Identification= E. coli

10.2 Using Phenotypic Characteristics to Identify Prokaryotes 253

rides, can be detected using techniques that rely on the specificity of interaction between antibodies and antigens. Methods that exploit these interactions are called serology and will be discussed in more detail in later chapters. Some serological tests, such as those used to confirm the identity of S. pyogenes, are quite simple and rapid. ■ serology, p. 426 ■ antibodies, p. 394 ■ antigens, p. 397

Fatty Acid Analysis (FAME)

Bacteria differ in the type and relative quantity of fatty acids that make up their membranes; thus, the cellular fatty acid composition can be used as an identifying marker. In the case of Gram-negative bacteria, the fatty acids are contained in both the cytoplasmic and outer membranes. Gram-positive bacteria, however, lack an outer membrane; the cytoplasmic membrane is the source of their fatty acids. To analyze their fatty acid composition, bacterial cells are grown under standardized conditions. The cells are then chemically treated with sodium hydroxide and methanol to release the fatty acids and to convert those acids to their more volatile methyl ester form (FAME stands for fatty acid methyl ester). The resulting fatty acid methylated esters can then be separated and analyzed using gas chromatography. By comparing the pattern of peaks, or chromatogram, to those of known species, an isolate can be identified (figure 10.7).

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