Different types of 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. He returned from holiday and noticed penicillium mould growing on a petri dish of bacteria that he had left. The mould appeared to be preventing the growth of bacteria around it.

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

Different bacteria cause different diseases, so different bacterial diseases must be treated with different antibiotics that are known to work on them. Some antibiotics work on one bacterial disease, but some can work on a few types.

Most antibiotics treat bacterial diseases, however, some can 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 most bacterial diseases are now treatable. However, antibiotics don’t just kill harmful bacteria, they can also kill good 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 certain types of diseases. However, many antibiotics are no longer effective against certain bacteria because they have been overused. Scientists discovered that many bacteria have evolved, so antibiotics are unable to kill them. 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.

With lower competition for nutrients, the population of antibiotic-resistant bacteria will reproduce and the resistance will spread.

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 not effective at treating diseases caused by 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 – There is a large cost to treating healthy animals with antibiotics to promote growth and reduce disease. 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 that relieve the symptoms. Unlike antibiotics, they do not treat the cause of the disease, they just make it more manageable for the patient. So the immune system still needs to fight the pathogen.