Microbiology Lecture - Microbial Structures, Growth, and Controls

Vocabulary practice flashcards covering fundamental microbiology concepts, key historical contributors, staining and microscopy methods, cellular envelopes, transport mechanisms, division mechanics, growth dynamics, antimicrobial controls, and viral/phage biology.

Microbiology

The branch of science studying microorganisms (microbes) and their biological activities and interactions.

Microbes

Organisms or infectious agents that are generally too small to be seen without a microscope, including bacteria, archaea, fungi, protozoa, microscopic algae, and viruses.

RNA World Hypothesis

The hypothesis that early biological life relied on RNA for both storing genetic information and catalyzing chemical reactions before DNA and proteins evolved.

Ribozymes

RNA molecules capable of acting as biological catalysts to perform enzymatic chemical reactions.

Carl Woese

The microbiologist who introduced the three-domain system (Bacteria, Archaea, Eukarya) by analyzing ribosomal RNA (rRNA) sequence relationships.

Antonie van Leeuwenhoek

The 'Father of Microbiology' who built simple microscopes and became the first person to observe and describe live microscopic organisms ('animalcules').

Louis Pasteur

The scientist who established germ theory, disproved spontaneous generation using swan-neck flasks, invented pasteurization, and created rabies and anthrax vaccines.

Robert Koch

The physician who formulated Koch's postulates to establish cause-and-effect relationships between specific pathogenic microbes and specific infectious diseases.

John Snow

An epidemiology pioneer who mapped cholera cases in London to a Broad Street water pump, removing its handle to curb the outbreak before the causative bacterium was identified.

Koch's Postulates

A four-step set of criteria used to link a pathogen to a disease: presence in diseased hosts, pure culture isolation, disease induction in healthy hosts, and re-isolation.

Simple Stain

A staining procedure utilizing a single basic dye to determine cell shape, size, and cellular arrangement.

Gram Stain

A differential staining procedure that classifies bacteria into Gram-positive (purple) or Gram-negative (pink/red) based on peptidoglycan thickness and outer membrane structure.

Acid-Fast Stain

A differential staining technique used to identify bacteria with high mycolic acid content in their cell walls, such as Mycobacterium species.

Endospore Stain

A specialized differential stain designed to visualize resilient, non-reproductive endospores formed by certain bacterial species during unfavorable conditions.

Capsule Stain

A negative staining method that reveals the clear protective polysaccharide or protein halo surrounding certain bacterial cells.

Bright-Field Microscopy

Standard light microscopy where light passes through a specimen to form an image against a bright background.

Dark-Field Microscopy

Microscopy in which light hits the specimen from the side, producing a bright image against a dark background.

Phase-Contrast Microscopy

Microscopy that converts refractive index differences into brightness variations to visualize live, unstained biological specimens.

Transmission Electron Microscopy (TEM)

Electron microscopy that passes electrons through a specimen to capture high-resolution $2\text{D}$ cross-sectional views of internal cell structures and viruses.

Scanning Electron Microscopy (SEM)

Electron microscopy that scans an electron beam over a specimen's surface to produce detailed $3\text{D}$-like morphological images.

Cell Membrane

A selectively permeable phospholipid bilayer surrounding the cytoplasm that regulates transport, signaling, and cellular boundary functions.

Peptidoglycan

A structural polymer consisting of alternating NAG and NAM sugar chains cross-linked by short peptides that forms the bacterial cell wall.

Lipopolysaccharide (LPS)

An outer membrane component of Gram-negative bacteria containing Lipid A, an endotoxin capable of inducing severe inflammatory responses and septic shock.

Simple Diffusion

Unassisted passive movement of small, nonpolar molecules across a lipid bilayer down their concentration gradient without energy or carrier proteins.

Facilitated Diffusion

Passive movement of molecules across a cell membrane down their concentration gradient via channel or carrier proteins without requiring ATP.

Primary Active Transport

Direct ATP-driven movement of solutes across a cell membrane against their concentration gradient.

Secondary Active Transport

Solute movement against a concentration gradient driven by the stored potential energy of an ion gradient created by primary active transport.

Symporter

A cotransporter membrane protein that moves two different substances across a cell membrane in the same direction.

Antiporter

A membrane transport protein that exchanges two different substances by moving them in opposite directions across the membrane.

Glycocalyx

An outer extracellular polysaccharide or protein layer surrounding cells that provides protection, surface adherence, and biofilm formation.

Plasmids

Small, extrachromosomal circular DNA molecules in bacteria that replicate independently and carry non-essential genes conferring advantageous traits.

Endospores

Highly dormant and resistant non-reproductive structures formed by bacterial genera like Bacillus and Clostridium to withstand extreme heat, desiccation, and chemical exposure.

