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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)
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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)
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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
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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
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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. |
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