Option D6: Antibacterials

D.6.1 Outline the historical development of penicillin

The discovery of the chemicals known as penicillin truly revolutionized modern medicine, as this gave birth to drugs now known as antibiotics. These are chemicals, usually produced by microorganisms, which act as against other microorganisms. Their discovery is generally credited to Alexander Fleming, who was a Scottish microbiologist, working in 1928 on bacteria cultures. He noticed that a fungus (or mould) known as Penicillium notatum had contaminated some of his cultures. It created a clear region around it where no bacterial colonies were growing.

The Australian bacteriologist Howard Florey and German-born biochemist Ernst Chain, working in Oxford, England, picked up the research and successfully isolated penicillin as the antibacterial agent produced by the penicillin mold.


D.6.2 Explain how penicillin work and discuss the effects of modifying the side-chain

Its core structure is a four-membered ring consisting of one nitrogen and three carbon atoms and known as beta-lactam, This part of the molecule is known to be responsible for its antibacterial properties. By acting as an irreversible inhibitor of an enzyme, it prevents the development of cross-links in bacterial cell walls, so weakening the walls and causing the bacteria to rupture and die during their reproductive phase.

D.6.3 Discuss and explain the importance of patient compliance and the effect of penicillin overprescription

A major problem with the us of penicillin and other antibiotic is that of bacterial resistance. This was observed as early as the 1940s when penicillin proved to be ineffective against some populations of bacteria. It is now known that these resistant bacteria produced an enzyme, penicillinase, which can open penicillin's beta-lactam ring and render it inactive.

Antibiotic resistance arises by genetic mutation in bacteria and would normally account for a very small proportion of the population. But the number of resistance organisms increases dramatically with increased exposure to the antibiotic. The problem of resistance has been compounded by the wide use of penicillin in animal feeds to lower the incidence of disease in stock.