Evaluating the use of fatty acid profiles to differentiate human pathogenic and nonpathogenic Listeria species

Listeria monocytogenes is a Gram-positive human pathogen that is responsible for serious infections in immunocompromised individuals and pregnant women. Because of recent epidemics caused by food contaminated with L. monocytogenes, rapid methods for the detection of this pathogen in food are of interest. Capillary gas chromatography with flame ionization detection (GC-FID) was used to determine the cellular fatty acid profiles of six species of Listeria. The six different species are L. monocytogenes, L. ivanovii, L. innocua, L. welshimeri, L. seeligeri, and L. grayi. For GC-FID analysis, whole cell fatty acid methyl esters (FAMEs) from cells cultured on brain heart infusion (BHI) agar at 35 degrees C for 24 h were obtained by saponification, methylation, and extraction into hexane/methyl tert-butyl ether. A preliminary data set for 15 strains of Listeria species was prepared using fatty acid profiles from two or three replicates prepared on different days. Major fatty acids of the Listeria strains evaluated in this study were C15:0 iso, C15:0 ante iso, C16:0 iso, C16:0, C17:0 iso, and C17:0 ante iso. All of the major fatty acids differ significantly among these six species. The two fatty acids C17:0 ante iso and C15:0 ante iso showed the highest percentages, and the ratio of the two clearly showed significant differences between the human pathogen L. monocytogenes and the five nonpathogenic species. Analysis of FAMEs from Listeria strains grown on BHI agar by a GC-FID method is a sensitive procedure for identification of these organisms and differentiation between pathogenic and nonpathogenic species.