2.2 Introducing acquired resistance
As its name suggests,
Unlike intrinsic resistance, acquired resistance is only found in some populations of a bacterial type. This makes acquired resistance harder to track since each new outbreak or isolate may have acquired resistance to a different spectrum of antibiotics.
Acquired resistance is a very significant healthcare concern. Infections caused by bacteria that have acquired resistance to an antibiotic can no longer be treated with that antibiotic. Consequently, identifying the type of pathogenic bacteria causing an infection may not always be sufficient to determine which antibiotics will be effective treatments. Resistant isolates must be tested to determine which antibiotics are effective before treatment can be prescribed.
Activity 2 Acquiring multidrug resistance
The treatment options for infections caused by bacteria with acquired resistance can be further limited because bacteria can accumulate resistance to a variety of antibiotics over time. This is known as
Perhaps the most often cited example of intrinsic resistance is the multidrug resistance of Gram-negative bacteria.
Can you suggest why Gram-negative bacteria might be intrinsically resistant to many antibiotics?
Answer
Unlike Gram-positive bacteria, Gram-negative bacteria have an outer membrane which is impermeable to many antibiotics.
Now read the following BBC news article which highlights that, although multidrug resistance is rare, it can have a devastating impact.
Article 1 Bug resistant to all antibiotics kills woman [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)]
While you read the article, note down the answers to the following questions.
1 Which bacterium caused the patient’s infection?
Answer
The patient’s infection was caused by the Gram-negative bacterium Klebsiella pneumoniae.
2 How many antibiotics was the infection resistant to?
Answer
It was resistant to 26 different antibiotics, including the ‘drug of last resort’ – colistin.
3 Is resistance to all antibiotics a common occurrence?
Answer
No, infections that are resistant to all antibiotics are uncommon.
Acquired resistance can occur as a result of genetic mutations or the transfer of resistance elements from other bacteria through a process called horizontal gene transfer. Don’t worry if you don’t understand these terms yet. You will return to these processes in Week 4.
Activity 3 Comparing intrinsic and acquired resistance
Look at the following statements in the table. Decide whether they are about intrinsic or acquired resistance or both and type your answer into the right-hand column.
| Statement | Intrinsic resistance, acquired resistance, or both? |
|---|---|
| Mechanism only present in a subpopulation of bacteria of a given type | |
| Difficult to track | |
| Can be identified if the bacterial type is known | |
| Normal for bacteria of that type | |
| Limits treatment options | |
| Mechanism present in all bacteria of a given type | |
| Occurs as a result of genetic mutation or horizontal gene transfer |
Answer
| Statement | Intrinsic resistance, acquired resistance, or both? |
|---|---|
| Mechanism only present in a subpopulation of bacteria of a given species | Acquired resistance |
| Difficult to track | Acquired resistance |
| Can be identified if the bacterial species is known | Intrinsic resistance |
| Normal for bacteria of that species | Intrinsic resistance |
| Limits treatment options | Both |
| Mechanism present in all bacteria of a given species | Intrinsic resistance |
| Occurs as a result of genetic mutation or horizontal gene transfer | Acquired resistance |