MCB 2010C Midterm Study Guide: Microbiology Core Concepts (Chapters 8, 9, 10 Focus)

Introduction to Microbiology and Historical Foundations

Louis Pasteur’s S-necked Flask Experiment

The S-necked flask experiment by Louis Pasteur was pivotal in disproving the theory of spontaneous generation and establishing the principle of biogenesis.

• Design: Broth was boiled in flasks with S-shaped necks, which allowed air in but trapped dust and microbes.

• Result: No microbial growth occurred unless the flask was tilted, allowing particles to reach the broth.

• Significance: Demonstrated that life does not arise spontaneously; microbes come from other microbes.

• Application: Foundation for aseptic techniques in microbiology.

Koch’s Postulates

Koch’s postulates are a set of criteria used to establish a causative relationship between a microbe and a disease.

• Postulate 1: The microorganism must be found in all organisms suffering from the disease, but not in healthy organisms.

• Postulate 2: The microorganism must be isolated from a diseased organism and grown in pure culture.

• Postulate 3: The cultured microorganism should cause disease when introduced into a healthy organism.

• Postulate 4: The microorganism must be re-isolated from the inoculated, diseased experimental host and identified as being identical to the original specific causative agent.

• Limitations: Some pathogens cannot be cultured, and some diseases are caused by multiple organisms or only in humans.

Microbial Taxonomy and Nomenclature

Binomial Nomenclature

Binomial nomenclature is the formal system of naming species using two names: genus and species.

• Format: Genus is capitalized, species is lowercase, both italicized (e.g., Escherichia coli).

• Importance: Provides a universal language for scientists.

Microscopy and Staining Techniques

Acid-Fast Stain

The acid-fast stain is used to identify bacteria with waxy cell walls, such as Mycobacterium species.

• Steps: Application of carbol fuchsin (primary stain), heating, decolorization with acid-alcohol, counterstaining with methylene blue.

• Chemistry: Acid-fast bacteria retain carbol fuchsin due to mycolic acid in their cell walls.

• Usefulness: Diagnosing tuberculosis and leprosy.

Gram Staining

Gram staining differentiates bacteria into Gram-positive and Gram-negative based on cell wall structure.

• Steps: Crystal violet (primary stain), iodine (mordant), alcohol (decolorizer), safranin (counterstain).

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

• Troubleshooting: Omitting decolorizer results in all cells appearing purple; omitting mordant may cause poor retention of crystal violet.

Streak Plate Technique

The streak plate technique is used to isolate pure bacterial colonies.

• Method: Spreading bacteria over the surface of an agar plate in a pattern to dilute the sample.

• Purpose: To obtain isolated colonies for further study.

Bacterial Colony

A bacterial colony is a visible mass of microbial cells originating from a single parent cell.

• Significance: Used to estimate the number of viable organisms in a sample.

Prokaryotic and Eukaryotic Cell Structure

Bacterial Cell Shapes and Arrangements

• Cocci: Spherical

• Bacilli: Rod-shaped

• Spirilla: Spiral-shaped

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

Extracellular Structures

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

• Pili and Fimbriae: Attachment and conjugation.

• Capsules: Protection from desiccation and immune system.

Bacterial Endospores

• Structure: Highly resistant, dormant forms produced by some bacteria (e.g., Bacillus, Clostridium).

• Function: Survival under harsh conditions.

Prokaryotic vs. Eukaryotic Cells

• Prokaryotes: No nucleus, circular DNA, 70S ribosomes, no membrane-bound organelles.

• Eukaryotes: Nucleus, linear DNA, 80S ribosomes, membrane-bound organelles.

Eukaryotic Organelles

• Nucleus: Contains genetic material.

• Mitochondria: ATP production.

• Endoplasmic Reticulum: Protein and lipid synthesis.

• Golgi Apparatus: Protein modification and sorting.

Bacterial Intracellular Features

• Genome: Usually a single circular chromosome in the nucleoid region.

• Plasmids: Small, extrachromosomal DNA.

• Ribosomes: 70S, site of protein synthesis.

Taxonomic Kingdoms

Kingdom	Key Features
Animalia	Multicellular, heterotrophic, no cell walls
Plantae	Multicellular, autotrophic, cell walls of cellulose
Fungi	Unicellular/multicellular, chitin cell walls, decomposers
Protista	Mostly unicellular, diverse nutrition
Bacteria	Prokaryotic, peptidoglycan cell walls
Archaea	Prokaryotic, unique membrane lipids, extreme environments

Fungi and Mycoses

• Ringworm: A fungal infection of the skin (not caused by a worm).

• Mycoses: Fungal diseases; often difficult to treat due to similarity to human cells.

