What are pathogens?
- Infectious organisms which spread communicable diseases.
- Includes bacteria, viruses, fungi and protoctista. The type of pathogen determines how it spreads.
- A vector is something which carries a pathogen from one organism to another.
- They are prokaryotes so they have v. different ultrastructure to the organisms they infect. Most bacteria are not pathogens.
They can be identified in 2 main ways:
1) Cell walls: bacterial cell walls react differently to a process called gram staining because of their different structures - gram pos. bacteria appears purple whereas gram neg. bacteria appears red.
- This is useful as bacteria with diff. cell walls respond differently to antibiotics.
2) Basic shapes: Bacillus (rod), Streptobacillus, Coccus (sphere), Streptococcus, Staphylococci, Vibrio (comma), Spirillum (spiral), Spirachaete (corkscrew)
- Non living infectious agents, 0.2-0.3um in diameter. All viruses are pathogens.
- Basic structure is some DNA/RNA surrounded by protein.
- They invade living cells where the genetic material takes over the host to make more viruses. They reproduce rapidly and evolve by adapting to the host.
- Bacteriophages are viruses which attack bacteria and use them to replicate, destroying them at the same time, and can be used to identify and treat disease.
- A group of eukaryotic organisms with a variety of feeding mechanisms, which can be uni- or multicellular. Only a small amount of protoctista are pathogens.
- Parasitic, so use animals as their host organism. They may need a vector to transfer them from one organism to another, or enter directly.
- Generally multicellular eukaryotic organisms which are major problem in plants, but can affect animals.
- Digest their food extracellularly and then absorb the nutrients, meaning they feed on decaying matter.
- Fungal infections kill plants by attacking leaves and stopping them from photosynthesising.
- Reproduce by releasing millions of spores which can travel long distances.
Pathogenic modes of action: Damaging host directly
- Viruses take over cell metabolism as the viral DNA/RNA is inserted into host DNA, causing new viruses to be synthesised. When viruses burst out to spread to another cell, the cell dies.
- Some protoctista take over cells and kill them as a new generation emerges like viruses. They don’t take over the genetic material but they only digest cell contents as they reproduce.
- Fungi digest living cells and destroy them.
Pathogenic modes of actions: Producing toxins
- Bacteria produce toxins which poison or damage the host in some way, causing disease. Such as breaking down membranes, inactivating enzymes or interfering with genetic materials. Toxins are a by-product of normal functioning.
- Fungi can also produce toxins.
How bacteriophages work
1) Attach to host.
2) Insert viral DNA/RNA
3) Replication of DNA/RNA
4) Assembly of viral protein
5) Assembly of virus
6) Lysis of host