Infectious Diseases - Pathogens

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  • Infectious Diseases: Pathogens
  • Bacteria
  • Fungi
  • Viruses
  • Protozoa
  • Parasites
  • How pathogens are spread
  • How pathogens cause disease
  • Growth of pathogen populations
  • Quiz

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Fungi are called microorganisms but some can easily be seen with the naked eye. Mushrooms, toadstools and bread mould are all types of fungi. Individual fungus cells have a nucleus, cell wall and structures like mitochondria can be seen in their cytoplasm. They can join together to form long tubes, called hyphae, that grow as a network of fibres in the material the fungus is feeding on. Mushrooms and toadstools are specialised structures involved in reproduction and the formation of fungal spores that can spread for many miles on the wind.

Fungi play a vital role in decomposing dead material and recycling the nutrients to make them available for the growth of other plants. Brewers' and bakers' yeast are types of fungi that grow as individual cells. They have been used for many centuries in the production of beer, wine and bread.

The fungus Penicillium notatum helps to save lives by producing the antibiotic penicillin.

Obesity causes raised fatty acid levels which can cause diabetes.

Yeast cells under the scanning electron microscope.
Photo provided by CDC/Dr. Libero Ajello.

Pathogenic fungi tend to be ones that cause infections to the surface of the body. Their fibres grow in the upper layer of the skin which causes inflammation and damage. This can also provide a route into the body for other opportunistic infections. Diseases such as athlete's foot, ringworm, oral and vaginal thrush are examples of fungal infections.

Fungi can cause infections inside the body such as in the lungs, brain and heart which can be very serious and even fatal.

The structure of yeast

Yeast is a type of single celled fungus which we use to make bread and beer. Yeasts can also cause disease. Yeast cells are smaller than plant and animal cells. They are around 0.01mm in diameter. They reproduce asexually by budding. There are different types of yeast but their cells all have some components in common:

  • Nucleus
    contains the genetic material which controls the cell activities and reproduction
  • Cytoplasm
    liquid gel in which many of the chemical reactions of the cell take place
  • Cell wall
    maintains the shape of the cell
  • Bud
    new yeast cell forming by asexual reproduction
The components of a yeast cell

The components of a yeast cell

Medicine that acts against bacterial infections. Penicillin is an example of an antibiotic.
Protein that is produced by lymphocytes (white blood cells) and that attaches to a specific antigen.
Molecule on the surface of a pathogen that identifies it as a foreign invader to the immune system.
Single-celled organism. Has a cell wall, cell membrane, cytoplasm. Its DNA is loosely-coiled in the cytoplasm and there is no distinct nucleus.
The use of biological organisms or enzymes to create, break down or transform a material
To cut apart, or separate, tissue especially for anatomical study.
Exponential growth
If something is growing exponentially the larger the quantity gets, the faster it grows
Micro-organism that can grow in long tubes called hyphae or as single cells. Fungi have a nucleus, cytoplasm and a cell wall.
Herd immunity
If a high percentage of a population is immune to a disease the disease cannot be passed on because it cannot find new hosts.
Infection caused by the human immunodeficiency virus (HIV). It attacks and destroys the immune system.
Hybridoma cells are formed by fusing a specific antibody-producing cell with a type of cancer cell that grows well in tissue culture
Immune system
The body's natural defence mechanism against infectious diseases.
A process which gives immune resistance to a particular disease. The human or animal is exposed to a harmless antigen in order to raise antibodies and provide an immune memory.
A type of white blood cell that make antibodies to fight off infections.
A type of white blood cell that consumes dead pathogens that have been killed by antibodies.
Organism that feeds off another living host and causes it some damage. An example of a parasite is a tapeworm that lives in the digestive system of a host organism.
A micro-organism that causes disease.
Phagocytes are the white blood cells that protect the body by ingesting harmful foreign particles, bacteria, and dead or dying cells.
A polymer made up of amino acids joined by peptide bonds. The amino acids present and the order in which they occur vary from one protein to another.
Protozoa are one-celled animals
A spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavourable conditions.
A poisonous or toxic substance - produced by pathogens.
A small amount of dead or weakened pathogen is introduced into the body. It prepares the immune system to prevent future infections with the live pathogen.
Medicine that contains a dead or weakened pathogen. It stimulates the immune system so that the vaccinated person has an immunity against that particular disease.
The smallest of living organisms. Viruses are made up of a ball of protein that contains a small amount of the virus DNA. They can only reproduce after they have infected a host cell.
Opportunistic Infections
An infection that would not normally cause disease in a healthy person but which can take hold when a person's normal immune defences are reduced.