Genetics and Molecular Biology

DNA and RNA Structure

• DNA: Double helix, deoxyribose sugar, bases A-T, G-C.

• RNA: Single-stranded, ribose sugar, bases A-U, G-C.

Epigenome

• Definition: Chemical modifications to DNA and histones that affect gene expression without altering the DNA sequence.

DNA Replication

• Enzymes: Helicase (unwinds DNA), DNA polymerase (synthesizes new strand), ligase (joins fragments).

• Process: Semi-conservative; each new DNA has one old and one new strand.

Building Blocks of DNA and RNA

• Nucleotides: Composed of a sugar, phosphate group, and nitrogenous base.

Protein Synthesis

• Transcription: DNA to mRNA in the nucleus (eukaryotes).

• Translation: mRNA to protein at the ribosome.

Horizontal Gene Transfer in Bacteria

• Transformation: Uptake of naked DNA from the environment.

• Transduction: Transfer by bacteriophages.

• Conjugation: Direct transfer via pilus.

Mutations

• Types: Point mutations, insertions, deletions, frameshifts.

• Outcomes: Silent, missense, nonsense, or frameshift effects on proteins.

Viruses and Prions

Viruses as Non-Living Entities

• Reason: Cannot reproduce independently; require host cells.

Viral Replication Stages

• Attachment, penetration, uncoating, biosynthesis, assembly, release.

• Drug Targets: Entry inhibitors, protease inhibitors, reverse transcriptase inhibitors.

Viral Structure

• Components: Nucleic acid (DNA or RNA), capsid, envelope (in some viruses).

Viral Release Mechanisms

• Budding: Enveloped viruses acquire membrane from host.

• Lysis: Non-enveloped viruses rupture host cell.

Types of Infections

• Acute: Rapid onset, short duration (e.g., influenza).

• Chronic: Persistent, long-term (e.g., hepatitis B).

• Latent: Dormant periods with reactivation (e.g., herpes simplex).

Viral Evolution

• High Mutation Rates: Especially in RNA viruses due to lack of proofreading.

• Genetic Drift: Small, gradual changes.

• Genetic Shift: Major changes, often by reassortment.

Oncogenic Viruses

• Definition: Viruses that can cause cancer (e.g., HPV, EBV).

Prions

• Definition: Infectious proteins causing neurodegenerative diseases (e.g., Creutzfeldt-Jakob disease).

Microbial Metabolism

Catabolic vs. Anabolic Reactions

• Catabolic: Breakdown of molecules, releases energy.

• Anabolic: Synthesis of molecules, requires energy.

Enzymes and Coenzymes

• Enzymes: Biological catalysts, lower activation energy.

• Coenzymes: Organic cofactors (e.g., NAD+, FAD) required for enzyme function.

Cellular Respiration Pathways

Pathway	Location	Key Inputs	Key Outputs
Glycolysis	Cytoplasm	Glucose	2 ATP, 2 NADH, 2 pyruvate
Intermediate Step	Cytoplasm (prokaryotes), mitochondria (eukaryotes)	Pyruvate	Acetyl-CoA, CO2, NADH
Krebs Cycle	Cytoplasm (prokaryotes), mitochondria (eukaryotes)	Acetyl-CoA	2 ATP, 6 NADH, 2 FADH2, CO2
Electron Transport Chain	Cell membrane (prokaryotes), inner mitochondrial membrane (eukaryotes)	NADH, FADH2, O2	~34 ATP, H2O

• CO2 Loss: Occurs in intermediate step and Krebs cycle.

Aerobic vs. Anaerobic Respiration

• Aerobic: Uses O2 as final electron acceptor; higher ATP yield.

• Anaerobic: Uses other inorganic molecules (e.g., nitrate, sulfate); lower ATP yield.

Fermentation

• Definition: Anaerobic process; regenerates NAD+ for glycolysis.

• Benefits: Allows ATP production without oxygen.

Principles of Infectious Disease and Epidemiology

Pathogen Types

• True Pathogen: Causes disease in healthy hosts.

• Opportunistic Pathogen: Causes disease in immunocompromised hosts.

Key Epidemiological Terms

Term	Definition
Endemic	Constantly present in a population
Pandemic	Worldwide epidemic
Epidemic	Sudden increase in cases in a region
Immunocompromised Host	Weakened immune system
Virulence	Degree of pathogenicity
Pathogenicity	Ability to cause disease
Attenuated Pathogen	Weakened form, often used in vaccines

Antiseptics, Disinfectants, and Microbial Control

• Antiseptic: Used on living tissue to reduce microbes.

• Disinfectant: Used on inanimate objects.

• Microbiostatic: Inhibits growth.

• Microbiocidal: Kills microbes.

