(11) Antiseptics and antiviral drugs kill or inhibit the growth of pathogens

See also Culturing microorganisms like bacteria - testing antiseptics and antibiotics

(11a) Antiseptics

Antibiotics kill pathogens in your body, antiseptics kill pathogens outside of your body e.g. on the surface of your skin or disinfecting surfaces in the kitchen.

Antiseptics are used to clean wounds by killing microorganisms or stopping them multiplying.

The use of antiseptics in hospitals and GP surgeries is vital to prevent the spread of infectious diseases like MRSA.

You should always cleanse-disinfect your hands with the facilities provided before visiting someone in hospital.

There are many commercial antiseptic cleaning substances available for your kitchen, toilets etc.

Most claim to 'kill 99% of all germs' !!!!

 

(11b) Antifungal agents

Fungal infections can be treated with antifungal chemicals that kill or inhibit the growth of a fungus.

e.g. antifungal chemicals kill or prevent the growth of fungi microorganisms like creams used for the treatment of the fungal infection athlete's foot.

 

(11c) Antiviral drugs

Viral infections

It isn't just bacteria that can mutate, viruses can also evolve via new mutations.

Viruses are notable for the rapidity with which they can mutate which makes it difficult to develop new vaccines.

The reason being that changes in the virus (or bacteria) DNA leads to different gene expression in the form of different antigens, so different antibodies are needed.

The flue virus is a never ending problem and in the past pandemics (epidemics across many countries at the same time) have killed millions of people, mercifully this rarely happens these days thanks to antibiotics.

As I'm re-editing this page in 2020, the World is suffering from the Covid-19 pandemic!

Antivirals are drugs used to treat viral infections.

Most antiviral drugs do not kill the virus but stop them reproducing.

Since the virus uses your cell chemistry to reproduce, it is difficult to develop a drug that only targets the virus with side-effects and tissue damage i.e. killing your own body cells.

They are not easy to develop as effective anti-virus agents because it is difficult to target the virus without damaging the host cells.

They are also costly to develop.

 

(11d) Why don't antiseptics and antibiotics counteract viral infections?

Antibiotics can't destroy viruses like the common cold or flue.

This is because a virus is NOT a living organism like plant or animal cells, so viruses don't have a cell wall or any of the organelles that function in living cells for life maintenance, growth and reproduction.

Antibiotics work by interfering with these life processes, but since viruses don't function like this, antibiotics don't affect viruses.

Viruses replicate in host cells by 'hijacking' their genetic machinery, but antibiotics are designed not to attack your healthy cells, so they don't affect the viral infection of your healthy cells.

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Key points Source of information is based on textbooks and syllabus-specifications for students taking the AQA GCSE, Edexcel GCSE and OCR GCSE level biology examinations (~US grades 9-10).

Key points and more examples of anti-pathogens like antiseptics, antifungal agents and antiviral drugs

Controlling Pathogens: Antiseptics, Antifungals and Antivirals

1. Antiseptics

• Definition: Chemicals applied to the outside of the body or on surfaces to kill or inhibit the growth of microorganisms.

• How they work:

  • Disrupt microbial cell membranes.

  • Denature proteins and enzymes.

  • Prevent replication of bacteria, fungi, and some viruses.

• Examples: Alcohol-based hand sanitizers, iodine, hydrogen peroxide.

• Uses:

  • Cleaning wounds.

  • Sterilising surgical tools and hospital surfaces.

  • Reducing spread of infections like MRSA.

2. Antifungal Agents

• Definition: Drugs that kill or inhibit the growth of fungi.

• How they work:

  • Disrupt fungal cell membranes (e.g. by targeting ergosterol, a key component).

  • Inhibit fungal enzymes or DNA replication.

• Examples: Clotrimazole, miconazole, fluconazole.

• Uses:

  • Treating athlete’s foot, ringworm, and thrush.

  • Often applied as creams, sprays, or oral medication.

3. Antiviral Drugs

• Definition: Drugs used to treat viral infections by interfering with virus replication.

• How they work:

  • Block virus entry into host cells.

  • Inhibit viral enzymes (e.g. reverse transcriptase in HIV).

  • Prevent release of new viruses from infected cells.

• Examples: Oseltamivir (Tamiflu), acyclovir, antiretrovirals for HIV.

• Challenges:

  • Viruses mutate rapidly.

  • Drugs must target viruses without harming host cells, which is difficult since viruses replicate inside them.

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Why Don’t Antiseptics and Antibiotics Work Against Viruses?

• Antiseptics:

  • Mostly act on external surfaces.

  • May reduce viral particles on skin or surfaces but do not treat internal viral infections.

• Antibiotics:

  • Target bacterial structures like cell walls, ribosomes, or metabolic pathways.

  • Viruses lack these structures — they are not cells and don’t carry out their own metabolism.

  • Viruses replicate inside host cells, making them inaccessible to antibiotics.

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Importance in Human Biology and Exam Relevance

Understanding these agents is crucial because:

• It helps explain how we prevent and treat infectious diseases.

• It highlights the differences between pathogens (bacteria, viruses, fungi).

• It reinforces the concept of selective toxicity — drugs must harm pathogens without damaging human cells.

• It links to public health: overuse of antibiotics leads to resistance (e.g. MRSA), and misuse of antivirals can lead to treatment failure.

• It supports scientific literacy: knowing why antibiotics don’t work on colds or flu helps reduce unnecessary prescriptions.

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Learning objectives for this section on antiseptics and antiviral drugs

Know how antiseptics, antifungal agents and antiviral drugs kill or inhibit the growth of pathogens like bacteria and be able to explain why antibiotics don't kill viruses.

• Be able to describe how antiseptics can be used to prevent the spread of infection.

  • Antiseptic chemicals are designed to prevent infection rather than treat and cure an existing infection - prevention is always better than a cure!

  • Antiseptics are chemicals that are applied to the outside of your body to kill pathogens like bacteria or prevent their growth.

  • Antiseptics help to prevent infection of cleaned skin wounds and the surface of the skin e.g. a larger area where a surgical operation might be done and they are also applied to surfaces where hygiene is important e.g. in the bathroom.

  • Antiseptics range from those used in the home e.g. for cuts and bruises, toilet cleaners, treating food preparation surfaces, and in GP surgeries, and in hospitals to prevent infection during operations and on hospital wards to prevent the spread of dangerous pathogens like MRSA - you should always clean your hands with the antiseptic facilities provided when visiting friends or relatives in hospital.

• Antifungal to treat fungal infections

  • Antifungal chemicals kill or prevent the growth of fungi microorganisms e.g creams for the treatment of the fungal infection athlete's foot.

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