Some Enterococcus faecalis strains have adapted to become tolerant to daptomycin, a lipopeptide that disrupts the continuity of the membrane, by incorporating exogenous unsaturated fats. Quantifying changes in membrane composition is a trade-off between sensitivity and coverage. Cardiolipins are notorious for being difficult to detect due to solubility issues, separation challenges, and low concentrations in vivo. A novel method has been developed based on hydrophilic interaction liquid chromatography coupled to a Q Exactive Plus mass spectrometer to detect 23 unique cardiolipins, 11 phosphatidylglycerols, and 11 lysyl-phosphatidylglycerol compounds. With the use of a quadrupole Orbitrap, tandem mass spectrometry can quantify whole classes of lipids by detecting a common head group fragment and the exact concentrations as low as 50 nM can be determined by using non-natural lipids as internal standards. Utilizing parallel reaction monitoring, data can also be gathered simultaneously regarding the identity of each fatty acid tail. This method can quantify changes in lipid species as well as the tail composition, and these alterations can be correlated with antibiotic resistance.

Absolute quantitation of cardiolipin, phosphatidylglycerol, and lysyl-phosphatidylglycerol using HILIC based separation coupled to a Q Exactive Plus mass spectrometer

256th National Meeting (2018)

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