Microbiology: Structure and Functional Anatomy of Bacteria and Viruses

A complete vocabulary set covering key concepts in bacterial morphology, cell wall composition, internal/external structures, Gram staining, and viral morphology, capsids, envelopes, and replication cycles based on Dr S.L. Nouar's lecture notes.

Animalcules

Microscopic living organisms discovered in the microbial world and described by Anthonie Van Leeuwenhoek ($1632$–$1723$).

Microbe

A general term introduced by surgeon Sedillot in $1878$ to refer to all microscopic microorganisms.

Protists

A kingdom of organisms subdivided into higher protists (eukaryotes such as fungi, algae, and protozoa) and lower protists (prokaryotes such as bacteria).

Prokaryotic Ribosomes

Protein synthesis organelles in bacteria with a sedimentation coefficient of $70\text{ S}$, as opposed to eukaryotic $80\text{ S}$ ribosomes.

Mycoplasma

The only genus of bacteria that naturally lacks a cell wall.

Protoplasts

Spherical cell structures obtained when the cell wall is completely removed from Gram-positive bacteria.

Spheroplasts

Spherical cell structures obtained when the cell wall is partially removed or altered from Gram-negative bacteria.

Peptidoglycan

Also called murein, a heteropolymer structure forming the rigid basic constituent of the bacterial cell wall, made of alternating N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) sugars.

Cocci

Spherical or round-shaped bacterial cells.

Diplococci

Spherical bacteria arranged in pairs.

Streptococci

Spherical bacteria arranged in chains.

Staphylococci

Spherical bacteria arranged in grape-like clusters.

Tetrads

An arrangement of four spherical bacterial cells grouped in a square.

Coccobacilli

Short, rod-shaped bacteria intermediate in shape between cocci and bacilli.

Vibrios

Curved, comma-shaped rod bacteria.

Spirochetes

Flexible helical or spiral-shaped bacteria, reaching extreme lengths up to $250\,\mu\text{m}$.

Gram-Positive Cell Wall

A thick cell wall composed mainly of peptidoglycan and teichoic acid, lacking an outer membrane.

Gram-Negative Cell Wall

A thin peptidoglycan cell wall located between two membranes (cytoplasmic and outer membrane), rich in lipids and proteins.

Gram Stain Process

A differential staining method involving four reagents: Crystal violet (Reagent 1), Iodine mordant (Reagent 2), Alcohol wash (Reagent 3), and Safranin or fuchsin counterstain (Reagent 4).

Cytoplasmic Membrane

A thin, triple-layered membrane composed of lipids and proteins that delimits the cytoplasm and serves as a selective permeability barrier, respiratory center, and energy plant ($ATP$) in bacteria.

Nucleoid

The nuclear apparatus of a bacterium, consisting of a single double-stranded circular DNA chromosome composed of $60\%$ DNA, $30\%$ RNA, and $10\%$ proteins.

Capsule

An optional polysaccharide structure with a regular, well-defined shape surrounding the bacterial cell wall that promotes attachment, prevents phagocytosis, and inhibits antibiotic penetration.

Glycocalyx

A surface slime layer on the exterior of the bacterial cell wall or outer membrane that facilitates attachment to biological cells or inert surfaces.

Biofilm

Layers of glycocalyx/slime containing slow-metabolizing bacteria that adhere to host tissues or catheters and protect microbes from antibiotics and disinfectants.

Plasmid

An extrachromosomal, double-stranded circular DNA molecule ($0.5\text{ to }500\,\text{kb}$) that replicates independently of the bacterial chromosome and transfers via sex pili.

Common Pili

Filiform appendages (fimbriae) composed of adhesin proteins that allow bacteria to attach to target host cells and move by sliding on solid surfaces.

Sex Pili

Thicker and longer plasmid-encoded surface appendages that mediate genetic transfer between bacterial cells during conjugation.

Flagellum

A thin, rigid locomotory appendage made of the protein flagellin that extends outside the plasma membrane and allows movement in liquid media.

Flagellar Arrangements

Patterns of flagella distribution across bacteria, classified as monotrichous (single), lophotrichous (tuft at one pole), amphitrichous (at both poles), and peritrichous (around entire surface).

Bacterial Spore

A small oval or spherical dormant cell structure produced under nutrient deprivation that survives extreme dehydration and harsh environmental conditions.

Virion

A mature, fully formed infectious viral particle existing outside living host cells.

Nucleocapsid

The core structure of a virus composed of the viral nucleic acid genome surrounded by its protein capsid.

Icosahedral Capsid

A viral capsid with cubic symmetry formed by $20\text{ equilateral triangular faces}$, $30\text{ edges}$, and $12\text{ vertices}$.

Helical Capsid

A viral capsid structure where protein subunits assemble in a spiral helix forming a rigid tube enclosing the viral nucleic acid.

Complex Symmetry Capsid

A type of viral capsid structure that does not exhibit pure helical or icosahedral symmetry, such as in bacteriophages or poxviruses.

Viral Envelope

A lipid bilayer membrane containing carbohydrates and proteins acquired by certain viruses through budding from host cell membranes.

Spikes

Glycoproteins of viral origin embedded in the viral envelope that facilitate viral attachment to host cell surface receptors.

Enveloped vs Non-Enveloped Virus

Structural classification distinguishing naked viruses (consisting only of a nucleocapsid and possessing greater environmental resistance) from enveloped viruses (enclosed in a lipid bilayer).

Viral Replication Stages

The six sequential steps of viral infection: attachment, penetration, uncoating, gene replication and expression, assembly, and release.

Budding

A release mechanism where enveloped viruses exit the host cell wrapped in a fragment of the host cell membrane.

Cell Lysis

A viral release process in which the infected host cell bursts, freeing $100\text{ to }1000\text{ new virions}$.