The Importance of Bacteria

Much of our experience with bacteria involves disease. Although some bacteria do cause disease, many kinds of bacteria live on or in the human body and prevent disease. Bacteria play important roles in the environment and in industry. In most cases the bacteria that cause disease are not part of the bacteria that normally inhabit the body. They are picked up from sick people, sick animals, contaminated food or water, or other external sources. Bacterial disease also can occur after surgery, an accident, or some other event that weakens the immune system.

When the immune system is not functioning properly, bacteria that usually are harmless can overwhelm the body and cause disease. These organisms are called opportunistic because they cause disease only when an opportunity is presented. For example, cuts or injuries to the skin and protective layers of the body enable normally friendly bacteria to enter the bloodstream or other sterile parts of the body and cause infection. Surgery may enable bacteria from one part of the body to reach another, where they cause infection. A weakened immune system may be unable to prevent the rapid multiplication of bacteria and other microorganisms.

Opportunistic infections became more important in the late 20th century because of diseases such as acquired immunodeficiency syndrome (AIDS), a viral disease that ravages the immune system. Some dramatic infectious diseases result from exposure to bacteria that are not part of our normal bacterial community. Cholera, one of the world's deadliest diseases today, is caused by the bacterium Vibrio cholerae. Cholera is spread in water and food contaminated with the bacteria, and by people who have the disease. After entering the body, the cholera bacteria grow in the intestines, often along the surface of the intestinal wall, where they secrete a toxin (poison). This toxin causes massive loss of fluid from the gut, and an infected person can die of dehydration (fluid loss) unless the lost fluids, and the salts they contain, are replaced.

Задание 1. Ответьте на вопросы:

1. Do all bacteria cause disease?

2. Where do bacteria play important roles?

3. In what cases can bacterial disease occur?

4. Can bacteria that are usually harmless cause disease?

5. Why do opportunistic infections become more important in the late 20^th century?

Задание 2. Из списка болезней выберите те, о которых идет речь в тексте:

tuberculosis, cholera, pneumonia, acquired immunodeficiency syndrome, anthrax.

Задание 3. Опишите течение холеры, используя текст и следующие глаголы: to be caused, to be spread, to grow, to secrete, to cause, to die.

Дата добавления: 2015-07-11