Understanding antibiotic resistance
Understanding antibiotic resistance

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Understanding antibiotic resistance

Week 3: How do bacteria become resistant to antibiotics?

Introduction

In Week 2 you looked at how antibiotics target bacteria, either killing them or preventing their growth. But bacteria are constantly fighting back against this threat to their survival. Antibiotic resistance is the ability of pathogenic bacteria to resist the action of antibiotics so that they survive exposure to antibiotics that would normally kill them or stop their growth (CDC, 2017; PHE, 2017).

You could be forgiven for thinking that antibiotic resistance has been caused by our use, and misuse, of antibiotics. However, as you will see in the following video, bacteria that have not interacted with humans have acquired resistance to many of the antibiotic medicines we use to treat infections.

Download this video clip.Video player: Video 1
Skip transcript: Video 1 Antibiotic resistance is a natural bacterial defence mechanism.

Transcript: Video 1 Antibiotic resistance is a natural bacterial defence mechanism.

MICHAEL MOSLEY
It was in 2012 in a cave much deeper than I'm able to go that Hazel's team made their breakthrough discovery.
HAZEL BARTON
So the kind of areas that we sample look quite a bit like this.
MICHAEL MOSLEY
Hazel took a bunch of bacterial samples from the cave and sent them off to a lab for analysis. The results shocked everyone.
HAZEL BARTON
So I sent him just 100, and he started testing them. And he's like, you're not going to believe this, but they're resistant to everything. Everything that's used--
MICHAEL MOSLEY
So these were bacteria you found on a wall in a cave.
HAZEL BARTON
Much, much more remote than this, much further way.
MICHAEL MOSLEY
Had not seen humans for--
HAZEL BARTON
We know humans had never been in there because we have the exploration records. So there was no impact on it. And they were resistant to practically every antibiotic that's used in the clinic.
MICHAEL MOSLEY
That is both incredibly exciting and incredibly scary. Nobody had ever thought that you would find resistant bacteria down at the bottom of a bloody cave.
They had had no interaction with humans. But the bacteria Hazel found in the cave were resistant to a huge array of antibiotics we use in modern medicine. This resistance had clearly evolved over millions of years without us having anything to do with it. Why?
Well, it makes sense when you think of antibiotics not as man-made, but the byproduct of war between microbes. They make chemical weapons to destroy their enemies and steal their resources, weapons we have learned to exploit as antibiotics. The bacteria living deep in the cave have had millions of years to evolve weapons that can target and destroy even their toughest rivals. The battle for scarce resources, like nutrients and energy, is particularly brutal down here in the caves.
HAZEL BARTON
It's really starved down here. There's no resources. It's probably one of the most starved environments on Earth. Because if you think about it, any energy needs to come in through the rock. And so there's a big competition for nutrients.
MICHAEL MOSLEY
The fewer the resources, the more intensely the microbes battle. And that creates resistance. Because the bacteria under attack don't just lie back and die. When billions of bacterial cells are bombarded, all it takes is for one cell to mutate its DNA in such a way that the antibiotic can no longer kill it. This ability to resist then spreads fast. So developing resistance to antibiotics is an entirely natural process which the bacteria of Carlsbad have taken to the extreme.
End transcript: Video 1 Antibiotic resistance is a natural bacterial defence mechanism.
Video 1 Antibiotic resistance is a natural bacterial defence mechanism.
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You will return to look at how resistance has evolved and spread in Week 4. In this week, you will focus on how bacteria develop resistance in order to protect themselves from antibiotics. You will start by considering several mechanisms of antibiotic resistance before moving on to look at the differences between intrinsic and acquired antibiotic resistance. You will end the week by returning to the case study to explore the mechanisms responsible for resistance to third generation cephalosporins.

By the end of this week, you should be able to:

  • state what is meant by the term ‘antibiotic resistance’
  • recognise that antibiotic resistance evolved to protect bacteria
  • describe the three main mechanisms of resistance that bacteria have developed to counteract the action of antibiotics
  • give examples of these resistance mechanisms
  • distinguish between intrinsic and acquired antibiotic resistance.
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