Pathogens and Pathogenesis – General View

Vocabulary flashcards summarizing fundamental terms, factors, and examples related to microbial pathogens and the mechanisms of pathogenesis, as presented in 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 in which a pathogen lives and potentially causes disease.

Pathogenicity

The ability of a pathogen to cause disease.

Virulence

The degree or extent of pathogenicity; often reflected by the number of microbial cells required to cause disease.

True Pathogen

A microbe that readily overcomes host defenses to cause disease (e.g., Vibrio cholerae, Yersinia pestis).

Opportunistic Pathogen

Normally commensal microbe that causes disease when host defenses are impaired (e.g., Staphylococcus spp., Pseudomonas aeruginosa).

Microbiota

The total collection of microbes (internal and external) inhabiting the human body.

Microbiome

The collective genomes of the microbiota.

Gnotobiology

The study of organisms raised in germ-free or defined-microbe conditions to understand host–microbe interactions.

Symbiosis

A mutually beneficial association between two different organisms.

Commensalism

A relationship in which one organism benefits while the other is neither helped nor harmed.

Parasitism

An association where the parasite benefits at the host’s expense, often causing harm.

Balanced Pathogenicity

Evolutionary concept that successful pathogens limit host damage to ensure their own survival and transmission.

Attenuation

Loss or reduction of virulence during prolonged culture; basis of many live vaccines.

Portal of Entry

Site through which a pathogen enters the host (skin, mucous membranes, parenteral route).

Parenteral Route

Entry via breaks in skin—needles, wounds, insect bites—bypassing mucous membranes.

Portal of Exit

Route by which pathogens leave the host, commonly via secretions, blood, urine, or feces.

Infection

Colonization and growth of a pathogen within a host.

Disease

Dysfunctional state of the body resulting from infection or other causes.

Incubation Period

Time between infection and onset of disease symptoms.

Acute Period

Phase of maximal disease severity with pronounced clinical signs.

Convalescence

Recovery phase during which the host returns to normal health.

Biofilm

Structured microbial community encased in a self-produced polymeric matrix attached to surfaces; aids persistence and colonization.

Adhesin

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

Polysaccharide Capsule

Extracellular coating that passively inhibits phagocytosis and increases virulence (e.g., Streptococcus pneumoniae).

Hyaluronidase

Extracellular enzyme that degrades hyaluronic acid, enhancing microbial spread through tissues.

Collagenase

Enzyme (e.g., from Clostridium perfringens) that breaks down collagen, promoting tissue invasion.

Coagulase

Staphylococcal enzyme that triggers clot formation around bacteria, shielding them from immune attack.

Streptokinase

Streptococcal enzyme that dissolves fibrin clots, facilitating bacterial dissemination.

Leukocidin

Toxin that destroys white blood cells, weakening host immune response (e.g., Panton-Valentine leucocidin).

Hemolysin

Cytolytic toxin that lyses red blood cells and other host cells.

Exotoxin

Protein toxin secreted by living Gram(+) or Gram(−) bacteria; includes cytolytic toxins, A-B toxins, and superantigens.

A-B Toxin

Two-component exotoxin with B (binding) and A (active) subunits; example: diphtheria toxin.

Cytolytic Toxin

Exotoxin that disrupts host cell membranes, leading to lysis (e.g., α-toxin of C. perfringens).

Superantigen

Exotoxin that nonspecifically activates large numbers of T-cells, causing massive cytokine release (e.g., TSST-1).

Enterotoxin

Exotoxin acting on the small intestine, causing fluid secretion, vomiting, and diarrhea (e.g., cholera toxin, staphylococcal enterotoxins).

Endotoxin

Lipid A component of Gram(−) LPS released on cell lysis; triggers fever, inflammation, shock.

Lipid A

Toxic moiety of lipopolysaccharide responsible for endotoxin effects.

Botulinum Toxin

A-B neurotoxin from Clostridium botulinum that blocks acetylcholine release, causing flaccid paralysis.

Diphtheria Toxin

A-B toxin from Corynebacterium diphtheriae that inactivates EF-2, halting host protein synthesis.

TSST-1

Toxic shock syndrome toxin-1, a staphylococcal superantigen causing systemic inflammation and shock.

Scalded-Skin Syndrome

Illness caused by staphylococcal exfoliative toxin leading to epidermal separation and widespread skin peeling.

Sepsis

Life-threatening systemic response to infection, often with circulating bacteria (bacteremia) and endotoxin.

Nosocomial Infection

Hospital-acquired infection, frequently affecting compromised hosts.

Innate Resistance

Non-specific physical and chemical barriers (skin, low pH, lysozyme, mucociliary escalator) that prevent pathogen invasion.

Mucociliary Escalator

Ciliated epithelium of respiratory tract that moves mucus-trapped microbes upward for removal.

Normal Flora

Resident microbes that typically do not cause disease and may inhibit pathogen colonization.

Methanogen

Archaeal microbe producing methane; emerging evidence links some species to human disease.

Archaea as Pathogens

Concept recognizing certain archaea (e.g., methanogens) as potential contributors to human infections.

Epidemiology

Study of disease occurrence, distribution, and control within populations.

Attenuated Vaccine

Immunization using live pathogens with reduced virulence to elicit protective immunity.