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Antibiotics

Antibiotic is a drug produced by certain microbes. Antibiotic sub­stances are obtained from bacteria and fungi that live in the air, soil, and water. Most antibiotics are used by physicians to fight various diseases caused by harmful microbes. A few are used to treat certain cancers.

Antibiotics are selectively toxic — that is, they damage certain types of cells, but do not damage others. Many antibiotics are harmful to the cells of pathogenic (disease-causing) microbes, but they do not normally damage human cells. Physicians use these types of antibio­tics to treat a variety of bacterial diseases, including gonorrhea, syphi­lis, and tuberculosis, and infections caused by staphylococcal and streptococcal bacteria. A small number of antibiotics, however, were developed to attack human cells. Some of these are used to treat can­cer. They are selectively toxic mostly because they only damage cells that are in the process of dividing.

Antibiotics are sometimes called "wonder drugs" because they can cure many diseases that once were often fatal. The number of deaths that are caused by meningitis, pneumonia, and scarlet fever has de­clined drastically since people began using antibiotics.

Antibiotics are also used to treat infectious diseases in animals and to control bacteria and fungi that damage fruits and grains. Farmers sometimes add small amounts of antibiotics to livestock feed to stimu­late the animals growth.

Text 2

Read the text and choose the correct variant.

  1. Antibiotics are used to treat viral/bacterial infections.

  1. Limited-spectrum/broad-spectrum antibiotics fight G+ and G- in­fections.

  2. Antibiotics that fight pathogenic fungi/G+ infections include ny­statin and griseofulvin.

  3. Every/No broad-spectrum antibiotic is effective against all bacte­rial infections.

Kinds of Antibiotics

There are more than 70 clinically useful antibiotics. Most of them are used to treat bacterial infections. Others fight harmful fungi and protozoa, and a few are used to treat cancer. Antibiotics are not effec­tive against most viruses, and so they cannot be used for chickenpox, measles, and most other viral diseases.

Antibacterial antibiotics. Many bacteria can be classified as either Gram-positive (G+) or Gram-negative (G-). This classification meth­od was developed by Hans C. J. Gram, a Danish bacteriologist of the late 1800s. According to Gram's system, many bacterial infections are classified as either G+ or G-, depending on the type of bacteria that caused them. The bacteria in each group have certain characteristics that help determine the sensitivity of these microorganisms to antibio­tics. Some antibiotics are most effective against G+ infections, and others work best for G- infections. Both these kinds of drugs are called limited-spectrum antibiotics. However, various broad-spectrum antibiotics fight G+ and G- infections, as well as other bacterial in­fections.

Antibiotics used to treat chiefly G+ infections include clindamy­cin, erythromycin, and penicillin G. Those used for mainly G- infec­tions include colistin and gentamicin. Such antibiotics as chloram­phenicol and tetracycline fight both G+ and G- infections, as well as other types of bacterial infections. No limited-spectrum antibiotic works against all G+ infections or against all G- infections. Similarly, no broad-spectrum antibiotic is effective against all bacterial infec­tions. Research has shown which antibiotics work best against certain infections, and physicians follow these guidelines when prescribing drugs.

Other kinds of antibiotics. Antibiotics that fight pathogenic fungi include nystatin and griseofulvin. For example, griseofulvin is used to treat various fungus diseases, such as ringworm and other types of skin infections. Paromomycin is used to treat amebiasis, a disease caused by protozoa. Anticancer antibiotics include doxorubicin, which is used to treat acute leukemias, and bleomycin, which is used to treat Hodg-kin's disease.

Text 3

Read the text and say how antibiotics work according to the following plan:

  1. Prevention of cell wall formation.

  2. Disruption of the cell membrane.

  3. Disruption of chemical processes.

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