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Body defences: 11. The use of antibiotics - antibacterials

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There are various sections to work through, after 1 they can be read and studied in any order.

Sub-index of notes: Our body's defence mechanisms against infections from pathogens, help from vaccines & drugs


(10) Antibiotics (antibacterials) to kill or inhibit bacterial pathogens

See also Culturing microorganisms like bacteria - testing antiseptics and antibiotics  gcse biology revision notes

Note on terminology

An antibiotic is a chemical compound that inhibits the growth or kills bacteria.

In recent years, 'antibiotic' has become synonymous with the term 'antibacterial'.

An antibacterial is defined as a drug, chemical or other substance that kills bacteria (bactericidal) or stops their growth (bacteriostatic).

Some diseases can be prevented by vaccination and some can be cured with drugs.

Unlike 'symptom relievers' like aspirin, antibiotics like penicillin do kill or inhibit the growth of certain bacterial infections.

However, they are not a 'blanket cure', different types of bacteria require different types of antibiotic and the correct match is required to effect a cure.

Never-the-less, the widespread use of antibiotics has greatly reduced the number of deaths from communicable diseases caused by bacteria.

Unfortunately, antibiotics do NOT destroy virus infections from e.g. flue or cold viral infections.

Virus attacks can be treated with very specialised and expensive anti-viral drugs, but since viruses reproduce in your own body cells, its difficult to avoid damage to you own healthy body cells.

Other drugs e.g. the antibiotic penicillin do kill or inhibit the growth of certain bacterial infections by interfering with the pathogen's metabolism e.g. the biochemical processes that build bacterial cell walls.

Antibiotics do not affect human cells AND they do not kill fungal, protist and viral pathogens - they only kill bacteria.

Bacteria are single-celled organisms that rapidly divide.

Most are harmless, but some are not, causing bacterial infections.

Antibiotics, including penicillin, are medicines that help to cure bacterial disease by killing infectious bacteria or inhibiting their growth inside the body, without killing your own body cells!

What is an antibiotic? How do they work?

NOTE: An antibiotic kills bacteria in the body.

BUT an antiseptic kills bacteria outside the body e.g. on the skin or disinfecting a worktop in the kitchen - do NOT ingest an antiseptic.

Antibiotics cannot be used to kill viral pathogens, which live and reproduce inside cells.

Antibiotics do NOT destroy viruses, typified by the cold and flue viruses we all suffer from.

Why don't antibiotics kill viruses?

Viruses and bacteria have significantly different structure and a different way of surviving.

Viruses are surrounded by a protective protein coating and don't have cell walls that can be attacked by antibiotics - antibiotics prevent bacteria building cell walls and the membrane bursts destroying the bacterial cell.

Viruses make your own body cells reproduce the invasive virus and unfortunately anti-viral drugs may attack good cells too!

It is quite difficult, and costly, to develop and market anti-viral drugs that will only kill the virus and not your own body's healthy cells.

Antibiotics like penicillin kill or prevent the growth of harmful pathogens, they kill the bacteria but not your own healthy body cells.

Antibiotics work by inhibiting processes in bacterial cells inhibiting cell division, eventually killing them, but they do NOT affect the cells of the host organism.

Some antibiotics inhibit the building of the cell walls of bacteria, which prevents cell division - these antibiotics do not affect human cells which do not have cell walls.

Different antibiotics attack different bacteria, so it is important that specific bacterial infections should be treated with the appropriate specific antibiotics.

Doxycycline is an antibiotic to treat infection from the chlamydia bacteria.

Doxycycline works by interfering with the synthesis of important proteins inside the bacterial cells, that chlamydia need to survive.

Other antibiotics like penicillin are not as effective, hence the need to constant research and develop new antibiotics, especially more resistant strains of bacteria evolve.

The use of antibiotics has greatly reduced deaths from infectious bacterial diseases.

However, overuse and inappropriate use of antibiotics has increased the rate of development of antibiotic resistant strains of bacteria.

You need to be aware that it is difficult to develop drugs that kill viruses without also damaging the body’s tissues.

Explaining the use of antibiotics to control infection:

Antibiotics are taken internally e.g. intravenous syringe injection, or orally taken by tablet or liquid suspension.

Antibacterials to treat bacterial infections

Probably the most well known antibacterial is the antibiotic penicillin which is effective against many bacterial infections BUT NOT viruses like the common cold or flue.

An antibiotics can kill bacteria or prevent them growing and reproducing.

Many strains of bacteria, including MRSA, have developed resistance to antibiotics due to mutations, which cause stronger more resilient strains of bacteria to survive as a result of natural selection.

To prevent further resistance arising it is important to avoid over-use of antibiotics and only use when necessary and complete the course of treatment..

Knowledge of the development of resistance in bacteria is limited to the fact that pathogens mutate, producing resistant strains.

Mutations of pathogens produce new strains.

Antibiotics and vaccinations may no longer be effective against a new resistant strain of the pathogen.

The new strain will then spread rapidly because people are not immune to it and there is no effective treatment.

Can bacteria become resistant to antibiotics?

Unfortunately the answer is yes! Bacteria will sometimes quite naturally mutate into forms that are resistant to current antibiotics, so if you are infected with a new strain of bacteria, your resistance from your 'current' antibiotic is not as effective.

If an infection is treated with an antibiotic, any resistant bacteria from any mutations will survive and this means more resistant bacteria can survive and reproduce to infect other people, while the non-resistant strains will tend to be reduced.

