Microbiologists use various methods to identify organisms cultivated from patient specimens. Although many of the principles and issues about bacterial identification discussed in this chapter are generally applicable to most
Rat Raised Convex
Entire (smooth) Irregular
Figure 7-11 Colony morphologic features and descriptive terms for commonly encountered bacterial colonies.
clinically relevant bacteria, specific information regarding particular organism groups is covered in the appropriate chapters in Part HI.
The importance of accurate bacterial identification cannot be overstated because identity is central to diagnostic bacteriology issues, including:
The identification of a bacterial isolate requires analysis of information gathered from laboratory tests that provide characteristic profiles of bacteria. The tests and the order in which they are used for organism identification are often referred to as an identification scheme. Identification schemes can be classified into one of two categories: (1) those that are based on genotypic characteristics of bacteria and (2) those that are based on phenotypic characteristics. Certain schemes rely on both genotypic and phenotypic characteristics. Additionally, some tests, such as the Gram stain, are an integral part of many schemes used for identifying a wide variety of bacteria, whereas other tests may only be used in the identification scheme for a single species such as the fluorescent antibody test for identification of Legionella pneumophila.
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