Pathogenicity: the capacity of microbes to cause disease
Virulence: the degree of pathogenicity of a specific microbe
Based on:
- Invasive qualities
- Toxic qualities
- Presence of pile or fimbriae for adhesion
- Ability to avoid host defenses (mutate)
Virulence Factors and Toxins
- Enzymatic Virulence Factors Examples: Coagulase (Staphylococcus aureus), Streptokinase (Streptococcus pyogenes), Hyaluronidase (Many pathogens), Collagenase (Many pathogens), Leukocidin (Many pathogens), Hemolysin (Many pathogens)
- Adhesion Factors Examples: Protein A (Staphylococcus aureus), Protein M (Streptococcus pyogenes)
- Virulence factors help bacteria to, invade the host, cause disease, and evade host defenses.
- The following are types of virulence factors:
- Adherence Factors: Many pathogenic bacteria colonize mucosal sites by using pili (fimbriae) to adhere to cells.
- Invasion Factors: Surface components that allow the bacterium to invade host cells can be encoded on plasmids, but more often are on the chromosome.
- Capsules: Many bacteria are surrounded by capsules that protect them from opsonization and phagocytosis
- Exotoxins - A type of bacterial toxin with the following properties: May be produced by either gram-positive or gram-negative bacteria, The action of the exotoxin does not necessarily require the presence of the bacteria in the host and Most exotoxins are peptide or protein
- Most exotoxins are heat sensitive (exception: enterotoxin of Staphylococcus aureus)
- Exotoxins include several types of protein toxins and enzymes produced and/or secreted from pathogenic bacteria. Major categories include cytotoxins, neurotoxins, and enterotoxins.
Classes of exotoxins: Neurotoxic, cytotoxic, or enterotoxic exotoxins
- Neurotoxins: Interfere with proper synaptic transmissions in neurons
- Cytotoxins: Inhibit specific cellular activities, such as protein synthesis
- Enterotoxins: Interfere with water reabsorption in the large intestine; irritate the lining of the gastrointestinal tract
Endotoxins
- A type of bacterial toxin having the following properties:
- Produced only by gram-negative bacteria
- Endotoxins are a component of the gram-negative cell wall
- The action of endotoxin requires the presence of the bacteria in the host. The endotoxin may be released from the cell wall as the cells die and disintegrate
- Endotoxin is composed of Lipid A: Part of the lipopolysaccharide layer
- Mode of action: Irritation/inflammation of epithelium, GI irritation, capillary/blood vessel inflammation, hemorrhaging
- Endotoxins: The lipopolysaccharide endotoxins on Gram-negative bacteria cause fever, changes in blood pressure, inflammation, lethal shock, and many other toxic events.
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