Treating, Curing & Preventing Disease

• Pathogens are microbes that cause diseases.
• Vaccination introduces small quantities of dead or inactive forms of a pathogen into the body to stimulate the immune system (white blood cells) to produce specific antibodies to target and attach to the pathogen, so that if the same pathogen re-enters the body, antibodies can be produced rapidly.
• When a white blood cell engulfs and digests a pathogen it is called phagocytosis.
• During an initial infection, antibodies slowly increase, peak at around ten days, then gradually decrease.

  A second exposure to the same pathogen causes the white blood cells to respond quickly in order to produce lots of the specific antibodies, which prevents infection.
• Herd Immunity

  • A person can become immune to a disease after vaccination.
  • This immunity gives protection against illness in an individual.
  • The majority of the population must be vaccinated against serious diseases, which can reduce the chance of people coming into contact with specific pathogens, leading to herd immunity.
• Recognised scenarios surrounding herd immunity - 1

  • The majority of the population are not vaccinated against a specific disease, however, a few people are ill and contagious. This can develop easily into a mass infection because the majority of the population are not vaccinated.
• Recognised scenarios surrounding herd immunity - 2

  • Most of the population are not vaccinated against the specific disease but are well, some are vaccinated and healthy, and a few are not vaccinated, but ill and contagious. Mass infection can result again, but a small number of vaccinated individuals remain healthy and some that are not vaccinated will also be healthy.
• Recognised scenarios surrounding herd immunity - 3

  • The majority of the population are vaccinated and healthy against a specific disease, a few are not vaccinated but well. A few are not vaccinated against the disease, and they are ill and contagious. The result is that the majority are protected due to the high level of vaccination. A few individuals will still become ill, but the large number of vaccinated individuals gives protection.
• If the number of people vaccinated against a specific disease drops in a population, it leaves the rest of the population at risk of mass infection, as they are more likely to come across people who are infected and contagious. This increases the number of infections, as well as the number of people who could die from a specific infectious disease.
• Painkillers

  • Chemicals that relieve symptoms but do not kill pathogens.
  • Common examples include paracetamol and aspirin, which can relieve a headache or a sore throat.
• Antibiotics

  • Substances that slow down or stop the growth of bacteria.
  • They are commonly prescribed medicines - e.g. penicillin and amoxicillin.
  • These can be taken to cure the disease by killing the pathogen.
  • Only cure bacterial diseases and not viral ones.
• Penicillin

  • First antibiotic discovered in 1928 by Alexander Fleming.
  • He noticed that some bacteria he had left in a Petri dish had been killed by the naturally occurring Penicillium mould.
• Antibiotics damage bacterial cells but do not damage host cells.

  They can cure some bacterial diseases that would have previously killed many people.

  Since their introduction, they have had a large influence on the world's health and death rate.
• Different bacteria cause different diseases.

  One antibiotic may only work against one type of bacteria, or a few types.

  This means that a range of different antibiotics is needed for the treatment of the whole range of bacterial diseases.
• Viral diseases cannot be cured by antibiotics, as they reproduce inside the host cells.

  It is very difficult to develop antiviral drugs, as they might damage the host cell whist killing the virus.

  Antiviral drugs only slow down viral development, and viruses change their antigens quickly which means new drugs have to be generated regularly.
• Commonly prescribed antibiotics are becoming less effective due to:

  • Overuse of antibiotics
  • Failing to complete the fully prescribed course by a doctor
  • Use of antibiotics in farming
• The effectiveness of antibiotics is being reduced, and the incidence of antibiotic resistance increasing.

  These bacteria are commonly known as superbugs.
• Overuse

  People feel unwell and when going to the doctors, they expect antibiotics to be prescribed.

  If patients have viral infections, such as the common cold and not a bacterial one, the antibiotics are ineffective and unnecessary.
• Failing to complete the course

  Patients should always fully complete the prescribed course of antibiotics, every time they are taken.

  This ensures all bacteria are killed, so none survive which can subsequently mutate and produce resistant strains.

  Patients begin to feel well after a few days of taking the medicine, and stop taking them.

  This is potentially very harmful, as random mutations can occur which can lead to antibiotic resistance.

  The resistant bacteria reproduce quickly, and the resistance spreads.
• Agricultural use

  Previously, antibiotics were regularly used in farming, and these can be used to prevent disease, keep the animals well and allow them to grow quickly.

