Different medicines serve different purposes. For example, some treat the cause of the disease (such as antibiotics), whereas some only treat the symptoms of the disease (such as painkillers).


Antibiotics are medicines that fight infections caused by bacteria. They do this in two main ways:

  • Killing bacteria
  • Slowing down the growth of bacteria or stopping its spread completely

So any substance that slows the growth and replication of bacteria or kills it completely is an antibiotic.

In 1928, Alexander Fleming discovered the first antibiotic, which is called penicillin. Upon returning from a holiday, he noticed that penicillium mould had grown on a petri dish containing bacteria. The mould appeared to be preventing the bacteria’s growth around it.

Comparative illustration of two Petri dishes. On the left, under "BEFORE", a Petri dish filled with agar shows dense, uniform bacterial growth. A close-up magnifies this growth, emphasising the bacterial colonies. On the right, under "AFTER", a similar Petri dish depicts the effect of an antibiotic disc, with a clear, bacteria-free zone surrounding it, known as the zone of inhibition. The close-up highlights the contrast between the dense bacterial colonies and the clear area resulting from antibiotic activity.

  • A zone of inhibition is an area around the antibiotic where bacteria growth is slowed or stopped completely

Different bacterial diseases, caused by various bacteria, require specific antibiotics for effective treatment. Some antibiotics work on one bacterial disease, but some can work on a few types.

Most antibiotics treat bacterial diseases, however, some can also treat parasitic and fungal diseases. Antibiotics are unable to treat viral diseases because they have a very different structure and method of survival than bacteria.

Antibiotics work by targeting structures and processes that bacteria have but animal cells and other pathogens do not. This means that antibiotics do not harm animal cells, which makes them an effective treatment.

  • For example, the antibiotic penicillin prevents bacteria from building a cell wall. Many types of bacteria have cell walls, but animal cells do not, so it is not harmful to animal cells.

The presence of antibiotics means that many bacterial diseases are now treatable. However, antibiotics not only target harmful bacteria but can also eliminate beneficial bacteria. This is bad because good bacteria often help our body fight infections.

Antibiotic resistance

Since their discovery, antibiotics have been widely used to treat various diseases. However, many antibiotics are no longer effective against certain bacteria because they have been overused. Scientists have found that many bacteria have evolved resistance to antibiotics. This is known as antibiotic resistance.

  • In some cases, this means that there are no treatments for certain conditions.

When we take an antibiotic, some bacteria are eliminated. However, there are some types of bacteria that survive because they are resistant to the antibiotic. They may have unique characteristics that prevent the antibiotic from working on them.

Illustration depicting the process of antibiotic resistance. Initially, a Petri dish contains a mix of both resistant (represented as pink capsules) and non-resistant bacteria (shown as yellow capsules). Upon adding antibiotics, as shown by a dropper, only the non-resistant bacteria are killed, leaving the resistant bacteria unaffected in a subsequent Petri dish. The final Petri dish showcases the multiplication of the antibiotic-resistant bacteria, dominating the environment. A legend at the bottom identifies the colours: yellow for non-resistant and pink for resistant bacteria.

With less competition for nutrients, the population of antibiotic-resistant bacteria will grow rapidly, spreading the resistance.

Reducing antibiotic resistance

If antibiotic resistance continues to grow, then bacterial diseases will become more difficult to treat in the future. Some methods of reducing antibiotic resistance are:

  • Using specific antibiotics to treat specific bacteria – If doctors prescribe the wrong antibiotics for treatment, this can promote the growth of antibiotic resistance.
  • Patients need to complete the prescribed course of antibiotics – Ensures that no bacteria are left, which can mutate to produce resistant strains.
  • Doctors should not prescribe antibiotics to treat viral diseases – Antibiotics are ineffective against viruses.
  • Patients infected with resistant strains of bacteria should be isolated from other patients – Prevents the spread of bacteria that is difficult to treat.
  • The use of antibiotics in agriculture should be limited – Administering antibiotics to healthy animals to promote growth and reduce disease has significant consequences. Some types of bacteria that are harmful to humans have developed a resistance and these bacteria can spread from animal to human hosts. However, there are now legal controls in place to limit their use.


Painkillers are medicines designed to relieve symptoms. Unlike antibiotics, they do not treat the cause of the disease, they just make it more manageable for the patient. This means that the immune system still needs to combat the pathogen.

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