from seaweed and is uniquely suitable for bacterial cultivation because of its general
resistance to bacterial action and its property of dissolving at 212F (100C), but not
gelling until cooled below 113F (45C). It is heated to a liquid, poured either into test
tubes or petri dishes and allowed to cool. When the agar media cools and gels, it is
ready to have microorganisms placed on it (inoculated). Also, bacteria can be
suspended in the agar while it is still a liquid. Both nutrient broth and nutrient agar
media may or may not have special nutrients added, depending upon the needs of the
species of microorganisms that are to be cultured.
(2) In test tubes. When agar is placed in test tubes, the contents are
allowed to either gel in an upright position or are slanted to create a larger surface area.
The former are called "deeps" and are usually inoculated by placing microorganisms on
a needle and stabbing the media. The latter are called "slants" and are inoculated by
smearing organisms across the surface of the agar.
(3) In petri dishes (plating). Plating is the process of inoculating
microorganisms on the surface of the agar media in petri dishes. This method is most
often used to grow large populations of organism colonies for further study. After the
agar plates have been inoculated, they are kept at temperatures optimum for the growth
of the organisms. The act of establishment, growth, and multiplication of
microorganisms at a specific temperature for a given time is termed incubation.
Following the establishment of organisms on agar media, the colonies and media
together are termed a culture.
EARLY DEVELOPMENTS IN MICROBIOLOGY
a. Leeuwenhoek. Anton Van Leeuwenhoek was the first man to see
microorganisms. He ground lenses as a hobby and made his discovery while observing
a drop of water. Seeing many tiny organisms moving rapidly under the lens, he called
them "animalcules" (little animals). He is credited with inventing the microscope, and
his invention made possible the development of the science of microbiology.
Leeuwenhoek continued to work with microscopes until his death in 1723 and made
many important discoveries. He observed bacteria on houseflies; he saw bacteria in the
excreta of man and animals; and he discovered the presence of bacteria in the human
b. Koch. Robert Koch was another important worker in the field of microbiology.
He proved that bacteria cause disease by discovering the causative organisms of
anthrax, cholera, and tuberculosis.
c. Pasteur. Louis Pasteur is credited with being the founder and originator of
the science of microbiology. He immunized sheep against anthrax and introduced a
treatment for the prevention of rabies. Our pasteurization process for milk and other
foods also bears his name.