Flashcards in GENERAL Deck (62)
Describe the 5 steps of Koch's postulates
1. The microorganism is present in every case of the disease but absent from healthy organism
2. The suspected organism must be isolated and grown in a pure culture
3. The same disease must result when the isolated microorganism is inoculated into a healthy host
4. The same microorganism must be isolated again from the diseased host
5. The antibody to the organism should be detected in the patient's serum
What does endogenous mean?
Associated with the body
What is the term used to describe bacteria associated with the body
What does exogenous mean?
Associated with the environment
What is the relationship between the bacteria and host if the host does not gain from the association with the bacteria, but is also unharmed, while the bacteria gains advantage?
What is the relationship between the bacteria and host if they both gain mutual value? Explain how this happens
Organism can produce nutrients or vitamins that can degrade harmful chemicals. Idea of colonisation resistance where endogenous microbial population confer protection against exogenous pathogens
Describe a parasitic relationship between bacteria and host
Host is harmed but parasite gains
A microbe that is capable of causing host damage, includes classical pathogens and opportunistic pathogens, and damage produced directly or via the host immune response.
Pathogenicity refers to the capacity to cause disease or damage
Virulence refers to the capacity of a microbe to cause damage to the host. It is related to an organism's toxigenic potential and invasiveness.
What is LD50?
The lethal dose required to kill 50% of the host
What is ID50?
The infectious dose required to infect 50% of the hosts.
Define virulence factor
A component of a pathogen that enhances its pathogenicity, helping it to damage the host.
List the 5 steps of molecular koch's postulates
- A virulence trait should be strongly associated with pathogenic strains of the species
- Inactivation of the gene(s) associated with the virulence trait should decrease pathogenicity
- Restoration of an inactivated/mutant gene with the wild type restores pathogenicity
- The gene is expressed at some point during infection
- Antibodies directed against the gene product protects the host
List 2 limitations of koch's postulates.
1. Organism cannot be cultured/isolated - obligate intracellular organisms
2. Unethical to inoculate a human with the pathogen - no model organisms to inoculate since organism is a human pathogen
What is an obligate pathogen?
Bacteria that must cause disease in order to be transmitted from one host to another. Bacteria must also infect a host in order to survive as it is incapable of surviving outside of host.
What is an opportunistic pathogen?
Bacteria that do not have to cause disease for transmission i.e. can be transmitted from one host to another without having to cause disease. However, in a host whose immune system is not functioning properly, the bacteria can cause an infection that leads to a disease.
What are accidental pathogens?
Pathogens whose transmission are prevented or hindered by disease. They can be part of normal flora but not transmitted as a result of disease.
Give an example of an obligate pathogen
Give an example of an opportunistic pathogen
Give an example of an accidental pathogen
A biofilm of bacteria that grows on surfaces within the mouth, such as the tooth surface.
List 3 main components of dental plaque
1. Living and dead bacteria
2. Extra-cellular bacterial products
3. Host compounds (from gingival crevicular fluid + saliva)
Biofilm refers to an aggregation or community of bacteria that grows on surfaces, embedded within a self-produced extracellular matrix.)
How many % of bacteria causing human infections exist as biofilm?
List 3 properties of a typical biofilm
1. Spatially organized in a 3D structure
2. Bacterial cells are enclosed in extra-cellular matrix
3. Increases habitat range of individual bacteria - confers a selective advantage
What is the major non-living component of plaque?
Extracellular Polymeric Substances (EPS) / Glycocalyx
How many % of total plaque volume is the Extracellular Polymeric Substance?
What is the extracellular polymeric substance composed of?
Host products and bacterial products;
incorporates the gingival and proteins from the crevicular exudate.