Unit 4222-265 Causes and spread of infection (ICO2)
Understand the causes of infection
1. The differences between bacteria, viruses, fungi and parasites
Bacteria belong to a group of single celled microorganisms which are classified as prokaryotes i.e. they do not have membrane bound organelles. They have no true nucleus as the DNA is not contained within a membrane or separated from the rest of the cell, but is coiled up in a region of the cytoplasm called the nucleoid and the cell is surrounded by a cell wall an outer covering that protects the bacterial cell and gives it shape.
Viruses are infectious agents, often highly host-specific, consisting of genetic material surrounded by a protein coat. Viruses are not alive, they cannot grow or multiply on their own and need to enter cell and take over the cell to help them multiply.
Fungi – these are members of a large group of eukaryotic organisms that includes microorganisms such as yeast and molds, as well as the more familiar mushrooms. Fungi can be single-celled, multinucleated, or multicellular organisms. Although they are eukaryotes like plants and animals, the major difference is that fungal cells have cell walls that contain chitin, unlike the cell walls of plants, which contain cellulose. Fungi lack the chlorophyll necessary for photosynthesis and must therefore live as parasites or saprophytes
Parasites: plant or animal that at some stage of its existence obtains its nourishment from another living organism called the host. Parasites may or may not harm the host, but they never benefit it. They include members of many plant and animal groups, and nearly all living things are at some time hosts to parasitic forms. Many bacteria are parasitic on external and internal body surfaces; some of these invade the inner tissues and cause disease.
Most parasites are obligate; i.e., they are unable to survive apart from their hosts. Often this is because they have lost various of the organs necessary...