D.6 Antibacterials

D.6.1 Outline the historical development of penicillins.
Discovered by Alexander Fleming, developed by Florey and Chain

Alexander Fleming (1928)
- mould contaminated some of his cultures, around it was a clear region where no bacterial colonies grew
- mould produced something that inhibited bacterial growth

Howard Florey & Ernest Chain (1940s)
- isolated penicillin as antibacterial agent
- used for the first time in WWII
- 1941: large scale production used deep fermentation tanks containing corn steep liquor & sterile air was forced in.

Dorothy Hopkins (1945)
- x-ray crystallography determine penicillin G structure


D.6.2 Explain how penicillins work and discuss the effects of modifying the side-chain.
Penicillin
- chemical used to kill pathogens (methylene blue in malaria treatment)
- 'magic bullet' - chemical designed to target a specific disease but not host cells (treated syphilis with arsenic bug)
- Prontosil: sulfonamide drug to cure septicaemia

*****Penicillin G can be broken down by stomach acid, therefore needs to be directly injected into the blood.
'R' = modified side chain - different forms of penicillin, therefore some enable drug to retain activity when ingested as a pill.*****

Bacterial resistance
- penicillin ineffective against some bacteria
- bacteria produced enzyme 'penicillinase' which can open the beta-lactam ring rendering it ineffective.

Antibiotic resistance
- bacteria genetic mutation
- no. of resistant organisms increase with increase exposure to antibiotics

Superbugs: bacteria which carry several resistant genes


D.6.3 Discuss and explain the importance of patient compliance and the effect of penicillin overprescription.
Response to antibiotic resistances:
- developing different forms of penicillin (modified side chains able to withstand penicillinase)
- controlling and restricting antibiotic use to make them prescription-only, encourage doctors not to prescribe them
- education and encouragement of patients in the importance of completing full treatment with an antibiotic - 'patient compliance', essential to prevent resistant bacteria prolonging

The use of penicillin in animal feed-stock when they are not ill also contributes to the resistance problem.