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Science Week 2013
Post-primary classroom notes
Introduction to Microbes
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Microbes are very small living organisms
They are too small to be seen with the naked eye so we use microscopes to
magnify them
They are found almost everywhere on earth and some can be useful, some
harmful to humans
There are three different types of microbes
o Viruses
o Bacteria
o Fungi
They come in many different shapes and sizes
Viruses
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Smallest of the Microbes
Mostly harmful to humans
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Viruses are not free living – they MUST live inside another living cell/organism.
Once inside the host cell they rapidly multiply, destroying the host cell
Bacteria
Single celled organisms that can multiply once every 20 minutes
Some can be harmful to humans and cause disease, these are known as
pathogenic
Other types of bacteria can be really helpful to us and we even need some to
help us survive
Fungi
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Are multi-cellular organisms and obtain food by decomposing dead organic
matter or by living as parasites on a host.
Range in size from being microscopic such as dermatophytes which cause to
very large such as mushrooms!
Some fungi can be harmful by causing diseases or by being poisonous to eat
Some fungi can be beneficial e.g. Penicillium produces the antibiotic penicillin
and some mushrooms can be eaten.
They spread through the air in small hard seed like spores which open and grown
under the right conditions.”
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Useful Microbes
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There are more useful microbes than harmful microbes.
Most of these microbes are either necessary for our survival, good for our health
or can be used for our benefit in industry.
In Nature
Bacteria – Plant Interaction:
 Many microbes are found in nature and help plants to grow
 Rhizobacteria found in the soil fixate nitrogen which is required for many crops
to grow
Oxygen production
 Cyanobacteria or ‘blue-green algae’ produce oxygen in the ocean
Decomposition
 Defined as the breakdown of raw organic materials to a finished compost
 The fungi invade the organic matter in soils first and are then followed by
bacteria.
 Without this recycling of inorganic nutrients, primary productivity on the globe
would stop.
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In the Food Industry
Cheese and yogurt
 Lactic acid fermentation produces yogurt and cheese. Some fungi are also
used to make the cheese turn blue!
Bread and dough products
 Yeast is used to make bread and dough products.
Alcohol Production
 Yeast is also used in alcohol production when fermentation occurs without air
In Medicine
Penicillin
 Discovered by Alexander Fleming in 1928
 Produced by the fungus Penicillium notatum
 One of the most commonly used antibiotics today
Vaccines
 Discovered by Edward Jenner in 1796
 Usually made from weak or inactive versions of the same microbes that make
us ill
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Harmful Microbes
Some microbes can be harmful to humans and cause disease
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The influenza virus can cause the flu. When viruses enter our body they
live inside our cells, multiply and then burst free when fully grown,
destroying the cell in the process.
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Campylobacter bacteria can make us ill through food poisoning.
Harmful bacteria produce harmful toxins when they multiply inside our
body and it is these toxins which can make us ill.
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Dermatophyte fungi such as Trichophyton can cause diseases such as
Athlete’s foot and Ringworm. Fungi prefer to grow under our skin and it
is the products they produce while feeding that cause swelling and
itching.
Our bodies have adapted to help us get rid of these infections; this may be in
the form of
Fever: Microbes prefer to live at normal body temperature at 37 °C. A fever is
considered one of the body’s immune mechanisms to attempt at
neutralization of a perceived threat inside the body, be it bacterial or viral.
Swelling: A cut in the hand will generally result in swelling around the cut; this
is our body responding in a similar way to a fever only in a more localized way.
Rash: This is our body’s reaction to microbial toxins.
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Hand Hygiene
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Our hands are covered by our useful bacteria – harmless specie of
Staphylococcus.
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We collect lots of other microbes from our surroundings (e.g. home,
school, garden, animals, pets, food). Some of these microbes can
make us ill if ingested.
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Our hands are covered in natural oil which helps keep our skin moist
and stops it getting too dry. This oil provides a perfect place for
microbes to grow and multiply and also helps microbes ‘stick’ to our
skin.
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Microbes spread rapidly from person to person by touch and the best
way to prevent this from happening is to wash our hands regularly.
Do you know HOW to wash your hands?
Washing hands in water alone or in cold water eliminates visible dirt and grime,
however, soap is required to break up the oil on the surface of the hands which
traps microbes.
Do you know WHEN to wash your hands?
Hands should be washed:
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Before, during and after preparing food, especially raw meat
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After using the bathroom
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After exposure to animals or animal waste
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After coughing, sneezing or blowing your nose
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If you’re ill or have been around ill people
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Respiratory Hygiene
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Colds and flus are some of the most common illnesses.
