Microbial Mechanisms of Pathogenicity and Host Defenses

Comprehensive vocabulary flashcards covering microbial mechanisms of pathogenicity, bacterial toxins, innate and adaptive immunity, the complement cascade, and antibody classes.

Pathogenicity

The ability of a microorganism to cause disease.

Virulence

The degree of pathogenicity possessed by a microbe.

Parenteral route

A portal of entry where microorganisms are deposited directly into tissues when protective barriers are penetrated through injections, bites, wounds, cuts, or surgery.

ID50

The infectious dose required to cause infection in 50% of a sample population; used to measure the virulence of a microbe.

LD50

The lethal dose for 50% of a sample population; used to measure the potency of a toxin.

Adhesins (ligands)

Surface molecules on a pathogen—such as glycocalyx, fimbriae, or viral spikes—used to attach to host cell receptors.

M protein

A heat- and acid-resistant cell wall protein in Streptococcus pyogenes that impairs phagocytosis by acting as an invisibility cloak against the immune system.

OPA protein

An outer membrane protein in Neisseria gonorrhoeae that facilitates host cell attachment and inhibits T cell activation.

Mycolic acid (waxy lipid)

A cell wall component of Mycobacterium tuberculosis that resists digestion by phagocytes.

Coagulases

Bacterial enzymes that coagulate fibrinogen into fibrin, forming blood clots that shield bacteria from host immune defenses.

Kinases

Bacterial enzymes that digest and break down fibrin clots.

Hyaluronidase

A bacterial enzyme that digests hyaluronic acid, which holds host cells together, facilitating bacterial spread.

Collagenase

An enzyme produced by pathogens that breaks down collagen fibers, separating host connective tissues.

IgA proteases

Enzymes produced by certain pathogens that destroy host IgA antibodies.

Antigenic Variation

The process by which pathogens alter their surface antigens to evade recognition by pre-existing host antibodies.

Invasins

Surface proteins produced by microbes that rearrange actin filaments of the host cytoskeleton to induce membrane ruffling for entry.

Siderophores

Proteins secreted by pathogens that bind tightly to host iron, directly competing with and scavenging iron from host iron-binding proteins.

Toxigenicity

The capacity of a microorganism to produce toxins.

Toxemia

The presence of toxins in the host bloodstream.

Intoxication

A condition caused by the ingestion or presence of a specific toxin, independent of active microbial growth.

Exotoxins

Soluble proteins produced inside pathogenic bacteria (both Gram-positive and Gram-negative) and secreted into the surrounding medium.

Toxoids

Inactivated exotoxins that are no longer toxic but can stimulate antibody formation; commonly used in vaccines.

A-B toxins

Bacterial exotoxins consisting of two parts: an active enzyme component (A part) that damages host cells, and a binding component (B part) that attaches to the host cell receptor.

Genotoxins

A type of A-B toxin that damages host DNA, inducing mutations, disrupting cell division, and potentially causing cancer.

Leukocidins

Membrane-disrupting exotoxins that kill phagocytic leukocytes by forming pores in their plasma membranes.

Hemolysins

Membrane-disrupting exotoxins that destroy erythrocytes (red blood cells) by creating protein channels in cell membranes.

Superantigens

Bacterial toxins that provoke an intense, non-specific immune response by triggering massive cytokine release from T cells.

Lipid A

The lipid portion of lipopolysaccharides (LPS) found in the outer membrane of Gram-negative bacteria that acts as an endotoxin causing fever.

Ergot

An alkaloid fungal toxin that causes hallucinations and convulsions.

Alfatoxins

Carcinogenic genotoxins produced by Aspergillus fungi that damage DNA and cause mutations.

Innate immunity

Non-specific host defenses present from birth that provide rapid protection against any pathogen.

Adaptive immunity

Targeted host defenses against a specific pathogen characterized by a slower initial response and long-term immunological memory.

Toll-like receptors (TLRs)

Receptors located on host defense cells that attach to pathogen-associated molecular patterns (PAMPs) and trigger the release of defensive cytokines.

PAMPs (Pathogen-associated molecular patterns)

Conserved molecular structures associated specifically with microorganisms that are recognized by host immune receptors.

Margination

The sticking of phagocytes to the endothelial lining of blood vessels during the early stages of inflammation.

Diapedesis

The emigration process where phagocytes squeeze between endothelial cells of capillary walls to reach damaged tissues.

Membrane attack complex (MAC)

A complex assembled from complement proteins (triggered by C3b) that punches circular channels or pores into pathogen plasma membranes, causing cytolysis.

Opsonization

The immune coating of a pathogen with complement fragments (such as C3b) or antibodies to enhance phagocytic attachment and ingestion.

Interferons (IFNs)

Host defense cytokines with antiviral activity that interfere with viral multiplication in adjacent cells.

Transferrin

An iron-binding transport protein found primarily in human blood and tissue fluids that restricts iron availability to microbes.

Class I MHC

Cell-surface proteins located on all nucleated human cells that identify the cell as self to the immune system.

Class II MHC

Cell-surface proteins found specifically on antigen-presenting cells (APCs) that present processed antigenic fragments to helper T cells.

Chemokines

A group of cytokines that induce directed chemotaxis (migration) of leukocytes to areas of infection or tissue damage.

IgM

The first class of antibody produced in response to an initial infection; highly effective at agglutinating antigens.

IgG

The predominant antibody class in serum that enhances phagocytosis, neutralizes bacterial toxins and viruses, and crosses the placenta.

IgA

The primary antibody class that provides localized protection on mucosal surfaces, saliva, tears, and breast milk.

IgE

The antibody class that binds to mast cells and basophils, mediating allergic reactions and defense against parasitic worms.