Microbiology Exam 1 Study Guide: Chapters 1-4 (History, Chemistry, Cell Structure, Microscopy & Staining)

Chapter 1: Introduction & History of Microbiology

Binomial Nomenclature

Binomial nomenclature is the formal system for naming organisms, providing each with a unique scientific name.

• Genus: The first part, always capitalized and italicized (e.g., Escherichia).

• Specific epithet: The second part, lowercase and italicized (e.g., coli).

• Names are italicized when typed or underlined when handwritten.

• Example: Staphylococcus aureus

The Spontaneous Generation Debate

Historically, scientists debated whether life could arise from non-living matter.

• Spontaneous Generation: The belief that living organisms originate from non-living material.

• Biogenesis: The principle that living cells arise only from preexisting living cells.

• Key Experiments:

  • Francesco Redi: Demonstrated that maggots only appeared in meat when flies could lay eggs.

  • Lazzaro Spallanzani: Showed that boiled broth in sealed flasks remained free of microbes.

  • Louis Pasteur: Used swan-necked flasks to show that microbes in air, not spontaneous generation, caused contamination.

The Germ Theory of Disease

The germ theory established that microorganisms are the cause of specific diseases.

• Ignaz Semmelweis: Introduced handwashing to reduce puerperal fever.

• John Snow: Traced cholera outbreak to contaminated water, founding epidemiology.

• Joseph Lister: Applied aseptic techniques in surgery using carbolic acid.

• Robert Koch: Developed Koch’s Postulates to link microbes to diseases.

Key Pioneers in Microbiology

• Edward Jenner: Developed the first vaccine (smallpox).

• Paul Ehrlich: Pioneered chemotherapy; developed Salvarsan for syphilis.

• Alexander Fleming: Discovered penicillin, the first antibiotic.

• Margaret Pittman: Identified Haemophilus influenzae type b as cause of meningitis.

• Rebecca Lancefield: Created serological classification for streptococci.

Chapter 2: Basic Chemistry & Biochemistry

Chemical Bonding & Water Dynamics

Chemical bonds are the forces holding atoms together, crucial for biological molecules.

• Ionic Bonds: Electrons are transferred, forming charged ions (e.g., NaCl).

• Covalent Bonds: Electrons are shared between atoms.

  • Non-polar: Equal sharing (e.g., CH4).

  • Polar: Unequal sharing due to electronegativity (e.g., H2O).

• Hydrogen Bonds: Weak attractions between partial charges, important for water’s properties.

Metabolic Reactions

Metabolism includes all chemical reactions in cells, divided into anabolic and catabolic processes.

• Anabolism (Dehydration Synthesis): Building larger molecules from smaller ones, removing water, requires energy.

• Catabolism (Hydrolysis): Breaking down molecules, adding water, releases energy.

Macromolecules of Life

Cells are composed of four major macromolecule types, each with distinct functions.

• Carbohydrates: Monosaccharides linked by glycosidic bonds; energy storage and structural roles (cellulose, chitin).

• Lipids:

  • Triglycerides: Glycerol + 3 fatty acids; energy storage.

  • Phospholipids: Glycerol + 2 fatty acids + phosphate; amphipathic, form membranes.

  • Sterols: Ringed structures (cholesterol, ergosterol); maintain membrane fluidity.

• Proteins: Polymers of amino acids joined by peptide bonds; four structural levels:

  1. Primary: Linear sequence of amino acids.

  2. Secondary: Local folding into $\alpha$-helices or $\beta$-sheets via hydrogen bonds.

  3. Tertiary: 3D shape from interactions among R-groups.

  4. Quaternary: Multiple polypeptides forming a functional unit (e.g., hemoglobin).

• Nucleic Acids: Polymers of nucleotides (sugar, phosphate, base).

  • DNA: Double helix, deoxyribose, stores genetic information (A, T, C, G).

  • RNA: Single-stranded, ribose, protein synthesis (A, U, C, G).

  • ATP: Energy currency, stores energy in phosphate bonds.

Chapter 3: Cell Structure & Morphology

Prokaryotes vs. Eukaryotes

Cells are classified as prokaryotic or eukaryotic based on structural features.

• Prokaryotes: No membrane-bound nucleus or organelles; circular DNA in nucleoid; 70S ribosomes; divide by binary fission.

• Eukaryotes: Membrane-bound nucleus; linear DNA; specialized organelles; 80S ribosomes (except mitochondria/chloroplasts with 70S); divide by mitosis.

Bacterial Morphology & Arrangements

Bacteria exhibit characteristic shapes and arrangements.

• Shapes: Bacillus (rod), Coccus (sphere), Spiral (vibrio, spirillum, spirochete).

