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

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

Microbiology History Microbes 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

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

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

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

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”.