Microbiology Study Guide: Chapters 1, 3, 4, 6, and 7

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Ch. 1 – The Microbial World and You

Introduction to Microbes

Microorganisms, or microbes, are tiny living organisms that are found everywhere. They play essential roles in ecosystems, human health, and industry.

Destructive Actions: Some microbes cause diseases (pathogens), spoil food, and damage materials.
Beneficial Actions: Many microbes decompose waste, recycle nutrients, produce food (e.g., cheese, yogurt), and synthesize antibiotics and vitamins.
Examples: Lactobacillus in yogurt production; Escherichia coli in the gut synthesizing vitamin K.

Scientific Nomenclature

The system of naming organisms uses two names: the genus (capitalized) and the specific epithet (lowercase). Both are italicized or underlined.

Genus: The first part of the name, e.g., Staphylococcus.
Specific Epithet: The second part, e.g., aureus in Staphylococcus aureus.

Major Groups of Microorganisms

Bacteria: Prokaryotes, unicellular, peptidoglycan cell walls.
Archaea: Prokaryotes, lack peptidoglycan, often live in extreme environments.
Fungi: Eukaryotes, chitin cell walls, include yeasts and molds.
Protozoa: Eukaryotes, unicellular, often motile.
Algae: Eukaryotes, photosynthetic, cellulose cell walls.
Viruses: Acellular, consist of DNA or RNA core surrounded by protein coat.
Helminths: Multicellular animal parasites.

Prokaryotes: Bacteria and Archaea Eukaryotes: Fungi, Protozoa, Algae, Helminths

The Three Domains

Bacteria
Archaea
Eukarya (includes fungi, protozoa, algae, plants, and animals)

Historical Contributions

Hooke: Observed cells in cork, leading to cell theory.
van Leeuwenhoek: First to observe live microorganisms.
Cell Theory: All living things are composed of cells.

Spontaneous Generation vs. Biogenesis

Spontaneous Generation: Hypothesis that life arises from nonliving matter.
Biogenesis: Life arises from preexisting life.
Evidence: Pasteur's experiments disproved spontaneous generation by showing that microbes come from other microbes.

Key Figures in Microbiology

Needham: Supported spontaneous generation.
Spallanzani: Disproved spontaneous generation with sealed flasks.
Virchow: Proposed biogenesis.
Pasteur: Disproved spontaneous generation, developed pasteurization.
Koch: Developed Koch's postulates to link microbes to disease.
Jenner: Developed the first vaccine (smallpox).
Ehrlich: Searched for "magic bullet" drugs (chemotherapy).
Fleming: Discovered penicillin.

Subfields of Microbiology

Bacteriology: Study of bacteria.
Mycology: Study of fungi.
Parasitology: Study of parasites.
Immunology: Study of immunity.
Virology: Study of viruses.

Microbial Genetics and Molecular Biology

Microbial Genetics: Study of how microbes inherit traits.
Molecular Biology: Study of how genetic information is carried in molecules of DNA.

Beneficial Activities and Biotechnology

Beneficial Activities: Decomposition, nitrogen fixation, food production, bioremediation.
Biotechnology: Use of microbes to produce foods and chemicals.
Recombinant DNA Technology: Insertion of genes into microbes to produce desired products.

Normal Microbiota, Resistance, and Biofilms

Normal Microbiota: Microbes normally present in and on the human body.
Resistance: Ability to ward off disease.
Biofilm: Community of microbes attached to a surface; important in infections and industry.

Emerging Infectious Diseases

Definition: New or changing diseases increasing in incidence.
Contributing Factors: Evolution, antibiotic resistance, global travel, ecological changes.

Ch. 3 – Observing Microorganisms Through a Microscope

Microscopy Basics

Metric Units: Microorganisms are measured in micrometers (μm, 10-6 m) and nanometers (nm, 10-9 m).
Conversion Example: 10 μm = 10,000 nm.

