Germs: Viruses, Bacteria, and Fungi Part 3




Viruses and Bacteria

Germ and Bacteria

Fungi and Bacteria

What is a fungus?

Fungi (plural for fungus) are different from both viruses and bacteria in many ways. They are larger, plant-like organisms that lack chlorophyll (the substance that makes plants green and converts sunlight into energy). Since fungi do not have chlorophyll to make food, they have to absorb food from whatever they are growing on. Fungi can be very helpful – brewing beer, making bread rise, decomposing trash – but they can also be harmful if they steal nutrients from another living organism. When most people think of fungi they picture the mushrooms that we eat. True, mushrooms are important fungi, but there are other forms such as molds and yeasts.

Structure: The main identifying characteristic of fungi is the makeup of their cell walls. Many contain a nitrogenous substance known as “”chitin,”” which is not found in the cell walls of plants, but can be found in the outer shells of some crabs and mollusks. Most fungi are multicellular (made up of many cells), with the exception of the yeasts. The cells make up a network of branching tubes known as “”hyphae,”” and a mass of hyphae is called a “”mycelium.”” The insides of the cells look a little different than bacterial cells. First of all, the genetic material is gathered together and enclosed by a membrane in what is called the “”nucleus.”” Also, there are other structures called “”organelles”” in the cell that help the cell to function, such as mitochondria (converts energy), endoplasmic reticulum (ER) (makes complex proteins), and other organelles. The Golgi apparatus forms many types of proteins and enzymes. Lysosomes contain enzymes and help digest nutrients. Centrioles are necessary for proper division of the cell. Both bacteria and fungi have ribosomes, but those of the bacteria are smaller in size and also reproduce differently.

Reproduction: Fungi can reproduce in multiple ways depending upon the type of fungus and the environmental conditions:
Production of spores asexually
Production of spores sexually

Budding occurs in yeasts, which are only made up of one cell. Budding is somewhat similar to binary fission in bacteria, in that the single cell divides into two separate cells.

Fragmentation is a mode of reproduction used by those fungi that form hyphae. During fragmentation, some of the hyphae break off and simply start growing as new individuals.

Spores are tiny single cells that are produced by fungi that have hyphae. They can be produced asexually by a process in which the tips of the hyphae form specially encased cells – the spores. Some fungi also produce spores sexually. Two types of special cells called “”gametes”” are produced. One of each type unite to produce a new individual spore. Spores are tiny single cells that are usually very resistant to environmental changes. They can remain dormant for long periods of time until the conditions are right for them to develop into mature individuals.

Hosts and resistance: Fungi are heterotrophs, meaning that they secrete digestive enzymes and absorb the resulting soluble nutrients from whatever they are growing on. For this reason they are great decomposers in the ecosystem, but they can also cause problems when they begin to absorb nutrients from a living organism. They most commonly are breathed in or have contact with the skin. If conditions are right and they start to reproduce, disease can result. Some antifungal agents are available to treat these infections, but it has been much more difficult for scientists to create successful antifungal drugs than antibacterial drugs because the cells of fungi are much closer in structure to the cells of animals than are bacteria.

In creating drugs, it is hard to find an agent that will kill the fungal cells and leave the animal cells unharmed. The most successful drugs that have been created prevent the formation of chitin, and therefore prevent the fungus from creating new cell walls and spreading. The cell wall is the only structure that is not shared by the animal and fungal cells. Other drugs bind to specific fungal proteins and prevent growth. Unfortunately, many of the drugs available are only fungistatic, meaning they can only prevent further growth rather than fungicidal, meaning to kill the fungus. Many of the drugs used for serious fungal infections have potentially toxic side effects.

Which diseases are which?

When a pet or a human contracts an infection, it is important to understand how the disease works, and where it came from. This is important for treatment, as well as to protect other animals or humans from becoming ill. The following table categorizes some common diseases in various species of animals as viral, bacterial, or fungal.

Bulgaria, Sofia
Wodonga, Victoria
St. Louis, Missouri
Portugal, Lisbon
Lesotho Maseru
Kyrgyzstan Bishkek
Montenegro, Podgorcia,
Victorville California USA
Oklahoma City, Oklahoma
San Buenaventura (Ventura), California