Untangling metabolism between infected mammalian host cells and intracellular pathogen

Several recent reports encourage targeting bacterial central metabolic pathways as a new strategy for antimicrobial drug discovery based on lessons learned from oncology and virus infection. The hitherto limited experimental evidence for the metabolic interference by intracellular bacteria in their host emphasizes the urgent need for enabling methodologies to study the metabolism of the bacterial pathogens in their target cells. Stable Isotope Resolved Analysis with Hyperpolarized NMR (SIRAH-NMR) is a new method providing metabolic fingerprint with few features and high contrast to noise. Here we use SIRAH-NMR to gain information on metabolic pathway utilization when the intracellular bacterial pathogen Shigella flexneri adapt to the intracellular lifestyle of the infected host cell.
Distinct differences are observed from the host cell (HeLa) and the bacteria alone when [U-13C]glucose is used as substrate and the metabolic fingerprint is analyzed with SIRAH-NMR. Lactate and pyruvate are observed from the host cell whereas Shigella produces acetate and formate as main metabolites. Since there is no overlap between the metabolic fingerprint produced by HeLa and Shigella we use this method to investigate the metabolic cross-talk when HeLa cells are infected with Shigella (MOI=6). Under these conditions three of the four metabolites are observed. Lactate is unchanged which corresponds to unchanged flux through glycolysis of the HeLa cells while pyruvate is decreased and replaced by a similar amount of acetate -a metabolic product from Shigella. Formate is not observed in the infected cells. This indicates a different use of metabolic pathways in the bacteria when inside the host. SIRAH-NMR provides sensitivity and specificity to study and untangle the metabolic cross-talk between host cells and intra cellular pathogens in vivo.