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Microbes: Friend & Foe
Friendly Microbes
Without microbes, there would be no fertile soil to grow vegetables and flowers, no bread or cheese, and no beer or wine! Long ago, before people were able to see microbes under microscopes or even knew that they existed, human societies began learning how to put them to use. Commercial use of microorganisms, called biotechnology, has been revolutionized through the advent of genetic engineering, which has shown great potential for medical use.
For example, many people cannot digest the sugar present in raw milk (lactose). When animals were domesticated about 10,000 years ago, people learned how to use bacteria to digest raw milk from domesticated animals and turn it into yogurt and cheese, which are more palatable. An entire dairy industry was born from bacteria.
Sumerian Medical Tablet, ca. 2100 B.C. (replica) |
Humans also learned how to use yeast, another kind of microbe, to digest the sugars in fruit such as grapes, into alcohol to make wine. Yeast also digests sugars in grains like barley malt to make alcohol in beers. Some experts think that the ancient Egyptians developed grain and yeast to make beer even before they used it to make bread. The tablet, from Nippur in Iraq, contains prescriptions for salves and internal remedies. Most of the medicines are to be taken with beer. |
Microbes as Foe
The microbes that threaten us come in a vast variety of shapes, sizes, and lifestyles. They stand ready to invade the body, feed off our bodies' cells, grow and reproduce, causing an infection. Microbes are constantly changing, adapting to new environments, finding new places to live and survive. They are found in soil, water, and animals as well as inside our bodies. They can cause minor illness, such as a cold or stomach flu, or deadly diseases such as AIDS/HIV, tuberculosis or Ebola fever.
Fungi
Child with tinia captitis (ringworm) |
Fungi are not plants. While they show a closer relation to animals, fungi are unique and separate life forms given a category all their own. There are about 100,000 known species of mushrooms, rusts, molds, mildews and other organisms assigned to the Kingdom of Fungi, and hundreds of new species are described each year. Most fungi are unable to make their own food. Instead they live by digesting the tissues of plants and animals. Some fungi cause diseases after entering the body; these infections or mycoses create problems for humans such as ringworm, athlete's foot, yeast infections or diaper rash. Over the last 10 years, the incidence of serious fungal infections has been increasing, particularly in hospital settings and in people with compromised immune systems. |
Protozoa
Ebola hemorrhagic fever |
Protozoa are one-celled organisms that inhabit water and soil. Most protozoa are free-living and cause people and other animals no harm. Several protozoa are parasitic, presenting a number of serious health problems including trypanosomiasis (African sleeping sickness), malaria, and cryptosporidiosis. Giardiasis is the most frequent cause of non-bacterial diarrhea in North America and is most frequently associated with consumption of contaminated water. |
Viruses
Hantavirus |
A virus is a microbe that cannot grow or reproduce apart from a living cell. It forces the cell to make vast numbers of new similar viruses, which then spread to take over and destroy other cells. It is the smallest of all infectious agents, averaging about 100 nanometers (110 billionths of a meter) in length. Viruses cause many common infections such as the common cold, influenza, genital herpes, chickenpox and shingles. Viruses are also responsible for causing many serious illnesses such as HIV/AIDS, smallpox rabies, and hepatitis. Newly recognized viruses include hantavirus, Ebola. dengue, Lassa and Marburg. Most are zoonotic diseases, appearing in humans only from infectious contact with animal hosts. |
