Evaluating the use of fatty acid profiles to identify Francisella tularensis

Rapid capillary gas chromatography (GC) with flame-ionization detection was used to determine the cellular fatty acid profiles of Francisella tularensis. Two subspecies of F. tularensis, the live vaccine strain (LVS) derived from holarctica and a novicida strain Utah 112 (U112), were used to compare the extracted fatty acid methyl esters (FAMEs). A data set for the 2 subspecies was prepared using fatty acid profiles of bacteria grown on 2 types of media, Mueller-Hinton and cysteine heart agar supplemented with 5% rabbit blood (CHAB), and harvested at various time intervals (Day 1 through Day 4) with replicates prepared on different days. A total of 204 samples were analyzed. The results showed that these fatty acid quantitative profiles were unique for each of the subspecies and could be used as a fingerprint for the organism. It was determined by this rapid method that approximately 88% of the fatty acids in both the LVS and U112 strains included 6 saturated fatty acids: 10:0, 12:0, 14:0, 16:0, 18:0, and 20:0; and 4 hydroxy fatty acids 10:0 2OH, 16:0 3OH, 17:0 3OH, and 18:0 3OH. Data analysis and determination of clustering were performed by principal component analysis (PCA) and soft independent modeling of class analogy (SIMCA). Both PCA and SIMCA showed clear separation of the LVS and U112 strain and would be useful for prediction of unknowns. It was determined that the incubation time can be reduced from 48 to 24 h, and results are highly predictive for the identification of F. tularensis. In summary, analysis of FAMEs from F. tularensis subspecies LVS and U112 grown on CHAB or Mueller-Hinton media, and using a rapid GC method can provide a sensitive procedure for identification of these organisms.