Animal and Plant Pathogens
Pathogens
- Infectious organisms which spread communicable diseases are known as pathogens.
- Pathogens include 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.
- More bacteria than any other type of organism. Prokaryotes, so have a very different ultrastructure to the organisms they infect. Most bacteria are not pathogens.
- Bacteria can be identified in two main ways:
- Cell Walls; bacterial cells walls react differently to a process called gram staining because of their different structures. Gram positive bacteria appear purple/blue but gram negative bacteria appear red.
- Gram staining is useful as bacteria with different cell walls respond differently to antibiotics.
- Basic Shapes;
- Cell Walls; bacterial cells walls react differently to a process called gram staining because of their different structures. Gram positive bacteria appear purple/blue but gram negative bacteria appear red.
Viruses
Pathogenic Modes of Action
- Non-living infectious agents, 0.2-0.3um in diameter. All viruses are pathogens.
- Basic structure is some DNA or 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 a major problem in plants, but can affect animals.
- Digest their food extracellularly and then absorb the nutrients, meaning they feed of decaying matter.
- Fungal infections kill plants by attacking the leaves stopping them photosynthesising.
- Reproduce by releasing millions of spores which can travel long distances.
Pathogenic Modes of Action
- By Damaging the Host Directly
- Viruses take over cell metabolism as the viral DNA/RNA is inserted into host DNA, causing new viruses to be synthesised. When the viruses burst out to spread to other cells, 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 however as they only digest cell contents as they reproduce.
- Fungi digest living cells and destroy them.
- By Producing Toxins
- Bacteria produce toxins which poison or damage the host in some way, causing disease. This may be breaking down cell membranes, inactivating enzymes or interfering with genetic materials. These toxins are a by-product of normal functioning.
- Fungi can also produce toxins.