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Chapter 24: Problem 6

On the news, you hear a CDC scientist explaining that the widespread overuse of antibiotics will do nothing but select for antibiotic-resistant bacteria. You argue with your friend, who is also watching the segment, that the drugs do not cause the resistance. He doesn't believe you. Explain to your friend, then, how excessive use plays a role in resistance.

Short Answer

Expert verified
Overuse of antibiotics selects for, but does not cause, antibiotic resistance.

Step by step solution

01

Understanding Natural Selection

The process of natural selection is key to understanding antibiotic resistance. In any population of bacteria, there are natural variations with some individuals potentially having or developing traits, like resistance to antibiotics. These variations are crucial as they determine who survives environmental pressures.
02

Antibiotics as Environmental Pressure

When antibiotics are used extensively, they act as a selective pressure, killing off susceptible bacteria and leaving only those with resistance. This resistant population then has more space and resources to grow.
03

Survival of the Fittest Bacteria

The resistant bacteria, having survived the antibiotic treatment, reproduce and pass on their resistant traits to their offspring. Over time, the population shifts to being predominantly resistant.
04

Role of Overuse in Resistance

Overusing antibiotics accelerates the natural selection process by frequently exposing bacteria to these drugs, thereby giving an advantage to resistant strains and rapidly increasing their prevalence.
05

Clarifying the Role of Antibiotics

Thus, while antibiotics do not create resistance, their misuse and overuse select for resistant bacteria by giving them a survival advantage over non-resistant strains.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Natural Selection
Natural selection is a fundamental concept explaining how antibiotic resistance develops. In any population, such as bacteria, not all individuals are identical.
Some bacteria might carry random genetic mutations that provide resistance to antibiotics, while others do not.
These genetic variations, though small, are crucial when the population is faced with changes in their environment.

When bacteria are exposed to antibiotics, those with favorable traits, such as antibiotic resistance, survive and reproduce.
  • This process means that stronger traits are passed down to the next generation.
  • The "fittest" bacteria continue to thrive, multiplying over time.
As a result, natural selection plays a critical role in shaping resistant populations over successive generations.
Antibiotics Misuse
Misuse of antibiotics is a significant factor that accelerates the development of resistant strains. Every time antibiotics are used unnecessarily or incorrectly, they create a spot of "training ground" for bacteria to test their resistance.
Common scenarios of misuse include:
  • Using antibiotics for viral infections where they are ineffective.
  • Not completing the prescribed course, which leaves behind surviving bacteria.
  • Overprescribing antibiotics or using them as preventive measures in agriculture.
Each instance of misuse contributes to the bacteria's exposure to these medications, promoting the survival and spreading of resistant strains.
This misuse, therefore, does not cause resistance itself but supercharges the process, making resistant strains more common and harder to eliminate.
Bacterial Evolution
Bacterial evolution describes the change in genetic makeup of bacterial populations over time, driven by factors like natural selection.
When antibiotics are applied, they eliminate susceptible bacteria but leave the resistant ones unharmed.
These surviving bacteria then reproduce, and
  • pass on their resistant traits to successive generations,
  • gradually shifting the overall population toward resistance.
Evolution in bacteria occurs rapidly compared to multicellular organisms, due to their fast reproduction rates.
This quick turnover means that antibiotic-resistant traits can spread swiftly within a population, challenging the effectiveness of our current treatments.
Selective Pressure
Selective pressure refers to environmental factors that influence which individuals survive and reproduce. In the context of antibiotic resistance, antibiotics act as powerful selective pressures.
When they are used:
  • They kill non-resistant bacteria, removing them from the population.
  • Resistant bacteria remain and have less competition for resources.
Consequently, these conditions favor resistant bacteria, allowing them to multiply more effectively.
The pressure exerted by antibiotics hastens the natural selection process, ensuring that only bacteria with resistance traits thrive. This rapid adaptation highlights the importance of using antibiotics carefully, to avoid enhancing this selective pressure and reducing our ability to treat bacterial infections effectively.

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Most popular questions from this chapter

You learned that combating fungal and protozoal infections is complicated by the fact that these microbes share many of the same features with the cells of their hosts. Explain how the antifungal drugs known as polyenes and the antiprotozoal drug chloroquine can still show selective toxicity.

Your family friend is HIV positive and takes the drug AZT, along with a cocktail of other antiviral medications. You learn that AZT specifically targets retroviruses, but that HIV develops resistance to this drug. Explain the mechanism that this drug uses to combat a retrovirus such as HIV, and how resistance to AZT develops.

You are part of a research team that has managed to resurrect microbes from the frozen remains of several Ice Age mammals. Out of curiosity, you elect to run a Kirby-Bauer disk diffusion test on one of the bacterial isolates. To your surprise, the lce Age isolate shows resistance to several antibiotics. Explain why this is possible.

You learned in this chapter that there are varied recommendations for use of the oral and/or inactivated polio vaccines, depending upon the location. Explain the reasoning behind these recommendations in a way that members of the general population could understand and accept.

According to the World Health Organization, drug-resistant strains of Mycobacterium tuberculosis are more likely to appear in HIV patients than in tuberculosis patients that are HIV-negative. Provide a hypothesis of why this occurs.
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