Compound Microscope

Path of Light: Light passes through the condenser lens, specimen, objective lens, and ocular lens.
Total Magnification: Product of objective and ocular lens magnifications.
Resolution: Ability to distinguish two points as separate; a resolution of 0.2 nm means two points 0.2 nm apart can be distinguished.
Formula for Total Magnification:

Types of Microscopy

Brightfield: Standard light microscopy.
Darkfield: Enhances contrast for unstained specimens.
Phase-Contrast: Visualizes internal structures in living cells.
Differential Interference Contrast: 3D images of live cells.
Fluorescence: Uses fluorescent dyes; useful for identifying microbes.
Confocal: 3D images using lasers.
Two-Photon: Imaging living tissues up to 1 mm deep.
Scanning Acoustic: Uses sound waves; studies living cells attached to surfaces.

Electron Microscopy

Transmission Electron Microscope (TEM): Internal structures, high resolution.
Scanning Electron Microscope (SEM): Surface structures, 3D images.
Scanned-Probe Microscopy: Surface features at atomic level.
Reason for Higher Resolution: Electrons have shorter wavelengths than light.

Staining Techniques

Acidic Dye: Negatively charged, stains background.
Basic Dye: Positively charged, stains cells.
Simple Stain: Uses one dye to highlight cells.
Fixing: Attaches cells to slide and preserves structure.

Gram Stain Procedure

Crystal violet (primary stain)
Iodine (mordant)
Alcohol (decolorizer)
Safranin (counterstain)

Gram-Positive: Purple after staining.
Gram-Negative: Red/pink after staining.

Other Staining Methods

Acid-Fast Stain: Identifies Mycobacterium and Nocardia.
Capsule Stain: Visualizes capsules.
Endospore Stain: Detects endospores.
Flagella Stain: Visualizes flagella.

Ch. 4 – Functional Anatomy of Prokaryotic and Eukaryotic Cells

Prokaryotes vs. Eukaryotes

Prokaryotes: No nucleus, no membrane-bound organelles, smaller size.
Eukaryotes: Nucleus, membrane-bound organelles, larger size.

Bacterial Shapes and Arrangements

Coccus: Spherical
Bacillus: Rod-shaped
Spiral: Twisted
Arrangements: Chains (strepto-), clusters (staphylo-), pairs (diplo-)

Glycocalyx and Capsules

Glycocalyx: Sticky, external layer; can be a capsule (organized) or slime layer (unorganized).
Medical Importance: Capsules prevent phagocytosis, aiding in pathogenicity.

Surface Structures

Flagella: Motility structures.
Axial Filaments: Found in spirochetes, enable corkscrew movement.
Fimbriae: Attachment structures.
Pili: Involved in DNA transfer (conjugation).

Cell Walls

Gram-Positive: Thick peptidoglycan, teichoic acids.
Gram-Negative: Thin peptidoglycan, outer membrane, lipopolysaccharide (LPS).
Acid-Fast: Mycolic acid in cell wall.
Archaea: No peptidoglycan.
Mycoplasmas: No cell wall, sterols in membrane.

Cell Wall-Related Terms

Protoplast: Gram-positive cell without cell wall.
Spheroplast: Gram-negative cell with partial cell wall loss.
L Form: Bacteria that have lost their cell wall.

Plasma Membrane

Structure: Phospholipid bilayer with proteins.
Function: Selective permeability, energy generation.
Injury Agents: Alcohols, detergents, antibiotics (e.g., polymyxin).

Transport Mechanisms

Simple Diffusion: Movement from high to low concentration.
Facilitated Diffusion: Uses transport proteins.
Osmosis: Diffusion of water.
Active Transport: Requires energy (ATP).
Group Translocation: Substance is chemically altered during transport.

Internal Structures

Nucleoid: Region containing DNA.
Ribosomes: Protein synthesis (70S in prokaryotes, 80S in eukaryotes).
Inclusions: Reserve deposits (e.g., metachromatic granules, lipid inclusions).
Endospores: Resistant structures formed under stress.

Comparisons: Prokaryotic vs. Eukaryotic Structures

Flagella: Prokaryotic flagella rotate; eukaryotic flagella undulate.
Cell Walls: Peptidoglycan in prokaryotes; cellulose/chitin in eukaryotes.
Plasma Membranes: Sterols in eukaryotes, rarely in prokaryotes.
Cytoplasm: More complex in eukaryotes.
Ribosomes: 70S (prokaryotes), 80S (eukaryotes); antibiotics like erythromycin target 70S ribosomes.

