Principles of Diagnostic Microbiology

For more than 100 years, from the time Louis Pasteur (1822–1895) reformulated the germ theory of disease, and Robert Koch (1843–1910) developed his famous “postulates” for establishing the relationship of microbes to disease, clinical microbiologists have been at work isolating and identifying the causative agents of infections. In principle, many of the methods in common use today are the same as those developed more than a century ago. However, a great deal has been learned about the biochemical, immunologic, and molecular characteristics of microbes. This knowledge has greatly improved the speed, ease, and precision with which today’s microbiologists identify pathogenic microorganisms.

Even with technical advances that allow rapid microbial detection and identification (sometimes directly in the patient specimen), an understanding of the metabolic behavior of microorganisms in culture is essential. In most instances, prompt, accurate recognition of pathogenic species is still achieved by choosing appropriate culture media for isolating these organisms from clinical specimens and by selecting proper tests for determining their characteristic metabolic behavior.

In the exercises of Section Principles of Diagnostic Microbiology, classic methods for isolating and identifying microorganisms will be described and performed. Some of the newer assays are also described.