Pathogenicity & Virulence Flashcards
What is a pathogen?
A bacterium, virus or other microorganism that can cause disease
What is a primary pathogen?
Can cause disease in a host regardless of the host’s resident microbiota or immune system
What is an opportunistic pathogen?
Can only cause disease in situations that compromise the host defences
Give an example of host difences?
Body barriers , immune system or normal microbiota
What is pathogenicity?
The ability of an organism to cause disease
An organism is either pathogenic or isn’t
What is virulence?
The degree of intensity of damage caused by the organism
A measurement of pathogenicity
What is avirulent?
Not harmful
Mild infection no severe
Fever, headaches
What is highly virulent?
Almost always lead to disease state
Multi-organ and body system failure
What affects virulence?
How well it adheres to host cells
Its ability to colonise the host
Its ability to invade host tissues
The arsnal of virulence factors
Are highly virulent pathogens gram positive?
Yes
What are the symptoms of the highly virulent Bacillus anthracis?
High fever, difficulty breathing, vomiting, couching up blood, severe chest pains
How can virulence be measured?
Through tests on animals
What is median infection dose (IDSD)?
Number of pathogenic cells required to cause active infection in 50% of innoculated animals
What is median lethal dose (LDSD)?
Number of pathogen cells (or amount of toxin) requires to kill 50% of infected animals
What is on the X axis of a pathogenicity graph?
The number of pathogenic agents (cells or virons)
What is the Y axis of a pathogenicity graph?
The percentage morality in experimental group
What does a pathogenicity graph show?
The percentage of aimals that have been infected (IDSD) or killed (LDSD) is plotted against the concentration of pathogen inoculate
How can virulence change?
Attenuation
What is attenuation?
The loss or decrease in virulence of a pathogen
When kepts in a lab culture vs isolated from diseased animal
Do weakly virulent strains grow more quickly?
Yes
Why is it important to know which pathogen is responsible for an infection?
Prescribe effective treatments
Eradicate the infection
Accurate records for infection control
Prevent further infections
Who is Robert Koch?
founder of modern bacteriology
Invented the concept of infectious disease
How do we know that a specific pathogen is responsible for an infection?
Each of Koch’s postulates represents a criterion that must be met before a disease can be positively linked with a pathogen
What is number 1 of Kochs postulates?
The suspected causative agent must be absent from all healthy organisms but present in all diseased organisms
What is number 2 of Kochs postualtes?
The causative agent must be isolated from the diseased organism ans grown in pure culture
What is munber 3 of Kochs postulates?
The cultured agent must cause the same disease when inoculated into a healthy, susceptible organism
What is number 4 of Kochs postulates?
The same causative agent must then be reisolated from the inoculated, diseased organism
What are the limitations of Kochs number 1 postuate?
Assumes that pathogens are only found in diseased, not healthy individuals
Not absent from from healthy cells
What are the limitations of Kochs number 2 postuate?
Not all pathogens can be grown in pure culture
Only grow when inside a host cell, postulate 2 not met
What are the limitations of Kochs number 3 postuate?
Many human infections cannot be replicated in animal hosts
Do not cause infection
Cannot meet postulate 3