They are caused by viruses and as such cannot be cured by antibiotics
The most common way cold and flu viruses spread is by being carried in the tiny
droplets of saliva we sneeze into the air
These viruses can also spread through touching, sneezing and eating
contaminated food
Sneezing
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Sneezing is the way in which our body tries to get rid of any harmful
microbes and dust we breathe in through our nose. The harmful microbes
and dust get caught in the nose hair and tickle our nose. The hair sends a
message to the brain which then sends a message back to the nose,
mouth, lungs and chest telling them to blow the irritation away.
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When we sneeze, millions of viral particles rush out and contaminate the
surfaces on which they land
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The best way to stop the spread of these viruses spreading from person to
person is by covering your coughs and sneeze with a tissue
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If you don’t have a tissue then you could sneeze in your sleeve or your
hand but it is important to wash your hands straight away to stop the
viruses spreading through touch
The Body’s natural Defences
Our body fights harmful microbes every day. Microbes must fight through three levels of
our body’s defences before they can cause us harm:
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The first line of defence
The second line of defence
The third line of defence
The FIRST line of defence – our bodies have many natural barriers on the outside of our
bodies to stop microbes entering:
Eyes: Tears produce chemicals called enzymes which can kill some microbes on the
surface of the eye
Skin: Stops microbes entering the body unless it is cut or damaged
Respiratory System: Mucus and tiny hairs in the nose stop microbes entering our lungs.
We sometimes sneeze or cough these harmful microbes away from our body.
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The SECOND line of defence – if a microbe does enter our blood stream we have a
second line of defence known as non-specific white blood cells.
The White Blood Cells called ‘phagocytes’ notice anything foreign or strange that gets
through the first line of defence and move towards that ‘foreign object’. The
phagocytes then surround and destroy the foreign object.
The THIRD line of defence – specific white blood cells
All invading cells have distinctive markers known as antigens on their surface.
When the specific white blood cell comes across a microbe, it will
a) Make an antibody to match that microbes antigen
b) Tell all the other specific white blood cells to make lots of that antibody
The body’s antibodies find their matching antigen on the harmful microbes and lock on
to them, when locked they either
a) Mark the harmful microbes for destruction by the phagocytes
b) Stay in the blood after the harmful microbes have been killed ready to fight
them if they should ever return
Vaccines
What are vaccines?
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Vaccines are a way to help our immune system fight pathogenic microbes
Vaccines are used to prevent NOT treat infections
A vaccine is usually made from a weak or harmless version of the microbe it is
trying to prevent
Immune means that we are protected from serious infection
Immunisation is a way of increasing the body’s protective immunity to microbial
disease
How vaccines work
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The body fights the vaccine as if it were the harmful microbe
The white blood cells make lots of antibodies to attach to the antigens on the
surface of the vaccine which the body thinks is the harmful microbe
The immune system now remembers how to make these antibodies if the real
harmful microbe enters the body and will be able to destroy it much quicker
Antibodies can also pass from mother to unborn child in the womb and also
through breast milk
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Vaccinations
In some cases the body needs reminding, and this is why some vaccines need ‘booster
jabs’. Some microbes, like influenza, change their antigens a lot, meaning that the
body doesn’t always recognize how to change them. This is why we need annual flu
jabs.
Sometimes enough people in a population (herd) are vaccinated to stop the microbe
from spreading to the unvaccinated people. This is known as herd immunity.
Antibiotics
Antibiotics are powerful medicines used to kill bacteria. They will not harm viruses
therefore cannot be used to treat illnesses caused by viruses such as the cold and flu.
Some antibiotics work by stopping the bacteria multiplying, while others kill the
bacteria instantly.
Antibiotics can be broad spectrum and kill a lot of different types of bacteria or they
can be narrow spectrum and kill just one type of bacteria.
Most antibiotics prescribed by the doctor are broad spectrum and these also kill our
useful bacteria.
When the useful bacteria are gone, there is more room for the harmful bacteria to
invade.
Using antibiotics too often and in the wrong way has led to many bacteria becoming
resistant to the antibiotics. This is known as antibiotic resistance.
Antibiotic Resistance – The Causes
Overuse
Antibiotics used to treat infections when they are not needed or not
effective i.e. for the flu
Misuse
Not completing a prescribed course. Using antibiotics not
prescribed for you.
How can antibiotics resistance be prevented?
 Antibiotics should be the last line of defence NOT the first
o Most common infections will get better by themselves through time,
bed rest, liquid intake and healthy living.
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 Only take antibiotics
prescribedand
by games
a doctor
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If prescribed antibiotics, finish the course
Do not use other peoples or leftover antibiotics, they may be specific for some
other infection