Norharmane matrix enhances detection of endotoxin by MALDI-MS for simultaneous profiling of pathogen, host and vector systems

The discovery of novel pathogenic mechanisms engaged during bacterial infections requires the evolution of advanced techniques. Here, we evaluate the dual polarity matrix norharmane (NRM) to improve detection of bacterial lipid A (endotoxin), from host and vector tissues infected withFrancisella novicida (Fn). We evaluated NRM for improved detection and characterization of a wide range of lipids in both positive and negative polarities, including lipid A and phospholipids across a range of matrix-assisted laser desorption-ionization-coupled applications. NRM matrix improved the limit of detection (LOD) for monophosphoryl lipid A (MPLA) down to picogram level representing a 10-fold improvement of LOD versus 2,5-dihydroxybenzoic acid and 100-fold improvement of LOD versus 9-aminoacridine (9-AA). Improved LOD for lipid A subsequently facilitated detection of theFn lipid A major ion (m/z 1665) from extracts of infected mouse spleen and the temperature-modifiedFn lipid A atm/z 1637 from infectedDermacentor variabilis ticks. Finally, we simultaneously mapped bacterial phospholipid signatures within anFn-infected spleen along with an exclusively host-derived inositol-based phospholipid (m/z 933) demonstrating coprofiling of the host-pathogen interaction. Expanded use of NRM matrix in other infection models and endotoxin-targeting imaging experiments will improve our understanding of the lipid interactions at the host-pathogen interface.