Pathogens and Pathogenesis – Core Vocabulary

A comprehensive set of vocabulary flashcards covering key terms, factors and concepts related to microbial pathogenesis, transmission, host interaction and toxin biology, drawn from the lecture notes.

Pathogenesis

The set of mechanisms by which an etiological factor produces disease in a host.

Pathogen

A microorganism capable of causing disease in a host organism.

Host

The organism that harbors a pathogen and may develop disease as a result.

Microbiota

The complete collection of microbes (internal and external) residing on and in the human body.

Microbiome

The collective genomes of the microbiota inhabiting the body.

Gnotobiology

The study of organisms raised in germ-free or microbiologically controlled conditions to examine immune development and disease.

Bloat

Post-mortem swelling caused by gas accumulation from bacterial decomposition and autolysis.

Putrefaction

Anaerobic protein decomposition producing foul-smelling polyamines such as putrescine and cadaverine.

Parasitism

A relationship in which one organism benefits at the expense of another, often causing harm.

Symbiosis

A biological association where both partners benefit from living together.

Commensalism

An association in which one organism benefits while the other is neither helped nor harmed.

Commensal flora

The normal, typically harmless microbial population living on or in the human body.

True pathogen

A microbe that readily overcomes host defenses and causes disease even in healthy hosts.

Opportunistic pathogen

Normally commensal microbe that causes disease when host defenses are compromised.

Pathogenicity

The ability of a microorganism to cause disease.

Virulence

The degree or extent of pathogenicity expressed by a pathogen.

Attenuation

Laboratory-induced reduction of a pathogen’s virulence, often used in vaccine production.

Balanced pathogenicity

Evolutionary concept that a successful pathogen limits host destruction to ensure its own survival and transmission.

Epidemiology

The study of disease occurrence, distribution and control within populations.

Etiological factor

A primary, independent cause of a disease.

Portal of entry

Any site through which a pathogen gains access to the body (skin, mucous membranes, parenteral).

Parenteral route

Entry of pathogens via breaches in skin or mucosa, such as injections, cuts, surgical procedures or insect bites.

Vector transmission

Transfer of pathogens into a host through the bite of an arthropod vector.

Portal of exit

Body site or secretion through which pathogens leave a host to spread to others.

Incubation period

Time between pathogen entry and appearance of disease symptoms.

Acute period

Stage of an infectious disease when symptoms are most severe.

Convalescent period

Phase during which symptoms decline and the patient returns to normal health.

Adhesin

Microbial surface molecule (often on pili or fimbriae) that binds to specific host receptors for attachment.

Invasin

Bacterial protein that facilitates penetration of host cells or tissues (e.g., Shigella invasin for M-cells).

Biofilm

Structured community of microbes encased in self-produced polysaccharide matrix adhering to each other and surfaces.

Localised infection

Infection confined to a single site or tissue in the host.

Systemic infection

Dissemination of a pathogen to multiple body sites, frequently via the bloodstream.

Bacteremia

Presence of viable bacteria circulating in the bloodstream.

Mucociliary escalator

Ciliated epithelial mechanism in the respiratory tract that moves mucus-trapped particles upward for elimination.

Capsule (polysaccharide capsule)

External, sticky polysaccharide layer that passively protects bacteria from phagocytosis.

Mycolic acid

Waxy cell-wall lipid of Mycobacterium species that impedes phagocytosis and antibiotic entry.

Passive defense (pathogen)

Protection afforded by structural components such as capsule or resistant cell wall.

Active defense (pathogen)

Production of extracellular proteins or toxins that actively interfere with host defenses.

Hyaluronidase

Bacterial enzyme that degrades hyaluronic acid, promoting tissue penetration and spread.

Collagenase

Clostridial enzyme that breaks down collagen, aiding invasion (notably in gas gangrene).

Coagulase

Staphylococcal enzyme that triggers fibrin clot formation, shielding bacteria from immune cells.

Streptokinase

Streptococcal enzyme that dissolves fibrin clots, facilitating bacterial dissemination.

Hemolysin

Cytolytic exotoxin that lyses red blood cells; visible as blood-agar hemolysis.

Leukocidin

Exotoxin that destroys white blood cells, weakening host immunity (e.g., Panton-Valentine leucocidin).

Exotoxin

Heat-labile protein toxin secreted by living Gram(+) or Gram(−) bacteria.

A-B toxin

Two-component exotoxin with B subunit that binds host cell and A subunit that exerts toxic activity.

