Antibiotics and Bacterial Resistance

The discovery of antibiotics forever changed the way disease is treated. These “wonder drugs” save millions of lives every year by killing or stopping the reproduction of potentially deadly bacteria. Diseases such as scarlet fever have been virtually wiped out in developed countries. Many fewer people die from infections today than 100 years ago. Still, despite these important gains, the future of this medical treatment is uncertain, due to the very nature of bacteria. Bacteria are single-celled organisms that are too small to be seen with the naked eye. They reproduce by simple cell division; offspring are therefore usually genetically identical to their parent. Bacteria replicate very quickly, on average about once very 20 minutes. So, within the span of a few days, a small number of bacteria can grow to millions. Bacteria are everywhere. Therefore, if a type of bacteria is harmful, it threatens and can affect a large number of people very quickly. For this reason, it is important to have a means to prevent bacteria from spreading and thereby stop the disease from spreading. Antibiotics work either by killing specific bacteria, called strains, or by slowing their growth. Alexander Fleming of Scotland discovered antibiotics in 1929 when he found that penicillium mold could stop bacteria from growing. This mold contains a compound called penicillin that stops the growth of bacteria by hindering their ability to build cell walls. This helps prevent the bacteria from reproducing and leaves them vulnerable to attack by the body’s immune system. After Fleming’s initial discovery, biologists found many additional substances capable of destroying bacteria by stopping their cellular functions. Some are chemicals extracted from living things; others are developed in laboratories. Antibiotics are used to treat a wide variety of bacterial illnesses such as strep throat, infections of wounds, and pneumonia. One problem that has arisen with antibiotics is that some bacteria are able to resist them. Antibiotic resistance occurs when bacteria become immune to a substance that is designed to kill them. Bacteria can become resistant to drugs quite easily. Their ability to do this relates to a driving force of nature known as “survival of the fittest.” When bacteria reproduce, resistant bacteria will continue to reproduce as other strains die out. Eventually the resistant bacteria become the norm. If these bacteria are disease causing they can pose serious threat to human populations. Improper use of antibiotics can contribute to the development of super-resistant bacteria. Antibiotics do not work on viral illnesses such as colds and flu. If people take antibiotics for such illnesses, the drugs will do nothing to make them feel better and will kill nonresistant bacteria unnecessarily. Resistant bacteria will not be killed, and they will take over the bacteria population. Although the development of super-resistant bacteria is unfortunate from a medical standpoint, it is a remarkable process. By introducing antibiotics into bacteria populations, humans have accelerated bacterial evolution, creating bacteria that are more fit to survive attacks by their enemies, including antibiotics. Prelab: Answer the questions below based upon what you read on the previous page.

1. It sates in the passage that resistant bacteria could become the “norm.” What is meant by this term?

2. Which of the following statements could be inferred from this passage?

a. Reducing the inappropriate use of antibiotics would lessen the threat of super-resistant bacteria. b. All bacteria will eventually become antibiotic-resistant. c. Medical researchers are paying increasing attention to super-resistant bacteria.

3. If I were to catch a cold, would it benefit me to take antibiotics? Why or why not?

4. Identify three antibiotics.

5. Antibiotics interfere with a bacteria’s ability to ______. Bacterial Resistance To Antibiotics (Evolution in Action)

Generation # of # of Non- Total # of Freq of Freq of Resistant resistant Alleles Resistant Non- Genes Genes (Red) Genes resistant (Black) (Black) Genes (Red) Gen. 0

Gen. 1

Gen. 2

Gen. 3

Gen. 4 *

Gen. 5

Gen. 6

Gen. 7 *

Gen. 8

Gen. 9 *

Gen. 10

Gen. 11

Gen. 12 *

Gen. 13

Gen. 14

NOTE: Those generations marked with an asterisk (*) are those that have been exposed to penicillin. Analysis

1) Graph the changes in gene frequency for both the resistant and non- resistant gene over the 14 generations.

2) Describe the changes in frequency, if any, of the resistant and non- resistant genes in each of the following generation spans. Be sure to explain the reasons for these results and support with data.

a) Generations 0-3:

b) Generations 4-8:

c) Generations 9-14:

3) Has evolution occurred? How do you know?

CRITICAL THINKING

 Have any mutations occurred? What does this tell us about the role of mutations in evolution?

 Predict what will happen to the frequencies of each gene of the next 30 generations if penicillin usage is continued. Why do you think this?

 If our bacterial population becomes completely immune to penicillin how will we fight a future infection of the same bacteria?