This bacterial mutation is an example of natural selection at the individual cell level and drug companies are constantly trying to develop new antibiotics to combat the new evolving strains of harmful bacteria - but new harmful 'superbugs' are becoming more common the more we use antibiotics and new epidemics can break out!

MRSA, methicillin-resistant staphylococcus aureus causes serious wound infections (including after surgery in a hospital), can't be treated with many current antibiotics and causes serious wound infections that can be fatal to young babies or elderly people in particular.

Misuse by over-prescribing antibiotics is believed to be causing the rise of mutant resistant strains of bacteria, so doctors are being advised to avoid over-prescribing antibiotics to reduce the mutation rate and not treating mild infections with antibiotics.

Symptoms like headaches or sore throats are not a justification for being prescribed antibiotics. Unfortunately, many patients (for various reasons) are prescribed antibiotics when they are actually suffering from a viral infection.

BUT, if an antibiotic is appropriately prescribed, you should always complete the course, even if you feel a lot better, this is to maximise killing the bacterial infection and minimise the chance of passing on of the infection.

Understand that antibiotics kill individual pathogens of the non-resistant strain.

Individual resistant pathogens survive and reproduce, so the population of the resistant strain increases.

Now, antibiotics are not used to treat non-serious infections, such as mild throat infections, so that the rate of development of resistant strains is slowed down.

The development of antibiotic-resistant strains of bacteria necessitates the development of new antibiotics.

See also Culturing microorganisms like bacteria - testing antiseptics and antibiotics  gcse biology revision notes


Learning objectives for this section on antibiotics

Be able to describe, and why, the treatment of patients with antibiotics to kill or inhibit bacterial.

Know that in treating pathogen infections, overuse of antibiotics leads to the evolution of superbugs like MRSA which is very difficult to treat.

Know the mutations of strains of bacteria easily occur and antibacterial pathogens can evolve.

  • Be able to explain the use of antibiotics to control infection, including:

  • Antibiotics are taken internally e.g. intravenous syringe injection, or orally taken tablet or liquid suspension.

  • In other words they are treating you from the inside and treat an existing pathogen infection you have (bacterial or fungal microorganism)

  • Compare these two point with the external use of antiseptics in preventing infection.

  • Antibacterials to treat bacterial infections

    • Probably the most well known antibacterial is the antibiotic penicillin which is effective against many bacterial infections BUT NOT viruses like the common cold or flue.

    • An antibiotic can kill bacteria or prevent them growing and reproducing.

  • Be able to evaluate evidence that resistant strains of bacteria, including MRSA, can arise from the misuse of antibiotics.

    • Antibiotics, including penicillin, are medicines that help to cure bacterial disease by killing infectious bacteria inside the body.

      • What is an antibiotic?

      • Antibiotics cannot be used to kill viral pathogens, which live and reproduce inside cells.

      • Antibiotics do not destroy viruses, typified by the cold and flue viruses we all suffer from. Viruses make your own body cells reproduce the invasive virus and unfortunately anti-viral drugs may attack good cells too!

      • Antibiotics like penicillin kill or prevent the growth of harmful pathogens, they kill the bacteria but not your own body cells.

      • Different antibiotics attack different bacteria, so it is important that specific bacteria should be treated by specific antibiotics.

      • The use of antibiotics has greatly reduced deaths from infectious bacterial diseases.

      • However, overuse and inappropriate use of antibiotics has increased the rate of development of antibiotic resistant strains of bacteria.

      • You need to be aware that it is difficult to develop drugs that kill viruses without also damaging the body’s tissues.

    • Many strains of bacteria, including MRSA, have developed resistance to antibiotics due to mutations, which cause stronger more resilient strains of bacteria to survive as a result of natural selection.

      • To prevent further resistance arising it is important to avoid over-use of antibiotics and only use when necessary and complete the course of treatment.

      • Knowledge of the development of resistance in bacteria is limited to the fact that pathogens mutate, producing resistant strains.

    • Mutations of pathogens produce new strains.

      • Antibiotics and vaccinations may no longer be effective against a new resistant strain of the pathogen.

      • The new strain will then spread rapidly because people are not immune to it and there is no effective treatment.

      • Can bacteria become resistant to antibiotics?

        • Unfortunately the answer is yes! Bacteria will sometimes quite naturally mutate into forms that are resistant to current antibiotics, so if your infected with a new strain of bacteria, your resistance is not as effective.

        • If an infection is treated with an antibiotic, any resistant bacteria will survive and this means resistant bacteria can survive and reproduce to infect other people, while the non-resistant strains will tend to be reduced.

        • This is an example of natural selection at the individual cell level and drug companies are constantly trying to develop new antibiotics to combat the new evolving strains of harmful bacteria - but new harmful 'superbugs' are becoming more common the more we use antibiotics and new epidemics can break out!

        • MRSA, methicillin-resistant staphylococcus aureus, can't be treated with many current antibiotics and causes serious wound infections that can be fatal to young babies or elderly people in particular.

        • Misuse by over-prescribing antibiotics is believed to be causing the rise of mutant resistant strains of bacteria, so doctors are being advised to avoid over-prescribing antibiotics to reduce the mutation rate and not treating mild infections with antibiotics.

        • 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.

        • Individual resistant pathogens survive and reproduce, so the population of the resistant strain increases.

        • Now, antibiotics are not used to treat non-serious infections, such as mild throat infections, so that the rate of development of resistant strains is slowed down.


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