Exam 1

Introduction to Microbiology

Microbes and Their Impact

Microorganisms, or microbes, are ubiquitous and play essential roles in both beneficial and destructive processes affecting human life and the environment.

• Destructive Actions: Cause diseases, spoil food, and contribute to environmental pollution.

• Beneficial Actions: Decompose organic matter, recycle nutrients, produce antibiotics, and aid in food production (e.g., yogurt, cheese).

• Examples: Lactobacillus in yogurt production; Escherichia coli in vitamin K synthesis in the gut.

Scientific Nomenclature

The binomial system of nomenclature assigns each organism a two-part name: genus and specific epithet.

• Genus: First part, capitalized (e.g., Escherichia).

• Specific epithet: Second part, lowercase (e.g., coli).

• Example: Escherichia coli

Major Groups of Microorganisms

Microorganisms are classified into several groups based on cellular structure and function.

• Prokaryotes: Bacteria and Archaea (lack a nucleus).

• Eukaryotes: Fungi, protozoa, algae (have a nucleus).

• Viruses: Acellular, require host cells for replication.

Three Domains of Life

All living organisms are classified into three domains based on genetic and biochemical differences.

• Bacteria

• Archaea

• Eukarya

Historical Contributions

Early observations and experiments laid the foundation for microbiology.

• Hooke: Observed cells in cork, leading to cell theory.

• van Leeuwenhoek: First to observe living microbes.

• Cell Theory: All living things are composed of cells.

Spontaneous Generation vs. Biogenesis

Spontaneous generation posited that life arises from nonliving matter; biogenesis states that life arises from pre-existing life.

• Evidence for Spontaneous Generation: Needham's experiments with broth.

• Disproving Spontaneous Generation: Spallanzani, Virchow, and Pasteur's experiments showed that microbes come from other microbes.

• Pasteur's Influence: Led to germ theory of disease, influencing Lister (antiseptics) and Koch (postulates).

Koch's Postulates

Koch's postulates are criteria used to establish a causal relationship between a microbe and a disease.

• Microbe must be found in all cases of the disease.

• Microbe must be isolated and grown in pure culture.

• Microbe must cause disease when introduced into a healthy host.

• Microbe must be re-isolated from the experimentally infected host.

Other Key Contributors

• Jenner: Developed the first vaccine (smallpox).

• Ehrlich: "Magic bullet" concept for selective toxicity (chemotherapy).

• Fleming: Discovered penicillin.

Branches of Microbiology

• Bacteriology: Study of bacteria.

• Mycology: Study of fungi.

• Parasitology: Study of parasites.

• Immunology: Study of immune system.

• Virology: Study of viruses.

Microbial Genetics and Molecular Biology

• Microbial Genetics: Study of inheritance in microbes.

• Molecular Biology: Study of molecular mechanisms (DNA, RNA, protein synthesis).

Biotechnology and Recombinant DNA Technology

• Biotechnology: Use of microbes for practical applications (e.g., fermentation).

• Recombinant DNA Technology: Manipulation of genes for new products (e.g., insulin production).

• Examples: Recombinant DNA: insulin, growth hormone; Non-recombinant: cheese, wine.

Normal Microbiota, Resistance, Biofilms, and Emerging Diseases

• Normal Microbiota: Microbes normally present in/on the body.

• Resistance: Ability to ward off disease.

• Biofilm: Community of microbes attached to a surface; important in infection and resistance.

• Emerging Infectious Diseases: New or increasing diseases; factors include evolution, travel, and environmental changes.

Microscopes

Measurement Units in Microbiology

Microbes are measured using metric units: micrometers (μm) and nanometers (nm).

• 1 μm = 1 x 10-6 meters

• 1 nm = 1 x 10-9 meters

• Conversion: 10 μm = 10,000 nm

Compound Microscope: Path of Light

Light passes through several lenses in a compound microscope.

• Path: Light source → condenser lens → specimen → objective lens → ocular lens (eyepiece)

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 the microscope can distinguish objects 0.2 nm apart.

Types of Microscopy

• Brightfield: Standard illumination.

