2.7 & 2.8 - Microorganisms and Disease

• Aseptic technique


  • Prevents contamination of work and environment when working with micro-organisms
• Growing bacteria and fungi on nutrient agar

  1. Sterilise Petri dishes and nutrient agar before pouring

  2. Use inoculating loop to transfer bacteria, sterilise before and after use

  3. Only lift Petri dish lid slightly to prevent contamination

  4. Secure lid with adhesive tape, label and date

  5. Incubate at 25°C for 24-48 hrs

  6. Sterilise plates and equipment after use
• Colony


  Growth from a single bacterium, indicates number in original sample
• 20-200 colonies on each plate is a reliable number to count
• Fewer than 20 colonies is not a reliable number to count
• Growing Penicillium fungus in a fermenter

  1. Provides optimum pH, temperature, oxygen, nutrients

  2. Organism grows and secretes antibiotic into medium

  3. Culture medium removed, filtered, penicillin extracted
• Temperature control


  Affects bacterial growth in food storage
• Antibiotic resistance

  1. Antibiotics usually break down the cell wall of a bacteria
  2. When a course of antibiotics is stopped early the chances of a mutation increases
  3. Mutations can be beneficial to the bacteria
  4. These bacteria are not killed by antibiotics and survive
  5. They replicate and spread - this causes an outbreak of antibiotic resistant disease
• What is an antigen?


  Receptors on the surface of pathogens
• Why are antigens important?


  They alert the immune system
• What is an antibody?

  A special protein found in the blood. This recognises antigens on pathogens surface.
• Where are antibodies made?

  B-cells lymphocytes
• Antigen - Substance that causes an immune response
• Antibody - Protein produced by white blood cells that attaches to the antigens on pathogens and destroy the pathogens
• Vaccines

  1. Weak or dead version of the pathogens is injected
  2. White blood cells remember this and make antibodies quickly
  3. Next time you are exposed, white blood cells quickly produce antibodies
  4. You don't get ill
• Herd immunity

  • When a large portion of the population is immune to a disease
  • The spread of pathogens is reduced and the disease may disappear
  • If the number of people taking the vaccine falls, the herd immunity is lost and the disease can reappear
• What are monoclonal antibodies?

  Antibodies produced by identical immune cells.
• Where do monoclonal antibodies come from?

  Single cell immune cells
• What do we use monoclonal antibodies for?

  Diagnosing and treating disease
• How do we produce monoclonal antibodies?

  We make them in a lab by injecting mice with a vaccine
• Lymphocyte - Antibody producing white blood cell that cannot divide (B cell)
• Tumour cell - Cancer cell that reproduces rapidly but cannot produce antibodies
• Hybridoma - Cell formed from a combination of a lymphocyte and a tumour cell that can divide and produce antibodies
• What does a new medicine need to be?

  • Effective - It has to prevent or cure disease
  • Safe - It must not be toxic or cause dangerous side effects
  • Stable - It has to be able to be stored over time
  • Successfully taken into and removed from the body - Target the disease and be cleared from your body once it has done the job
• Medicine development process

  1. Research and discovery
  2. Preclnical trials
  3. Clinical trials
• Medicine development - stage 1: Research

  Researchers target a disease and identify lots of possible new medicines
• Medicine development - stage 2: Preclinical testing

  Testing that takes place in laboratories

  The drugs are tested on:

  • Cells
  • Tissues
  • Live animals
• Medicine development - stage 3: Clinical trials

  The drugs are tested on human volunteers

  1. Healthy people - To test for side effects (toxicity)
  2. Patients with the disease - To test for efficacy and dosage
• What are the 2 types of trials conducted when testing a new drug?

  • Blind trial
  • Double blind trial
• Blind trial

  • Patient does not know if they are receiving drug or placebo
  • Doctor can put bias on people
• Double blind trial

  • Neither the patient or doctors know who is receiving the medication and who isn't
  • This stops bias
• Production of monoclonal antibodies

  1. B lymphocytes (taken from rats) make specific antibodies but do not divide
  2. Tumour cells that do not make antibodies but divide
  3. B lymphocytes and tumour cells combined to make a hybridoma cell (makes specific antibodies and divides)
  4. The cells are cloned
  5. Monoclonal antibodies are separated, purfied and can be used
• Give 5 feature of bacteria cells:

  • Cell membrane
  • Cell wall
  • Cytoplasm
  • Plasmid loops of DNA
  • No nucleus but large DNA loop inside
• Describe the structure of a virus:

  They contain some genetic material surrounded by a protein shell
• What is the name of the pathogen that causes AIDS?


  Human immunodeficiency virus (HIV)
• What is the name of the pathogen that causes chlamydia?

  Chlamydia trachomatis bacteria
• 5 human defences to disease:

  • The skin acts as a barrier
  • Stomach acid kills ingested pathogens
  • Mucus traps pathogens
  • Sweat contains antimicrobial chemicals
  • Blood clots prevent pathogen entry into a wound
• 2 ways that lymphocytes can respond to detecting a pathogen:

  • They can produce antibodies that are specific to the antigens on the pathogen that activates the phagocytes
  • They can produce antitoxins to neutralise the toxins released by the pathogens
• How do phagocytes respond to detecting a pathogen?


  Phagocytes engulf and break down pathogens in a process known as phagocytosis
• What 2 types of pathogens can vaccines protect against?

  • Virus
  • Bacteria