Chemotyping

Analysis of cellular fatty acids - CFA (FAME)

Since the early 1970s, analysis of cellular fatty acids between 9 and 20 carbons in length have been used as an aid in rapid identification and classification of microorganisms. In practice, whole cells of bacteria or yeasts are treated to cause release of their fatty acids, which are converted to a methyl ester derivative (FAME) and then analyzed by gas chromatography. The result is a “fatty acid fingerprint” of the organism. At the CCUG, the method has been in use since the end of the 1980:s and an extensive library of bacterial fatty acid profiles has been generated.

For identification of the fatty acids, a peak naming table makes it possible to recognize 164 of the most abundant peaks in the chromatograms. One single peak naming table is used for all types of bacteria, which is a difference compared to the commercial Sherlock Microbial Indentification System system that has several tables specific for certain groups of organisms. For some peaks two alternative names have to be given because the two compounds are too close to be clearly chromatographically separated. Some peaks still remain listed as “unknown”.

The service includes fatty acid characterization, and for certain organisms identification to genus or species level by comparison (matching) with a stored database. Identification is expressed using a similarity index number. An exact match of the unknown and a database entry would generate a similarity index of 1.000. In the report, the best matches are listed with the highest indexes at the top. However, the CFA profiling analysis has been discontinued at the CCUG, although CFA profile data on strains is still available online.

CFA method
CCUG peak naming table
CFA method for publications

Analysis of metabolic products of anaerobic bacteria – VFA, nVFA

Anaerobic bacteria produce characteristic metabolic products, which can be analyzed to help identifying the bacteria. Gas chromatography is used for determination of the C1-C7 volatile fatty acids, nonvolatile acids (which must be analyzed as methyl esters), and alcohols in the growth medium. Extracts of the melted agar samples are prepared for the analysis, and peaks are identified by comparing with standards. After determining which metabolites are present, identification charts are used for identification of the anaerobes. However, analysis of metabolic products has been discontinued at the CCUG.

Procedure adopted from Anaerobe Laboratory Manual, 4th ed. 1977. Virginia Polytechnic Institute and State University, Blacksburg, USA.

VFA method