• Darkfield: Highlights specimens against a dark background.

• Phase-Contrast: Enhances contrast in transparent specimens.

• Differential Interference Contrast: Provides 3D-like images.

• Fluorescence: Uses fluorescent dyes.

• Confocal: Uses laser scanning for detailed images.

• Two-Photon: Allows imaging of living cells.

• Scanning Acoustic: Uses sound waves.

Electron Microscopy

• Transmission Electron Microscope (TEM): Internal structures.

• Scanning Electron Microscope (SEM): Surface structures.

• Scanned-Probe Microscopy: Atomic-level imaging.

• Reason for Higher Resolution: Electrons have shorter wavelengths than light.

Staining Techniques

• Acidic vs. Basic Dyes: Acidic dyes stain background; basic dyes stain cells.

• Simple Staining: Highlights entire organism.

• Fixing: Preserves and attaches cells to slide.

• Gram Stain: Differentiates gram-positive (purple) and gram-negative (pink) bacteria.

• Acid-Fast Stain: Identifies Mycobacterium and Nocardia.

• Special Stains: Capsule, endospore, flagella stains for specific structures.

Cell Structure: Prokaryotes vs. Eukaryotes

Cell Structure Comparison

Prokaryotes and eukaryotes differ in cellular organization.

• Prokaryotes: No nucleus, simple structure.

• Eukaryotes: Nucleus, complex organelles.

Bacterial Shapes

• Bacillus: Rod-shaped

• Coccus: Spherical

• Spiral: Spiral-shaped

• Example: Streptococci are chains of cocci.

Glycocalyx and Capsules

• Glycocalyx: Sticky layer outside cell wall; capsule is organized, slime layer is unorganized.

• Medical Importance: Capsules prevent phagocytosis, aiding pathogenicity.

Motility Structures

• Flagella: Movement

• Axial Filaments: Movement in spirochetes

• Fimbriae: Attachment

• Pili: DNA transfer

Cell Walls

• Gram-Positive: Thick peptidoglycan

• Gram-Negative: Thin peptidoglycan, outer membrane

• Acid-Fast: Mycolic acid

• Archaea: Pseudomurein

• Mycoplasmas: No cell wall

Protoplast, Spheroplast, L Form

• Protoplast: Gram-positive cell without cell wall

• Spheroplast: Gram-negative cell with partial cell wall

• L Form: Bacteria that lost cell wall

Plasma Membrane

• Structure: Phospholipid bilayer

• Function: Selective permeability, transport

• Agents Causing Injury: Alcohols, detergents, antibiotics

Transport Mechanisms

• Simple Diffusion: Movement down concentration gradient

• Facilitated Diffusion: Uses transport proteins

• Osmosis: Water movement

• Active Transport: Requires energy

• Group Translocation: Substance chemically altered during transport

Nucleoid and Ribosomes

• Nucleoid: Region containing DNA

• Ribosomes: Protein synthesis; 70S in prokaryotes, 80S in eukaryotes

Inclusions

• Function: Storage of nutrients (e.g., glycogen, polyphosphate, sulfur granules)

Endospores

• Function: Survival under harsh conditions

• Sporulation: Formation of endospores

• Germination: Return to vegetative state

Prokaryotic vs. Eukaryotic Structures

• Flagella: Prokaryotic (rotary), Eukaryotic (whip-like)

• Cell Walls: Prokaryotic (peptidoglycan), Eukaryotic (cellulose/chitin)

• Plasma Membranes: Eukaryotes have sterols

• Cytoplasm: Eukaryotes have cytoskeleton

• Ribosomes: Erythromycin binds 50S in prokaryotes, inhibiting protein synthesis; less effect on eukaryotes.

