Microbiology Exam 1 Study Guide: Introduction, Cell Structure, and Microbial Taxonomy

Chapter 1: Introduction to Microbiology

Scientific Method and Experimental Design

The scientific method is a systematic approach to investigating natural phenomena. Valid experiments require careful planning and control to ensure reliable results.

• Elements of a Valid Experiment: Hypothesis, control and experimental groups, variables (independent, dependent, controlled), replication, and analysis.

• Scientific Method Steps: Observation, question, hypothesis, experiment, analysis, conclusion.

Autotrophs vs. Heterotrophs

• Autotrophs: Organisms that produce their own food from inorganic sources (e.g., photosynthetic bacteria, plants).

• Heterotrophs: Organisms that obtain energy by consuming organic molecules (e.g., animals, most bacteria).

Eukaryotes vs. Prokaryotes

• Eukaryotes: Cells with a true nucleus and membrane-bound organelles (e.g., fungi, protozoa, algae, plants, animals).

• Prokaryotes: Cells lacking a nucleus and most organelles (e.g., bacteria, archaea).

Key Scientists and Their Contributions

• John Snow: Father of epidemiology; traced cholera outbreak to contaminated water.

• Robert Koch: Developed Koch's postulates to link specific microbes to diseases.

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

• Ignaz Semmelweis: Advocated handwashing to prevent puerperal fever.

• Joseph Lister: Introduced antiseptic surgery using carbolic acid.

• Carl Woese & George Fox: Identified Archaea as a separate domain using rRNA sequencing.

• Edward Jenner: Developed the first vaccine (smallpox).

Major Theories

• Spontaneous Generation: Disproven idea that life arises from nonliving matter.

• Cell Theory: All living things are composed of cells; cells are the basic unit of life.

Human-Microbe Relationships

• Burden of Infectious Disease: Infectious diseases remain a major cause of morbidity and mortality worldwide.

• Nosocomial (Healthcare-Associated) Infections: Infections acquired in healthcare settings.

• Pathogen: A microorganism capable of causing disease.

• Sanitation: Practices that reduce microbial contamination to safe levels.

• Antibiotic Resistance: The ability of microbes to withstand the effects of antibiotics; caused by misuse/overuse of antibiotics, genetic mutations, and horizontal gene transfer.

• Selective Toxicity: The ability of a drug to target pathogens without harming the host.

• Microbiome: The collection of all microorganisms living in association with the human body.

• Symbiosis: Close association between different species; includes mutualism, commensalism, and parasitism.

• Uses of Microorganisms: Sewage treatment, food production (e.g., yogurt, cheese), biotechnology, bioremediation.

Lab Methods (Ch 1B, 3, 10)

Types of Media

• Defined Media: Exact chemical composition is known.

• Complex Media: Contains extracts (e.g., peptone, yeast extract); composition varies.

• Selectives Media: Inhibits growth of some organisms while allowing others.

• Differential Media: Distinguishes organisms based on metabolic traits.

Types of Microscopy

• Light Microscopy: Uses visible light; includes brightfield, darkfield, phase-contrast.

• Electron Microscopy: Uses electron beams; includes transmission (TEM) and scanning (SEM).

Parts of the Microscope

• Ocular lens (eyepiece), objective lenses, stage, condenser, light source, coarse/fine focus knobs.

Staining Techniques

• Gram Staining: Differentiates bacteria into Gram-positive (purple) and Gram-negative (pink) based on cell wall structure.

• Endospore Staining: Identifies spore-forming bacteria (e.g., Bacillus, Clostridium).

• Why Use Stains? Increases contrast, identifies structures, and differentiates cell types.

• Primary Stains: Crystal violet (Gram), malachite green (endospore).

Aseptic Technique

• Prevents contamination of cultures and the environment.

Biosafety Levels (BSL)

• BSL-1: Non-pathogenic microbes.

• BSL-2: Moderate risk; associated with human disease.

• BSL-3: Serious or potentially lethal pathogens.

• BSL-4: High-risk, life-threatening agents (e.g., Ebola).

Chapter 3: Cell Structure and Function

Prokaryotic vs. Eukaryotic Cells

• Prokaryotes: No nucleus, no membrane-bound organelles, smaller size, circular DNA.

• Eukaryotes: Nucleus, membrane-bound organelles, larger size, linear DNA.

Classification of Prokaryotes

• Based on morphology, staining, metabolic traits, genetic analysis.

Gram-Positive vs. Gram-Negative Bacteria

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

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

• Lipid A: Endotoxin component of LPS in Gram-negative bacteria.

