Health, disease, defence mechanisms and treatments

• Microorganisms and Communicable Diseases


  A communicable disease can be passed from one organism to another. Also known as infections.

  Bacteria, virus and fungi are the causes of most communicable diseases
• HIV which leads to aids

  • caused by virus
  • spread by exchange of body fluids during sex and infected blood
  • controlled by drugs
  • using a condom will reduce risk of infection, as will not sharing needles
• Colds and Flu

  • caused by virus
  • spread by airborne
  • treated by flu vaccination for targeted groups
• Human Papilloma Virus (HPV)

  • caused by virus
  • spread via sexual contact
  • prevented by HPV vaccination given to 12-13 year old girls to protect against developing cervical cancer
• Salmonella

  • caused by bacterium
  • spread via contaminated food
  • prevented by always cooking food thoroughly, not mixing cooked and uncooked foods can control spread
  • treatment with antibiotics
• Tuberculosis (TB)

  • caused by bacterium
  • airborne
  • prevented via BCG vaccination
  • if contracted, treated with drugs including antibiotics
• Chlamydia

  • caused by bacterium
  • spread via sexual contact
  • using a condom will reduce the risk
  • treatment with antibiotics
• Athletes Foot

  • caused by fungus
  • spread via contact
  • reduce infection risk by avoiding direct contact in areas where spores are likely to be present e.g wear flip flops in changing rooms/swimming pools
• Potato Blight

  • Plant disease
  • caused by fungus
  • Spores spread in air from plant to plant, particularly in humid and warm conditions
  • prevented by crop rotation and spraying plants with fungicide
• The body’s defence mechanisms

  These involve both stopping the harmful microorganisms gaining entry to the body and destroying them in the blood
• Stop entry of microorganisms by:

  • Skin- barrier that stops microorganisms entering
  • Mucous Membranes- thin membranes in the nose and respiratory system that trap and expel microorganisms
  • Clotting- closes wounds quickly to form a barrier that stops entry of microorganisms and prevent blood loss
• White Blood Cells 


  Role is destroy microorganisms entering the body
• Types of WBC

  • Lymphocytes
  • Phagocytes
• Lymphocytes 


  produce antibodies when microorganisms enter the blood.
• Protection from antibodies

  • Microorganisms have special marker chemicals on their surface called antigens which lead to the body producing specific antibodies
  • These antigens cause lymphocytes to produce antibodies which are complementary shape to antigens and can attach on
  • The antibodies latch on to the antigens, linking them together
  • This immobilises the microorganisms and they can be destroyed
  • After an infection, the body produces memory lymphocytes that remain in the body for a very long time.These can respond quickly and produce antibodies if body is infected again by same microorganism
• Phagocytes 


  Once the microorganisms are clumped together, they are destroyed by a second type of white blood cells-phagocytes. These destroy microorganisms by engulfing them and destroying them in a process called phagocytosis
• Primary Response


  Individuals infected by a disease-causing bacterium or virus are often ill for a few days before the antibody numbers are high enough to provide immunity
• Secondary Response 


  Once infected, the body is able to produce memory lymphocytes that remain in the body for many years. This means that if infection by the same type of microorganism occurs again, the memory lymphocytes will be able to produce antibodies very quickly to stop the individual catching the same disease again
• Immunity 


  means the antibody levels are high enough to combat microorganism infection if it occurs. It is freedom from disease.
• Active Immunity 


  the body produces antibodies used to combat the infectious microorganism. its slower acting by usually lasts for a long period of time
• Passive Immunity 


  antibodies from another source (e.g produced by pharmaceutical companies) are injected into the body. These are fast acting but only last for short time period. Allows for rapid medical treatment of very serious infections
• Vaccinations 


  involve the use of dead or modified disease-causing pathogens that are injected into the body with the purpose of raising antibody and memory lymphocyte levels in blood
• How vaccinations work

  • Antigens on the dead or modified pathogens cause the body to produce antibodies
  • This raises antibody levels in the blood
  • If body becomes infected with disease-causing microorganism at a later date, memory lymphocytes are already present to rapidly produce antibodies to prevent disease developing
• If vaccinations aren’t dead or modified:

  the vaccination will give you the disease you are trying to avoid
• Booster


  sometimes we need more than one vaccination to make sure that we remain immune for a reasonable time period
• Active Immunity by Vaccination

  1. Vaccination contains dead or weakened microbes causing body to produce antibodies in the same way without having the disease
  2. Booster is often used if initial vaccination does not produce enough antibodies to reach immunity level
• Active immunity acquired by having the disease

  1. Antibody rises slowly in response to infection
  2. Effective antibody level remains high for a long period of time due to the body having a memory of the antigen and the memory lymphocytes can produce antibodies very quickly the next time antigen enters the body
• Passive Immunity by injection of ready made antibodies 


  antibodies acts very quickly but are short lasting as they are not produced in the body
• Antibiotics 


  antibiotics such as penicillin are chemicals produced by fungi that are used against bacterial diseases to kill bacteria or reduce their growth. Have no effect on viruses
• Antibiotic Resistance 


  sometimes bacteria can evolve so antibiotics no longer have an effect

  • bacteria can mutate
  • their DNA changes and the bacteria develops new properties
  • this can make them resistant to antibiotics
  • antibiotics will not work against these particular bacteria or cure disease caused by them
• What causes antibiotic resistance?


  Overuse of antibiotics has been a major factor in the development of bacterial resistance to antibiotics and superbugs
• MRSA 


  a type of bacterium that is resistant to most antibiotics-an example of a superbug. Antibiotic resistant bacteria have been a particular problem in hospitals
• Procedures to reduce the incidence of superbugs

  • not overusing antibiotics when not needed e.g against viral diseases
  • increased hygiene measures in hospitals e.g washing hands, using hand-gel
  • isolating patients infected with MRSA or other superbug infections
• Aseptic Techniques 


  when working with bacteria and fungi in a lab, it is important that great care is taken to avoid:

  • contamination of the cultures used
  • the growth of unwanted, pathogenic microorganisms
• Aseptic Techniques Equipment

  • Tube A bacteria growing on agar
  • inoculating loop
  • bunsen burner
  • Petri dish B with agar
• Aseptic techniques


  Techniques used when transferring microorganisms to prevent contamination
• Transferring microorganisms using aseptic techniques

  1. Pass metal loop through Bunsen burner flame

  2. Allow metal loop to cool

  3. Remove lid of culture bottle (Tube A)

  4. Glide loop over agar surface without applying pressure (inoculation)

  5. Replace lid of culture bottle, sweep neck through flame

  6. Spread microbes over agar surface in Petri dish by gently gliding metal loop (plating)

  7. Hold Petri dish lid at an angle rather than removing completely

  8. Heat metal loop again to high temp to destroy any remaining microorganisms

  9. Tape Petri dish 3-4 times and incubate at 25C
• Working close to a Bunsen burner creates an upward current of air that carries microorganisms away from the area where microorganisms are being transferred, thus avoiding contamination
• When the investigation is complete, it is important to clean all work surfaces and hands and safely dispose of bacterial cultures
• Autoclaving will sterilise glass Petri dishes and culture bottles