Microbiology Study Guide: Microbial World, Cell Structure, Eukaryotic Microbes, and Viruses

Chapter 1: The Microbial World and You

Definition, Scope, and Importance of Microbiology

• Microbiology is the study of microorganisms—living things too small to be seen with the naked eye.

• Scope: Includes bacteria, viruses, fungi, protozoa, algae, archaea, and microscopic parasites.

• Importance:

  • Medicine: Understanding diseases, infections, vaccines, and antibiotics.

  • Science: Study of cells, genetics, and organismal function.

  • Food: Production of bread, yogurt, cheese, and fermented products.

  • Environment: Waste breakdown, nutrient recycling, ecosystem maintenance.

  • Biotechnology: Production of medicines, insulin, enzymes.

  • Public Health: Disease identification, outbreak prevention.

Major Groups of Microorganisms

Group	Description	Examples
Bacteria	Single-celled prokaryotes; no nucleus; diverse roles	E. coli, Streptococcus
Archaea	Single-celled prokaryotes; genetically distinct; often extremophiles	Methanogens, halophiles
Fungi	Eukaryotic; absorb nutrients; cell wall with chitin	Yeast, mold, mushrooms
Protozoa	Single-celled eukaryotes; motile; ingest/absorb nutrients	Amoeba, Giardia
Algae	Photosynthetic eukaryotes; oxygen producers	Green algae, diatoms
Viruses	Acellular; genetic material + protein coat; require host	Influenza virus, HIV

• Cellular: Bacteria, Archaea, Fungi, Protozoa, Algae

• Acellular: Viruses

• Prokaryotes: Bacteria, Archaea

• Eukaryotes: Fungi, Protozoa, Algae

Prokaryotic vs. Eukaryotic Cells

Feature	Prokaryotic	Eukaryotic
Nucleus	No true nucleus	True nucleus
DNA Location	Nucleoid region	Inside nucleus
Size	Smaller	Larger
Organelles	None	Present (membrane-bound)
Cell Division	Binary fission	Mitosis/meiosis
Examples	Bacteria, Archaea	Fungi, Protozoa, Algae, Plants, Animals
Ribosomes	70S	80S

Historical Development of Microbiology

Scientist	Contribution
Robert Hooke	Observed cork; coined "cells"
Antonie van Leeuwenhoek	First to observe living microbes; "Father of Microbiology"
Louis Pasteur	Disproved spontaneous generation; developed pasteurization; vaccines
Robert Koch	Identified specific microbes causing diseases; Koch's postulates
Joseph Lister	Antiseptic surgery
Edward Jenner	First smallpox vaccine
Ignaz Semmelweis	Handwashing reduces infection
Alexander Fleming	Discovered penicillin

Pasteur’s Experiments: Spontaneous Generation vs. Biogenesis

• Spontaneous generation: Life arises from nonliving matter (disproved).

• Biogenesis: Life arises from pre-existing life.

• Pasteur’s swan-neck flask experiment: Broth remained sterile unless exposed to microbes from the environment, supporting biogenesis.

Koch’s Postulates

1. Microorganism must be found in all cases of the disease.

2. Must be isolated and grown in pure culture.

3. Pure culture must cause disease in a healthy host.

4. Same microorganism must be re-isolated from the experimentally infected host.

• Established the link between specific microbes and specific diseases.

Microorganisms in Ecological Balance

• Nutrient cycling: Bacteria and fungi recycle carbon, nitrogen, phosphorus.

• Photosynthesis: Algae and cyanobacteria produce oxygen and organic matter.

• Decomposition: Breakdown of dead matter, returning nutrients to the environment.

Normal Microbiota and Human Health

• Normal microbiota: Microbes living on/in the human body without causing disease.

• Functions: Compete with pathogens, aid digestion, produce vitamins, support immunity.

• Opportunistic pathogens: Normal microbiota causing disease if displaced or if immunity is compromised (e.g., E. coli in urinary tract).

Chapter 4: Functional Anatomy of Prokaryotic and Eukaryotic Cells

Prokaryotic vs. Eukaryotic Cell Structure and Function

• Both have cell membrane, DNA, cytoplasm, and ribosomes.

• Prokaryotes: Small, simple, no nucleus, no membrane-bound organelles, DNA in nucleoid.

• Eukaryotes: Larger, complex, true nucleus, membrane-bound organelles (mitochondria, ER, Golgi, etc.).

Major Shapes and Arrangements of Bacteria

Shape	Description	Example
Coccus	Round/spherical	Staphylococcus
Bacillus	Rod-shaped	E. coli
Vibrio	Comma-shaped	Vibrio cholerae
Spirillum	Rigid spiral	Spirillum
Spirochete	Flexible corkscrew	Treponema

• Arrangements: Diplococci (pairs), Streptococci (chains), Staphylococci (clusters), Tetrads (fours), Sarcinae (cubes).

