Option D.6 – Antibacterials

Option D.6 – Antibacterials

D.6.1 – Outline the historical development of penicillins.

Bacteria are single-celled microorganisms that often act as pathogens to infect humans and cause disease and death. Antibacterials began to be developed in the late 1800s. However, the discovery of penicillin in 1928 is considered to be the biggest turning point in the development of drugs called antibiotics.

 

Alexander Fleming was a Scottish microbiologist who came across penicillin by accident. When some of the bacterial cultures he was working with were contaminated by the fungus Penicillium notatum, he noticed that the bacterial colonies did not grow in the region around it. He identified that there must have been something produced by the mould that inhibits bacterial growth, but he did not continue his research to isolate the active ingredient.

 

 

It was not until Australian scientist Howard Florey and German-born Ernest Chain did further investigation that the drug itself was isolated and could be used to cure many lethal infections. They also determined its chemical composition and theorised its structure. However, it was Dorothy Hodgkin who actually confirmed its structure.

Testing penicillin on humans was initially very hard because of their difficulties with extracting penicillin in sufficient quantities to treat patients.

By 1944, during World War II, methods of producing large quantities of penicillin had been developed, which saves many lives during the war. Fleming, Florey and Chain all received the Nobel Prize for Medicine in 1945. Hodgkin received the Nobel Prize for Chemistry in 1964.

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

Penicillins work by interfering with the chemicals needed to form normal cell walls. This means that when water enters the cell by osmosis, the mechanical pressure on the cell causes it to burst and die. A cell wall that has its crosslinks successfully formed can resist this pressure. Penicillins are in a group called β-lactams, and all have the same general structure.

Depending on its R-group, penicillin will work in different environments. Some are acid-resistant. In other cases, modifying the side-chain results in penicillins which are more resistant to the penicillinase enzyme, which is produced by some bacteria. Amoxicillin is able to destroy a wider range of bacteria, and is usually given with clavulanic acid to inhibit penicillinase enzymes.

It is important to be aware that some people are allergic to penicillin, which can sometimes lead to serious reactions, anaphylactic shock and even death.

Also, when taken orally, penicillin may upset the balance of beneficial bacteria in the stomach and intestine, possibly leading to gastrointestinal disturbances, thrush or other infections.

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

If a patient is taking antibiotics, but does not complete the full course, any bacteria that are resistant to it will survive to pass on their genes. The problem of resistance in many pathogens has been caused by the fact that some patients stopped taking medication once their symptoms ceased, but not all of the bacteria had been killed yet. Therefore, patient compliance in completing their antibiotic courses is essential. Some bacteria have developed altered cell walls that prevent penicillin from binding.

 

 

Also, penicillin has sometimes been incorrectly prescribed to patients with viral infections, which has no effect on the virus, but may give further opportunity for the development of resistant strains of bacteria. Overprescription was a factor in the development of Methicillin-resistant Staphyloccus aureus, which is of major concern in hospitals. In addition, some farmers give animals antibiotics to control disease, but this means that drug-resistant bacteria are passed on to humans that consume them. With increasing cases of resistance in bacteria, research into developing new antibiotics is essential.