope: Uses light to view cells and bacteria.

• Transmission Electron Microscope (TEM): Shows internal cell structures (2D image).

• Scanning Electron Microscope (SEM): Shows cell surface (3D image).

• Staining: Enhances visibility of cells and structures.

• Oil immersion: Improves image clarity by reducing light refraction.

Key Microscopy Terms

• Total magnification: Product of ocular and objective lens magnifications.

• Resolution: Ability to distinguish two close objects as separate.

• Refractive index: Measure of how much light bends passing through a substance.

Comparison of TEM and SEM

• TEM: Reveals internal structures, 2D images.

• SEM: Reveals surface details, 3D images.

Staining Techniques

• Simple stain: One dye; shows shape, size, arrangement.

• Differential stain: Multiple dyes; distinguishes cell types (e.g., Gram stain).

• Structural stain: Highlights specific structures (capsules, spores, flagella).

• Clinical application: Identifies bacteria and guides treatment.

Gram Stain Procedure and Interpretation

• Steps: crystal violet → iodine → acetone-alcohol → safranin.

• Gram-positive: Thick peptidoglycan, retains purple.

• Gram-negative: Thin peptidoglycan, turns pink.

• Errors: Over-decolorizing, thick smears, old cells.

Acid-Fast Stain

• Genera: Mycobacterium, Nocardia.

• Reason: Mycolic acid in cell walls.

• Clinical use: Detects tuberculosis and related infections.

Microbiome and Microbial Interactions

Healthy Microbiome

• Normal microbes on skin, mouth, intestines.

• Roles: protect against pathogens, aid digestion, maintain health.

Microbe-Host Interactions

• Beneficial: Aid digestion, protect from infection.

• Harmful: Cause disease.

• Neutral: No effect on host.

Symbiotic Relationships

• Parasitism: One benefits, other harmed.

• Mutualism: Both benefit.

• Commensalism: One benefits, other unaffected.

Biofilms and Microbial Applications

Biofilm Formation and Healthcare Implications

• Microbes attach to surfaces, multiply, and produce a protective layer.

• Healthcare implications: Biofilms are hard to remove, antibiotic-resistant, and common on medical devices.

Beneficial Roles of Microbes

• Bioremediation: Cleaning pollutants (oil spills, toxic waste).

• Food production: Yogurt, cheese, bread, beer, wine.

• Drug production: Antibiotics, insulin, vitamins, enzymes, biofuels.

Aseptic Techniques and Lab Safety

Aseptic Techniques

• Prevent contamination and infection (handwashing, gloves, sterilization, disinfecting).

Lab Safety and PPE

• PPE: Gloves, lab coat, goggles, closed-toe shoes.

• Allowed: Wearing PPE, disinfecting, aseptic technique, labeling cultures.

• Not allowed: Eating/drinking, touching face, horseplay, leaving cultures open.

Disposal of Cultures

• Petri plates and test tubes: Place in biohazard waste, autoclave before disposal.

Microscope Structure and Function

Parts of the Compound Light Microscope

• Ocular lens (eyepiece): Viewing lens.

• Objective lenses: Magnification.

• Stage: Holds slide.

• Coarse/fine adjustment knobs: Focus.

• Light source: Illumination.

• Arm/base: Support.

Calculating Total Magnification

• Formula:

• Example: 10× ocular × 40× objective = 400×

Scientific Method Steps

• Ask a question/make observation

• Form hypothesis

• Perform experiment

• Collect data

• Analyze results

• Draw conclusion

Microbial Growth and Culture Techniques

Best Practices for Aseptic Technique

• Wash hands, disinfect workspace, flame loop, keep plates closed, use sterile instruments, wear gloves.

• Invert plates: Prevent condensation from spreading bacteria.

Media Types and Formats

• General-purpose media: Nutrient agar, nutrient broth.

• Formats: Broth, plates, slants, deeps.

Streak Plate Method for Isolation

1. Sterilize loop

2. Collect sample

3. Streak first section

4. Flame loop

5. Streak subsequent sections

6. Invert and incubate

Goal: Isolate individual colonies from single cells.

Biochemistry and Cell Structure

Macromolecules and Chemical Bonds

• Dehydration synthesis: Joins molecules by removing water.

• Hydrolysis: Breaks molecules by adding water.

• Covalent bonds: Share electrons.

• Ionic bonds: Transfer electrons.

• Hydrogen bonds: Weak attractions between molecules.

Acids, Bases, and pH

• Acid: pH < 7

• Base: pH > 7

• Neutral: pH = 7

Major Macromolecules

Cell Types and Taxonomy

Bacteria, Archaea, and Eukaryotes

• Bacteria: Prokaryotic, peptidoglycan cell wall.

• Archaea: Prokaryotic, no peptidoglycan.

• Eukaryotes: Nucleus and organelles.

Scientific Naming and Taxonomy

• Genus: Capitalized, italicized (e.g., Escherichia).

• Species: Lowercase, italicized (e.g., coli).

• Hierarchy: Domain → Kingdom → Phylum → Class → Order → Family → Genus → Species

• Strain: Variant within a species.

Prokaryotic vs. Eukaryotic Cells

Binary Fission

• DNA replicates → cell grows → septum forms → two identical daughter cells.

Bacterial Structures and Functions

Endosymbiotic Theory and Mitochondria

• Mitochondria have their own DNA, ribosomes, double membrane, and divide like bacteria, supporting the endosymbiotic theory.

Eukaryotic Cell Structures and Functions

Gram-Positive vs. Gram-Negative Cell Walls

Osmosis and Bacterial Cells

• Osmosis: Movement of water across a membrane.

• Hypertonic: Water leaves cell, cell shrinks.

• Hypotonic: Water enters, cell swells.

• Isotonic: No net movement.

Eukaryotic Plasma Membranes

• Phospholipid bilayer controls entry/exit.

• Animals: Cholesterol

• Fungi: Ergosterol

• Plants: Phytosterols