  The high use of antibiotics in agriculture may have a cost as it could lead to spread of antibiotic resistance from animals into human hosts. Legal controls are now in place to try and reduce the use of antibiotics in this way.
• Ways to reduce antibiotic resistance

  • Only take antibiotics when necessary.
  • Treat specific bacteria with specific antibiotics.
  • High hospital hygiene levels, including regular hand washing by staff and visitors.
  • Patients who are infected with antibiotic resistant strains of bacteria should be isolated from other patients.
• The development of new antibiotics stopped years ago, as they were hailed as the solution to a very difficult disease control problem. Some limited success with new antibiotic search has occurred recently.
• Bacteria can replicate approximately every 20 minutes by binary fission, which is a simple form of cell division.
• The level of bacteria replication will depend on the availability of nutrients and other suitable conditions such as temperature.
• Ways to culture bacteria include:

  • Nutrient broth solution
  • Colonies on an agar plate
• Nutrient broth solution or culture medium, allows a liquid or gel to provide all the nutrients needed for bacteria to grow successfully. These must include: carbohydrates for energy, nitrogen for protein synthesis, plus other minerals.
• Agar plates are created by pouring hot molten agar into sterile Petri dishes, which are then allowed to set.

  Bacteria can be spread onto the plates, and allowed to form individual colonies of the specific bacterium.
• Uncontaminated Cultures

  If a specific bacterium is going to be cultured or grown, other contaminating bacteria would compete for nutrients in the broth or agar.

  Plus some bacteria could be harmful (such as pathogens) and would complicate the results of experiments when testing the efficiency of antibiotics or other anti-microbial compounds.
• Preparing the agar plates of a colony of bacteria

  1. Glass Petri dishes and agar gel must be sterilised before use in an autoclave, or pre-sterilised plastic Petri dishes can be bought.

  • Reason – this will kill any bacteria that are present in the solution or on the Petri dishes.
• Preparing the agar plates of a colony of bacteria

  2. Pour the sterile agar plates and allow to set fully.

  • Reason – this provides the selected bacterium with all the nutrients needed to grow.
• Preparing the agar plates of a colony of bacteria

  3. Sterilise the inoculating loop, by heating it in the Bunsen burner flame.

  • Reason - kills any bacteria that are present on the loop.
• Preparing the agar plates of a colony of bacteria

  4. Dip the inoculation loop into the microorganism solution and make streaks on the surface of the agar plate.

  • Reason – this allows the bacteria to spread out and to grow in individual colonies on the agar plate. A lawn of bacteria can be produced by using a sterile spreader to evenly spread the bacteria across the whole of the plate.
• Preparing the agar plates of a colony of bacteria

  5. Replace the lid as soon as possible, secure with tape. Label and invert the plate, and store upside down.

  • Reason -this stops additional unwanted bacteria in the air contaminating the plate. Do not fully seal the lid, as this will stop oxygen reaching the bacterium, and this may encourage harmful anaerobic bacteria to grow. Labels are important, as this identifies the growing bacterium.
• Preparing the agar plates of a colony of bacteria

  6. Incubate at a maximum temperature of 25°C in schools and colleges.

  • Reason – this reduces the chance of growing harmful pathogens. Hospital laboratories would incubate plates at 37°C (body temperature) to allow quick growth and identification.
• The drug digitalis comes from foxglove.
• Aspirin comes from willow tree bark.
• Adding antibiotic or antiseptic soaked patches to pre-prepared agar plates.

  By adding filter paper soaked in a variety of anti-microbial solutions to a pre-prepared agar plate (agar plate method), the effective of the solutions can be tested experimentally.

  A clear area (zone of inhibition) indicates that the bacteria have been killed by the solution or have not been able to reproduce.
• Adding antibiotic or antiseptic soaked patches to pre-prepared agar plates.

  1. Soak filter paper disks in a variety of solutions, use either different concentrations of the same solution, or a variety of different solutions.

  • Reason – this will kill any bacteria that are present in the solution or on the petri dishes.
• Adding antibiotic or antiseptic soaked patches to pre-prepared agar plates.

  2. Pour the sterile agar plates and allow to set fully.

  • Reason – the effectiveness of the solutions at killing the bacteria can be tested.
• Adding antibiotic or antiseptic soaked patches to pre-prepared agar plates.

  3. Measure the clear area around the soaked filter paper disks. A control disk must be also included.

  • Reason - size of zone indicates the effect of the substance tested on the growth of the specific bacteria.