• Arrangements: Diplo- (pairs), Strepto- (chains), Staphylo- (clusters).

• Examples: Streptobacillus (chain of rods), Staphylococcus (cluster of spheres).

The Bacterial Cell Wall: Gram-Positive vs. Gram-Negative

The cell wall provides structural support and determines Gram staining characteristics.

• Peptidoglycan: Repeating NAG and NAM sugars cross-linked by peptides.

• Gram-Positive: Thick peptidoglycan, teichoic acids, no outer membrane, high penicillin susceptibility.

• Gram-Negative: Thin peptidoglycan, periplasmic space, outer membrane with LPS (Lipid A endotoxin), low penicillin susceptibility.

External Structures

Bacteria possess various external features aiding survival and pathogenicity.

• Glycocalyx: Gelatinous layer; capsule (organized, prevents phagocytosis), slime layer (unorganized, aids biofilm formation).

• Flagella: Motility; arrangements include monotrichous, amphitrichous, lophotrichous, peritrichous.

• Axial Filaments: Endoflagella in spirochetes; corkscrew motion.

• Fimbriae: Adherence to surfaces and tissues.

• Pili: DNA transfer via conjugation.

Internal Dynamics

Internal structures are essential for cell function and survival.

• Plasma Membrane: Selectively permeable phospholipid bilayer; passive and active transport.

• Ribosomes: Protein synthesis; prokaryotic 70S (target for antibiotics), eukaryotic 80S.

• Inclusions: Storage of nutrients (e.g., metachromatic granules, lipid, sulfur).

• Endospores: Dormant, resistant structures (Bacillus, Clostridium); formed during sporulation, germinate when conditions improve.

Chapter 4: Visualizing Microorganisms

Microscope Structure & Optics

Microscopes are essential tools for observing microorganisms.

• Stage & Controls: Holds slide; mechanical controls adjust X/Y axes.

• Focus Knobs: Coarse (large increments, low power), fine (small increments, high power).

• Condenser & Iris Diaphragm: Focuses and regulates light.

• Total Magnification: Ocular lens x objective lens.

  • Scanning Power: $4\times$ x $10\times$ = $40\times$

  • Low Power: $10\times$ x $10\times$ = $100\times$

  • High Power: $60\times$ x $10\times$ = $600\times$

  • Oil Immersion: $100\times$ x $10\times$ = $1000\times$

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

• Oil Immersion: Prevents light refraction, increases resolution at high magnification.

Microbiology Staining Procedures

Staining enhances contrast and allows differentiation of microbial structures.

• Principles: Bacterial envelopes are negatively charged.

  • Basic Dyes: Positive chromophores, bind to cells (e.g., Crystal Violet, Methylene Blue, Safranin).

  • Acidic Dyes: Negative chromophores, stain background (e.g., Nigrosin, India Ink).

• Smear Prep & Heat-Fixing: Air-dry, then flame to kill microbes and fix cells. Do not heat-fix negative or capsule stains.

1. Simple Stain

• Purpose: Observe morphology, size, arrangement.

• Method: Flood heat-fixed smear with basic dye, rinse, blot.

2. Negative Stain

• Purpose: View heat-sensitive structures without distortion.

• Method: Mix bacteria with Nigrosin, spread, air dry. Cells appear clear against dark background.

3. Gram Stain (Differential)

• Purpose: Differentiate Gram-positive and Gram-negative bacteria.

• Method:

  1. Crystal Violet (primary stain)

  2. Gram's Iodine (mordant)

  3. 95% Ethanol (decolorizer)

  4. Safranin (counterstain)

• Results: Gram-positive = purple; Gram-negative = pink/red.

• Troubleshooting: Over-decolorizing or under-decolorizing can cause false results; old cultures may yield variable results.

4. Acid-Fast Stain (Differential)

• Purpose: Identify Mycobacterium species with mycolic acid in cell walls.

• Method: Carbolfuchsin with steam, acid-alcohol decolorizer, methylene blue counterstain.

• Results: Acid-fast = bright red/fuchsia; non-acid-fast = blue.

5. Endospore Stain (Structural)

• Purpose: Detect dormant endospores (e.g., Bacillus, Clostridium).

• Method: Malachite green with steam, water rinse, safranin counterstain.

• Results: Endospores = green; vegetative cells = pink.

6. Capsule Stain (Structural Combo)

• Purpose: Visualize extracellular capsule (glycocalyx).

• Method: Negative stain with Nigrosin, air dry, crystal violet, rinse with copper sulfate.

• Results: Capsule = clear halo around purple cell body on dark background.