CHAPTER 1.

Introduction to microbiology

What is microbiology?
"Specialized area of biology that studies living things, ordinarily too small"

     bacteria
     fungi
     protozoan
     algae
     viruses        Are viruses living things?

 Why to study it?

  •  Microorganisms are part of the human environment and important in human health
  •  Provide insight into life processes in all life forms (Genetics, Biochemistry, Physiology)
  •  Microorganisms help maintain the balance of nature (food chain, nutrient recycling)
  •  Important in food-making processes (and spoilage)
  •  Important to tbioremediation (biodegradation, toxic dumps and spills, sewage treatment)
  •  Industrail applications (antibiotics, vitaminas, enzymes, solvents)
  •  Bioengineering (products manufactured through recombinant DNA techniques)
  •  Biological control - Bacillus thuringensis


    • What is a microorganism?
         An organism that is too small to be seen clearly with the naked eye.
         Generally single cells, but some exist as cell clusters

    How small are microbes?
              Limits of human resolution = 100 micrometers
              smallest microbe <0.2 micrometers
              largest microbe > 500 micrometers
              typical bacterium = 1-2 micrometers

    I. TYPES OF MICROORGANISMS
        * Unicellular VS multicellular
        * Prokaryotes VS eukaryotes
        * Five kingdome classification: Monera, Protista, Fungi, Plantae, Animalia
        * Three kingdome classification: Eubacteria, Archaebacteria, Eukaryotes

    II. Historical overview of microbiology
    Early microbiology
    Ancient cultures and civilizations had no idea that microbes existed but they did comprehend some of their important effects. For example:

    Key figures of the late seventeenth century (1600's)
    * Robert Hooke: using a compound microscope described cork cells as "little boxes" that
        reminded him of the cells used by monks. He introduce the term "cell", he also described fungi but
        his microscope was unable to resolve bacteria.
    * Anton van Leeuwenhoek: considered by many to be the "Father of Microbiology". Leeuwenhoek
        was not the first to develop a lens or microscope but was the first to describe LIVING microbes,
        including bacteria. He accurately described microbes as little "animalcules" in a report to the Royal
        Society in 1676.

    II. SPONTANEOUS GENERATION AND ABIOGENESIS
     (Source:J. Strick ASM News. April 1997).
     

  • This long held theory advocated that life could arise spontaneously from nonliving or decomposing

    •     matter.
  •   Aristotle claimed that moist soil was the generator of snakes, toads and mice.
  •  Maggots were supposed to be generated by decaying meat.
  •  1600's - Francesco Redi's experiment with meat in a jar with gauze proved that you needed flies to

    •      get maggots, settling at least part of the spontaneous generation debate.
  •  1700's - Spallanzani did experiements with broth and showed that when sealed and boiled no

    •       microbial growth occured. However, flasks which were boiled but left open, became cloudy with
          growth. THESE EXPERIMENTS WERE CRITICIZED BECAUSE OF THE LACK OF
          VITAL  FORCE IN THE SEALED FLASKS.
  •  1800s - Rudolf Virchow - introduced biogenesis: "living cells can only arise from preexisting cells"
  •  1800S - Louis Pasteur and his gooseneck flasks finally settled spontaneous generation!

    •      1.) Allowed free entry of air (therefore vital force was present).
         2.) Gooseneck baffle prevented the entry of particles.
         3.) If broke the neck then the broth got cloudy.
         4.) Therefore no spontaneous generation -- The microbes were found in the air. Also  microbes
                could be destroyed by heat. This was the beginning of aseptic technique.

    Note:  Henry Bastian of University College Medical School in London. Bastian conducted many
        experiments that showed microbes could still grow in various broth's that had been boiled for hours.
        Although his observations were accurate the growth was not due to abiogenesis. The riddle was
        solved in 1876 when a German botanist, Cohn identified species of Bacillus, common to hay and
        cheese, that contained heat-resistant endospores. If Pasteur had used these cultures in his flasks the
        debate over spontaneous generation could have ended up very differently!

