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Germ is a general term used to designate any minute pathogenic agent. The term germ became widely used after Louis Pasteur's development of the germ theory of disease in the 19th century. The term is applied to disease-producing micro organisms, such as bacteria, Protozoa, and fungi, and to pathogenic agents of uncertain classification, such as Rickettsia and viruses.
Bacteria are micro organisms that lack internal cell membranes. The most common and ancient organisms on earth, bacteria are intimately connected to the lives of all organisms.
Most bacteria are less than 1 micron (0.001 mm/0.00004 in.) in length. Hundreds of thousands of bacteria can fit into a space the size of the period at the end of this sentence. However, colonies of bacteria, such as on a laboratory culture plate or on the surface of salt marsh mud, can easily be viewed without a microscope.
A large number of bacteria, such as the green bacteria, purple bacteria, and cyanobacteria, are called Phototrophs. These bacteria are able to convert the sun's energy into food in a process called photo synthesis. Phototrophic bacteria have dominated earth's seas and landscapes for hundreds of millions of years and remain common today.
Micro biologists (scientists who study life forms that can only be observed with the aid of a microscope) also classify bacteria according to whether or not they require oxygen to survive. Bacteria that require oxygen are called aerobic bacteria, or aerobes. Bacteria that live without oxygen are called anaerobic bacteria, or anaerobes. Both aerobes and anaerobes can be either phototrophic or nonphototrophic.
In the late 17th century, Antoni van Leeuwenhoek, a custodian and town caretaker of Delft, Holland, became the first person to make a systematic study of bacteria. Leeuwenhoek spent hundreds of hours to make the finest ground glass for his simple microscopes. Considered the founder of micro biology, he was the first to discover and describe a variety of very minute organisms, many of which we now know were bacteria. Leeuwenhoek's work set the stage for later researchers such as Louis Pasteur of France, who showed that microbes do not arise from non living matter, as scientists of his day believed, and Robert Koch of Germany, who showed that bacteria could cause disease.
Protozoa is the collective name for animal-like, single-celled organisms of the Protista kingdom. Protozoa have little or no differentiation into tissue systems. Several phyla are commonly recognized. They include flagellated Zoomastigina, many species of which live as parasites in plants and animals; the amoeboid Sarcodina, which includes the Foraminifera and Radiolaria both important components of the plankton; ciliated Ciliophora, many with specialized structures suggesting the mouth and anus of higher organisms; Cnidosporidia, parasites of invertebrates, fish, and a few reptiles and amphibians; and Sporozoa, many species of which are parasites of animals (including humans). More than 20,000 species are known, including such familiar forms as paramecium and amoeba.
Most species are found in such aquatic habitats as oceans, lakes, rivers, and ponds. They vary in length from 2 to 70 micrometers. Protozoa obtain their food by ingesting bacteria, waste products of other organisms, algae, or other protozoa. Most species are mobile, either by whip like structures called flagella, hair like structures called cilia, or amoeboid motion, a streaming type of movement involving the formation of pseudopods (foot like extensions).
Fungi are either single-celled or multicellular organisms that obtain food by direct absorption of nutrients. The food is dissolved by enzymes that the fungi excrete, is then absorbed through thin cell walls, and is distributed by simple circulation, or streaming, of the protoplasm. Together with bacteria, fungi are responsible for the decay and decomposition of all organic matter and are found wherever other forms of life exist. Some are parasitic on living matter and cause serious plant and animal diseases. The study of fungi is called mycology.
The hydrolytic enzymes of fungi are useful for a number of industrial processes. When grown on steamed wheat bran or rice bran, one fungal species produces an amylase product useful in alcoholic fermentation. Proteases obtained from another fungus are used in the manufacture of liquid glue. Commercial production of industrial ethyl alcohol is accomplished by fermentation of sugar cane molasses or hydrolyzed starch by means of enzymes formed by another fungus. In the process of making bread, yeast is added to dough to produce carbon dioxide.
Fungus is used for the commercial production of citric acid and in the production of gluconic acid and of gallic acid, which is used in the manufacture of inks and dyes. Synthetic resins are manufactured from fumaric acid formed by black bread mold. Gibberellic acid, which promotes increased growth of plant cells, is formed by a fungus causing disease in rice plants. Commercially usable oils have been obtained from species of several genera, and one species is a practical source of edible proteins. Vitamin D is prepared by irradiation of ergosterol, a substance which may be obtained from the waste brewer's yeast. A yeast like fungus is a source of riboflavin, and biotin accumulates during production of fumaric acid by another fungus. Fungi are also used to produce Roquefort cheese and to ripen Camembert cheese.
