Microbial Mechanisms of Pathogenicity (Part 1)

Vocabulary practice flashcards covering entry portals, virulence factors, adherence, immune evasion mechanisms, enzymes, and bacterial toxins from Microbial Mechanisms of Pathogenicity (Part 1).

Pathogenicity

The ability of a microorganism to cause disease.

Virulence

The degree or intensity of pathogenicity.

Portals of Entry

Avenues through which pathogens gain entrance to a host, primarily consisting of mucous membranes, skin, and the parenteral route.

Parenteral Route

A portal of entry in which microorganisms are deposited directly into deeper tissues when protective skin and mucous membrane barriers are penetrated (e.g., via punctures, bites, cuts, or wounds).

Preferred Portal of Entry

The specific entry route that a particular pathogen must utilize in order to successfully establish an infection and cause disease.

$$\text{ID}_{50}$$

The infectious dose required to cause infection in $50\%$ of a sample population; serves as a quantitative measure of microbial virulence.

$$\text{LD}_{50}$$

The lethal dose of a toxin required to kill $50\%$ of a sample population; serves as a quantitative measure of toxin potency.

Bacillus anthracis $\text{ID}_{50}$

The portal-specific infectious dose of Bacillus anthracis: $10\text{ to }50\text{ endospores}$ via the skin, $10{,}000\text{ to }20{,}000\text{ endospores}$ via inhalation, and $250{,}000\text{ to }1{,}000{,}000\text{ endospores}$ via ingestion.

Botulinum Toxin Potency

A highly potent bacterial toxin with an $\text{LD}_{50}$ (or $\text{ID}_{50}$) of $0.03\,\text{ng/kg}$, exhibiting greater potency than Shiga toxin ($250\,\text{ng/kg}$), Staphylococcal enterotoxin ($1350\,\text{ng/kg}$), and Salmonella toxin ($12\,\text{mg/kg}$).

Adherence (Adhesion)

The process by which pathogens attach themselves to host tissues at their portal of entry, an essential early step in pathogenicity.

Adhesins (Ligands)

Surface molecules on a pathogen (such as components of the glycocalyx or fimbriae) that bind specifically to complementary surface receptors on target host cells.

Biofilms

Microbial communities that adhere to surfaces and share nutrients, depending crucially on cellular adherence mechanisms.

Capsules

Organized glycocalyx layers surrounding the bacterial cell wall that impair host phagocytosis; found in Streptococcus pneumoniae, Haemophilus influenzae, Bacillus anthracis, and Yersinia pestis.

M Protein

A heat- and acid-resistant cell wall component produced by Streptococcus pyogenes that mediates attachment and resists host phagocytosis.

Opa Protein

An outer membrane cell wall protein in Neisseria gonorrhoeae that mediates attachment and uptake into host cells.

Waxy Lipid (Mycolic Acid)

A cell wall component of Mycobacterium tuberculosis that resists phagocytic digestion.

Coagulases

Bacterial enzymes that clot fibrinogen in the blood, producing a fibrin barrier that shields the pathogen from host defenses.

Kinases

Bacterial enzymes that digest and dissolve fibrin clots formed by the host to isolate an infection.

Hyaluronidase

An enzyme secreted by pathogens that hydrolyzes hyaluronic acid polysaccharides that hold host tissue cells together, facilitating bacterial spread.

Collagenase

An extracellular enzyme that breaks down collagen connective tissue, promoting pathogen dissemination through tissues.

IgA Proteases

Enzymes produced by certain pathogenic microbes that selectively cleave and destroy host protective IgA antibodies.

Antigenic Variation

A strategy by which pathogens alter their surface antigens during an infection, rendering existing host antibodies ineffective.

Invasins

Surface proteins produced by bacteria that rearrange actin filaments of the host cytoskeleton, causing membrane ruffling to facilitate bacterial engulfment.

Membrane Ruffling

The disruption and wave-like folding of the host plasma membrane triggered by bacterial invasins, leading to the uptake of the bacterium.

Actin-Based Motility

The mechanism by which intracellular bacteria, such as Shigella and Listeria, hijack host cell actin filaments to propel themselves from one host cell into an adjacent cell.

Siderophores

High-affinity iron-binding proteins secreted by pathogenic bacteria that scavenge iron from the host by binding $\text{Fe}^{3+}$ more tightly than host proteins.

Enterobactin

A specific bacterial siderophore molecule that coordinates and tightly binds ferric iron ($\text{Fe}^{3+}$).

Direct Damage

Host damage caused when pathogens disrupt host cell function, consume host cell nutrients, produce waste products, and multiply intracellularly to the point of host cell rupture.

Toxins

Poisonous substances produced by microorganisms that can cause fever, cardiovascular problems, diarrhea, and shock.

Toxigenicity

The capacity or ability of a microorganism to produce toxins.

Toxemia

The clinical condition marked by the presence of toxins circulating in the host's bloodstream.

Intoxications

Diseases or pathological states caused by the ingestion or presence of a microbial toxin in the body without the requirement of active microbial growth.

Exotoxins

Soluble toxic proteins produced inside pathogenic bacteria (most commonly gram-positive bacteria) as part of their growth and metabolism, released into the surrounding medium during the log phase (e.g., Clostridium botulinum).

Endotoxins

Lipopolysaccharide (LPS) toxins located within the outer membrane of gram-negative cell walls that are liberated when bacteria die and the cell wall lyses (e.g., Salmonella typhimurium).

Lipid A

The lipid portion of lipopolysaccharide (LPS) found in the outer membrane of gram-negative bacteria that functions as an endotoxin upon release.