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D6-Antibacterials

D6-Antibacterials

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D6-Antibacterials

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  1. D6-Antibacterials

  2. D.6.1 Outline the historical development of penicillins. • In 1928, Alexander Fleming was working with cultures of Staphylococcus aureus, a bacterium that causes boils and other types of infections. • He accidently left open one of the petri dishes (ooops!) • He later found mold growing, but no bacteria around the mold. • He concluded that the mold (Penicilliumnotatum) inhibited growth of bacteria, but he could not isolate and purify it.

  3. D.6.1 Outline the historical development of penicillins. • In 1941, Ernst Chain and Howard Florey were able to isolate the fungus and test it with mice which were injected with a deadly bacteria. The mice treated with penicillin survived. • After testing it on a policeman with an infection, the mass development of penicillin began in the U.S. • Thousands of troops during WWII survived infections caused by wounds due to the penicillin.

  4. D.6.2 Explain how penicillins work and discuss the effects of modifying the side-chain. • Bacteria have cell walls which eukaryotic cells do not. • The cell walls are created by cross-linking of peptidoglycan. • Penicillin G interferes with the enzyme that creates these cross-links. • The cell wall weakens, causing the bacteria to burst (lyse) easily due to osmotic pressure.

  5. D.6.2 Explain how penicillins work and discuss the effects of modifying the side-chain. Modifying the Side Chain • Penicillin G is deactivated by stomach acid, but can resistant to acid by modifying the side chain.

  6. D.6.2 Explain how penicillins work and discuss the effects of modifying the side-chain. • Bacteria can also become resistant to penicillin by building enzymes which deactivate the penicillin (pencillinase) or having a modified enzyme for building the cell wall which does not allow the penicillin to bind to it. • Modifying the side chain can sometimes overcome these types of resistance.

  7. D.6.3 Discuss and explain the importance of patient compliance and the effect of penicillin overprescription. • Antibacterials can wipe out helpful bacteria (especially in the gastrointestinal system). • Because of overprescription and use in animal feedstock, some bacteria have evolved to become extremely resistant to penicillin. • With drug-resistant bacteria, a “cocktail” of different antibacterials are used to overcome the infection.