1. What Is Microbiology About and Why Is It Important?
Microbiology is the study of very small organisms Microorganisms aka microbes Microbes play important roles in medicine, agriculture, and industry Microbes dominate the environment

2. Key Concepts in Microbiology
Form and Function Metabolism Genetic Systems Evolution Impact on Humans Communities

3. Microbiology History
First observed in 1600’s Could not be systematically studied until 1800’s due to technical limitations The role of microbes in nature was not clear at first Most early studies focused on the role of microbes in disease

4. Influence of Robert Koch
Rigorously demonstrated the link between microbes and infectious diseases Identified causative agents of anthrax and tuberculosis Developed rules called “Koch's Postulates” Developed techniques (solid media) for obtaining pure cultures of microbes, some still in existence today

5. KOCH'S POSTULATES
Theoretical aspects
Experimental aspects
Postulates:
Laboratory
tools:
Diseased
animal
Healthy
animal
1. The suspected pathogen
must be present in all
cases of the disease
and absent from healthy
animals.
Microscopy,
staining
Red
blood
cell
Observe
blood/tissue
under the
microscope.
Red
blood
cell
Suspected
pathogen
2. The suspected pathogen
must be grown in pure
culture.
Laboratory
cultures
Streak agar plate
with sample
from either a
diseased or a
healthy animal. No
organisms
present
Colonies
of suspected
pathogen
Inoculate healthy animal with
cells of suspected pathogen.
3. Cells from a pure culture
of the suspected
pathogen must cause
disease in a healthy
animal.
Experimental
animals
Figure 1.20 Koch’s postulates for proving cause and effect in infectious diseases.
Diseased animal
Remove blood or tissue sample
and observe by microscopy.
4. The suspected pathogen
must be reisolated and
shown to be the same
as the original.
Laboratory
reisolation
and culture
Suspected
pathogen
Laboratory
culture
Pure culture
(must be
same
organism
as before)
Figure 1.20 5

6. Koch, Infectious Disease, and Pure Cultures
Koch’s Postulates and techniques dominated the science of microbiology for almost a century His emphasis on pure cultures grown under lab conditions misled microbiologists Modern microbiology has shifted to more of an emphasis on microbial communities in natural conditions

7. Koch, Infectious Disease, and Pure Cultures
Koch’s work was “culture-dependent” So was the science of microbiology for its first 120 years. Modern methodology is “culture-independent”.