    Louis Pasteur's other contributions
      Fermentation -- The transformation of a food through the growth and metabolism of a
                                microorganism. This work was done on beer and wine.
      Developed the process known as Pasteurization -- as a way to kill "bad fermentations" present in
         alcoholic beverages and milk
      Vaccinations for CHICKENS (Cholera), CATTLE (Anthrax), HUMANS (Rabies)

    Development of the Germ Theory of Disease
    This theory provided us with knowledge of the causal relationship between microbes and disease and was an outgrowth of the work of numerous scientists and medical professionals including:

              * Koch's postulates are a series of procedures to prove that a particular microorganisms
                    causes disease.

    Further contributions of Koch

    3) Vaccination (1798)- atributed to Edward Jenner. Using cowpox material he was able to
        protect (immunize) humans aganist smallpox. Edward Jenner was told by a milkmaid that she
        never had to worry about catching smallpox as she had already had cowpox. This observation was
        backed up by villagers "if you want to marry a woman who will never be scarred by the pox, marry
        a milkmaid." Jenner demonstrated that inoculation with scrapings from cowpox provided immunity
        to the more virulent smallpox virus. He used an 8 year old boy called James Phipps to test his
        vaccine. James was inoculated with virulent matter from cowpox lesions on the fingers of a
        milkmaid called Sarah Neimes. Phipps developed a mild fever and some cowpox lesions. Several
        weeks later Phipps was injected with LIVE smallpox (Today we call this a "challenge experiment").
        Thankfully, James was protected from the disease. Jenner noted that this immunity was "a change,
        which endures throughout life."

    The type of experiment tried by Jenner is against medical ethics of today. It is not possible to use young children in challenge experiments with live viruses or other microbes.

    IV. Emergence of specialized fields of microbiology
      Near the end of the nineteenth century, the field of microbiology began to divide into specialized
        areas of interest

     Immunology

  • Jenner (cowpox --> smallpox) and Pasteur pioneered the area of immunization.
  • Elie Metchnikoff (1880s) discovered cells could ingest microbes - phagocytes.


    • Chemotherapy
    * Mid 1600's. The British physician, Thomas Sydenham introduces quinine-containing Cinchona
        bark from South America. Quinine has long been used as an antimalarial.
    * Paul Ehrlich (in 1910)  Developed Salvarsan (compound 606) for the treatment of syphilis. Ehrlich
        worked under Robert Koch. While working on differential staining techniques Ehrlich developed the
        idea of using a "magic bullet" that would kill disease-causing microbes but spare the host with
        minimal toxicity.

  •  Alexander Fleming discovered lysozyme in 1922 and then, based on the work of others,

    •      developed penicillin in 1928. Fleming observed that penicillium mold inhibited growth of
        Staphylococci growing on a petri plate. Penicillin became widely available and known as the
        "wonder-drug" with the advent of world war II.
  •  Selman Waksman , fueled by the discoveries of the 30s, surveyed many soil samples and isolated

    •     streptomycin. This antibiotic was the first effective drug available to treat infections with gram
        negative bacteria and tuberculosis. . He termed the agents "antibiotics".
    * Domagk in 1930's developed sulfa drugs. These drugs are especially useful in treating urinary tract
        infections and are used in combination formulas to prevent pneumocystis pneumonia.
  • 1987. AZT becomes the first drug licensed for treating HIV disease. This was the same year that

    •     President Reagan made his first public mention of AIDS. By that time, 25,000 Americans had
        already died of AIDS and countless others overseas. The first cases of AIDS in the U.S. were
        reported in 1981.
    * 1995. First generation of drugs called protease inhibitors are approved to help treat HIV disease.
        These drugs continue to extend an improve the quality of life for many recipients. However, there is
        a constant threat of drug resistance and the majority of HIV+ people around the world do NOT

         The fields of microbiology are diverse and microbiologists, like microorganisms, are everywhere.


    V. Current Issues in Infectious Disease

    EMERGING INFECTIONS: -- often due to evolutionary changes, movement to new geographic locations, new exposures due to ecologic changes