Chap. 1 – Scope and History of Microbiology


Why Study Microbiology?

1.    Impact on Human Health

2.    Balance of Nature - food source, play a role in decomposition, help other animals digest grass (cattle, sheep, termites).

3.    Environmental – provide safe drinking water; development of biodegradable products; use bacteria to clean up oil spills, etc. – called bioremediation.

4.    Industrial – foodstuffs (beer, wine, cheese, bread), antibiotics, insulin, genetic engineering

5. Agricultural - research has led to healthier livestock and disease-free crops.


I.    Microbiology defined - The study of microbiology is the study of microorganisms, which are organisms that are invisible to the naked eye.    


II.  Classification of Microorganisms

The 5 major groups of microorganisms: bacteria, algae, fungi, protozoa, and viruses.  We will also study some other smaller groups such as prions and viroids.  The one property that links these groups together is their very small size! 

       2 types of cells (viruses, prions and viroids are acellular – “without a cell”):

1.        Prokaryotic ("before nucleus") – these guys are cells, but they have no internal membrane bound structures (no membrane-bound nucleus or membrane-bound organelles); includes only the bacteria.

2.       Eukaryotic ("true nucleus") – do have internal membrane bound structures (membrane bound nucleus and membrane-bound organelles); includes organisms such as protozoans, fungi, algae, animals, plants.     


          A.  Bacteria   (singular - bacterium)  (study of bacteria – bacteriology)

                   1.  prokaryotic

                   2.  unicellular

                   3.  size:  1/1000 the volume of a typical eukaryotic cell

                   4.  2 groups (discovered in 1970's) - we'll discuss more later

                             a.  Archaeobacteria - ancient bacteria

                             b.  Eubacteria - true bacteria

5.     some shapes:  bacillus (rod), coccus (spherical), spirillum (spiral), vibrio (curved rod)

6.     motile or nonmotile

                   7.  how do they obtain their energy? 

a.      photosynthetic autotrophs - use energy from the sun to produce their own carbohydrates for energy.

b.     chemosynthetic autotrophs - process inorganic molecules for energy (ex. sulfur or iron).

c.      heterotrophs - depend on outside sources of organic molecules (ex. carbohydrates or sugars) for energy

8.     temperature extremes:  -20oC to 110oC (that’s really cold & really hot! freezing is OoC and boiling is 100oC)

9.     examples of diseases?


       B.  Algae   (singular - alga) - not a focus in this course.

1.        eukaryotic

2.      unicellular or multicellular

3.      size:  some microscopic, some macroscopic (ex. kelp)

4.      motile or nonmotile

5.      how do they obtain their energy?   photosynthetic autotrophs

6.      disease causing? no


C.       Fungi  (singular - fungus)     (study of fungi – mycology)

1.       eukaryotic

2.     unicellular or multicellular (yeasts are unicellular, molds are multicellular)

3.     nonmotile

                   4.  how do they obtain their energy?

a.      heterotrophs

b.     Why are they ecologically important? Scavengers; they live off dead matter and thus, decompose it.

5.     examples of diseases (called mycoses)? 

examples of nonpathogenic fungi?


       D.  Protozoa   ("first animals")

1.        eukaryotic

2.      unicellular

3.      motile or nonmotile

4.      how do they obtain their energy?     Heterotrophs

5.      disease causing – 2 examples:  malaria & giardiasis (one of the “don’t drink the water diseases”)


       E.  Viruses - (study of viruses – virology)

1.       acellular, so not considered prokaryotic or eukaryotic; obligate intracellular parasites; when they are outside of a host cell, there is no evidence that these guys are alive.

2.     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.

3.     size - 1/10 to 1/1000 the size of an ordinary bacterial cell.

4.     nonmotile

5.     examples of diseases? 


Important Note:  We will consider a sixth group, the helminths (worms), in our study of microbiology.  While most of the adult stages of these worms are macroscopic, many of them go through a microscopic stage in their life cycles (egg & larval stages).  Some examples of helminths are tapeworms, hookworms, pinworms, heartworms, and Chinese liver flukes.  More to come later!!


