4.1.1(m)-(n) - Medicines, antibiotics and resistance

Medicine Sources

A medicine is a substance used to prevent, treat or manage disease. Microorganisms and plants are possible sources of medicines. This does not mean every useful medicine is simply eaten as a plant or grown as a mould; it means living organisms can produce chemicals that scientists isolate, test, modify, manufacture and regulate.

Microorganisms are a major source because they compete chemically with other organisms. The classic example is penicillin, an antibiotic first discovered from a Penicillium fungus. Other antibiotics have been found from soil microorganisms, including bacteria in the genus Streptomyces. In each case, the useful medical story begins with a molecule made by a living organism, but it only becomes a medicine after evidence shows that it can be used safely and effectively.

Plants are also important sources. Paclitaxel, used in cancer treatment, was originally developed from the Pacific yew tree. Artemisinin, used against malaria parasites, comes from sweet wormwood. These are not examples to memorise as a fixed list; they show the principle that different species may contain different biologically active chemicals.

Maintaining biodiversity matters because a species that becomes extinct can no longer be studied as a possible source of new useful compounds. There is also genetic biodiversity within a species: different populations may produce slightly different chemicals or different quantities of a useful compound. Conserving habitats, plants and microorganisms therefore preserves future options for medicine discovery.

A common mistake is to write as if "natural" means "safe". It does not. Many natural compounds are toxic. A biological source is only the start of the evidence chain: scientists still need controlled testing, dose studies, peer review and regulation before a compound can become a medicine.

Personalised Medicines

Personalised medicine has potential, but this is a developing application of biology, not a promise that every treatment can already be perfectly tailored.

The basic problem is that patients can respond differently to the same drug. One patient may break down a drug slowly and experience side effects at a normal dose. Another may have a disease with a molecular marker that makes one treatment more likely to work. Personalised medicine aims to use biological information before treatment, rather than relying only on trial and error after symptoms or side effects appear.

The potential benefits are clear:

There are limits and risks too. A genetic association must be validated by good evidence before it is used for patient care. Genomic data are personal, so privacy and consent matter. Tests may not work equally well for all populations if the original research did not include diverse groups. Personalised medicine is therefore a good HSW example: science can improve decisions, but society must evaluate benefits, risks, cost and access.

Antibiotics And Penicillin

An antibiotic is a medicine used to manage bacterial infection by killing bacteria or inhibiting their growth. Antibiotics do not treat viral infections, because viruses do not have the same bacterial structures or processes for antibiotics to target.

The discovery and development of penicillin changed medicine in the mid-20th century. Before effective antibiotics were widely available, bacterial infections from wounds, childbirth, pneumonia or surgery could be much more dangerous. Once penicillin and later antibiotics could be produced and prescribed widely, many bacterial infections became treatable.

The benefits of antibiotics include:

• reducing bacterial growth so the immune system can clear infection more effectively
• preventing a local bacterial infection from spreading or becoming life-threatening
• making surgery, cancer treatment and other medical procedures safer because bacterial infection can be managed

The risks come from the same biological fact that makes antibiotics powerful: they affect living bacterial populations. Antibiotics can cause side effects or allergic reactions in some people, and they can also kill useful bacteria in the body. A major risk is that antibiotic use selects for antibiotic-resistant bacteria.

Penicillin interferes with formation of the bacterial peptidoglycan cell wall. In susceptible growing bacteria, a weakened wall cannot withstand osmotic pressure and the cell may lyse. Viruses have neither a peptidoglycan wall nor their own bacterial ribosomes, explaining why a bacterial target cannot simply be transferred to antiviral treatment.

Resistance Selection

Antimicrobial resistance means microorganisms are no longer controlled effectively by a medicine that would normally act against them. Antibiotic resistance specifically concerns bacteria.

Resistance usually begins with genetic variation. A bacterial cell may already carry a mutation that changes the antibiotic target, increases antibiotic breakdown, reduces antibiotic entry, or pumps the antibiotic out. A bacterium may also acquire a resistance gene from another bacterium, often on a plasmid. You do not need detailed molecular mechanisms here; the key is that the bacterial population is not genetically uniform.