Cellular fatty acid-based microbial identification and antimicrobial susceptibility testing

Bacteria produce a wide array of complex lipids and fatty acids. Both fatty acids and complex lipids can vary in chain length, number and position of functional groups, and number and position of double bonds. As early as 1963, the analysis of cellular fatty acid (CFA) for the purpose of bacterial identification was introduced by Abel et al. and Kaneda [1, 2]. The variability of fatty acid structure in bacteria has led to the characterization of over 300 bacterial fatty acids and related compounds [3]. These fatty acids and related compounds range from relatively polar lipids found in bacterial membranes to more complex lipids found in lipooligosaccharides and lipopolysaccharides. Other fatty acids are components of highly specialized lipids, such as the mycolic acids, found in Mycobacteria, Nocardia, and related genera. Specialized methods have been developed for detailed analysis of fatty acids and related lipids. These methods have aided efforts in bacterial classification yielding both qualitative and quantitative analysis of specific fatty acids and their constituent components. Such methods have provided the basis for bacterial identification and taxonomic classification and continue to be used by many laboratories as an inexpensive and rapid screening tool or as an ancillary test to other standard bacterial identification methods. More recently, CFA analysis has been used to identify bacterial agents of bioterrorism [4].