The History of Microbiology (Key events that advanced our
understanding of microorganisms) Slide 2 Microbes have been around
for a long time Thought to be the first living entities on
earth::photosynthetic bacteria were responsible for generating
oxygen for the support of life Cyanobacteriaphotosynthetic
microorganisms were the first O 2 -evolving organisms on Earth and
may have been responsible for oxygenating the atmosphere Slide 3
Evidence for the production of beer, wine and bread Evidence for
food preservation with salt and drying. (Ships undertaking long
passages to the Americas used these practices) Francis Bacon
(1561-1626) Had a theory that freezing should retard the spoilage
of chickensdied testing the theory People were aware of an
invisible force that affected food and involved microbes. Slide 4
Production of beer, wine and bread @ 2400 BCE Slide 5 People were
aware that an invisible force caused sickness and death 1300s
height of the first plague: implementation of quarantenaria by the
Italians Slide 6 More evidence for human awareness of disease
causing microorganisms Girolamo Fracastoro 1546 (200 years after
the first plague) Philosophical treatise De Contagione et
Contagiosis Morbis --some diseases are caused by the transmission
of germs 3 possible modes for the transmission of contagion 1.
Direct contact 2. Transmission via inanimate objects 3.
Transmission from a distance --contagion or disease processes and
the putrefaction of food are analogous. Slide 7 Germs have a
form::invention of the microscope Johannes and Zacharias Jansen
(spectacle makers) 1590two convex lenses in sequence magnifies and
image Galileo (Italian astronomer) 1624 improved precursor to the
light microscope Anton van Leeuwenhoek (cloth draper) 1674 designed
own microscopes, first to describe bacteria, yeasts and protozoa
wee animalcules Ernst Abbe (German physicist) --1882 developed
better lenses for microscopes, developed the oil immersion lens
Paul Ehrlich 1881 staining with methylene blue Christian Gram 1884
differential staining with methylene blue and safronin. Slide 8
Leuwenhoeks microscope and drawings of some of his wee animalcules
Slide 9 Hookes microscope (progenitor to the modern day microscope)
and his observations Hooke was a contemporary of Leuwenhoek and
invented the microscope around the same time Slide 10 The
controversy regarding spontaneous generation in food spoilage The
belief that living forms sprang from non-living matter proponents:
putrefaction is a result of chemical events opponents: putrefaction
is caused by germs Francesco Redi 1668 Showed that flies were
responsible for maggots found on the surface of rotting meat. John
Needham 1748 organic infusions spoiled in stoppered bottles Abbe
Lazzaro Spellanzani1765 boiled the organic infusions, infusions
remained barren for a long time unless the seal was broken Louis
Pasteur 1861trained as a scientist and used scientific method to
address the issue. Slide 11 Scientific Method 1.STATE THE PROBLEM
2.FORM A HYPOTHESIS AFTER GATHERING ALL INFORMATION ON THE TOPIC
3.DEVISE EXPERIMENTS TO TEST THE VALIDITY OF THE HYPOTHESIS
4.OBSERVE RESULTS OF THE EXPERIMENT 5.INTERPRET THE DATA 6.DRAW
CONCLUSIONS 7.ALWAYS CAREFULLY DOCUMENT DESIGN AND RESULTS OF THE
EXPERIMENT!!! Slide 12 Pasteurs Scientific Method 1.STATE THE
PROBLEM A. Food allowed to stand for some time spoiled B. Wine and
beer do not always come out the way it should Slide 13 Pasteurs
Scientific Method 2. FORM A HYPOTHESIS AFTER GATHERING ALL
INFORMATION ON THE TOPIC Observed that structures in the air that
resembled micro organisms found in putrefied materials Passed air
through cotton/ released trapped materials in liquid and observed
microorganisms via microscopy HYPOTHESIS: Microorganisms found in
putrefying food originate from microbes in the airfoods protected
from the airbourne microbes should not putrefy. Slide 14 1861Louis
Pasteur refutes the theory of spontaneous generation (good example
of a controlled experiment) Slide 15 Some of Pasteurs swan necked
flasks Slide 16 Pasteurs Scientific Method 4.DRAW CONCLUSIONS The
souring of milk, beer and wine is due to microorganisms
Microorganisms in these products can be killed by heating Some
advancements from these studies and conclusions: 1867pasteurization
heating food to 55-60 o C for a short time Slide 17 Pasteurization
is commonly used to remove pathogenic organisms from food products
Historically: Used to kill organisms causing brucellosis, typhoid
fever and tuberculosis in dairy products Today: Used to kill
Salmonella spp and Escherichia coli O157:H7 Doesnt kill all of the
organisms Process: Passing raw milk through a heat exchanger such
that small volumes of milk are briefly heated to 71 o C for 15
seconds, the milk is rapidly cooled and maintained at the low
temperature Slide 18 The effect of temperature on the viability of
a typical mesophillic bacterium Decimal Reduction Time = the length
of time a bacterial population must be exposed at a given
temperature to kill 90% of the population Slide 19 Caveats to using
lower temperatures for the eradication of microorganisms The
thermal death time depends on the size of the initial bacterial
population The high sugar, protein and fat content of some products
decrease heat penetration and increase the resistance of the
organisms in these products to heat Endospores are moderately heat
resistantcontain compounds that are resistant to heat, have little
water activity, are metabolically inert and are surrounded by a
thick keratin coat. Slide 20 John Tyndall and Ferdinand Cohn1877
Discovery of heat resistant forms of bacteria John Tyndall:
bacteria have a heat labile or heat sensitive form and a heat
resistant form Cohn the heat resistant forms of bacteria form
endospores endospores become vegetative after one heating process.
Repeated heating and cooling eliminates viable organisms
Tyndallization Charles Chamberland1881 designed an autoclave large
pressure cooker, Slide 21 Endospores Accumulation of Calcium, small
acid soluble spore proteins (SASPs) and Dipicolinic acid that forms
a gel like structure which excludes water Contraction of the cortex
st.V results in a shrunken protoplast Slide 22 Endospores: Note how
these structures are resistant to heat, irradiation and chemicals
compared to vegetative cells and note how they are low in water
content and metabolically inert * Slide 23 The Autoclave an
effective means for killing heat resistant bacteria and endospores
The chamber is heated under low atmospheric pressure conditions
such that it is possible to increase the chamber temperature to 121
o C. Slide 24 High Temperatures (121 o C) for at least 15
minuteslonger for larger volumes that take longer to reach this
temperature Endospores require approximately 5 minutes for a
decimal reduction The autoclave (contd)
