Comprehensive Microbiology Study Guide: Key Concepts and Exam Review

Microbial Growth and Culturing

Classification of Microbiological Growth Media

Microbiological growth media are substances used to support the growth of microorganisms. They can be classified based on their composition and purpose.

• Defined (synthetic) media: Exact chemical composition is known.

• Complex media: Contains extracts (e.g., peptones, yeast extract) with unknown exact composition.

• Selectivity: Select for or differentiate between types of microbes (e.g., MacConkey agar).

• Enriched media: Supplemented with nutrients for fastidious organisms.

Example: Blood agar is an enriched medium used to grow pathogenic bacteria.

Types of Media and Culture

• Broth: Liquid media for growing large numbers of bacteria.

• Agar plates: Solid media for isolating colonies.

• Slants and deeps: Used for storage and biochemical testing.

Types of Microbes

• Bacteria: Prokaryotic, unicellular organisms.

• Viruses: Acellular, require host cells for replication.

• Fungi: Eukaryotic, includes yeasts and molds.

• Protozoa: Unicellular eukaryotes.

• Algae: Photosynthetic eukaryotes.

Oxygen Requirements

• Obligate aerobes: Require oxygen.

• Obligate anaerobes: Killed by oxygen.

• Facultative anaerobes: Can grow with or without oxygen.

• Microaerophiles: Require low oxygen levels.

• Aerotolerant anaerobes: Do not use oxygen but tolerate it.

Reduction of Microbial Load

• Sterilization: Complete destruction of all forms of microbial life.

• Disinfection: Elimination of most pathogens (not spores).

• Pasteurization: Reduces microbial load in liquids by heating.

Bacterial Structure and Function

Bacterial Forms and Structures

• Bacteria exist in two forms: Vegetative cells (active) and endospores (dormant, resistant).

• Fimbriae: Short, hair-like structures for attachment.

• Flagella: Long, whip-like appendages for motility. Arrangements include monotrichous, lophotrichous, amphitrichous, and peritrichous.

• Sex pili: Involved in conjugation (DNA transfer).

• Capsule: Polysaccharide layer for protection and adherence.

• Mesosome: Infoldings of the plasma membrane, possibly involved in cell division.

Endospores

• Function: Survival under harsh conditions (heat, desiccation, chemicals).

• Produced by: Genera such as Bacillus and Clostridium.

Cell Wall Differences

• Gram-positive: Thick peptidoglycan, teichoic acids, stains purple.

• Gram-negative: Thin peptidoglycan, outer membrane with lipopolysaccharide (LPS), stains pink.

Gram Stain Principle: Based on cell wall structure differences.

Shapes and Arrangements of Bacteria

• Cocci: Spherical.

• Bacilli: Rod-shaped.

• Spirilla: Spiral-shaped.

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

Microbial Genetics and Biotechnology

Genetic Engineering and Biotechnology

• Genetic engineering: Manipulation of an organism's DNA to achieve desired traits.

• Biotechnology: Use of living organisms or their products for human benefit.

• Recombinant DNA technology: Combining DNA from different sources.

• Plasmids: Small, circular DNA molecules used as vectors in genetic engineering.

PCR (Polymerase Chain Reaction)

• Technique to amplify specific DNA sequences.

• Uses DNA polymerase, primers, nucleotides, and thermal cycling.

$\text{PCR cycle: Denaturation} \rightarrow \text{Annealing} \rightarrow \text{Extension}$

DNA Replication Models

• Conservative: Parental DNA remains intact, new molecule is all new DNA.

• Semi-conservative: Each new DNA has one old and one new strand.

• Dispersive: DNA strands are mixtures of old and new segments.

Central Dogma of Molecular Biology

• Describes the flow of genetic information: DNA → RNA → Protein.

$\text{DNA} \xrightarrow{\text{transcription}} \text{RNA} \xrightarrow{\text{translation}} \text{Protein}$

Mutations

• Mutation: Permanent change in DNA sequence.

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

Enzymes in Genetics

• Ligase: Joins DNA fragments.

• Restriction endonucleases: Cut DNA at specific sequences (e.g., EcoRI, HindIII, HaeIII).

Microbial Physiology and Metabolism

Cellular Respiration and ATP Production

• Phases: Glycolysis, Krebs cycle, Electron Transport Chain (ETC).

• ATP Yield: Total from one glucose molecule is about 36-38 ATP (in eukaryotes).

$\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + 36-38\ \text{ATP}$

Enzymes and Cofactors

• Enzyme: Biological catalyst, usually a protein.

• Cofactor: Non-protein component required for enzyme activity (e.g., metal ions).

