Comparison of Five Extraction Methods for Intracellular Metabolites of Salmonella typhimurium.

Salmonella enterica serovar typhimurium (S. typhimurium) causes food poisoning in human and animals. Its infection rate is the highest among all salmonella serotypes. Metabolomics is a potential way to study the pathogenesis of S. typhimurium via analysis of various small molecular substances. Due to the lack of a uniform protocol for the extraction of metabolites, we evaluated five commonly used extraction methods including cold methanol (CM), hot ethanol (HE), chloroform-methanol cocktail (CMC), perchloric acid (PCA), and alkali (AL) for their efficacy in extracting the intracellular metabolites of S. typhimurium. Samples were quenched in 60% methanol at - 40 °C, and then the five methods were used to extract the metabolites. After derivatization, all samples were analyzed on a gas chromatography-triple quadrupole mass spectrometry (GC-MS/MS). Our results suggest that CM and HE extraction methods provide the best compromise allowing identification of 98 and 95 metabolites in a single analysis. For targeted metabolome analysis, the optimal extraction method for alcohols and organic acids is HE. CMC preferentially extracted lipid metabolites. PCA is suitable for extraction of small molecular carbohydrates. The optimal extraction method for macromolecular carbohydrates is the CM method.