B3 3.5
WALT: What is penicillin?
• All: define penicillin
• Most: describe how penicillin was
discovered
• Some: explain how to mass produce
penicillin
• Task: What is penicillin?
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B3 3.5
How do microbes kill microbes?
• The fungus Penicillium makes a chemical
that kills bacteria.
• The chemical can be extracted and purified
to make penicillin, a medicine that is safe for
people to use and cures many bacterial
diseases.
• Penicillin is produced in large fermenters.
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The story of penicillin
Alexander Fleming was a scientist
who studied bacteria. He was keen to
find ways of killing them.
In 1928, he was growing lots of
bacteria known as staphylococci on
agar plates.
Photo: Duncan Smith/Photodisc 72(NT)
Alexander’s lab was rather untidy,
and he sometimes left the lids off his
plates, letting the air in.
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Returning from a holiday, Alexander noticed that
lots of his culture plates were mouldy.
A common mould that
might have grown happily
on a slice of bread had
landed on Fleming’s plates
– a stroke of luck that has
saved millions of lives.
Photo: Ann Fullick
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Fleming noticed that, although plenty of bacteria
were growing on the agar, there was a clear ring
around some of the mould.
Something had killed the
bacteria. Straight away
Fleming saw that this
might be important. He
even labelled and saved
the plates!
Photo: Pfizer
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Fleming worked hard on his mould, which was
called Penicillium notatum. He squeezed out
some ‘mould juice’ which he called penicillin.
But he couldn’t get much penicillin from the
mould. It wouldn’t keep – even in the fridge – and
he couldn’t prove it would actually kill bacteria and
make people better.
By 1934 Fleming gave up on penicillin and went
on to do different work!
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Ronald Hare
After Fleming stopped work on
penicillin, other people carried on the
story. Ronald Hare, one of Fleming’s
young assistants, found that Penicillium
mould grows best at quite low
temperatures.
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Dr Cecil Paine
Cecil Paine was another of Alexander
Fleming’s pupils.
He made a penicillin extract and was
the first person to try it out on a
person.
Photo: Nancy Cohen/Photodisc 46 (NT)
A local miner got a stone in his eye
and had a massive infection which
was making him blind. Cecil washed
the eye with his penicillin extract – and
it got better.
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Next, Cecil Paine treated a tiny
baby with his penicillin wash. It
had picked up an eye infection
as it was born.
The baby was cured and its
sight was saved!
Photo: Ann Fullick
Paine never published his
work, but he told a new
professor at the university, a
man called Howard Florey.
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Howard Florey and Ernst Chain worked at Oxford
University. In 1938 they decided to do some work
on penicillin using mice to try to get clear evidence
that penicillin worked.
Norman Heatley was a key man in their team. He
worked out a way of making enough penicillin to try
it out – and he was the man who watched over the
mice as the experiment went on.
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The mouse experiment
Eight mice were infected with
bacteria which would kill them
in 24 hours.
Four were given penicillin.
The four treated mice stayed
healthy – but the other four
died!
Photo: Hart/Photodisc 50 (NT)
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Norman Heatley
A human being is about 3000
times heavier than a mouse – so a
lot more penicillin was needed.
In 1940–1941, Norman Heatley
developed some special pot
vessels to grow more mould – and
collect more penicillin. In just a few
weeks, Norman made enough
penicillin for Howard Florey to try it
out on a fully grown man.
Photo of Norman Heatley by Mary Krinsky
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Albert Alexander was a 43-year-old policeman who
was dying of a blood infection. Florey and Chain gave
him penicillin for five days. Albert recovered well until
the penicillin ran out.
Florey and Chain tried everything – they even
collected spare penicillin from Albert’s urine but it was
no good. The infection came back and Albert died.
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Florey and Chain collected more
penicillin. They were determined to
succeed.
This time they tried their penicillin on a
15-year-old boy who had an infection after
an operation. He was completely cured.
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By 1941, Europe was in the grip of the Second
World War. Thousands of soldiers were dying
from infected wounds and infectious disease.
Potentially, penicillin could
save thousands of lives –
but the scientists still
couldn’t make enough of it.
Photo: Ann Fullick
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British laboratories and factories were busy with
the war effort.
Howard Florey had
contacts in America,
so the scientists took
their mould to the
United States where
some of the large
chemical companies
helped them to make
penicillin on a big scale.
Photo: Pfizer
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‘Mouldy Mary’
Penicillium notatum is slow growing and produces
little penicillin.
When Mary Hunt, a
member of the US team,
brought in a mouldy melon
she found on a market stall
it gave them a
breakthrough – a new and
better form of Penicillium!
Photo: Ann Fullick
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Chain, Fleming and Florey
all got a Nobel prize for
their work.
The number of people dying
from diseases caused by
bacteria in countries like
Britain and America dropped
dramatically.
Everyone thought the battle
against bacteria had been
won!
Photo: Pfizer
Sir Alexander Fleming opening
Pfizer’s new UK factory to make
penicillin in 1954
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Penicillin Production
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What does the penicillin
fungus need to grow?
 Pfizer Ltd
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This is Penicillium – the fungus
that produces penicillin, the
first of the antibiotic ‘wonder
drugs’. Antibiotics kill bacteria
without harming humans.
Penicillin has saved many, many
millions of lives since it was
discovered – and treated
millions of minor infections as
well.
 Alan Silverside
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As a fungus,
Penicillium cannot
photosynthesise. A
solution containing
corn liquor
(containing sugar),
nitrate fertilisers
and yeast extract
is added to the
fungus in a giant
tank or fermenter.
This provides all of
the required
nutrients, and
fermentation
begins.
 Pfizer Ltd
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Temperature,
oxygen
concentration
and pH are
controlled in the
fermenter. Large
paddles swirl the
medium around
to keep
everything well
mixed. Over the
next 140 hours
the fungus will
grow and start to
produce
penicillin.
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After about 140 hours
roughly 30% of the
mixture will be drained
off and fresh nutrient
added. The material
that has been drained
off is passed to a
separator. Why wait
until 140 hours before
this is done?
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The separator acts a
bit like a spin-dryer –
a vacuum draws
mixture onto a
rotating drum. The
drum is porous so the
dissolved penicillin
passes through into
the centre while the
fungal filaments are
stuck on the outside.
These filaments are
removed by a blade as
the drum rotates.
B3 3.5
 Pfizer Ltd
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The filtered liquid with the dissolved penicillin is
treated with potassium salts. This precipitates the
penicillin out of solution. This precipitate can then
be collected by filtering and the powder produced
can be as high as 99.5% pure penicillin.
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Penicillin and the other
antibiotics which have
been discovered are some
of the most useful
medicines we have.
Doctors all over the world
prescribe them to save
patients from the effects
of bacterial disease.
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