Understanding antibiotic resistance
Understanding antibiotic resistance

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Understanding antibiotic resistance

2.4 Transduction

The final mechanism of horizontal gene transfer you will look at is transduction. In this process, transfer of DNA from one bacterial cell to another is mediated by a virus.

Viruses that infect bacteria are called bacteriophages. When bacteriophages infect a bacterial cell, they insert their DNA into the bacterial cell genome. When it is time for the virus to replicate, it excises its DNA from the bacterial genome. However, this excision is imperfect and some bacterial DNA is accidentally excised and incorporated into the newly made virus. When these newly made viruses infect a different bacterial species, they carry this bacterial DNA, which may contain antibiotic resistance genes, and insert it into the genome of the new host bacterium (Figure 9).

Described image
Figure 9 Schematic diagram of transduction. When bacteriophage DNA, shown by a black dotted line, is excised from the bacterial genome it carries with it some bacterial DNA, shown in blue, from the infected bacteria. This DNA is incorporated into new bacteriophage particles which are released and infect new bacteria of a different species. The bacterial DNA from the original bacteria, in blue, is incorporated into the genome of the newly infected bacteria.

Activity 2 Comparing horizontal transfer mechanisms

Timing: Allow about 10 minutes

Below are some incomplete sentences. Type in the missing words using the following list of words:

horizontal, binary fission, vertical, conjugation, transformation, transduction, plasmid, chromosome, vertical gene transfer.

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Answer

Horizontal gene transfer can occur between bacteria of the same generation but vertical gene transfer requires binary fission.

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Answer

Conjugation is the only mechanism of horizontal gene transfer that requires direct contact between the donor and recipient bacteria.

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Answer

Conjugation, transduction and transformation can occur between bacteria of different types.

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Answer

Transduction is the only mechanism of horizontal gene transfer which requires a virus known as a bacteriophage.

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Answer

The bacterial genetic element transmitted by horizontal gene transfer is called a plasmid.

You will return to look at some specific examples of how genetic mutation and horizontal gene transfer can result in acquired resistance in the case study of cephalosporin antibiotics at the end of this week. Next you will look at how antibiotic resistance has developed through evolution and natural selection.

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