Microbiology and Immunology

WORLD OF MICROBIOLOGY AND IMMUNOLOGY Pasteur, Louis

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French revolution—one in winemaking, as Pasteur suggested

that greater cleanliness was need to eliminate bacteria and that

this could be accomplished using heat. Some wine-makers

were initially reticent to heat their wines, but the practice

eventually saved the wine industry in France.

The idea of heating to kill microorganisms was applied

to other perishable fluids, including milk, and the idea of pas-

teurization was born. Several decades later in the United

States, the pasteurization of milk was championed by

American bacteriologist Alice Catherine Evans, who linked

bacteria in milk with the disease brucellosis, a type of fever

found in different variations in many countries.

In his work with yeast, Pasteur also found that air

should be kept from fermenting wine, but was necessary for

the production of vinegar. In the presence of oxygen, yeasts

and bacteria break down alcohol into acetic acid, or vinegar.

Pasteur also informed the vinegar industry that adding more

microorganisms to the fermenting mixture could increase

vinegar production. Pasteur carried on many experiments with

yeast. He showed that fermentation can take place without

oxygen (anaerobic conditions), but that the process still

involved living things such as yeast. He did several experi-

ments to show (as Lazzaro Spallanzani had a century earlier)

that living things do not arise spontaneously but rather come

from other living things. To disprove the idea of spontaneous

generation, Pasteur boiled meat extract and left it exposed to

air in a flask with a long S-shaped neck. There was no decay

observed because microorganisms from the air did not reach

the extract. On the way to performing his experiment Pasteur

had also invented what has come to be known as sterile tech-

nique, boiling or heating of instruments and food to prevent

the proliferation of microorganisms.

In 1862, Pasteur was called upon to help solve a crisis

in another ailing French industry. The silkworms that pro-

duced silk fabric were dying of an unknown disease. Armed

with his microscope, Pasteur traveled to the south of France in

1865. Here Pasteur found the tiny parasitesthat were killing
      the silkworms and affecting their food, mulberry leaves. His
      solution seemed drastic at the time. He suggested destroying
      all the unhealthy worms and starting with new cultures. The
      solution worked, and soon French silk scarves were back in
      the marketplace.
      Pasteur then turned his attention to human and animal
      diseases. He supposed for some time that microscopic organ-
      isms cause disease and that these tiny microorganisms could
      travel from person to person spreading the disease. Other sci-
      entists had expressed this thought before, but Pasteur had
      more experience using the microscope and identifying differ-
      ent kinds of microorganisms such as bacteria and fungi.
      In 1868, Pasteur suffered a stroke and much of his work
      thereafter was carried out by his wife Marie Laurent Pasteur.
      After seeing what military hospitals were like during the
      Franco-Prussian War, Pasteur impressed upon physicians that
      they should boil and sterilize their instruments. This was still
      not common practice in the nineteenth century.
      Pasteur developed techniques for culturing and examin-
      ing several disease-causing bacteria. He identified
      Staphylococcus pyogenes bacteria in boils and Streptococcus

pyogenesin puerperal fever. He also cultured the bacteria that

cause cholera. Once when injecting healthy chickens with

cholera bacteria, he expected the chickens to become sick.

Unknown to Pasteur, the bacteria were old and no longer vir-

ulent. The chickens failed to get the disease, but instead they

received immunityagainst cholera. Thus, Pasteur discovered

that weakened microbes make a good vaccineby imparting

immunity without actually producing the disease.

Pasteur then began work on a vaccine for anthrax, a dis-

ease that killed many animals and infected people who con-

tracted it from their sheep and thus was known as “wool

sorters’ disease.” Anthrax causes sudden chills, high fever,

pain, and can affect the brain. Pasteur experimented with

weakening or attenuating the bacteria that cause anthrax, and

in 1881 produced a vaccine that successfully prevented the

deadly disease.

Pasteur’s last great scientific achievement was develop-

ing a successful treatment for rabies, a deadly disease con-

tracted from bites of an infected, rabid animal. Rabies, or

hydrophobia, first causes pain in the throat that prevents swal-

lowing, then brings on spasms, fever, and finally death.

Pasteur knew that rabies took weeks or even months to

Louis Pasteur, who refuted the theory of spontaneous generation and

developed the sterilization technique of pasteurization.

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