Endospores

• Dormant, resistant structures formed by some bacteria for survival in harsh conditions.

• Common in Bacillus and Clostridium species.

Biofilms

• Communities of microorganisms attached to surfaces, embedded in a self-produced matrix.

• Increase resistance to antibiotics and immune responses.

Pili and Conjugation

• Pili: Hair-like structures for attachment and DNA transfer.

• Conjugation: Transfer of genetic material between bacteria via sex pilus.

Cell Structures

• Glycocalyx: Gel-like coating outside cell wall; capsule (organized) or slime layer (loose).

• Flagella: Motility structures; different arrangements (monotrichous, lophotrichous, peritrichous).

• Fimbriae: Short, numerous projections for attachment.

• Cell Wall: Provides shape and protection; peptidoglycan in bacteria.

• Cytoplasmic Membrane: Phospholipid bilayer; controls transport via passive (diffusion, osmosis) and active (pumps, group translocation) processes.

• Cytoplasm: Contains cytosol, inclusions (storage), and endospores.

• Nonmembranous Organelles: Ribosomes (protein synthesis), cytoskeleton (shape, movement).

Differences Between Archaea and Eubacteria

• Archaea: Unique membrane lipids, no peptidoglycan, often extremophiles.

• Bacteria (Eubacteria): Peptidoglycan cell walls, diverse environments.

Obligate Intracellular Bacteria

• Cannot survive or reproduce outside host cells (e.g., Chlamydia, Rickettsia).

Species, Strains, and Types

• Species: Group of organisms sharing common characteristics.

• Strain: Genetic variant within a species.

• Serotype: Distinct variation based on antigenic properties.

Eukaryotic Cell Structures

• External Structures: Glycocalyx, flagella (complex, whip-like), cilia (short, numerous).

• Nonmembranous Organelles: Ribosomes, cytoskeleton, centrioles/centrosome.

• Membranous Organelles: Nucleus (DNA storage), endoplasmic reticulum (protein/lipid synthesis), Golgi body (modification/packaging), lysosomes (digestion), peroxisomes (detoxification), vacuoles/vesicles (storage/transport), mitochondria (ATP production), chloroplasts (photosynthesis in plants/algae).

Endosymbiotic Theory

• Explains origin of mitochondria and chloroplasts as formerly free-living bacteria engulfed by ancestral eukaryotes.

Types of Eukaryotic Pathogens

• Includes fungi, protozoa, helminths, and some algae.

Chapter 10: Microbial Taxonomy and Classification

Strategies for Classifying Microorganisms

• Biochemical Tests: Identify metabolic capabilities (e.g., sugar fermentation, enzyme activity).

• Microscopic Analysis: Cell shape, arrangement, staining properties.

• Culturing: Growth characteristics on various media.

• Nucleic Acid Testing: PCR, DNA hybridization, sequencing.

• Serology: Detection of specific antigens/antibodies.

• Antibiograms: Patterns of antibiotic susceptibility.

• rRNA Sequencing: Comparison of 16S/18S rRNA genes for phylogeny.

• Whole Genome Shotgun Sequencing: Comprehensive genetic analysis.

• Surveillance Tools: NextStrain, PulseNet for tracking outbreaks.

Taxonomic Hierarchy and Naming

• Taxa: Hierarchical groups (Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species).

• Scientific Naming: Binomial nomenclature (Genus species, e.g., Escherichia coli).

Three-Domain Classification

• Bacteria, Archaea, Eukarya: Based on genetic and biochemical differences.

Problems in Taxonomy

• Horizontal gene transfer, convergent evolution, and phenotypic plasticity can complicate classification.

Virus Classification

• Based on nucleic acid type (DNA/RNA), structure, replication strategy, and host range.

Distinguishing Strains and Serotypes

• Strains differ genetically; serotypes differ in antigenic properties.

Taxonomic Level	Example	Description
Domain	Bacteria	Highest rank; major cell type differences
Kingdom	Eubacteria	Broad grouping within domain
Phylum	Proteobacteria	Major lineages within kingdom
Class	Gammaproteobacteria	Subdivisions of phylum
Order	Enterobacteriales	Groups of related families
Family	Enterobacteriaceae	Groups of related genera
Genus	Escherichia	Closely related species
Species	Escherichia coli	Basic unit; organisms sharing key traits

Example: Escherichia coli O157:H7 is a pathogenic strain (serotype) of the species Escherichia coli.

Additional info: Modern taxonomy increasingly relies on molecular methods (e.g., whole genome sequencing) for accurate classification and epidemiological tracking.