Dynamics of Microbial Growth

Temperature Classification

• Psychrophiles: Cold-loving

• Mesophiles: Moderate temperature

• Thermophiles: Heat-loving

• Hyperthermophiles: Extreme heat, often in oceanic depths

pH and Osmotic Pressure

• pH Control: Buffers (phosphate salts) maintain pH in media

• Osmotic Pressure: High salt/sugar preserves food by inhibiting microbial growth

Elements Required for Growth

• Carbon: Structural backbone

• Nitrogen: Proteins, nucleic acids

• Sulfur: Amino acids, vitamins

• Phosphorus: Nucleic acids, ATP

• Example: Radioactive sulfur found in proteins

Oxygen Requirements

• Obligate Aerobes: Require oxygen

• Obligate Anaerobes: Cannot tolerate oxygen

• Facultative Anaerobes: Can grow with or without oxygen

• Microaerophiles: Require low oxygen

Protection from Toxic Oxygen

• Enzymes: Superoxide dismutase, catalase, peroxidase

• Strategy: Avoidance or neutralization of toxic forms

Biofilms

• Formation: Microbes adhere to surfaces, produce extracellular matrix

• Importance: Increased resistance to antibiotics, persistent infections

Culture Media

• Chemically Defined: Exact composition known

• Complex Media: Contains extracts, composition varies

Special Culture Techniques

• Anaerobic Techniques: Remove oxygen

• Living Host Cells: Required for viruses

• Candle Jars: Reduce oxygen

• Selective/Differential Media: Select for or distinguish microbes

• Enrichment Medium: Favors growth of specific microbes

Biosafety Levels

• BSL-1: Basic, non-pathogenic

• BSL-2: Moderate risk

• BSL-3: High risk, aerosol transmission

• BSL-4: Extreme risk, dangerous pathogens

Colony and Pure Culture

• Colony: Visible mass of cells from one cell

• Streak Plate Method: Isolates pure cultures

Preservation Methods

• Deep-Freezing: Preserves microbes at -80°C

• Lyophilization: Freeze-drying for long-term storage

Bacterial Growth and Binary Fission

• Bacterial Growth: Increase in cell number

• Binary Fission: Cell divides into two identical cells

• $N_t = N_0 \times 2^n$

• Phases: Lag, log, stationary, death

Measuring Cell Growth

• Direct Methods: Plate count, filtration, direct microscopic count

• Indirect Methods: Turbidity, metabolic activity, dry weight

Controlling 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

• Asepsis: Absence of contamination

Patterns of Microbial Death

• Microbial death occurs at a constant rate; larger populations take longer to sterilize.

Effects of Control Agents

• Agents may damage cell walls, plasma membranes, proteins, or nucleic acids.

• Chemicals affecting plasma membranes can also affect human cells.

Physical Methods

• Moist Heat: Boiling, autoclaving, pasteurization

• Dry Heat: Flaming, incineration

• Filtration: Removes microbes from liquids

• Low Temperatures: Inhibits growth

• High Pressure: Denatures proteins

• Desiccation: Removes water

• Osmotic Pressure: High salt/sugar inhibits growth

Radiation

• Ionizing Radiation: Damages DNA

• Non-ionizing Radiation: UV light

• Killing Effect: Related to formation of hydroxyl radicals

Chemical Methods

• Disinfectants: Alcohols, halogens, surface-active agents, glutaraldehyde

• Halogens: Used as antiseptics (e.g., Betadine) or disinfectants

• Surface-Active Agents: Soaps, detergents; useful in dairy industry

• Glutaraldehyde: Effective sporicide

• Chemical Sterilizers: Ethylene oxide, glutaraldehyde

Microbial Resistance

• Endospores: Highly resistant

• Gram-Negative Bacteria: More resistant to biocides than gram-positive

Testing Disinfectants

• Use-Dilution Test: Measures effectiveness

• Disk-Diffusion Method: Used in clinics

Table: Comparison of Physical and Chemical Methods of Microbial Control

Method	Mechanism	Example
Moist Heat	Denatures proteins	Autoclaving
Dry Heat	Oxidizes cell components	Incineration
Filtration	Removes microbes	HEPA filters
Radiation	Damages DNA	UV light
Alcohols	Denatures proteins, dissolves lipids	Ethyl alcohol
Halogens	Oxidizes cell components	Iodine, chlorine
Surface-Active Agents	Disrupts membranes	Soap
Glutaraldehyde	Cross-links proteins	Medical equipment sterilization