Fungi have been used medicinally since ancient times. The use of fungi as a purgative is no longer prevalent, but the alkaloid in the sclerotium of ergot still is used to produce uterine contractions in childbirth. Ergot alkaloids are also a source of lysergic acid diethylamide, commonly known as LSD, which produces hallucinogenic effects, often of a severe nature. The use of antibiotics in medical practice dates from recognition of the antibiotic properties of penicillin. Many antibiotics today are produced by non fungal microorganisms. Griseofulvin, however, is an anti fungal antibiotic formed by several species of a genus of fungi. The immunosuppressant drugs cyclosporine and tacrolimus (FK-105), both used in organ transplantation, are also derived from fungi.
Viruses are infectious agents that are found in virtually all life forms, including humans, animals, plants, fungi, and bacteria. Viruses consist of genetic material, either deoxyribonucleic acid (DNA) or ribonucleic acid (RNA).surrounded by a protective coating of protein, called a capsid, with or without an outer lipid envelope. Viruses are between 20 and 100 times smaller than bacteria and hence are too small to be seen by light microscopy. Viruses vary in size from the largest poxviruses of about 450 nanometers (about 0.000014 in) in length to the smallest polioviruses of about 30 nanometers (about 0.000001 in). Viruses are not considered free-living, since they cannot reproduce outside of a living cell; they have evolved to transmit their genetic information from one cell to another for the purpose of replication.
Viruses often damage or kill the cells that they infect, causing disease in infected organisms. A few viruses stimulate cells to grow uncontrollably and produce cancers. Although many infectious diseases, such as the common cold, are caused by viruses, there are no cures for these illnesses. The difficulty in developing antiviral therapies stems from the large number of variant viruses that can cause the same disease, as well as the inability of drugs to disable a virus without disabling healthy cells. However, the development of anti viral agents is a major focus of current research, and the study of viruses has led to many discoveries important to human health.
One of the easiest and most effective ways of protecting yourself from the damage that may be caused by germs it to simply wash regularly with soap. Soap safely removes germs by allowing water to wash the germs away or killing the germ outright by the addition of a germicidal component such as iodine or chlorine.
One of the most memorable tales of germ killing comes from the life of Joseph Lister (1827-1912). Lister was a British surgeon, whose discovery of antiseptics in 1865 greatly reduced the number of deaths due to operating room infections. Born in Upton, Essex, and educated at the universities of London and Edinburgh, Lister began to study the coagulation of blood and the inflammation that followed injuries and surgical wounds. In 1861 he was appointed surgeon of the Glasgow Royal Infirmary in a new surgery unit designed to reduce gangrene and other infections, then thought to be caused by bad air. Despite his efforts to keep surgical instruments and rooms clean, the mortality rate remained close to 50 percent.
Believing infection to be caused by airborne dust particles, Lister sprayed the air with carbolic acid, a chemical that was then being used to treat foul smelling sewers. In 1865 he came upon the germ theory of the French bacteriologist Louis Pasteur, whose experiments revealed that fermentation and putrefaction were caused by micro organisms brought in contact with organic material. By applying carbolic acid to instruments and directly to wounds and dressings, Lister reduced surgical mortality to 15 percent by 1869.
Lister's discoveries in antiseptics met initial resistance, but by the 1880's they had become widely accepted. In 1897 he was made Baron by Queen Victoria, who had been his patient.
It goes without saying today that the medical profession is firmly entrenched in the belief that the washing of hands is a fundamental practice in preventing the spread of germs. It has been estimated that people could reduce the amount of common illnesses (colds, stomach aches, diarrhea, etc.) they contract by 40% simply by washing their hands more regularly.
| Fight BAC! -- This site is excellent for learning about how to fight germs. |
| World Health Organization (WHO): Information Office -- Facts Sheets on diseases and other health issues, indexed alphabetically. |
| The Difference Between Soap and Detergent. |
| Teachnet.com --Lesson Ideas: Germs Everywhere |
| Hysteria Over Germs Unjustified, Experts Say. |
Children often have a hard time understanding about germs because they are invisible. Here, your students can see germ grow into mold.
Potato slices touched by the children with dirty hands grew much more mold than the potato slices which were touched by the children with clean hands.
This is a good demonstration for giving young children a clear picture of how germs are passed form person to person.
Point out that as you shook hands with the children, some of the "germs" (rice) from your hands were passed to theirs. When you picked up the toys, some of the "germs" stuck to them and were passed to children's hands as well. By the time you finished the activity, nearly everyone had some "germs" on their hands. This demonstrates fairly accurately the way germs can be passed in the classroom.
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