Ch. 6 – Microbial Growth

Physical Requirements for Growth

Temperature Groups:
- Psychrophiles: Cold-loving
- Mesophiles: Moderate temperature
- Thermophiles: Heat-loving
- Hyperthermophiles: Very high temperatures
pH: Most bacteria grow best at pH 6.5–7.5; buffers (e.g., phosphate salts) stabilize pH.
Osmotic Pressure: High salt/sugar inhibits growth; used in food preservation.

Chemical Requirements

Carbon: Structural backbone of organic molecules.
Nitrogen: Needed for proteins, nucleic acids.
Sulfur: Needed for amino acids, vitamins.
Phosphorus: Needed for nucleic acids, ATP, membranes.
Oxygen Requirements:
- Obligate aerobes: Require O2
- Facultative anaerobes: Grow with or without O2
- Obligate anaerobes: Cannot tolerate O2
- Aerotolerant anaerobes: Tolerate O2, do not use it
- Microaerophiles: Require low O2
Toxic Oxygen: Superoxide radicals, peroxide, hydroxyl radicals; enzymes like superoxide dismutase and catalase neutralize them.

Biofilms

Formation: Microbes adhere to surfaces, secrete extracellular matrix, form communities.
Importance: Increased resistance to antibiotics, cause persistent infections.

Culture Media

Chemically Defined: Exact chemical composition known.
Complex Media: Contains extracts, composition varies.
Special Techniques: Anaerobic jars, candle jars, selective/differential/enrichment media.

Biosafety Levels

BSL-1: No special precautions.
BSL-2: Moderate risk; lab coat, gloves, eye protection.
BSL-3: Biosafety cabinets, airborne precautions.
BSL-4: Sealed, negative pressure, "hot zone".

Colony and Pure Culture

Colony: Visible mass of cells from a single cell.
Streak Plate Method: Isolates pure cultures.

Preservation Methods

Deep-Freezing: -50°C to -95°C.
Lyophilization: Freeze-drying.

Bacterial Growth and Generation Time

Binary Fission: Most common method of reproduction.
Growth Curve Phases: Lag, log, stationary, death.
Generation Time Formula:

Measuring Microbial Growth

Direct Methods: Plate counts, filtration, MPN, direct microscopic count.
Indirect Methods: Turbidity, metabolic activity, dry weight.

Ch. 7 – The Control of Microbial Growth

Key Terms in Microbial Control

Sterilization: Removal of all microbial life.
Disinfection: Removal of pathogens.
Antisepsis: Removal of pathogens from living tissue.
Degerming: Removal of microbes from a limited area.
Sanitization: Lowering microbial counts to safe levels.
Biocide/Germicide: Kills microbes.
Bacteriostasis: Inhibits growth, does not kill.
Asepsis: Absence of contamination.

Patterns and Mechanisms of Microbial Death

Death Rate: Microbes die at a constant rate when exposed to antimicrobial agents.
Factors: Number of microbes, environment, time of exposure, microbial characteristics.
Targets: Plasma membrane, proteins, nucleic acids.

Physical Methods of Control

Moist Heat: Boiling, autoclaving, pasteurization.
Dry Heat: Flaming, incineration, hot-air sterilization.
Filtration: Removes microbes from liquids/air.
Low Temperature: Inhibits growth.
High Pressure: Denatures proteins.
Desiccation: Removes water.
Osmotic Pressure: Causes plasmolysis.
Radiation: Damages DNA (ionizing, nonionizing, microwaves).

Chemical Methods of Control

Disinfectants: Phenolics, halogens, alcohols, heavy metals, surfactants, aldehydes, peroxygens.
Halogens: Iodine (antiseptic), chlorine (disinfectant).
Surface-Active Agents: Soaps, detergents.
Glutaraldehyde: Effective, sporicidal.
Chemical Sterilizers: Ethylene oxide, plasma, peracetic acid.

Testing Effectiveness

Use-Dilution Test: Tests effectiveness of disinfectants.
Disk-Diffusion Method: Zone of inhibition indicates effectiveness.

Microbial Resistance

Endospores: Highly resistant.
Gram-Negative Bacteria: More resistant to biocides than gram-positive.