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Search for better health
Part 3
Louis Pasteur
Robert Koch
During the second half of the nineteenth century, the work of Pasteur and Koch and other
scientists stimulated the search for microbes as causes of disease
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
describe the contribution of Pasteur and Koch to our understanding of infectious
diseases
Louis Pasteur (1822-1895)
Created the science of microbiology
Demonstrated that microbes caused the
souring of wine and beer (lactobacilli)
Development of the process of
pasteurisation to kill bacteria
Conducted the swan-necked flask
experiment to disprove spontaneous
generation
Established the germ theory of disease, that
microbes caused disease
Robert Koch (1843-1910)
Developed many bacteriological techniques
Developed the agar plate technique for
growing microorganisms
Identified the bacterium Bacillus anthracis
responsible for anthrax disease.
Demonstrated that specific microbes are
responsible for causing specific diseases
Developed Koch’s postulates
Identified the bacterium responsible for
tuberculosis and cholera
Developed a vaccine for chicken cholera
Used Koch’s work on anthrax to develop a
vaccine for anthrax
Developed a vaccine against rabies and
used it on humans for the first time
Established the principle of immunity and
developed an effective way to prevent
infectious disease
Pasteur’s Flasks
Pasteur’s early research suggested the existence of spores. He hypothesised that
these spores were carried in air, where they were inactive. They developed into
active microorganisms when nutrients became available.
Pasteur designed the experiment as shown below. The flasks with the S shaped
neck allowed air to enter but dust and spores were trapped in the neck and could
not reach the broth. The other flask was directly open to the air.
Pasteur boiled the broth and subjected the glassware to steam to kill any microbes
present.
As Pasteur predicted the glassware with the S bend did not become contaminated
proving that the organisms that contaminated the broth must be carried in the air.
Pasteur’s flasks are still on display in the Pasteur Institute in Paris and after 150
years they are still not contaminated.
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Koch’s Postulates
Koch developed a set of procedures to follow, which will definitely and scientifically
identify the pathogen. These procedures are known as “Koch’s Postulates” and are
still used today when previously unknown infectious diseases are discovered.
Koch was the first person to develop a set of rules (postulates) which linked a
particular organism with a particular disease.
He was the first to develop a way of growing pure cultures of bacteria on agar
in a Petri dish.
He stained, described and identified many bacteria including TB, cholera and
anthrax.
The organism believed to be the cause of the disease must always be present when the
disease occurs.
The organism must be isolated from the host and grown in pure culture.
Organisms from the pure culture, when inoculated into healthy, suitable, susceptible
hosts must produce the disease.
The organism must be re-isolated, grown in pure culture and compared to the
organism first injected.
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
distinguish between:
 prions
 viruses
 bacteria
 protozoans
 fungi
 macro-parasites
and name one example of a disease caused by each type of pathogen
Pathogen
Prion
Virus
Bacteria
Characteristics
 Defective proteins:
proteinaceous
infectious particle
 Minuscule
 Not cellular
 No nucleic acids
 Causes degeneration
of brain tissue
 Diseases can be both
hereditary and
infectious
 Tiny: 30 to 300 nm
 Not cellular
 Can only reproduce
using host cells
 Can be crystallised
 Small: 0.5 to 5 µm
 Cellular
 Procaryotic: no
membrane bound
organelles
 Single strand of DNA
 Reproduce by binary
fission quickly inside
a host
 Waste products
(toxins) often harm
host
 Classified by shape
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Example
Fatal Familial Insomnia
Influenza
Tuberculosis


Protozoa





Fungi





Macro-parasites


Small: 2 to 1000 µm
Eucaryotic:
membrane-bound
nucleus
No cell wall
Many are free-living
Classified by the way
they move
Range in size,
unicellular to
multicellular
Eucaryotic:
membrane-bound
nucleus
Cell wall
No chloroplasts
Saprophytic (living
on dead matter) or
parasitic
Visible by the naked
eye
Endoparasites or
exoparasites
Endoparasites usually
have long association
with host
Ectoparasites usually
have brief association
with host
Prion
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Amoebic dysentery
Thrush
Tapeworm, lice
Virus
Bacteria
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Protozoa

identify the role of antibiotics in the management of infectious disease
When is a Microbe a Pathogen?
There are many microorganisms around us. Some cause us no problems, some are
beneficial and some cause disease.
An organism is a pathogen if it causes disease.
Antibiotics are chemical substances which destroy bacteria or inhibit their
growth. They target the bacteria without destroying the host. They are not
effective against viruses (other types of antimicrobial drugs can kill viruses and
fungi).
Mode of action: some antibiotics kill the microbe by destroying the cell wall eg
Penicillin (discovered by Alexander Fleming in 1928)
Some inhibit protein synthesis, bacteria are unable to make essential compounds,
resulting in the death of the cell)eg tetracyclines and streptomycin.
Others destroy the cell membrane thus effectively destroy the bacteria eg
amphotericin
Broad spectrum antibiotics act against a wide range of bacteria.
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
perform an investigation to model Pasteur’s experiment to identify the role of microbes
in decay

gather and process information to trace the historical development of our
understanding of the cause and prevention of malaria

identify data sources, gather process and analyse information from secondary sources
to describe one named infectious disease in terms of its:
– cause
– transmission
– host response
– major symptoms
– treatment
– prevention
– control

process information from secondary sources to discuss problems relating to
antibiotic resistance
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