Bacteria

A4

a

Antibiotics

In many cases the immune system can wipe out a bacterial infection on its own. But sometimes people become so sick from a bacterial disease that they require medical treatment. Antibiotics and other antibacterial drugs are the major weapons against disease-causing bacteria. Antibiotics act in a number of ways to kill bacteria or suppress their activity. Over time, however, bacteria can become resistant to antibiotics. As a result bacterial diseases have become more and more difficult to cure.

In an effort to control antibiotic resistance, physicians have tried to limit the use of antibiotics. In addition, they have advocated more vigorous efforts to improve the antibiotics we now have and to find new agents active against bacteria.

A4

b

Vaccines

Immunization through vaccines is important in the prevention of infectious diseases caused by bacteria. Vaccines expose a human being or other animal to a disease-causing bacterium or its toxins without causing the disease. As a result of this exposure, the body forms antibodies to the specific bacterium. These antibodies remain ready to attack if they meet the bacteria in the future. Some immunizations last a lifetime, whereas others must be renewed with a booster shot.

Tetanus provides a good example of a successful vaccine. The bacterium Clostridium tetani, found in soil and ordinary dirt, produces one of the most lethal toxins known. The toxin affects nerves, resulting in muscle rigidity and death. Tetanus infection has become very rare in developed countries such as the United States where nearly everyone is immunized against the toxin. The vaccine immunizes the body by means of toxins that have been chemically treated so they are no longer toxic. Health officials recommend getting a tetanus shot every ten years. In less developed countries where vaccination is not so common, tetanus is a major cause of death, especially of babies.

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A4

c

Public Health Measures

Public health measures provide major controls against infectious disease. Especially important are those measures leading to ready availability of clean water, safe food, and up-to-date medical care. Waterborne diseases, such as cholera and typhoid fever, kill an estimated 5 million to 10 million people worldwide each year, according to the United Nations. Sufficient sources of clean drinking water in developing countries could help prevent these deaths. Food-safety guidelines can help prevent the spread of disease through contaminated food. Proper medical care can prevent transmission of infectious diseases to others. Tuberculosis, for example, kills more people worldwide every year than any other single disease. But if identified early, cases of tuberculosis can be treated effectively with antibiotics and other means, thereby stopping transmission to others.

Maintaining a clean environment for medical care is also important in preventing the spread of infectious diseases. For example, medical instruments, such as needles and syringes, must be sterile and proper infection-control procedures must be followed in hospitals, medical and dental offices, and industries that use bacteria. However, it is never possible, or even desirable, to have an environment entirely free of bacteria.

B

Bacteria and the Environment

Bacteria play a major role in recycling many chemical elements and chemical compounds in nature. Without such bacterial activities as the recycling of carbon dioxide (CO₂) life on Earth would be impossible. Plants use CO₂ to grow and in the process they produce the oxygen humans and other animals breathe. Moreover, we would drown in garbage and wastes if bacteria did not speed the decomposition of dead plant and animal matter.

B

1

Nitrogen Fixation

Bacteria play a key role in making soil fertile. They convert nitrogen in Earth’s atmosphere into the nitrogen compound ammonia, which plants need to grow. Bacteria are the only organisms able to carry out this biochemical process known as nitrogen fixation. The bacteria able to fix atmospheric nitrogen usually live in association with plants, often integrated into the plant tissue. Bacteria in the genus Rhizobium, for example, form nodules (knobs) on the roots of beans and other plants in the legume family.

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