Pathogens

Pathogens

Pathogens
1. Two main types of Pathogen
  1. Bacteria are very small living cell
    1. They do two things
      1. Damaging cells
      2. Producing toxins (poisons)
    2. 1/100th the size of body cells
  2. Viruses are not cells- they are much smaller
    1. 1/100th the size of bacterium
    2. They replicate themselves by invading your cells and using the cells machinery to produce many copies of themselves
      1. The cell will usually then burst releasing all the new viruses
        This cell damage is what makes you feel ill
2. cause infectious disease
Fighting disease
1. Sophisticated defence system
  1. Your skin, plus hairs and mucus in your respiratory tract (breathing pipework) stop a lot of microorganisms getting inside your body
  2. Try to prevent microorganisms getting into the body through cuts, small fragments of cells (platelets) help blood clot quickly to seal wounds. If the blood contains low numbers of platelets then it will clot more slowly
  3. If something does make it through, your immune system kicks in. The most important part is the white blood cells. They travel around in your blood and crawl into every pare of you, constantly patrolling for microbes. When they come across an invading microbe they have three lines of attack
    1. Consuming them
      1. White blood cells can engulf foreign cells and digest them
    2. Producing Antibodies
      1. Every invading cell has unique molecules (antigens) on its surface
        When the white blood cells come across a foreign antigen (one it doesnt recognise) they will start to produce proteins called antibodies to lock on to and kill the invading cells. The antibodies produced are specific to that type of antigen they wont lock on to any others
        Antibodies are then produced rapidly and carried around the body to kill all similar bacteria or viruses
        If the person is infected with the same pathogen again the white blood cells will rapidly produce the antibodies to kill it the person is naturally immune to that pathogen and wont get ill
    3. Producing Antitoxins
      1. These counter toxins produced by the invading bacteria
Fighting disease - vaccination
1. Protects from future infection
  1. When your infected with a new microorganism it takes your white blood cells a few days to learn how to deal with it
    1. Vaccinations involve injecting small amounts of dead or denatured microorganisms. These carry antigens which cause your body to produce antibodies to attack them even though the microorganism is harmless
      1. But if live microorganisms of the same type appear after that, the white blood cells can rapidly mass produce antibodies to kill off the pathogen
        Some vaccinations wear off over time so booster injections may need to be given to increase levels of antibodies
2. Pros
  1. They help control lots of infectious diseases that were once common in the UK. Smallpox no longer occurs at all and polio infections have fallen by 99%
  2. Big outbreaks of disease (epidemics) can be prevented if a large percentage of the population is vaccinated. That way even the people who arent vaccinated are unlikely to catch the disease because there are fewer people able to pass it on
3. Cons
  1. Vaccines dont always work-they sometimes done give you immunity
  2. You can sometimes have a bad reaction to a vaccine e.g. swelling but there very rare
Fighting disease - drugs
1. Some drugs just relieve symptoms others cure the disease
  1. Painkillers (aspirin) just relieve pain however they dont actually tackle the cause of the disease they just reduce the symptoms
  2. Antibiotics (penicillin) work differently they kill (or prevent growth of) the bacteria causing the problem without killing you own body cells. Different antibiotics kill different types of bacteria so its important to be treated with the right one
    1. dont destroy viruses. Viruses reproduce using your own body cells which makes it very difficult to develop drugs that destroy just the virus without killing the bodys cells
  3. Bacteria can become resistant to antibiotics
    1. Bacteria can mutate - sometimes the mutations cause them to be resistant to (not killed by) an antibiotic
    2. If you have an infection some of the bacteria might be resistant to antibiotics
      1. only non resistant bacteria will be killed
        The individual resistant bacteria will survive and reproduce and the population of the resistant strain will increase
    3. Resistant strains could cause a serious infection that cant be treated by antibiotics
      1. To slow down the rate of development of resistant strains its important not to over prescribe drugs
        super bugs
2. Investigate antibiotics by growing microorganisms
  1. Microorganisms are grown (cultured) in a "culture medium". This is usually agar jelly containing carbohydrates, minerals, proteins and vitamins they need to grow
    1. Hot agar jelly is poured into shallow round plastic dishes called petri dishes
      1. When the jellys cooled and set inoculating loops (wire loops) are used to transfer microorganisms to the culture medium
        Paper discs are soaked in different types of antibiotics and places on the jelly. Antibiotic resistant bacteria will continue to grow around them but non resistant strains will die
3. Equipment is sterilised to prevent contamination
  1. if it isnt the unwanted microorganisms in the culture medium will grow and affect the result
4. The temperature must be kept fairly low in school labs
  1. Harmful pathogens are unlikely to grow at this temperature
Fighting disease - past and future
1. Ignaz Semmelweis believed doctors were spreading the disease on their unwashed hands. By telling doctors entering his ward to wash their hands in antiseptic solution he cut the death rate from 12% to 25
  1. The solution killed the bacteria but he couldnt prove it so his methods were dropped when he left the hospital
2. Bacteria and viruses are pretty fast at evolving to deal with threats
  1. Bacteria
    1. Bacteria can mutate for new strains
    2. New strain that no one has encountered before
      1. Spread rapidly in a population
  2. Viruses
    1. Mutate often hard to develop vaccines
    2. deadly and very infectious
    3. Worst case scenario a flu pandemic could kill billions of people all over the world
      1. A pandemic is when a disease spreads all over the world

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