Introduction to Microbiology

History and Development of Microbiology

Microbiology has evolved through key discoveries that shaped our understanding of microorganisms and their impact on health and society.

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

• Antonie van Leeuwenhoek (1632–1723): First to observe bacteria, termed them “animalcules.”

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

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

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

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

• Florence Nightingale: Established aseptic nursing techniques and improved hospital cleanliness.

Golden Age of Microbiology (1850–1920): Major discoveries in culturing and pathogen identification.

Theories of Spontaneous Generation and Biogenesis

• Spontaneous Generation: Belief that life arises from nonliving matter (e.g., maggots from meat).

• Biogenesis: Life arises from existing life.

• Evidence: Redi’s covered meat jars (no maggots); Pasteur’s swan-neck flask (microbes from air, not spontaneous).

Contributions of Key Scientists

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

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

• Joseph Lister: Introduced antiseptic surgery.

• Ignaz Semmelweis: Father of hand hygiene.

• Robert Hooke: First to observe and describe cells.

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

• Florence Nightingale: Founder of modern nursing, improved hospital cleanliness.

Characteristics and Classification of Microorganisms

Features of Living Things and Non-Cellular Microbes

Living things share cellular structure, metabolism, and genetic material. Viruses are acellular, consisting of genetic material (DNA or RNA) within a protein coat (capsid), sometimes with a lipid envelope. Viruses 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, flatworms).

Classification of Bacteria and Fungi

• Bacteria: Classified by shape (cocci, bacilli, spirilla), size, arrangement, Gram stain, physiology.

• Fungi: Classified by yeast vs mold, hyphae structure, spore formation.

• Mycosis: Fungal infection or disease.

Bacterial Endospores vs Fungal Spores

• Bacterial Endospore: Dormant survival structure, not for reproduction. Survives extreme conditions (heat, drying, chemicals, radiation, lack of nutrients).

• Fungal Spore: Reproductive structure for growth and spread.

• Healthcare Challenge: Endospores are difficult to kill, resist disinfectants, and may persist on medical equipment.

Classification of Protozoans and Helminths

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

• Helminths: Two main groups: roundworms (nematodes), flatworms (platyhelminths). Classified by body shape.

Microscopy and Staining Techniques

Types of Microscopes and Techniques

Microscopes are essential for visualizing microorganisms.

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

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

• Scanning Electron Microscope (SEM): Shows external surfaces (3D image).

Microscopy techniques include staining, oil immersion, and magnification to enhance visualization.

Key Terms in Microscopy

• Total Magnification: Product of ocular and objective lens magnifications. Formula:

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

• Refractive Index: Degree to which light bends passing through a substance.

• Oil Immersion: Reduces light refraction, improves resolution.

Staining Techniques

• Simple Stain: Uses one dye; shows shape, size, arrangement.

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

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

• Clinical Application: Identifies bacteria, guides treatment.

Gram Stain Procedure and Errors

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

• Gram-positive: Thick peptidoglycan, retains purple.

• Gram-negative: Thin peptidoglycan, turns pink.

• Errors: Over-decolorizing, thick smear, old/damaged cells.

Acid-Fast Stain

• Acid-Fast Genera: Mycobacterium, Nocardia.

• Reason: Cell walls contain mycolic acid (waxy lipid).

• Clinical Use: Detects tuberculosis and related infections.

Parts of the Compound Light Microscope

The compound light microscope consists of several parts, each with a specific function for viewing specimens.

• Ocular lens (eyepiece): Used for viewing.

• Objective lenses: Provide magnification.

• Stage: Holds the slide.

• Coarse adjustment knob: Large focus changes.

• Fine adjustment knob: Sharp focus.

• Light source: Illuminates specimen.

• Arm and base: Support microscope.

Calculating Total Magnification

• Formula:

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

Microbiome and Microbial Interactions

Healthy Microbiome

A healthy microbiome consists of normal microbes living on and inside the body (skin, mouth, intestines).

• Protects against pathogens

• Aids digestion

• Maintains health

Microbial 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 Healthcare Implications

Biofilms form when microbes attach to surfaces, multiply, and produce a protective layer.

• Hard to remove

• Resistant to antibiotics

• Common on medical devices (catheters, implants)

Beneficial Roles of Microbes

Food and Biotechnology Industry

Microbes are used in food production, medicine, and environmental cleanup.

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

• Food/Beverages: Yogurt, cheese, bread, beer, wine

• Drug Production: Antibiotics, insulin, vitamins, enzymes, biofuels

Aseptic Techniques and Lab Safety

Aseptic Techniques

Aseptic techniques prevent contamination and infection.

• Handwashing

• Using gloves

• Sterilizing instruments

• Disinfecting surfaces

Lab Safety and PPE

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

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

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

Disposal of Cultures

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

Biological Chemistry and Macromolecules

Chemical Reactions

• Dehydration Synthesis: Joins molecules by removing water

• Hydrolysis: Breaks molecules apart by adding water

Types of Chemical Bonds

• Covalent: Share electrons

• Ionic: Transfer electrons

• Hydrogen: Weak attraction between molecules

Acids, Bases, and pH Scale

• Acid: pH below 7

• Base: pH above 7

• Neutral: pH = 7

Macromolecules in Living Cells

Prokaryotes vs Eukaryotes

Differences Between Bacteria, Archaea, and Eukaryotes

• Bacteria: Prokaryotic, peptidoglycan cell wall

• Archaea: Prokaryotic, no peptidoglycan

• Eukaryotes: Nucleus and organelles

Scientific Naming and Taxonomy

• Genus: Capitalized, Escherichia

• Species: Lowercase, coli

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

• Strain: Variant within a bacterial species

Differences Between Prokaryotic and Eukaryotic Cells

• Prokaryotic: No nucleus, smaller, no organelles

• Eukaryotic: Nucleus, larger, organelles

Binary Fission

• DNA copies → cell grows → septum forms → two identical daughter cells

Bacterial Structures and Functions

• Nucleoid: DNA storage

• Flagella: Movement

• Pili: DNA transfer

• Fimbriae: Attachment

• Ribosome: Protein synthesis

• Capsule: Protection

Endosymbiotic Theory and Mitochondria

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

Eukaryotic Structures and Functions

• Nucleus: Stores DNA

• Rough ER: Protein synthesis

• Smooth ER: Lipid synthesis

• Golgi apparatus: Packages proteins

• Mitochondria: ATP/energy production

• Chloroplast: Photosynthesis

• Lysosome: Digestion

• Peroxisome: Detoxification

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, cell swells

• Isotonic: No net movement

Eukaryotic Plasma Membranes

• Phospholipid bilayer controls entry/exit

• Animals: cholesterol; fungi: ergosterol; plants: phytosterols

Microbiology Lab Practices

Best Practices for Aseptic Technique

• Wash hands

• Disinfect workspace

• Flame loop before/after use

• Keep plates closed

• Use sterile instruments

• Wear gloves

Inverting plates: Prevents condensation from spreading bacteria on agar.

Media for Growing Bacteria

• Nutrient agar and nutrient broth: General-purpose media

Common Media Formats

• Broth

• Plates

• Slants

• Deeps (additional info)

Streaking for Isolation

• Sterilize loop

• Collect sample

• Streak first section

• Flame loop

• Streak subsequent sections

• Invert and incubate plate

• Goal: Isolate individual colonies from single cells

Scientific Method Steps

• Ask a question / make observation

• Form hypothesis

• Perform experiment

• Collect data

• Analyze results

• Draw conclusion