Key Prokaryotic Cell Structures and Functions

Structure	Function
Cell wall	Shape, support, protection
Plasma membrane	Selective barrier, energy production
Ribosomes	Protein synthesis
Flagella	Motility
Fimbriae	Attachment
Pili	Attachment, DNA transfer (conjugation)

Gram-Positive vs. Gram-Negative Bacterial Cell Walls

Feature	Gram-Positive	Gram-Negative
Peptidoglycan	Thick	Thin
Outer membrane	Absent	Present
Teichoic acids	Present	Absent
LPS (endotoxin)	Absent	Present
Gram stain color	Purple	Pink/red
Antibiotic susceptibility	More susceptible	More resistant

• Gram-positive: Thick peptidoglycan, stains purple, more sensitive to cell wall antibiotics.

• Gram-negative: Thin peptidoglycan, outer membrane with LPS, stains pink, more resistant.

Plasma Membrane Structure and Transport Mechanisms

• Fluid mosaic model: Phospholipid bilayer with proteins, cholesterol, carbohydrates.

• Passive transport: No ATP; includes simple diffusion, facilitated diffusion, osmosis, filtration.

• Active transport: Requires ATP; moves substances against gradient (e.g., Na+/K+ pump).

• Bulk transport: Endocytosis (in), exocytosis (out).

Bacterial Motility: Flagella and Axial Filaments

• Flagella: Long, whip-like; rotate for movement; chemotaxis (toward/away from chemicals).

• Axial filaments: Found in spirochetes; corkscrew motion; movement through viscous environments.

Endospores: Formation, Function, and Significance

• Endospore: Dormant, highly resistant structure formed during unfavorable conditions (sporulation).

• Germination: Endospore returns to active cell when conditions improve.

• Significance: Survival under heat, drying, chemicals, radiation; not a reproductive process.

Prokaryotic vs. Eukaryotic Ribosomes

Feature	Prokaryotic	Eukaryotic
Size	70S (50S + 30S)	80S (60S + 40S)
Location	Cytoplasm	Cytoplasm, rough ER
Function	Protein synthesis	Protein synthesis

• Antibiotic target: Some antibiotics selectively inhibit 70S ribosomes (bacteria) but not 80S (humans).

Major Eukaryotic Cell Organelles

Organelle	Main Function
Nucleus	Stores DNA, controls cell
Nucleolus	Makes ribosomal subunits
Ribosomes	Protein synthesis
Rough ER	Protein production/transport
Smooth ER	Lipid synthesis, detoxification
Golgi complex	Modifies, sorts, packages proteins/lipids
Mitochondria	ATP production
Lysosomes	Digestion/recycling
Peroxisomes	Fatty acid breakdown, detoxification
Cytoskeleton	Shape, support, movement
Centrosome	Cell division organization
Vesicles	Transport materials
Chloroplasts	Photosynthesis (plants/algae)
Vacuoles	Storage

Chapter 12: The Eukaryotes—Fungi, Algae, Protozoa, and Helminths

Major Groups of Eukaryotic Microorganisms

Group	Structure	Nutrition	Key Feature	Examples
Fungi	Uni-/multicellular	Absorption	Chitin cell wall	Yeast, molds
Algae	Uni-/multicellular	Photosynthesis	Photosynthetic pigments	Green algae, diatoms
Protozoa	Unicellular	Ingestion/absorption	Motility	Amoeba, Giardia
Helminths	Multicellular	Parasitic	Parasitic worms	Tapeworms, roundworms

General Characteristics of Fungi

• Yeasts: Unicellular, reproduce by budding.

• Molds: Multicellular, composed of hyphae forming mycelium, reproduce by spores.

• Nutritional adaptations: Absorb nutrients after external digestion; decomposers, parasites, or mutualists.

Fungal vs. Bacterial Cell Walls

Feature	Fungi	Bacteria
Main wall material	Chitin, glucans	Peptidoglycan
Cell type	Eukaryotic	Prokaryotic
Antimicrobial target	Antifungals (chitin/glucan)	Antibiotics (peptidoglycan)

Asexual vs. Sexual Spore Formation in Fungi

Feature	Asexual Spores	Sexual Spores
Number of parents	One	Two
Genetic variation	Low	High
Cell division	Mitosis	Meiosis
Examples	Conidia, sporangiospores	Zygospores, ascospores, basidiospores

Medically Important Fungi

Fungus	Disease	Common Site/Effect
Candida albicans	Candidiasis	Mouth, skin, vagina, bloodstream
Aspergillus	Aspergillosis	Lungs/sinuses
Cryptococcus	Cryptococcosis	Lungs, brain (meningitis)

Key Features of Protozoa

• Motility structures: Flagella (long, few), cilia (short, many), pseudopodia ("false feet").

• Reproduction: Mainly asexual (binary fission), some sexual stages.

• Life cycles: Trophozoite (active), cyst (dormant, resistant).

