Lecture 3: Bacterial Pathogenesis Flashcards
What are the types of Pathogenic Microbes?
- Bacteria
- Fungi (yeasts and molds)
- Parasites
- Viruses
- Sub-viral agents (eg. prions)
What is Koch’s Postulates?
• Scientific basis for establishing cause and effect relationships between an organism and a disease.
What are the benefits of Koch’s Postulates?
- Act as a guide for determining the cause of a disease caused by an unknown infectious agent.
What is the First Postulate and exception?
• Microbe must always be associated with the lesions of the disease
Exception: Asymptomatic carriage
What is the Second Postulate and exceptions?
• Microbe must be isolated from lesions of disease and in pure culture
Exception: Some pathogen can not be grown in artificial culture and need other microorganisms to grow
Viruses.
What is the Third Postulate and exceptions?
• Pure culture of the microbe should produce the disease when inoculated into a human or animal
Exception:
-experimentation can be unethical (humans)
-Not all organisms exposed to an infectious agent will acquire the infection.
What is the Fourth Postulate and exceptions?
• Microbe must be re-isolated from the infected human or animal
Exception: problem for organisms that cannot be isolated in artificial culture media.
Whats is Koch’s possible Fifth Postulate and exception?
Therapeutic or preventative measures aimed at the microbe should control or eliminate the disease
Exception: There are no known cures for many infections.
Define Pathogenicity?
The ability to cause disease.
Define infection and cardinal signs?
invasion by pathogenic organisms resulting in a host response, usually inflammation
- Redness
- Swelling
- Pain
- Loss of function - Heat
Define Endogenous infection?
Infection by member of the normal flora.
Define Exogenous infection?
Infection by an organism that is not a member of the normal flora.
Define Local infection?
An infection restricted to a confined area.
Define Focal infection?
A localised site of infection from which pathogens and/or their products are disseminated to other parts of the body.
Define Systemic infection?
An infection spread throughout the body.
Define Primary Infection?
Initial infection caused by one pathogen.
Define Secondary Infection?
Infection that follows a primary infection as a complication.
Define Latent Infection?
Dormant infection that flares at a later date.
Define Acute Infections
Rapid in onset and often more severe.
Define Chronic Infection
Slow, progressive infection.
Define Disease
– Any deviation from or interruption of the normal structure or function of any body part, organ, or system.
Define Infectious Disease?
A disease caused by pathogenic microorganisms that causes significant overt damage to the host.
What does infection imply?
colonisation multiplication invasion persistence (symptom being inflammation).
Define Virulence?
Is the degree of pathogenicity.
Pathogen that has a single determinant of virulence?
Clostridium tetani
Example of pathogens that have a large repertoire of virulence factors?
Staphylococcus aureus
Streptococcus pyogenes
Define ID50 (infectious dose 50)?
Is the number of bacteria necessary to infect 50% of the population of animals exposed to the pathogen.
Define LD50 (lethal dose 50)?
Is the number of bacteria necessary to kill 50% of the population of animals exposed to the pathogen.
Microbes that rarely form disease?
Commensals.
Name and define the different Pathogen types?
Opportunistic pathogens
Infection by an organism that ordinarily doesn’t cause disease but becomes pathogenic under certain
circumstances (i.e. if an organism gains entry to a sterile site).
Obligate pathogens
-always cause disease in order to be transferred from one host to another and infect the host to survive.
Overt pathogens
-an organism that is ALWAYS regarded as being pathogenic.