Exam 1 Review: Foundations of Microbiology

The Microbial World and You

Scientific Nomenclature

Scientific names of organisms are written using the binomial system, which ensures clarity and universal understanding in microbiology.

• Genus name is capitalized; species name is lowercase.

• Both names are italicized (or underlined if handwritten), e.g., Escherichia coli.

• After first mention, the genus can be abbreviated (e.g., E. coli).

Three Domains of Life

All living organisms are classified into three domains based on cellular organization and genetics.

• Bacteria: Prokaryotic, peptidoglycan cell walls, unicellular, diverse metabolism.

• Archaea: Prokaryotic, lack peptidoglycan, often live in extreme environments (e.g., halophiles, thermophiles).

• Eukarya: Eukaryotic, includes protists, fungi, plants, and animals; membrane-bound organelles.

Historical Figures in Microbiology

• Robert Hooke: First to describe cells (1665); used a compound microscope.

• Antonie van Leeuwenhoek: Improved simple microscope; first to observe living microorganisms ("animalcules").

• Louis Pasteur: Disproved spontaneous generation; developed pasteurization; vaccines for rabies and anthrax.

• Robert Koch: Developed Koch's postulates; identified causative agents of tuberculosis and cholera.

• Alexander Fleming: Discovered penicillin (first antibiotic).

• Paul Ehrlich: Developed Salvarsan (treatment for syphilis); concept of selective toxicity.

• Edward Jenner: Developed first vaccine (smallpox).

Observing Microorganisms Through a Microscope

Units of Measurement

• Micrometer (µm): 1 µm = $1 \times 10^{-6}$ meters

• Nanometer (nm): 1 nm = $1 \times 10^{-9}$ meters

Types of Microscopes

• Light Microscope: Uses visible light; magnification up to ~1000x; resolution ~0.2 µm.

• Electron Microscope: Uses electron beams; much higher resolution (up to 0.2 nm); includes TEM and SEM.

Comparison: Electron microscopes provide greater detail but require more complex sample preparation and cannot view living cells.

Microscope Components and Techniques

• Blue Filter: Shortens wavelength of light, increasing resolution.

• Immersion Oil: Reduces light refraction, improving image clarity at high magnification.

Microscope Wavelength Utilization

• Different microscopes use various wavelengths (visible, UV, electrons) to enhance contrast and resolution.

Functional Anatomy of Prokaryotic and Eukaryotic Cells

Gram Stain

The Gram stain differentiates bacteria based on cell wall structure.

1. Crystal violet (primary stain)

2. Iodine (mordant)

3. Alcohol (decolorizer)

4. Safranin (counterstain)

• Gram-positive: Thick peptidoglycan, retain crystal violet (purple).

• Gram-negative: Thin peptidoglycan, lose crystal violet, take up safranin (pink).

Acid-Fast Stain

• Identifies bacteria with waxy cell walls (e.g., Mycobacterium).

• Uses carbol fuchsin, acid-alcohol, and methylene blue.

• Acid-fast bacteria retain red dye; non-acid-fast are blue.

• Difference: Acid-fast stain targets mycolic acids, not peptidoglycan.

Basic and Differential Stains

• Basic stains: Positively charged dyes (e.g., crystal violet) stain cell structures.

• Differential stains: Distinguish between types of organisms or structures (e.g., Gram, acid-fast).

Bacterial Morphology

• Shapes: Cocci (spherical), bacilli (rod), spirilla (spiral).

• Arrangements: Chains (strepto-), clusters (staphylo-), pairs (diplo-).

• Flagellar Types: Monotrichous (single), lophotrichous (tuft), amphitrichous (both ends), peritrichous (all over).

Fimbriae vs. Pili

• Fimbriae: Short, numerous; attachment to surfaces.

• Pili: Longer, fewer; involved in conjugation (DNA transfer).

Gram-Positive vs. Gram-Negative Cell Envelopes

Feature	Gram-Positive	Gram-Negative
Peptidoglycan	Thick	Thin
Outer Membrane	Absent	Present
Teichoic Acids	Present	Absent
Lipopolysaccharide (LPS)	Absent	Present

Cell Wall Loss

• Bacteria without cell walls (protoplasts/spheroplasts) are osmotically fragile.

• Some (e.g., Mycoplasma) naturally lack cell walls and survive in isotonic environments.

Ribosomes: Svedberg Units

• Prokaryotes: 70S (50S + 30S subunits)

• Eukaryotes: 80S (60S + 40S subunits)

• S: Svedberg unit, measures sedimentation rate; not additive due to shape and density differences.

Bacterial Inclusion Bodies

• Storage granules for nutrients (e.g., glycogen, polyphosphate, sulfur granules, gas vacuoles).

Bacterial Endospores

• Dormant, resistant structures for survival in harsh conditions.

• Produced by Bacillus and Clostridium species.

Microbial Growth

Types of Culture Media

• Selective media: Inhibits some microbes, allows others (e.g., MacConkey agar).

• Differential media: Distinguishes microbes by appearance (e.g., blood agar).

• Chemically defined media: Exact chemical composition known.

• Enriched media: Contains extra nutrients for fastidious organisms (e.g., chocolate agar).

Some media are both selective and differential (e.g., MacConkey agar selects for Gram-negative and differentiates lactose fermenters).

Bacterial Growth Curve

• Lag phase: Adaptation, no division.

• Log (exponential) phase: Rapid division.

• Stationary phase: Nutrient depletion, growth = death rate.

• Death phase: Decline in population.

Bacterial Population Calculation

• Formula: $N_f = N_i \times 2^n$

• $N_f$: Final cell number

• $N_i$: Initial cell number

• $n$: Number of generations

Bacterial Enumeration

• Direct: Plate counts, microscopic counts.

• Indirect: Turbidity, metabolic activity, dry weight.

The Control of Microbial Growth

Types of Microbial Control Agents

• Bacteriostatic: Inhibits growth (e.g., refrigeration).

• Bactericidal: Kills bacteria (e.g., autoclaving, bleach).

• Antiseptic: Used on living tissue (e.g., iodine, alcohol).

Disk Diffusion Test

• Measures zone of inhibition to assess chemical agent effectiveness.

• Larger zone = greater bactericidal activity.

Physical and Chemical Control Methods

• Dry heat: Incineration, hot air ovens; sterilizes by oxidation.

• Moist heat: Autoclaving, boiling; denatures proteins.

• Ionizing radiation: Gamma rays, X-rays; damages DNA, sterilizes medical supplies.

• Non-ionizing radiation: UV light; damages DNA, disinfects surfaces.

• Heavy metals: Silver, mercury; denature proteins (e.g., silver nitrate in newborn eyes).

• QUATs: Quaternary ammonium compounds; disrupt membranes, disinfect surfaces.

• Cold sterilization agents: Filtration, gases (e.g., ethylene oxide).

• Ethylene oxide and ozone: Gaseous sterilants for heat-sensitive materials.

• Hydrogen peroxide: Oxidizing agent, disinfects wounds and surfaces.

Example: Autoclaving (moist heat) is used to sterilize surgical instruments; UV light is used to disinfect laboratory hoods.

Additional info: This review covers foundational concepts in microbiology, including microscopy, cell structure, microbial growth, and control methods, essential for understanding laboratory and clinical applications.