Oxygen Requirements in Bacteria

Type	Oxygen Requirement
Aerotolerant Anaerobe	Does not use O2 but tolerates it
Microaerophile	Requires low O2
Facultative Anaerobe	Can use O2 or not
Obligate Aerobe	Requires O2
Obligate Anaerobe	Cannot tolerate O2

Physical and Chemical Growth Requirements

Term	Definition
Decimal Reduction Time (D-value)	Time to kill 90% of microbes at a given temperature
Thermal Death Point	Lowest temperature to kill all microbes in 10 min
Thermal Death Time	Time to kill all microbes at a set temperature
Barophiles	Grow best under high pressure
Acidophiles	Grow best at low pH
Halophiles	Grow best in high salt
Neutralophiles	Grow best at neutral pH
Psychrophiles	Grow best at low temperatures

Equipment and Germicides

Type	Examples
Critical Equipment	Surgical instruments
Non-critical Equipment	Stethoscopes
High-level Germicides	Sterilants
Intermediate-level Germicides	Disinfectants for surfaces
Low-level Germicides	General cleaners

Emerging and Reemerging Pathogens

• Emerging: Newly identified or increasing in incidence.

• Reemerging: Previously controlled but increasing again.

Pathogen Sources and Transmission

• Exogenous Pathogen: Originates outside the host.

• Endogenous Pathogen: Originates from host’s own flora.

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

• Biological Vector: Organism that transmits pathogen and is part of its life cycle (e.g., mosquito).

• Mechanical Vector: Transmits pathogen without being infected (e.g., fly).

• Source: Immediate origin of infection.

• Reservoir: Long-term host of pathogen.

• Asymptomatic Carrier: Infected but shows no symptoms.

• Chronic Carrier: Harbors pathogen long-term.

Morbidity and Mortality

• Morbidity: Incidence of disease.

• Mortality: Incidence of death.

ID50 and LD50

• ID50: Infectious dose for 50% of population.

• LD50: Lethal dose for 50% of population.

Toxemia

• Definition: Presence of toxins in the blood.

Ribozymes

• Definition: RNA molecules with enzymatic activity.

Disease Transmission Mechanisms

• Direct Transmission: Physical contact (e.g., touching, droplets).

• Indirect Transmission: Via fomites, vectors, or airborne particles.

Culture Media Types

Type	Description
Complex Media	Contains unknown components (e.g., nutrient broth)
Synthetic/Defined Media	Exact chemical composition known
Differential Media	Distinguishes microbes by biochemical reactions
Selective Media	Suppresses unwanted microbes, encourages desired ones

Healthcare-Acquired Infections (HAIs)

• Definition: Infections acquired in healthcare settings.

• Examples: MRSA, C. difficile, catheter-associated infections.

Septic Shock

• Definition: Life-threatening low blood pressure due to infection.

• Common Cause: Gram-negative bacteria (due to endotoxins).

• Symptoms: Fever, chills, rapid heartbeat, confusion, low blood pressure.

Disease Eradication

• Criteria: No new cases globally, pathogen eliminated from nature.

Immune Evasion Mechanisms

• Antigenic Variation: Changing surface proteins to avoid detection.

• Latency: Remaining dormant in host cells.

• Intracellular Survival: Hiding within host cells.

Stages of Infectious Disease

Stage	Features
Incubation	Time between infection and symptoms
Prodromal	Early, mild symptoms
Acute	Peak of illness
Period of Decline	Symptoms subside
Convalescence	Recovery

Endotoxins vs. Exotoxins

• Endotoxins: Lipid A of Gram-negative LPS; released on cell death; less potent, not easily neutralized.

• Exotoxins: Proteins secreted by bacteria; highly potent, specific effects, can be neutralized by antibodies.

Classes of Exotoxins

• Type I: Superantigens (e.g., toxic shock syndrome toxin).

• Type II: Membrane-disrupting toxins.

• Type III: A-B toxins (e.g., diphtheria toxin).

Biosafety Levels (BSL)

Level	Description
BSL-1	Non-pathogenic microbes
BSL-2	Moderate risk; gloves, lab coat
BSL-3	Serious/lethal pathogens; biosafety cabinets
BSL-4	High risk, no treatment; full-body suits

Diagnostic Test Specificity vs. Sensitivity

• Specificity: Ability to correctly identify those without disease (true negatives).

• Sensitivity: Ability to correctly identify those with disease (true positives).

Reporting Obligations and Public Health

• Obligation: Healthcare providers must report certain infections to public health authorities.

• Eradication Candidates: Diseases with no animal reservoir, effective vaccine, and clear symptoms are best candidates for eradication.

Additional info: Some explanations and tables were expanded for clarity and completeness based on standard microbiology curricula.