Antibiotic resistance

Antibiotic resistance is taught at a basic level at key stage 3 and in slightly more depth at GCSE. However, this tutorial is aimed at A Level.

Antibiotics normally work by weakening the cell wall. The antibiotics prevent the formation of peptide crosslinks. Water then enters the cell and the cell wall cannot withstand the pressure of the water and so the cell bursts which causes osmotic lysis.

However, due to random mutations it is possible for a single bacterium to gain resistance to an antibiotic. There are several ways that this can occur, but you need to know that the bacteria can produce a protein which is an enzyme that can break down the antibiotic.

Antibiotic resistance

Image of bacterium showing resistance supplied by Alila Medical Media. To see more microbiology images click on the link.

Once a bacterium has gained resistance, it is possible for it to either pass a copy of the gene onto another bacteria. This process is known as conjugation (Horizontal gene Transfer) or it can be passed onto daughter cells produced by the bacterium this is known as vertical gene transmission.

The Image below shows Horizontal gene transfer or conjugation. This image was supplied by Alila Medical Media. For more images of cells click on the link. This topic is normally taught at AS on AQA and A2 on OCR.

Bacterial conjugation

In the first diagram the conjugation tube starts to form.

On AQA the plasmid will replicate and then move through the conjugation tube.

However, on OCR the free DNA strand moves through the conjugation tube into the recipient cell and then replication starts to copy the DNA in both donor and recipient cells.

The conjugation tube will then close and the cells will move apart

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