Gas Chromatographic Analysis of Cellular Fatty Acids in the Identification of Foodborne Bacteria

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Abstract
The cellular fatty acid composition of about 160 strains of Bacillus, lactic acid bacteria, Enterobacteriaceae, and Staphylococcus was analyzed in order to identify foodborne bacteria. In a first step, the reproducibility of the procedure, from the bacterial growth to the extraction and analysis conditions, was evaluated. The stability of fatty acid composition under controlled conditions was confirmed through high similarity levels (So ≥ 94). Secondly, intraspecies similarity was estimated. The existence of low values (So ≤ 79) was demonstrated within each of the four groups of strains investigated, which stressed the importance of analyzing a high number of reference strains in each species. The intraspecies similarity was maximal under optimal growth conditions. Finally, interspecies similarity was compared to intraspecies similarity. The best results of discrimination between species was obtained for the heterogeneous genus Bacillus, for which the 12 species studied could be separated into 6 clusters at a similarity level of 79. The association of 27 species of lactic acid bacteria into 8 clusters should be useful to confirm results of other characterization methods. Only 3 clusters were formed for the 16 Enterobacteriaceae species studied. The genus Salmonella could not be discriminated. The 10 Staphylococcus species were separated into 5 clusters. Coagulase-positive and -negative strains were not differentiated. Since the fatty acid composition did not usually appear specific to single species, characterization of foodborne bacteria by the analysis of their cellular fatty acids should be used to complement other taxonomic methods.

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