Towards a Detailed Understanding of Bacterial Metabolism—Spectroscopic Characterization of Staphylococcus Epidermidis

Abstract

Bacteria are a major cause of infection. To fight disease and growing resistance, research interest is focused on understanding bacterial metabolism. For a detailed evaluation of the involved mechanisms, a precise knowledge of the molecular composition of the bacteria is required. In this article, various vibrational spectroscopic techniques are applied to comprehensively characterize, on a molecular level, bacteria of the strain Staphylococcus epidermidis, an opportunistic pathogen which has evolved to become a major cause of nosocomial infections. IR absorption spectroscopy reflects the overall chemical composition of the cells, with major focus on the protein vibrations. Smaller sample volumes—down to a single cell—are sufficient to probe the overall chemical composition by means of micro‐Raman spectroscopy. The nucleic‐acid and aromatic amino‐acid moieties are almost exclusively explored by UV resonance Raman spectroscopy. In combination with statistical evaluation methods [hierarchical cluster analysis (HCA), principal component analysis (PCA), linear discriminant analysis (LDA)], the protein and nucleic‐acid components that change during the different bacterial growth phases can be identified from the in vivo vibrational spectra. Furthermore, tip‐enhanced Raman spectroscopy (TERS) provides insight into the surface structures and follows the dynamics of the polysaccharide and peptide components on the bacterial cells with a spatial resolution below the diffraction limit. This might open new ways for the elucidation of host–bacteria and drug–bacteria interactions.