Major Protozoan Pathogens

Protozoan	Disease	Transmission	Main Target
Giardia	Giardiasis	Fecal-oral, contaminated water/food	Intestines
Plasmodium	Malaria	Anopheles mosquito bite	Liver, red blood cells
Trypanosoma	African sleeping sickness/Chagas disease	Tsetse fly/kissing bug	Blood, tissues, nervous system

Flatworms vs. Roundworms (Helminths)

Feature	Flatworms (Platyhelminthes)	Roundworms (Nematoda)
Body shape	Flat, ribbon/leaf-shaped	Long, cylindrical, round
Digestive tract	Incomplete/absent	Complete
Sexes	Some hermaphroditic	Usually separate
Examples	Tapeworms, flukes	Pinworms, hookworms, Ascaris

Helminth Life Cycles and Disease Transmission

• Pinworm: Eggs ingested, larvae hatch in intestine, adults lay eggs around anus, eggs spread by scratching.

• Hookworm: Eggs in feces, larvae in soil penetrate skin, migrate to lungs/intestine.

• Tapeworm: Animal eats eggs, larvae in muscle, human eats undercooked meat, adult in intestine.

• Ascaris: Eggs ingested, larvae migrate through lungs, return to intestine.

Arthropods as Disease Vectors

Arthropod	Pathogen Type	Example Disease
Mosquito	Protozoa, viruses	Malaria
Tick	Bacteria, protozoa	Lyme disease
Flea	Bacteria	Plague
Louse	Bacteria	Typhus
Tsetse fly	Protozoa	African sleeping sickness

Significance of Eukaryotic Microbes

• Ecosystems: Decomposition, nutrient cycling, oxygen production (algae).

• Medicine: Cause diseases (e.g., candidiasis, malaria), produce antibiotics.

• Biotechnology: Fermentation (bread, beer), enzyme/vitamin production.

Chapter 13: Viruses, Viroids, and Prions

General Properties of Viruses

• Acellular: Not made of cells.

• Genome: DNA or RNA (never both).

• Capsid: Protein coat.

• Envelope: Lipid membrane (some viruses).

• Obligate intracellular parasites: Require host cell for replication.

Structure and Chemical Composition of Viruses

Component	Chemical Composition	Function
Nucleic acid	DNA or RNA	Genetic information
Capsid	Protein	Protects genome, attachment
Envelope	Lipids + proteins	Entry into host cells
Spikes	Proteins/glycoproteins	Attachment to host

Virus Classification

• Host range: Bacteriophages (bacteria), animal viruses, plant viruses, fungal viruses.

• Morphology: Helical, icosahedral, complex, enveloped.

• Nucleic acid: DNA or RNA, single- or double-stranded.

Bacteriophage Multiplication Cycles

• Lytic cycle: Attachment → Penetration → Biosynthesis → Assembly → Release (cell lysis).

• Lysogenic cycle: Viral DNA integrates as prophage, replicated with host, can later enter lytic cycle (induction).

Animal Virus Replication vs. Bacteriophages

Feature	Animal Viruses	Bacteriophages
Host	Animal/human cells	Bacteria
Entry	Whole virus/nucleocapsid enters	Only nucleic acid injected
Uncoating	Yes	No
Release	Lysis or budding	Usually lysis

Laboratory Growth, Identification, and Quantification of Viruses

• Growth: Requires living cells (cell cultures, embryonated eggs, animals).

• Identification: Cytopathic effects, PCR (nucleic acid), antigen/antibody tests.

• Quantification: Plaque assay (PFU/mL), TCID50.

Types of Viral Infections

Type	Description	Example
Acute	Rapid onset, short duration	Influenza
Latent	Inactive, can reactivate	Herpes simplex virus
Persistent	Long-term, ongoing virus production	Hepatitis B/C
Slow	Long incubation, gradual disease	SSPE (measles-related)

Viral Latency and Reactivation

• Latency: Viral genome remains in host cell with little/no replication (e.g., HSV in neurons, HIV as provirus in T cells).

• Reactivation: Virus resumes replication, causing recurrent disease.

Oncogenic Viruses and Cancer

Virus	Associated Cancer
HPV	Cervical, anal, penile, head/neck cancers
EBV	Burkitt lymphoma, Hodgkin lymphoma, nasopharyngeal carcinoma
HBV/HCV	Hepatocellular carcinoma
HTLV-1	Adult T-cell leukemia/lymphoma
HHV-8	Kaposi sarcoma

• Mechanisms: Alter cell cycle, inhibit apoptosis, cause chronic inflammation, integrate into host DNA.

Prions vs. Viruses

Feature	Prions	Viruses
Composition	Protein only	DNA/RNA + protein
Genome	None	DNA or RNA
Replication	Induce misfolding of normal proteins	Use host cell machinery
Main diseases	Neurodegenerative (e.g., CJD, BSE)	Many types (e.g., influenza, HIV)

Prevention and Control of Viral Infections

• Vaccination: Stimulates immune memory (e.g., influenza, measles, HPV, hepatitis B, polio, COVID-19).

• Antiviral drugs: Inhibit viral replication (e.g., acyclovir, oseltamivir, ART for HIV).

• Hygiene and public health: Handwashing, respiratory etiquette, isolation, vector control.