Biological Agents as Causes of Disease Flashcards
Define pathogen
A disease-causing organism
Types of pathogens
- obligate
- facultative
- opportunistic
What is an obligate pathogen?
A pathogen that only survives in its host
What is a facultative pathogen?
A pathogen that is present in the environment, waiting for a host
What is an opportunistic pathogen?
A pathogen that is normally benign but causes disease in a compromised host
Why do pathogens make us sick?
- The symptoms of the disease usually help spread the pathogen
- Side effect of pathogen killing cells in order to replicate
Examples of diseases that bacteria cause
Gonorrhoea, syphilis, food poisoning, cholera
Examples of diseases that eukaryotes cause
Athlete’s foot, malaria, thrush
Examples of disease that viruses cause
AIDS, small pox, common cold
What are virulence genes?
The few genes that are different between two closely related species. Can be pathogenic/harmless
What do fungi often show in their life cycle?
Dimorphism
Using a example, describe dimorphism in a fungi
Candida albicans
The soil form grows as a mould - tubular cells
but in a warm body, switches to the yeast morphology
After macrophages engulf them, the fungi grows “germ tube”
This projection pierces and kills the macrophage
Example of disease associated with protozoa
Malaria
What is used as a vector in malaria?
Mosquitos
Barriers to pathogens
Bacteria, Flora, Fungi which densely populate most epithelium
What are epithelial cells held together by and why?
Tight junctions so that pathogens cannot squeeze between cells
Often epithelia secrete…
…mucous
What do white blood cells do in terms of epithelia?
Quickly recognise breaks in the epithelia
Breaks in the epithelia are quickly recognised by…
White blood cells
How do some bacteria anchor themselves to epithelia?
Some bacteria have P pili and use adhesins to anchor themselves to the epithelia
Why do pathogens breach the cell membrane?
To inject toxins or to replicate inside the cell
Why might a pathogen want to inject toxins into a host cell?
To kill the cell in order to provide itself with nutrients
Killing WBCs help in evading the immune system
3 main methods pathogens use to evade the immune system
- Type III secretion system
- Assemble a pedestal
- Hide
Many bacteria have type…
…III secretion systems that act like a syringe
___ assembles an ____ to anchor them and overcome barriers
E.coli. Actin pedestal
Bacteria ___ to enter cells
Hide
What bacteria causes Legionairre’s disease?
Legionella Pneumophila
What does legionella pneumophila normally infect?
Amoeba
If inhaled, legionella pneumophila is phagocytosed by macrophages. Which cells do they replicate inside?
Macrophages, unlike most bacteria
Two other ways bacteria invade non-phagocytic cells
- attaching to cell receptors like velcro
- forcing the cell to rearrange actin structures
Listeria entering the cell
L. monocytogenes secrete hemolysin which breaks down the membranes of lysosomes
Effects the stopped by PEST amino acid sequence which tags for destruction
L. monocytogenes then replicate inside the cell
Listeria entering neighbouring cells
After replicating inside the first cell, they assemble actin tails that push them into neighbouring cells. Uses ActA
What is ActA?
A bacterial protein that is localised to the tail end and nucleates actin polymerisation at that end of the cell. Listeria uses to enter neighbouring cells
How do antibiotics stop bacterial growth?
By stopping cell process.
