Food Microbiology
STUDY NOTES
Why Study Microbiology?
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Impact on Human Health
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Balance of Nature - food source, play a role in decomposition, help other animals digest
grass (cattle, sheep, termites).
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Environmental – provide safe drinking water; development of biodegradable products; use
bacteria to clean up oil spills, etc. – called bioremediation.
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Industrial – foodstuffs (beer, wine, cheese, bread), antibiotics, insulin, genetic engineering
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Agricultural - research has led to healthier livestock and disease-free crops.
Microbiology:
Is the study of microorganisms (organisms that are invisible to the naked eye).
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Classification of Microorganisms
The 5 major groups of microorganisms include bacteria, algae, fungi, protozoa, and viruses. The
one property that links these groups together is their very small size!
Prokaryotic ("before nucleus") – these are cells; however they have no internal membrane
bound structures (no membrane-bound nucleus or membrane-bound organelles); includes only
the bacteria.
Eukaryotic ("true nucleus") – do have internal membrane bound structures (membrane bound
nucleus and membrane-bound organelles); includes organisms such as protozoans, fungi, algae,
animals and plants.
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Bacteria [Singular - bacterium) bacteriology- study of bacteria]
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Prokaryotic
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Unicellular
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Size: 1/1000 the volume of a typical eukaryotic cell
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There are two groups, which were discovered in 1970's
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Archaeobacteria - ancient bacteria
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Eubacteria - true bacteria
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Some shapes: bacillus (rod), coccus (spherical), spirillum (spiral), vibrio (curved rod)
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Are motile or non-motile
Algae (Singular - alga) NOT A FOCUS IN THIS COURSE.
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Eukaryotic
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Unicellular or Multi-cellular
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Size: some are microscopic while others are macroscopic
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They are motile or non-motile
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How do they obtain their energy? They are photosynthetic autotrophs
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Disease causing? No
Fungi [(singular - fungus) mycology- study of fungi]
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Eukaryotic
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Unicellular or multicellular (yeasts are unicellular, molds are multicellular)
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Non-motile
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How do they obtain their energy? They are heterotrophs
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Why are they ecologically important? Scavengers; they live off dead matter and thus,
decompose it
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Diseases are called mycoses. Give examples
Protozoa ("first animals")
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Eukaryotic
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Unicellular
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Motile or nonmotile
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How do they obtain their energy?
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disease causing – e.g: malaria & giardiasis (one of the “don’t drink the water diseases”)
They are heterotrophs
Viruses - (virology– study of viruses)
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Acellular, so not considered prokaryotic or eukaryotic; obligate intracellular parasites;
when they are outside of a host cell, there is no evidence that they are alive.
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Basic structure of a virus - a piece of nucleic acid (RNA or DNA) enclosed by a protein
coat (capsid); possess no nucleus, organelles, cell membrane, or cytoplasm.
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Size - 1/10 to 1/1000 the size of an ordinary bacterial cell.
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Non-motile
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Give at least 5 examples of diseases?
A brief history of microbiology
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Antonie van Leeuwenhoeck (lived 1632-1723)
What discovery is he credited with? First person to use microscopes to observe microbes; as a
hobby he made small hand-held microscopes; he called microorganisms “animalcules.”
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Robert Hooke
What discovery is he credited with? He first described “cellulae” (small rooms) in cork in 1665.
His discovery led to the formulation of the cell theory, which states that cells are the basic
organizational units of all living things.
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Redi and Spontaneous Generation
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What is this theory? Living organisms arise from nonliving things (e.g.maggots come from
rotting meat).
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Who disproved this theory and how? In the late 1600’s Francisco Redi showed that
maggots developed only in meat that flies could reach to lay eggs on.
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Many insisted that he only disproved spontaneous generation for macroorganisms; maybe
microbes were an exception.
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Needham vs. Spallanzani - still trying to prove or disprove the theory of spontaneous
generation.
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What was Needham's hypothesis, experiment, & conclusions? Everyone knew boiling killed
microbes; so, he would boil chicken broth, put it in a flask, & seal it; if microbes grew, then it
could only be because of spontaneous generation; they did grow. [We now know that
microbes grew because the flask was not sterilized before he poured in the broth!].
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What was Spallanzani's hypothesis, experiment, & conclusions? He was not convinced by
Needham's experiment. He put broth in a flask, sealed it (creating a vacuum), & then boiled
it. There were no microbes in the cooled broth! Critics said he didn't disprove spontaneous
generation - they said he just proved that spontaneous generation required air.
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Louis Pasteur's classic Experiments (1859)
What was his experimental method?
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To offset the argument that air was necessary for spontaneous generation, Pasteur allowed
the free passage of air, but prevented the entry of microbes. He boiled meat broth in a
flask & then drew out & curved the neck of the flask in a flame. No microbes developed
in the flask. When he tilted the flask so some broth flowed into the curved neck & then
tilted it back so the broth was returned to the base of the flask, microbes grew. Gravity
had caused the microbes that had entered the flask in air & dust to settle at the low point
of the neck, never reaching the broth in the base until the broth washed them in.
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Pasteur's success was partly due to good luck. He used meat, which contains few
bacterial endospores (endospores are resistant to heat; many experiments done prior to
Pasteur's experiments used vegetable broths - plants contain many endospore-forming
bacteria.)
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What 3 things did Pasteur's experiments prove?
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No living things arise by spontaneous generation.
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Microbes are everywhere - even in the air and dust
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The growth of microbes causes dead plant & animal tissue to decompose & food to
spoil (this led him to develop the technique of pasteurization - he developed it to
keep wine from spoiling).
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Pasteur also contributed to the development of vaccines.
F. The Germ Theory of Disease
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What is the germ theory of disease?
Microbes (germs) cause disease and specific microbes cause specific diseases.
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Who proved this theory?
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Robert Koch in the late 1870's
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What disease was he studying?
Anthrax - disease of cattle/sheep; also in humans
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What was his experimental method?
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