IMPROVED IDENTIFICATION OF MYCOBACTERIA BY USING THE MICROBIAL-IDENTIFICATION-SYSTEM IN COMBINATION WITH ADDITIONAL TRIMETHYLSULFONIUM HYDROXIDE PYROLYSIS

The MIDI automated Microbial Identification System (MIS) ruses gas chr omatography (GC) analysis of whole-cell fatty acid methyl esters (FAME s) between 9 and 20 carbons in length to characterize a nide range of bacterial genera and species, including mycobacteria. Mycolic acid cle avage products (MACPs) with chain lengths of C-22 to C-26 are not rele ased by MIDI sample preparation of mycobacteria. Therefore, the MIS li brary search report often matches several mycobacterial species withou t any significant difference in the similarity indices. The problem is solved by adding trimethylsulfonium hydroxide (TMSH) instead of sodiu m sulfate in the last step of sample preparation, thus allowing the id entification of MACPs in addition to FAMEs. Only one GC run parameter has to be changed: the temperature program must be extended from 260 t o 310 degrees C. The MIS library search report for the identification of bacteria is not disturbed by TMSH. The combination of conventional library search report with the information of typical MACP patterns yi elds significantly better discrimination of mycobacterial species than the MIDI method allows.