Understanding antibiotic resistance
Understanding antibiotic resistance

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Understanding antibiotic resistance

7.1 Back to the soil

Recent technological advances and innovations have allowed a much wider range of microbes to be cultured and novel species and new metabolites to be identified. For example, Activity 7 reveals how teixobactin was discovered in 2015 by a team of scientists in the USA who managed to isolate and culture a previously unidentified soil bacterium. Teixobactin is a new class of antibiotic which is active against Gram-negative but not Gram-positive bacteria (Ling et al., 2015).

Activity 7 Discovering teixobactin

Timing: Allow about 15 minutes

First, listen to the interview with Dr Kim Lewis, leader of the research team who discovered teixobactin.

Download this audio clip.Audio player: Audio 2
Skip transcript: Audio 2 Discovery of teixobactin.

Transcript: Audio 2 Discovery of teixobactin.

This is a very old problem in microbiology on cultured microorganisms. It's more than 100 years old. And people have tried to replicate the natural environment in the laboratory, and that actually didn't work very well. So we decided to do the exact opposite and simply grow them in their natural environment. And so the way we do that is we have a simple gadget, which we call a diffusion chamber. So we take a sample from soil, for example, dilute it, mix it up with agar, and instead of pouring it in a Petri dish, we sandwiched it between two semi-permeable membranes. And then this contraption, which we call diffusion chamber, that goes back into the soil where we took bacteria from. And so essentially, what that does, that tricks bacteria. Now, they don't know that something happened to them. Everything diffuses through that chamber. They get all the nutrients or growth factors from soil. And once they grow into colonies, then what we found is that with a high probability, they will then grow in a Petri dish. And now you can screen these organisms for their ability to make antibiotics.
We've been collaborating with NovoBiotic, a startup company that does a fairly massive screening using our methods. And one of their typical sources for soil is the backyard of Lucy Ling, VP of biology. And she lives in Lexington, Massachusetts. We got a very large number of anti-microbial compounds, about 30% of soil bacteria will make anti-microbials. And so the next important step is to try to figure out which are the ones that are potentially interesting and useful. And so this new compound, teixobactin, came out of that effort.
End transcript: Audio 2 Discovery of teixobactin.
Audio 2 Discovery of teixobactin.
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Now put the steps below in the correct order to match the culturing technique described by Dr Lewis.

Using the following two lists, match each numbered item with the correct letter.

  1. Collect soil sample

  2. Mix diluted soil sample with agar

  3. Sandwich sample between semi-permeable membranes

  4. Place diffusion chamber in soil

  5. Remove diffusion chamber from soil

  6. Select colonies and grow in a Petri dish

  7. Screen for ability to make antibiotics

  8. Assess compounds for efficacy and usefulness

  • a.Fifth

  • b.Fourth

  • c.Eighth

  • d.First

  • e.Second

  • f.Seventh

  • g.Sixth

  • h.Third

The correct answers are:
  • 1 = d
  • 2 = e
  • 3 = h
  • 4 = b
  • 5 = a
  • 6 = g
  • 7 = f
  • 8 = c

What are the advantages of this new technique?


It re-creates the normal growing conditions of the bacteria, allowing them to be successfully cultivated. The recovery rate by this method is 50% compared with only 1% of cells from soil samples cultured on a Petri dish (Ling et al., 2015).


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