Chapter 15 Microbial Mechanisms of Pathogenicity

Pathogenicity

The ability to cause disease.

Virulence

The degree of pathogenicity.

Portals of Entry

The routes through which pathogenic microorganisms enter the host, including mucous membranes, skin, and parenteral routes.

Mucous Membranes

The inner linings of organs and body systems, commonly the portal of entry for pathogens, especially in the respiratory tract.

Adherence

The process by which almost all pathogens attach to host tissues via adhesins binding to host cell receptors.

Capsule

A glycocalyx around the cell wall that impairs phagocytosis, used by pathogens like Streptococcus pneumoniae.

Exotoxins

Toxins produced and secreted by bacteria that are soluble in bodily fluids and can destroy host cells.

Endotoxins

Lipids that are part of the bacterial cell wall of gram-negative bacteria and are released when the bacteria die, causing systemic effects.

Siderophores

Proteins secreted by pathogens that bind iron more tightly than host cells to acquire this vital nutrient.

Antigenic Variation

The alteration of surface antigens by pathogens to evade the immune response.

Biofilm

A community of microorganisms that adhere to surfaces and are encased in a protective layer, increasing resistance to immune responses and antibiotics.

Invasins

Surface proteins produced by bacteria that rearrange actin filaments in the host cytoskeleton to promote bacterial engulfment.

Cytopathic Effects (CPE)

Visible effects of viral infections on a cell, which can result in either cell death or damage.

Lethal Dose 50 (LD50)

The amount of a substance that kills 50% of a test population; a measure of toxin potency.

Infectious Dose 50 (ID50)

The number of pathogens required to cause disease in 50% of a test population; a measure of virulence.

Coagulases

Enzymes that coagulate fibrinogen to form a protective barrier against phagocytosis.

Hyaluronidase

An enzyme that digests hyaluronic acid, breaking down the extracellular matrix to facilitate spread.

IgA Proteases

Enzymes that destroy IgA antibodies, evading the immune system.