Cytolytic toxin

Exotoxin that disrupts host cell membranes, leading to cell lysis.

Superantigen

Exotoxin that non-specifically activates large numbers of T-cells, provoking massive cytokine release.

Enterotoxin

Exotoxin targeting the small intestine, causing fluid secretion, vomiting and diarrhea.

Endotoxin

Toxic lipid A component of LPS released from Gram(−) bacteria upon cell lysis.

Lipid A

The biologically active, toxic portion of Gram-negative lipopolysaccharide.

O-polysaccharide

Hydrophilic LPS component making endotoxin soluble and immunogenic.

Tetanus toxin

Clostridium tetani A-B neurotoxin causing irreversible muscle contraction (spastic paralysis).

Botulinum toxin

Clostridium botulinum A-B neurotoxin blocking acetylcholine release, leading to flaccid paralysis.

Diphtheria toxin

Corynebacterium diphtheriae A-B toxin that inactivates elongation factor-2 and halts host protein synthesis.

Toxic shock syndrome toxin-1 (TSST-1)

Staphylococcus aureus superantigen causing systemic inflammation and shock, classically linked to tampon use.

Scalded-skin syndrome

Staphylococcal disease where exfoliative toxin causes epidermal cleavage and widespread blistering.

Ritter’s disease

Neonatal form of scalded-skin syndrome with generalized erythema and skin peeling.

Septicaemia

Serious bloodstream infection accompanied by systemic inflammatory response and organ involvement.

Gangrene

Necrosis of tissue (often limbs) due to loss of blood supply and infection, may follow overwhelming sepsis.

Pustular impetigo

Superficial skin infection marked by pus-filled lesions, commonly caused by phage group II staphylococci.

Carbuncle

Deep staphylococcal infection involving multiple adjacent hair follicles, producing a large abscess.

Furuncle

Boil; acute, localized staphylococcal infection of a single hair follicle.

Folliculitis

Inflammation of hair follicles, often due to S. aureus infection.

Toxemia

Presence of toxins in the bloodstream resulting in systemic effects.

Innate resistance

Nonspecific host defenses (physical, chemical, cellular) that inhibit pathogen invasion.

Compromised host

Individual with weakened defenses, increasing susceptibility to opportunistic infections.

Sebaceous gland

Skin gland secreting fatty and lactic acids that lower pH and inhibit microbes.

Lysozyme

Antibacterial enzyme in tears, saliva and other secretions that degrades peptidoglycan.

β-lysins

Bactericidal proteins in blood that disrupt bacterial cytoplasmic membranes.

Acute-phase cytokines

Host mediators (e.g., IL-1, TNF-α) released in response to endotoxin, producing fever and inflammation.

Disseminated intravascular coagulation (DIC)

Widespread clotting triggered by high endotoxin levels, leading to hemorrhage and organ failure.

SNARE proteins

Synaptic vesicle fusion proteins cleaved by botulinum neurotoxin to block neurotransmitter release.

Phagocytosis

Engulfment and intracellular destruction of microbes by host phagocytes.

Methanogens

Methane-producing Archaea, recently implicated indirectly in certain human diseases.

Endodontic infections

Root-canal infections where methanogenic Archaea have been detected as potential contributors.

Nosocomial infection

Hospital-acquired infection, often affecting compromised patients.

M cells

Specialized intestinal epithelial cells that transport antigens; targets for invasion by Salmonella and Shigella.

Lipoteichoic acid

Streptococcus pyogenes adhesin that mediates attachment to epithelial cells.

F protein (Streptococcus pyogenes)

Surface protein that enhances adherence of S. pyogenes to host tissues.

Balanced pathogenicity

Evolutionarily moderated virulence enabling pathogen survival without killing its host population.

Portal of entry: skin

External body surface; breaches like cuts or hair follicles allow pathogen invasion.

Portal of entry: mucous membrane

Internal linings (respiratory, gastrointestinal, genitourinary, conjunctiva) directly exposed to environment.

Portal of entry: parenteral

Injection-like routes bypassing mucosa, including wounds, insect bites and medical procedures.

Archaea

Third domain of life; once thought non-pathogenic, now associated indirectly with certain diseases.

Mucous membranes

Moist epithelial linings that act as common portals for microbial entry.

IgA

Immunoglobulin predominant in mucosal secretions, contributing to local immunity.

IgG

Major serum immunoglobulin capable of opsonizing pathogens and neutralizing toxins.

Balanced pathogenicity

Principle that pathogen virulence evolves toward a level allowing both host and pathogen survival.