• Coenzyme: Organic cofactor (e.g., NAD+, FAD).

• Holoenzyme: Apoenzyme (protein part) + cofactor.

• Competitive inhibition: Inhibitor competes with substrate for active site.

• Non-competitive inhibition: Inhibitor binds elsewhere, changing enzyme shape.

Microbial Taxonomy and Classification

Taxonomy and Hierarchy

• Taxonomy: Science of classifying organisms.

• Hierarchy: Domain > Kingdom > Phylum > Class > Order > Family > Genus > Species.

Five Kingdom Classification

• Monera (Prokaryotes), Protista, Fungi, Plantae, Animalia.

Microscopy and Staining

Concepts of Microscopy

• Total magnification: Product of ocular and objective lens magnifications.

$\text{Total Magnification} = \text{Ocular Magnification} \times \text{Objective Magnification}$

• Resolution: Ability to distinguish two points as separate.

Staining Techniques

• Purpose: Increase contrast, differentiate cell types.

• Gram stain: Differentiates Gram-positive and Gram-negative bacteria.

• Acid-fast stain: Identifies Mycobacterium and Nocardia.

• Basic dyes: Positively charged, bind to negatively charged cell components.

Microbial Control and Chemotherapy

Physical and Chemical Control Methods

• Autoclave: Uses steam under pressure for sterilization.

• Pasteurization: Reduces pathogens in liquids.

• Filtration: Removes microbes from heat-sensitive solutions.

• HEPA filters: Remove airborne particles.

• Food irradiation: Uses ionizing radiation to kill microbes.

• Chlorhexidine, tincture of iodine, silver nitrate: Chemical disinfectants.

Antimicrobial Drugs

• Broad-spectrum: Effective against a wide range of microbes.

• Narrow-spectrum: Effective against specific microbes.

• Beta-lactams: Inhibit cell wall synthesis (e.g., penicillins).

• Macrolides, aminoglycosides, polymyxins: Different mechanisms of action.

Microbial Pathogenesis and Immunology

Pathogens and Infection

• Pathogen: Microorganism that causes disease.

• Nosocomial infection: Hospital-acquired infection.

• Infectious dose (ID): Number of organisms required to cause infection.

• Superinfection: Secondary infection by a different organism.

Stages of Infection and Disease

• Incubation period: Time between exposure and symptoms.

• Prodromal period: Early, mild symptoms.

• Acute period: Peak of symptoms.

• Convalescence: Recovery phase.

Transmission and Epidemiology

• Horizontal transmission: Person-to-person.

• Vertical transmission: Parent to offspring.

• Endemic: Constant presence in a population.

• Epidemic: Sudden increase in cases.

• Pandemic: Worldwide epidemic.

• Incidence: Number of new cases.

• Prevalence: Total number of cases.

Immunity and Immune Response

• Innate immunity: Non-specific, immediate defense.

• Adaptive immunity: Specific, involves B and T lymphocytes.

• Antigen: Substance that elicits an immune response.

• Antibody (Immunoglobulin): Protein produced by B cells to neutralize antigens.

• Types of immunity: Active (natural or artificial), passive (natural or artificial).

Inflammation and Hypersensitivity

• Inflammation: Redness, heat, swelling, pain, loss of function.

• Hypersensitivity: Exaggerated immune response (e.g., allergy).

Viruses and Viral Replication

Viral Structure and Classification

• Capsid: Protein coat made of capsomeres.

• Envelope: Lipid membrane surrounding some viruses.

• Genome: DNA or RNA, single or double-stranded.

• ssRNA (+) and (-): Single-stranded RNA viruses, positive or negative sense.

• Retrovirus: RNA virus that uses reverse transcriptase (e.g., HIV).

Viral Replication

• Attachment → Penetration → Uncoating → Replication → Assembly → Release

Viral Taxonomy and Specificity

• Classified by genome type, capsid symmetry, presence of envelope.

• Viral specificity: Host range and tissue tropism.

Tables

Comparison of Gram-Positive and Gram-Negative Bacteria

Feature	Gram-Positive	Gram-Negative
Peptidoglycan Layer	Thick	Thin
Teichoic Acids	Present	Absent
Outer Membrane	Absent	Present
LPS	Absent	Present
Gram Stain	Purple	Pink

Types of Immunity

Type	Natural	Artificial
Active	Infection	Vaccination
Passive	Maternal antibodies	Antibody therapy

Additional info:

• Some content was inferred and expanded for academic completeness, such as detailed explanations of terms and processes.

• Tables were constructed to clarify comparisons and classifications mentioned in the notes.