10.2- Introduction to Virulence Flashcards
Define virulence factors
The way that microbes overcome our defenses.
- Features that help microbes adhere to host cells, invade host tissues, acquire nutrients, and evade immune defenses. Toxins are also included.
Classic factors: pathogen toxicity, aggressiveness, and transmission.
What are virulence factors of toxins?
Lipopolysaccharides (LPS) in gram-negative
Diverse Secreted toxins
What are virulence factors of immune system evasion features?
Diverse enzymes
Various toxins
Capsules
What are virulence factors that effect invasion?
Flagella
Various toxins
Enzymes (kinases, coagulases, etc.)
What are nutrient acquisition virulence factors?
Diverse enzymes
Iron binding proteins
What are adhesion virulence factors?
Fimbrae
Binding factors
What is the difference between virulent and attenuated pathogens?
Attenuated pathogens don’t cause disease in a competent host as they have lost their virulence factors. This happens if they are grown in a petri dish where they are not exposed to environmental factors, and also occurs when pathogens are not exposed to certain environmental factors (like a specific antibiotic) for a long period of time.
What does ID50 mean?
Infectious dose 50
This describes how many cells (bacterial, fungal, or parasitic) are needed to establish an infection in 50% of exposed susceptible hosts.
Define LD50
Describes the amount of toxin required to kill 50% of affected hosts that are not treated.
Define mortality rate
The legality of an infectious agent.
Define toxins
Molecules that generate a number of adverse affects such as tissue damage and suppressed immune response.
Define toxogenic
Used to describe microbes that produce toxins.
Define toxemia
When toxins enter the blood stream and are spread throughout the body.
What type of microbe makes most types of toxins seen in clinical scenarios?
Bacteria
What are the seven properties of endotoxins?
Made of: Lipids
Made by: Gram-negative bacteria
Released from: Gram-negative cell wall when bacteria divide or die.
Vaccines: No
Fever: Yes
Can be neutralized in patient: No
Toxicity level: Low (relatively high LD50)
What are the seven properties of exotoxins?
Made of: Proteins
Made by: Gram negative and positive bacteria
Released from: Actively growing bacteria
Vaccines: Yes (some)
Fever: Sometimes (certain superantigens)
Can be neutralized in patient: Yes (some)
Toxicity level: High (many have low LD50)
When do gram negative bacteria release most of their endotoxins?
When they die, but a small amount is released when they divide.
Do gram positive bacteria make endotoxins?
No
What is type I exotoxin’s mode of action?
Bind to target host cells using receptors on their surface. By binding to the receptors they do, they propagate a signal cascade the can alter gene expression.
I.E. Superantigens- stimulate an over-reaction of the immune response and can cause massive inflammation.
What is type II exotoxin’s mode of action?
Membrane damaging toxins effect the host cell plasma membrane by forming pores or removing phosphate head groups from the phospholipids of the lipid membrane. This destabilizes the membrane and causes cell lysis.
What is type III exotoxin’s mode of action?
They bind to a receptor and then enter the cell to exert effects.
Define solubility
Describes a substances ability to dissolve in a solvent, especially water.
