MICR 2123 Exam 4 Study Guide: Chapters 23-27

Pathogen

A microbe that causes disease.

Commensal organisms

Normal microbes that live in/on us without causing harm.

Human microbiome

Collection of microbes living in and on the human body.

Most hospitable body sites

Intestines, skin, mouth.

Skin barriers

Dry, salty, acidic, sebum production.

P. acnes

Linked to acne.

S. mutans

Causes tooth decay.

Mucociliary escalator

Clears mucus and microbes from the lungs using cilia.

H. pylori

Causes stomach ulcers.

Gut microbiota factors

Diet, antibiotics, illness.

Dysbiosis

Imbalance in microbial communities.

Probiotics

Live bacteria that benefit gut health.

Fecal transplant

Transfer of stool to restore gut microbiota.

PAMPs (pathogen-associated molecular patterns)

Recognized by immune system.

PRRs (pattern recognition receptors)

Detect PAMPs (e.g., TLRs, NLRs).

Phagocytosis

Process by which immune cells (like macrophages) engulf and destroy microbes.

Cytokines

Signaling molecules for immune communication.

Complement system

C3b → MAC formation → kills Gram-negative bacteria.

Humoral immunity

Involves B cells and antibody production.

Cell-mediated immunity

Involves T cells.

Lymphocytes

B cells & T cells.

Lymphoid organs

Primary: Bone marrow, thymus; Secondary: Lymph nodes, spleen.

Antigen

Foreign molecule recognized by immune system.

Epitope

Specific part of an antigen recognized by an antibody.

Antibody structure

2 heavy + 2 light chains, variable & constant regions.

Antibody diversity

Created by genetic recombination (V(D)J).

B cell activation

Needs T cell help (for T-dependent antigens).

Plasma cells

Produce antibodies.

Memory B cells

Provide faster, stronger secondary response.

MHC

Presents antigen to T cells.

TCR (T-cell receptor)

Binds MHC-antigen complex.

Helper T cells (CD4)

Activate B cells.

Cytotoxic T cells (CD8)

Kill infected cells.

T cell education

Occurs in thymus (eliminate self-reactive cells).

Superantigens

Overactivate T cells → dangerous inflammation.

Vaccines

Stimulate adaptive immunity.

Herd immunity

Protection when most of population is immune.

Autoimmunity

Immune system attacks self.

Molecular mimicry

Can cause autoimmunity (e.g., M protein & rheumatic fever).

Parasite

Organism living at host's expense (e.g., worms, protozoa).

Endoparasite

Lives inside host (e.g., tapeworm).

Ectoparasite

Lives on surface (e.g., lice).

Primary pathogen

Causes disease in healthy host.

Opportunistic pathogen

Infects only immunocompromised hosts.

Pathogenicity

Ability to cause disease.

Virulence

Degree of pathogenicity (measured by LD50 or ID50).

Reservoir

Natural host of a pathogen.

Vector

Transmits pathogen (e.g., mosquito for malaria).

Transmission types

Vertical: Parent → offspring; Horizontal: Person → person; Accidental: From other species.

Virulence factors

Traits that help cause disease (e.g., toxins, pili).

Adhesins

Allow microbes to attach to host cells.

Type I pili

Static.

Type IV pili

Dynamic (extend & retract).

Exotoxins

Secreted (e.g., cholera, diphtheria toxins).

Endotoxins

LPS from Gram-negative bacteria.

Secretion systems

Type II: Cholera toxin; Type III: Injects toxins (e.g., Salmonella); Type IV: DNA/protein transfer (e.g., Agrobacterium).

Intracellular pathogens

Obligate: Must live inside cells; Facultative: Can live inside or outside.

Immune evasion

Escape phagosome; Inhibit phagolysosome fusion; Survive inside phagolysosome; Inhibit antigen presentation.

Antibiotic

Chemical that kills or inhibits bacteria.

Spectrum of activity

Broad vs. narrow range of bacteria targeted.

MIC (Minimum Inhibitory Concentration)

Lowest dose that stops growth.

Kirby-Bauer test

Uses disks to measure antibiotic sensitivity.

Antibiotic targets

Cell wall (β-lactams); Cell membrane; DNA/RNA synthesis; Protein synthesis.

β-lactams

Target cell wall (e.g., penicillin, cephalosporins).

Bactericidal vs. bacteriostatic

Cidal = kill; Static = stop growth.

Resistance mechanisms

Destruction/modification of antibiotic; Efflux pumps; Target modification.

Persister cells

Dormant, tolerant (not resistant).

Fungal infections

Harder to treat due to eukaryotic similarity to host cells.