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.

Evaluation of antibiotic effects on Pseudomonas aeruginosa biofilm using Raman spectroscopy and multivariate analysis

“…Figure 3 shows averaged Raman spectra for P. aeruginosa biofilm. It is characterized by vibrational bands typical for nucleic acids, proteins, lipids, carbohydrates and carotenoids (see Table 1) [19, [39][40][41][42]. The prominent Raman bands of biofilm belong to proteins: 1002 cm −1 (phenylalanine), 1243 cm −1 (amide III) and 1658 cm −1 (amide I).…”

Vibrational spectroscopic mapping and imaging of tissues and cells

“…For resonance enhancement, the absorbing photon is of sufficient energy to excite a chromophore into an electronic excited state, which results in a markedly increased probability that the scattered photon differs in energy by an amount that corresponds to the energy of a molecular vibration. This can increase the intensity of the Raman effect by up to six orders of magnitude and can, for instance, be used to selectively monitor heme proteins in biological samples using visible excitation into the Soret or Q bands (Wood et al 2005) or selective enhancement of nucleic acids and certain aromatic amino acid residues in proteins by UV excitation (Neugebauer et al 2007). This advantage, however, can often be outweighed by fluorescence and photodamage caused by such irradiation; thus, NIR excitation is also often used in dispersive Raman measurements with biological samples, albeit using shorter wavelength excitation than is used in FT-Raman spectroscopy, in order to enhance the Raman effect.…”

Raman spectroscopy: techniques and applications in the life sciences

“…Neugebauer et al measured TERS spectra from Staphylococcus epidermidis [370,371], while Cialla et al measured TERS spectra from tobacco mosaic viruses [372]. Other bacteria-derived samples, such as isolated membrane patches from Halobacterium salinarum have also been measured with TERS, with different patches able to be distinguished [373].…”