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Understanding antibiotic resistance
Understanding antibiotic resistance

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2.1 Inhibitors of cell wall synthesis

As you saw in Activity 2, the cell wall is essential for normal functioning of the bacterial cell. Antibiotic inhibitors of cell wall synthesis block the production of peptidoglycan, the main component of the cell wall. Cross-linking between peptidoglycan chains forms a strong, mesh-like structure that gives the cell wall structure and rigidity, and protects the underlying cell membrane from osmotic damage when water moving into the cell by osmosis could cause it to burst, or lyse. Disruption of the peptidoglycan layer of the cell wall can therefore result in cell lysis (Figure 3).

Described image
Figure 3 Lysis of a bacterium with a defective cell wall. (a) Diagram showing the sequence of events that lead to lysis. (b) Light micrograph of S. aureus: a lysed cell on the left and an intact dividing cell on the right.

Examples of cell wall synthesis inhibitors are the ß-lactam antibiotics. These include penicillin and its derivatives, and the cephalosporins. All ß-lactam antibiotics contain a core chemical structure called a ß-lactam ring (Figure 4) which determines the mode of action of this class of antibiotics.

An image of the core ring structures of penicillins (top) and cephalosporins (bottom).
Figure 4 Core ring structures of two types of β-lactam antibiotics. The β-lactam ring is shaded pink in each case.

The ß-lactam antibiotics interfere with the formation of the peptidoglycan cross-links, thereby weakening the cell wall. You will learn more about the precise mechanism in this week’s case study (Section 3). For now, you can see the effect of the disrupted cell wall on bacterial growth in Video 3.

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Video 3 A ß-lactam antibiotic in action.
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