Fimbriae

Short, thin, hair-like protein appendages on bacterial surfaces that enable adherence to surfaces, host tissues, or other cells.

Pili

Long protein filaments on bacterial surfaces that function in cell adhesion and transfer genetic material during bacterial conjugation.

Flagella

Helical proteinaceous surface appendages that rotate like propellers to propel bacteria through fluid environments.

Chemotaxis

Directed movement of a microorganism toward chemical attractants or away from chemical repellents.

Type III Secretion System (T3SS)

A syringe-like protein complex in Gram-negative bacteria that injects bacterial effector proteins directly into eukaryotic host cell cytoplasm.

Binary Fission

The primary mode of bacterial asexual reproduction where a cell duplicates its DNA, elongates, forms a septum, and splits into two daughter cells.

FtsZ

A tubulin homolog protein that forms a contractile Z-ring at the cell midplane to initiate bacterial cell division.

MinE

A bacterial cell division protein that oscillates to prevent FtsZ ring formation at cell poles, ensuring septum formation occurs at mid-cell.

MreB

An actin-like protein in non-spherical bacteria that forms helical filaments to direct peptidoglycan synthesis and maintain rod cell shape.

Crescentin

A cytoskeletal protein that localizes to the inner curvature of curved bacteria to induce and maintain crescent cell morphology.

Transpeptidase

A bacterial enzyme (penicillin-binding protein) that catalyzes peptide cross-linking in peptidoglycan, which is targeted and inhibited by $\beta\text{-lactam}$ antibiotics like penicillin.

Lag Phase

The initial bacterial growth curve stage where cells adapt to a new environment and synthesize necessary enzymes with no net increase in cell number.

Log Phase

The exponential bacterial growth stage characterized by rapid cell division at maximum rate, during which cells are most susceptible to antibiotics like penicillin.

Stationary Phase

The bacterial growth stage where nutrient exhaustion and metabolic waste accumulation cause the cell division rate to equal the cell death rate.

Death Phase

The terminal bacterial growth curve stage where dead cells outnumber viable cells, leading to an exponential decline in population size.

Plasmolysis

The shrinking of a plant or microbial cytoplasm away from its cell wall due to water loss in a hypertonic environment.

Decimal Reduction Time (D-value)

The time required at a specified temperature or condition to achieve a $90\%$ reduction (a $1\log_{10}$ reduction) in a microbial population.

Minimum Inhibitory Concentration (MIC)

The lowest concentration of an antimicrobial agent that completely prevents visible growth of a microorganism in vitro.

Bactericidal

An agent or treatment that directly kills bacterial cells.

Bacteriostatic

An agent or treatment that inhibits bacterial cell growth and reproduction without directly killing the cells.

Bacteriolytic

An antimicrobial agent that induces cell lysis and cell wall/membrane destruction in bacteria.

Bacteriophage

A virus that infects and replicates specifically within bacterial host cells.

Prion

An infectious pathogen composed solely of misfolded protein that induces healthy proteins to adopt the misfolded conformation, causing fatal neurodegenerative diseases.

Viroid

A small, unencapsulated circular single-stranded RNA pathogen that infects plant cells and disrupts gene expression.

RNA-Dependent RNA Polymerase (RdRP)

An enzyme required by negative-sense single-stranded RNA and double-stranded RNA viruses to replicate their RNA genomes and transcribe mRNA from an RNA template.

Reverse Transcriptase

A viral enzyme found in retroviruses that transcribes single-stranded RNA genomes into double-stranded DNA for host genome integration.

Prophage

A bacteriophage genome integrated into the circular bacterial host chromosome during the lysogenic replication cycle.

Lysogenic Conversion

A change in bacterial phenotype resulting from the presence and expression of prophage genes within the host chromosome.

Cytopathic Effects (CPE)

Observable structural and functional damage to host cells caused by viral infection, including cell rounding, detachment, syncytia formation, and lysis.

Cell Envelope Structural Comparison

Comparative structural arrangement of cell envelopes, contrasting Gram-negative, Gram-positive, Mycobacterium tuberculosis (mycolic acid layer), and fungal cell walls (chitin and $\beta\text{-glucan}$).

D-value Calculation

Determination of Decimal Reduction Time $D = \frac{\text{time}}{\text{number of log reductions}}$, calculated by taking the log reduction $\log_{10}\left(\frac{N_0}{N}\right)$ from initial to final microbial population over elapsed treatment time.

Reading a D-value Graph

Plotting $\log_{10}(\text{number of survivors})$ on the y-axis against time on the x-axis, where the D-value represents the time elapsed for a $1\log_{10}$ drop in population.