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Since the first antibiotic was discovered in 1928, many more have been developed
and used to treat bacterial infections. Some bacteria have mutated and become
resistant to antibiotics, but new drugs are constantly being developed and tested.
Antibiotics
Antibiotics are substances that kill bacteria or prevent their growth. They do not work
against viruses. It is difficult to develop drugs that kill viruses without damaging the
body's tissues.
Penicillin
A bacterium damaged and distorted by penicillin
The first antibiotic, penicillin, was discovered by Alexander Fleming in 1928. He noticed
that some bacteria he had left in a petri dish had been killed by naturally occurring
penicillium mould.
Since the discovery of penicillin, many other antibiotics have been discovered or
developed. Most of those used in medicine have been altered chemically to make them
more effective and more safe for humans.
Antibiotic resistance
Over time, bacteria can become resistant to certain antibiotics. This is an example of
natural selection. In a large population of bacteria, there may be some that are not
affected by the antibiotic. These survive and reproduce, creating more bacteria that are
not affected by the antibiotic.
MRSA
MRSA is methicillin-resistant Staphylococcus aureus. It is very dangerous because it is
resistant to most antibiotics. To slow down or stop the development of other strains of
resistant bacteria, we should:
always avoid the unnecessary use of antibiotics
always complete the full course
Development of resistance - higher only
The main steps in the development of resistance are:
1. Random changes or mutations occur in the genes of individual bacterial cells.
2. Some mutations protect the bacterial cell from the effects of the antibiotic.
3. Bacteria without the mutation die or cannot reproduce with the antibiotic present.
4. The resistant bacteria are able to reproduce with less competition from normal
bacterial strains.

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Drug testing
Drugs and their origins
Drugs are substances that cause changes to the body. Some can help the body, others
can harm it.
Certain drugs can be extracted from natural sources and their existence has been
recognised for a long time. For example, willow bark was used by the ancient Greeks to
help cure fevers and pains. It was later discovered that the active ingredient was salicylic
acid.…read more

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Salmonella bacterium cell
Bacteria come in many shapes and sizes, but even the largest are only ten micrometres
long (ten-millionths of a metre).
Bacteria are living cells and can multiply rapidly in favourable conditions. Once inside the
body, they release poisons or toxins that can make us feel ill.
Viruses
Hepatitis C virus. DNA are enclosed in a protein coat.
Viruses are many times smaller than bacteria.…read more

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The skin
Cross-section of skin
The skin covers the whole body and protects it from physical damage, microbe infection
and dehydration. It is difficult for microbes to penetrate the skin's dry, dead outer cells.
In addition the sebaceous glands produce oils which also help to kill microbes.
Stomach acid
The stomach contains hydrochloric acid. It destroys micro-organisms which you swallow
with your food and drink. This helps to protect against food poisoning caused by
salmonella and other harmful bacteria.…read more

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A white blood cell ingesting disease-causing bacteria
In a written examination, it is easy to get carried away and write about things like
invaders and battles. You should stick to the point. Note that:
The pathogens are not the disease, they cause the disease.
White blood cells do not eat the pathogens, they ingest them.
Antibodies and antitoxins are not living things, they are specialised proteins.
Types of white blood cell
There are several types of white blood cell, each with a different function.…read more

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Vaccination involves putting a small amount of an inactive form of a pathogen into the
body. Vaccines can contain:
live pathogens treated to make them harmless
harmless fragments of the pathogen
toxins produced by pathogens
dead pathogens
These all act as antigens. When injected into the body, they stimulate white blood cells
to produce antibodies to fight the pathogen.
The vaccine contains only a weakened or harmless version of a pathogen, which means
that the vaccinated person is in no danger of developing the disease.…read more

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Hepatitis C virus. DNA are enclosed in a protein coat.
Some common diseases like influenza (flu) and the common cold are caused by
viruses. These mutate quickly, and this changes their surface proteins. This makes
it almost impossible to develop a permanent vaccine against them. A new flu
vaccine has to be developed every year, after the strain has been analysed.
There is no vaccine for the common cold because the virus that causes it mutates
far too quickly.…read more

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This was
possible because smallpox is spread by direct contact, and not through the air.
This made it possible to vaccinate enough people in the world to completely stop the
disease from spreading.
Some other diseases are more infectious. But if we could vaccinate a sufficient number of
the world's population we could, in theory, eliminate the disease.…read more

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