Microbial Pathogenesis Virulence Flashcards
What is microbial virulence?
The ability of a microorganism to cause disease by overcoming host defenses.
What factors determine whether an infection causes disease?
Infectious dose, route of transmission, and host immunity.
Why is LD50 measured?
It quantifies the lethal dose required to kill 50% of a test population, helping to assess microbial virulence.
What are bacterial virulence factors?
Capsules, adhesins, enzymes, modulins, exotoxins, endotoxins, and mechanisms to evade the immune system.
What is the difference between exotoxins and endotoxins?
Exotoxins: Secreted proteins, highly potent, specific targets.
Endotoxins: Part of Gram-negative LPS, released upon bacterial death, causing systemic effects.
Higher virulence often reduces
transmissibility due to rapid host death.
Iron is essential for bacterial survival; many pathogens secrete
siderophores to scavenge iron.
Capsules help bacteria evade phagocytosis by
immune cells.
Quorum sensing allows bacteria to
coordinate gene expression collectively.
Myxoma virus in European rabbits caused
nearly 99% mortality upon introduction.
All microorganisms are pathogenic.
False
Siderophores help bacteria acquire iron from the host.
True
Virulence and transmissibility are always directly proportional.
False – High virulence can reduce transmissibility.
Botulism and tetanus are caused by bacterial exotoxins.
True
The term used to describe bacteria coordinating their behavior through chemical signals is ______________.
Quorum sensing
The ability of a microorganism to evade or overcome host defenses is called ______________.
Virulence
The ______________ is a key virulence factor that helps bacteria avoid phagocytosis.
Capsule
Gram-negative bacteria release ______________ upon cell death, which can trigger strong immune responses.
Endotoxins/LPS
Which of the following is NOT a bacterial virulence factor?
a) Capsule
b) Siderophores
c) Quorum sensing
d) Ribosomes
Answer: (d) Ribosomes
Which of the following diseases is caused by a bacterial toxin?
a) Malaria
b) Tetanus
c) Influenza
d) Tuberculosis
Answer: (b) Tetanus
What is the primary reason bacteria require iron?
a) Energy production
b) DNA replication
c) Membrane formation
d) None of the above
Answer: (a) Energy production
A patient presents with severe muscle spasms after stepping on a rusty nail. What is the likely pathogen and the mechanism of disease?
Clostridium tetani produces tetanospasmin, an exotoxin that inhibits neurotransmitter release, leading to muscle paralysis.
An outbreak of cholera occurs in a region with contaminated water. How does Vibrio cholerae cause disease?
It secretes cholera toxin, an exotoxin that disrupts ion transport in the intestines, leading to severe diarrhea and dehydration.
A rabbit population is introduced to a new area and declines sharply due to myxoma virus infection. What factors contributed to its high mortality?
High virulence, vector-borne transmission via fleas and mosquitoes, and lack of host immunity led to high mortality.
Pathogenicity:
The ability of a microorganism to cause disease.
Virulence:
The degree of pathogenicity of a microorganism.
Siderophores:
Molecules secreted by bacteria to bind and acquire iron from the host.
Exotoxins:
Secreted toxins that cause damage to host cells.
Endotoxins:
Lipopolysaccharides (LPS) from Gram-negative bacteria that trigger strong immune responses.
