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Antibiotics

 

Overview

Chances are you or somebody you know had a sore throat recently. Most sore throats are caused by viral infections. But some are caused by bacteria like streptococci.On occasion, sore throats caused by streptococci can lead to rheumatic fever, an illness which can cause pain in the joints and severe damage to heart valves. When examining a patient with a sore throat, a doctor does a throat culture to see if streptococcus is the responsible germ. This is done by wiping a cotton swab on the patient's throat and sending the sample to a laboratory. With the lab test results, the doctor can identify the causative germ and, if it is a bacterium, decide which antibiotic should be prescribed to help kill it. Antibiotics, once considered miracle drugs, have sadly been losing ground in the fight against the same disease-causing bacteria that they routinely vanquished in the past. Because bacteria grow rapidly, a single cell can potentially produce millions of new cells each day. As they divide and reproduce, these cells have a natural tendency to change or mutate. Since the 1950s, due in part to the improper use of antibiotics, mutations have led to bacteria developing traits that make them more resistant to antibiotics and thus more of a threat to public health. Through a complex process that involves the exchange of genetic information, some bacteria can even pass resistancealong to unrelated strains of bacteria. As people travel around the world they can spread resistant bacteria to other areas, further magnifying the extent of the problem. Antibiotics kill bacteria or arrest bacterial growth in a number of ways. Some, such as the quinolones and Rifampin, attack bacteria by interfering with their ability to divide. Others, such as the tetracyclines or aminoglycosides, prevent the manufacture of certain proteins essential to the bacteria. Penicillin antibiotics attack the ability of the bacterium to construct its cell wall. Through mutation, however, certain bacteria have acquired the ability to make a protein called penicillinase that destroys penicillin. Fortunately, scientists have been able to synthesize or make new antibiotics that penicillinase cannot destroy. Antibiotics frequently are viewed as a sure cure for whatever ails us and may be requested when they aren't necessary. For example, antibiotics don't work against diseases like the flu or sore throats caused by viruses. Inappropriate use contributes to the resistance problem. To stop this trend, you should take antibiotics only when needed. The proper antibiotic should be chosen and used exactly as directed. Even though you may feel better after taking the antibiotic for only a few days (since most of the bacteria causing the infection are killed), you should complete the entire recommended course for the medication to insure that all the germs are eliminated.
  • How do microbiologists determine which antibiotics are capable of killing particular bacteria?
  • What is the difference between prescription drugs and over-the-counter (OTC) medications?
  • Which bacteria are "good" bacteria, and what importance do they play in our lives?

Activity

Antibiotics are medications that can kill bacteria, but they are not bulletproof. The type of bacteria they destroy can vary and bacteria may develop resistance to antibiotics. Bacteria might undergo genetic changes that prevent the antibiotic from doing its job. If a bacterial cell is genetically changed it may continue to thrive, even when treated with an antibiotic. The following activity demonstrates how antibiotics work and how antibiotic-resistant bacteria can survive a medication's actions.

Materials

  • pieces of paper 7.5 cm x 15 cm (3" x 6"), one per person
  • straight pins, one per person
  • four different color markers--red, yellow, blue, and green
        
  1. On three of the pieces of paper, write the word green with the green marker to represent a trait that stops an antibiotic from working.
  2. On the remaining pieces of paper, write about an equal number of the words "red," "yellow," and "blue" in their corresponding ink, one per paper. The colors depict ways that an antibiotic can destroy a bacterial cell. Blue stands for the destruction of the cell's genetic material, red for breakdown of the cell wall, and yellow for an interruption in protein production critical to the cell's life.
  3. Combine the papers in a container. The participants should pick one paper each, to represent a specific trait of a bacterial cell, and pin their individual papers onto their clothes. Once done, each participant should stand next to her or his desk or chair.
  4. Explain what the blue, red, and yellow colors depict, omitting an explanation for the green resistance trait. After each color is explained, those "cells" wearing that color should sit down to indicate they've been destroyed by an effective antibiotic.
  5. Note that three people are still standing, each wearing a green tag. Explain that these cells represent antibiotic-resistant bacteria that contain a specific trait (the green tag) which protects them from the antibiotic and leaves them unharmed. In real life, these cells would survive, living in an environment with fewer bacteria to compete for food and space than before.
  6. If a bacterium can divide and produce 2 bacteria every 20 minutes, how soon will these three surviving resistant germs reach a total of one million organisms? 10 million? 100 million? One billion bacteria? Populations of this size, if pathogenic, are more than adequate to cause great harm.

    Questions

    1. What can happen to bacterial growth when there is little competition for food and space?
    2. How can a doctor know for sure that the prescribed antibiotic works against the bacteria causing a person's sickness?
    3. How many antibiotics do doctors have at their disposal? Which are the most common ones prescribed?

Resources

  • Levy, S.B. (1992) The antibiotic paradox: How miracle drugs are destroying the miracle.
    New York: DaCapo Press Inc.
  • Levy, S.B. (1993, Apr 14) Confronting multidrug resistance: A role for each of us.
    Journal of American Medical Association, pp. 1840-1842.
  • Schmidt, K.F. (1992, Oct 26) The troubling ghosts of scourges past. U.S. News & World
    Report, pp. 70-71.

Additional sources of information


Centers for Disease Control and Prevention
Center for Infectious Diseases
Office of Public Affairs
1600 Clifton Road NE
Atlanta, GA 30333
(404) 639-3401

American Society of Microbiology
1325 Massachusetts Ave.
Washington, DC 20005
(202) 737-3600

Community resources


Microbiology laboratory at hospital or clinic
Pharmacist