Pathogenicity and Virulence Factors Flashcards
What is the definition of “Pathogen”?
An organism that, by its actions, causes harm to its host
What is the definition of “Commensal”?
A commensal organism benefits from the interaction with the host and the host neither benefits nor is harmed (a very broad term)
What is the definition of “Opportunistic Pathogen”?
An organism that can cause disease in its host given the right set of circumstances but is otherwise a commensal
What is the definition of “Zoonotic Pathogen”?
An organism with an animal reservoir (either as a pathogen or commensal) that can be transmitted to and cause disease in humans
What are the two outcomes of disease progression?
- Asymptomatic carriage
>No symptoms of disease shown - Disease developed
>Death
>Or resolution of infection and recovery
What are the 2 classes of virulence factors and examples?
- For colonizing host
>E.g. adhesions, invasions (penetrate through epithelium), nutrient acquisition, motility and chemotaxis (can swim and detect chemical agents) - That damage host
>Exotoxins, endotoxins, proteases, DNase, Lipase, Hemolysins (these 4 degrade tissues as nutrient source for themselves)
What is the role of host defences from pathogens?
Host defence push pathogens to be more asymptomatic (suppressed by immune system) or recovered from disease
What are the 5 host defences for humans?
- Physical barriers
>Skin, gut epithelium, prevent bacteria from getting to more nutrients - Complement
>Secretion of complement, complement cascade. - Macrophages
- Antimicrobial peptides
>Lyse membranes - Adaptive immunity
>B cells and T cells response.
What is the purpose of Koch’s Postulates?
4 criteria that must be met in order to identify the etiological agent of a disease (Meet these 4 criteria to show if a pathogen causes the disease).
What are the 4 of Koch’s Postulates?
- The microorganism must be found in abundance in all organisms suffering from the disease but not in healthy organisms.
- The microorganism must be isolated from a diseased organism and grown in pure culture.
- The cultured microorganism should cause disease when introduced into a healthy organism and should cause the same disease.
- The microorganism must be re-isolated from the diseased experimental host and identified as being identical to the original causative agent.
(the organism must be detected in association with disease, cultured in the lab, reproduce the disease in some kind of model organism and then be reisolated from that experimental infection)
What are 4 reasons for Koch’s Postulates being unable to work and an example for each?
- When the pathogenic organism secretes something that causes disease symptoms – so the organism itself doesn’t need to be present to see disease. So pathogen cannot be isolated from the infected host as it is not there.
>Heat stable toxins from E.coli, food poisoning for a day. - When the organism cannot be grown in pure culture – usually because of complex or completely unknown nutritional requirements.
>E.g. Chlamydia, leprosy, syphilis - When growth in the lab leads to loss of virulence – so disease cannot be recapitulated in a model organism. When re-infecting a new host it doesn’t get sick due to loss of virulence.
>E.g. Puumala virus cultured in vivo cells can no longer infect bank voles - When no animal model is available so in the absence of human experimentation, disease cannot be reproduced in the lab.
>E.g. Leprosy, the bacteria causing this only infects humans and a specific armadillo, so trying to infect mice for an experiment wouldn’t cause infection. (most common issue)
What is the effect of the same pathogen infecting different parts of the body?
The same pathogen can infect different tissues and cause different symptoms (Pathogens damaging different body sites will cause different diseases and symptoms. ).
What are 5 characteristics of strict (professional) pathogens?
- Always cause disease on injection.
- highly adapted organisms for which the pathogenic lifestyle is their main or only option
- often can’t survive outside of the host often have nutritional requirements that can only be satisfied through pathogenesis (known as obligate pathogen)
- often access a unique niche in the host with little competition from other microorganisms
- usually transmit very efficiently between hosts
some are so adapted to the in-host lifestyle that their genome has reduced in size to the point that they can’t live independently
What are 5 examples of strict (professional) pathogens?
- Helicobacter pylori – live in the stomach, cause stomach ulcers and cancer, has no competitors due to low pH of stomach, causes acid reflux.
- Neisseria gonorrhoeae – sexually transmitted infection of the genitourinary tract
- Shigella dysenteriae – causes dysentery (diarriah), gut Infection
- Mycobacterium tuberculosis – TB, lung (mostly) and some systemic infections, most common pathogen on planet.
- Chlamydia trachomatis – intracellular sexually transmitted infection, genitourinary tract, eyes, lungs, etc. Obligate pathogen.
What are 3 characteristics of opportunistic pathogens?
- only cause disease when host defences are compromised in some way
- when not being a pathogen, they live in the environment or exist as commensals (in soils or water or in hosts)
- often not efficiently spread between hosts (due to less evolutionary pressure as professional pathogens) but there are exceptions
