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

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The Microbial World and You

Microbes and Their Impact

Microorganisms, or microbes, are ubiquitous and play essential roles in the environment, industry, and human health. They can be both beneficial and harmful.

Destructive Actions: Cause diseases (pathogens), food spoilage, and bio-deterioration.
Beneficial Actions: Decompose organic waste, perform photosynthesis, produce industrial chemicals (ethanol, acetone), and are used in food production (cheese, bread, yogurt).
Examples: Lactobacillus in yogurt production; Escherichia coli in vitamin K synthesis in the gut.

Scientific Nomenclature

The system of naming organisms uses two names: the genus and the specific epithet (species).

Genus: Capitalized, e.g., Staphylococcus
Specific epithet: Lowercase, e.g., aureus
Full name: Staphylococcus aureus

Major Groups of Microorganisms

Microbes are classified into several groups based on cellular organization and characteristics.

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, motile.
Algae: Eukaryotes, photosynthetic, cellulose cell walls.
Viruses: Acellular, DNA or RNA core, protein coat.
Helminths: Eukaryotic parasitic worms.

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

The Three Domains

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

Historical Contributions

Hooke: First to observe cells; led 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 posited life arises from nonliving matter; biogenesis states life arises from preexisting life.
Key Experiments: Needham (supported spontaneous generation), Spallanzani (disproved it), Virchow (biogenesis), Pasteur (definitively disproved spontaneous generation with swan-neck flask experiment).
Pasteur’s Influence: Led to aseptic techniques, influenced Lister (antiseptics) and Koch (germ theory).
Koch’s Postulates: Criteria to establish a causative relationship between a microbe and a disease.
Jenner: Developed first vaccine (smallpox).
Ehrlich: Developed "magic bullet" (selective drug for syphilis).
Fleming: Discovered penicillin.

Fields 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 DNA directs protein synthesis.

Biotechnology and Recombinant DNA Technology

Biotechnology: Use of microbes to produce foods and chemicals.
Recombinant DNA Technology: Genetic engineering to modify organisms for practical purposes.
Examples: Insulin production (recombinant), fermentation (non-recombinant).

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 environmental processes.

Emerging Infectious Diseases

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

Observing Microorganisms Through a Microscope

Units of Measurement

Micrometer (μm): meters
Nanometer (nm): meters
Conversion:

Compound Microscope: Path of Light

Light passes through the specimen, objective lens, body tube, ocular lens, and into the viewer's eye.

Total Magnification and Resolution

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.

Types of Microscopy

Brightfield: Standard light microscopy.
Darkfield: Enhances contrast in unstained samples.
Phase-Contrast: Accentuates differences in refractive index.
Differential Interference Contrast: Uses two beams of light for 3D images.
Fluorescence: Uses fluorescent dyes; useful for diagnostics.
Confocal: Uses lasers for detailed 3D images.
Two-Photon: Uses two photons for deep tissue imaging.
Scanning Acoustic: Uses sound waves.
Electron Microscopy: Uses electrons for higher resolution (TEM, SEM).

Staining Techniques

Acidic vs. Basic Dyes: Acidic dyes stain background; basic dyes stain cells.
Simple Stain: Uses one dye to highlight cells.
Gram Stain: Differentiates bacteria by cell wall structure.
Acid-Fast Stain: Identifies Mycobacterium and Nocardia.
Special Stains: Capsule, endospore, and flagella stains highlight specific structures.

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: Streptococci (chains), staphylococci (clusters)

Cell Structures

Glycocalyx: Capsule or slime layer; protects against phagocytosis.
Flagella: Motility structures; differ in prokaryotes and eukaryotes.
Fimbriae and Pili: Attachment and DNA transfer.

Cell Walls

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

Plasma Membrane and Transport

Structure: Phospholipid bilayer with proteins.
Functions: Selective permeability, energy generation.
Transport Mechanisms: Simple diffusion, facilitated diffusion, osmosis, active transport, group translocation.

Internal Structures

Nucleoid: Region containing DNA.
Ribosomes: Protein synthesis; 70S in prokaryotes, 80S in eukaryotes.
Inclusions: Storage granules.
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.

Microbial Growth

Physical and Chemical Requirements

Temperature: Psychrophiles (cold), mesophiles (moderate), thermophiles (hot), hyperthermophiles (extreme heat).
pH: Most bacteria grow best at pH 6.5–7.5; buffers maintain pH.
Osmotic Pressure: High salt/sugar inhibits growth (food preservation).
Elements Needed: Carbon, nitrogen, sulfur, phosphorus for cell components.

Oxygen Requirements

Obligate Aerobes: Require oxygen.
Facultative Anaerobes: Grow with or without oxygen.
Obligate Anaerobes: Killed by oxygen.
Aerotolerant Anaerobes: Tolerate oxygen, do not use it.
Microaerophiles: Require low oxygen.

Biofilms

Microbes form communities attached to surfaces; protected from environment and antibiotics.

Culture Media and Techniques

Chemically Defined Media: Exact composition known.
Complex Media: Contains extracts, composition varies.
Selective Media: Suppress unwanted microbes.
Differential Media: Distinguish between organisms.
Enrichment Media: Encourage growth of desired microbes.
Streak Plate Method: Isolates pure cultures.

Preservation of Microbial Cultures

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

Bacterial Growth and Measurement

Binary Fission: Main method of reproduction.
Growth Curve Phases: Lag, log, stationary, death.
Direct Measurement: Plate counts, filtration, MPN, direct microscopic count.
Indirect Measurement: Turbidity, metabolic activity, dry weight.

The Control of Microbial Growth

Key Terms

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

Microbial death occurs at a constant rate; more microbes require longer treatment.
Agents damage cell walls, membranes, proteins, or 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: Prevents metabolism.
Osmotic Pressure: Causes plasmolysis.
Radiation: Damages DNA (ionizing, nonionizing, microwaves).

Chemical Methods of Control

Disinfectants: Phenolics, halogens, alcohols, heavy metals, surfactants, aldehydes, peroxygens.
Factors Affecting Effectiveness: Concentration, presence of organic matter, pH, time.
Testing: Use-dilution and disk-diffusion methods.
Special Considerations: Some agents are sporicidal; some are more effective against certain microbes (e.g., gram-negative vs. gram-positive).

Method	Purpose	Example
Autoclaving	Sterilization	Media, instruments
Pasteurization	Disinfection	Milk, juices
Filtration	Removal of microbes	Heat-sensitive liquids
Alcohol	Disinfection/Antisepsis	Skin, surfaces
Glutaraldehyde	Sterilization	Medical equipment

Microbial Resistance

Endospores are highly resistant.
Gram-negative bacteria are more resistant to biocides than gram-positive bacteria.