Online Textbook Bacteriology is continuously updated and includes information on Staphylococcus, MRSA, Streptococcus, E. coli, anthrax, cholera, tuberculosis, Lyme disease and other bacterial diseases of humans.
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The Online Textbook of Bacteriology is a general and medical microbiology text and includes discussion of staph, MRSA, strep, Anthrax, E. coli, cholera, tuberculosis, Lyme Disease and other bacterial pathogens.
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Web Review of Todar's Online Textbook of Bacteriology. "The Good, the Bad, and the Deadly"

Tag words:bacteria, microbes, environmental microbiology, nitrogen fixation, nitrogen cycle, autotrophy, lithotroph, anaerobic respiration, decomposition, denitrification, anoxygenic photosynthesis.

Kenneth Todar currently teaches Microbiology 100 at the University of Wisconsin-Madison.  His main teaching interests include general microbiology, bacterial diversity, microbial ecology and pathogenic bacteriology.

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The Impact of Microbes on the Environment and Human Activities (page 2)

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© Kenneth Todar, PhD

Associations with Animals and Plants

Microbes invariably enter into beneficial, sometimes essential, associations with all higher forms of organisms, including insects, invertebrates, fish, animals and plants. For example, bacteria and other microbes in the intestines of animals and insects digest nutrients and produce vitamins and growth factors. In the plant world, leguminous plants (peas, beans, clover, alfalfa, etc.) live in intimate associations with bacteria that extract nitrogen from the atmosphere and supply it to the plant for growth.

Microbes in the rumen (forestomach) of cows, sheep and other ruminant animals are responsible for the initial digestion of nutrients (primarily cellulose), and they provide not only a source of carbon for their host, but also a source of protein and vitamins.

The mutualistic association between nitrogen fixing bacteria and leguminous plants. Left. Nitrogen-fixing Rhizobium bacteria colonized on the root hairs of clover plants. Right. Nodules containing Rhizobium bacteria on the plant roots. In the nodule, the bacteria fix nitrogen which they share with the plant. In exchange, the plant supplies the bacteria with a source of carbon and energy for growth.

The microbes that normally live in associations with humans on the various surfaces of the body (called the normal flora), such as Lactobacillus and Bifidobacterium, are known to protect their hosts from infections, and otherwise promote nutrition and health.

Lactobacillus acidophilus and a vaginal squamous epithelial cell. CDC. L. acidophilus (informally known as Doderlein's bacillus) colonizes the vagina during child-bearing years. As a lactic acid bacterium, the organism creates a low pH (acidic environment) on the tissues which prevents colonization by potentially harmful yeast and other bacteria.

Production of Foods and Fuels

In the home and in industry, microbes are used in the production of fermented foods. Yeasts are used in the manufacture of beer and wine and for the leavening of breads, while lactic acid bacteria are used to make yogurt, cheese, sour cream, buttermilk and other fermented milk products. Vinegars are produced by bacterial acetic acid fermentation. Other fermented foods include soy sauce, sauerkraut, dill pickles, olives, salami, cocoa and black teas. Yeast are also involved in fermentations to convert corn and other vegetable carbohydrates into ethanol to make beer, wine or gasohol, but bacteria are the agents of most other food fermentations.

A variety of fermented foods and beverages produced by microorganisms.

Medical, Pharmaceutical and Biotechnological Applications

In human and veterinary medicine, for the treatment and prevention of infectious diseases, microbes are a source of antibiotics and vaccines.

Antibiotics are substances produced by microorganisms that kill or inhibit other microbes which are used in the treatment of infectious disease. Antibiotics are produced in nature by molds such as Penicillium and bacteria such as Streptomyces and Bacillus.

Vaccines are substances derived from microorganisms used to immunize against disease. The microbes that are the cause of infectious disease are usually the ultimate source of vaccines. Thus, a version of the diphtheria toxin (called toxoid) is used to immunize against diphtheria, and parts of Bordetella pertussis cells are used to vaccinate against pertussis (whooping cough). The use of vaccines such as smallpox, polio, diphtheria, tetanus and whooping cough has led to virtual elimination of these diseases in regions of the world where the vaccines have been deployed.

Some antibiotics used in veterinary medicine.


Microbiology makes an important contribution to biotechnology, an area of science that applies microbial genetics to biological processes for the production of useful substances. Microorganisms play a central role in recombinant DNA technology and genetic engineering. Important tools of biotechnology are microbial cells, microbial genes and microbial enzymes.

The genetic information for many biological products and biological processes can be introduced into microbes in order to genetically engineer them to produce a substance or conduct a process. The genes can come from any biological source: human, animal, plant or microbial. This opens the possibility for microbial production of foods, fuels, enzymes, hormones, diagnostic agents, medicines, antibiotics, vaccines, antibodies, natural insecticides and fertilizers, and all sorts of substances useful in our civilization and society. Also, the microbial genes that encode for these substances, most of which are unknown, are a tremendous resource of information for application in medicine, pharmacy, agriculture, food science and biotechnology.

Human insulin for treatment of diabetes.

Streptokinase for dissolving blood clots.  Made by recombinant DNA technology. Other medical products include  hormones, vitamins, vaccines, antigens, antibodies, cytokines, antibiotics and diagnostic agents.

Basic research

Microorganisms, in particular the bacterium, Escherichia coli and the yeast, Saccharomyces, have been used as model organisms for basic research and the study of cellular life. Hundreds of thousands of scientific papers have been published on these two organisms. Because of cell theory and the unity of biological processes in all organisms, this information provides us with insight and understanding of life at all levels, including human.

The famous Meselson and Stahl experiment which proved that DNA replication is semiconservative was performed with E. coli DNA.

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Kenneth Todar is an emeritus lecturer at University of Wisconsin-Madison. He has taught microbiology to undergraduate students at The University of Texas, University of Alaska and University of Wisconsin since 1969.

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