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Understanding antibiotic resistance
Understanding antibiotic resistance

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1 Disrupting bacterial communication

Bacteria are single-cell organisms. For many years, they were thought to act as individuals and not be influenced by the bacteria around them. However, bacteria can communicate with each other in a process called quorum sensing.

Activity 1 What is quorum sensing?

Timing: Allow about 10 minutes

Watch part of the video at the following link in which Bonnie Bassler from Princeton University describes the discovery of quorum sensing.

The discovery of quorum sensing [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] . Watch from 51:24 until 53:57.

Now answer the following questions, based on the video.

  1. When do the fluorescent bacteria Vibrio fischeri fluoresce (emit light)?

a. 

a) When they detect other bacteria


b. 

b) When they are on their own


c. 

c) Always


d. 

d) Never


The correct answer is a.

Answer

The correct answer is (a) when they detect other bacteria. Vibrio fischeri use quorum sensing to detect the presence of other bacteria and alter their behaviour so that they fluoresce.

  1. How do the bacteria detect the presence of other bacteria?

a. 

a) Using chemical messengers


b. 

b) By touching each other


c. 

c) Both of the above


The correct answer is a.

Answer

The correct answer is (a) chemical messengers. Bacteria release chemical messengers that build up as the number of bacteria increases. Above a critical level, receptors on the surface of bacteria detect the chemical messenger and change their behaviour.

  1. Which of the following statements about quorum sensing are true?

a. 

(a) Quorum sensing is the mechanism that bacteria use to communicate.


b. 

(b) Quorum sensing allows bacteria to synchronise changes in their behaviour.


c. 

(c) Quorum sensing allows bacteria to detect the presence of other bacteria.


d. 

(d) All of the above


The correct answer is d.

Answer

The correct answer is (d) all of the above. Quorum sensing is the process by which bacteria use chemical messengers to detect and communicate with other bacteria, in order to synchronise changes in their behaviour.

As you saw in Activity 1, bacteria release chemical messengers which can be used to detect the presence of other bacteria. When the number of bacteria reaches a critical level, these chemical messengers cause bacteria to alter their behaviour (Figure 2).

A schematic diagram illustrating quorum sensing.
Figure 2 During quorum sensing, chemical messengers are produced and detected by bacteria. (a) When the number of bacteria (in blue) is low, levels of chemical messenger (red triangles) are low. (b) When the number of bacteria (in green) reaches a critical level, the high levels of chemical messenger (red triangles) are detected by other bacteria, causing them to alter their behaviour.