III.       A Brief History of Microbiology


C.        Leeuwenhoeck (lived 1632-1723)

1.       What discovery is he credited with?  First person to use microscopes to observe microbes; as a hobby he made small handheld microscopes; he called microorganisms “animalcules.”


C.       Hooke

1.       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 unit of all living things.


C.       Redi and Spontaneous Generation

1.       What is this theory? Living organisms arise from nonliving things (ex. maggots come from rotting meat)

2.     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. 

3.     Many insisted that he only disproved spontaneous generation for macroorganisms; maybe microbes were an exception.


D.      Needham vs. Spallanzani - still trying to prove or disprove the theory of spontaneous generation.

1.       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!]

2.     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.


          E.  Pasteur's Epic Experiments (1859)

1.       What was his experimental method?  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.  


2.     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 used vegetable broths - plants contains many endospore-forming bacteria.)


                   3.  What 3 things did Pasteur's experiments prove? 

a.        No living things arise by spontaneous generation.

b.       Microbes are everywhere - even in the air and dust

c.        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).


4.  Pasteur also contributed to the development of vaccines.


          F.  The Germ Theory of Disease

1.       What is the germ theory of disease?  Microbes (germs) cause disease and specific microbes cause specific diseases.

2.     Who proved this theory?  Robert Koch in the late 1870's.

3.     What disease was he studying?  anthrax - disease of cattle/sheep; also in humans

4.     What was his experimental method?  He observed that the same microbes were present in all blood samples of infected animals.  He isolated and cultivated these microbes (now known to be Bacillus anthracis ).  He then injected a healthy animal with the cultured bacteria & that animal became infected with anthrax & its blood sample showed the same microbes as the originally infected animals. 

5.     What did his experiments prove?  Particular microbes cause particular diseases.

                   6.   What are Koch's 4 Postulates?

1.)     The causative agent must be present in every individual with the disease.

2.)   The causative agent must be isolated & grown in pure culture (how did he invent pure cultures?; with Frau Hesse's help, he developed the agar plate method (see p. 13).

3.)   The pure culture must cause the disease when inoculated into an experimental animal.

4.)   The causative agent must be reisolated from the experimental animal & reidentified in pure culture.


          G.  What are Some Ways that We Can Control Infectious Diseases?


1.       Immunity - stimulating the body's own ability to combat infection; from ancient times it was a recognized fact that people who suffered from certain diseases never got them again; infection could produce immunity.

a.      Immunization defined:  produce immunity by providing exposure to altered organisms that do not cause disease.

b.     Jenner & Smallpox - observed that dairymaids that contracted a mild infection of cowpox seemed to be immune to smallpox.  He inoculated a boy with fluid from a cow pox blister and he contracted cowpox; he then inoculated him with fluid from a smallpox blister; the boy did not contract smallpox; the term vaccination came from vacca  for cow. 

                             c.  The first vaccines:

1.)    Pasteur's discovery? attenuated bacteria can produce immunity

2.)   Attenuated defined - weakened virus or bacteria that is unable to cause the disease (it was later discovered that killed microbes can also produce immunity)

3.)   What vaccines did Pasteur develop?  anthrax, rabies


                   2.  Public Hygiene

                             a.  Improving sewage disposal.

                             b.  Assuring a clean public water supply.

                             c.  Food preservation & inspection.

                                      ex. Pasteurization - kills most microbes by exposing to heat.

                             d.  Improving personal hygiene.

                                      Semmelweiss & childbed fever               

e.  Developing antiseptic techniques.

Lister & carbolic acid  – he developed the first aseptic techniques.


              3.  Chemotherapy


a.      Who is the father of chemotherapy?  Paul Ehrlich - he discovered a drug treatment for syphilis; he developed the guiding principle of chemotherapy, which is selective toxicity  (the drug must be toxic to the infecting microbe, but relatively harmless to the host’s cells).  

b.     What was the first major class of drugs to come into widespread clinical use?  sulfa drugs

c.      Who discovered the first antibiotic?  Flemming discovered (penicillin); antibiotics are antibacterial compounds produced by fungi and bacteria.       


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