Raman Spectroscopic Signatures of the Metabolic States of Escherichia Coli Cells and their Dependence on Antibiotics Treatment

Abstract

The metabolic states of Escherichia coli (E. coli) cells were characterized with laser tweezers Raman spectroscopy and the cellular response to the antibiotics Cefazolin and Penicillin/Streptomycin were correlated to spectroscopic changes.The Raman spectra of E. coli cells were measured at different time points in the bacterial growth curve, which revealed several spectral features applicable for identification of the bacterial cell's growth phase. The time dependent behavior of Raman peak intensities allowed us to identify four groups of Raman peaks with similar intensity time trends, displaying specificity to the same bio-molecule. The intensity of Raman peaks associated with DNA increased over time in contrast to protein specific Raman peaks, which decreased at different rates. In addition, the intensity of the adenine ring-breathing mode increased initially and decreased after approximately 10h. A separation of Raman spectra specific to different metabolic states of E. coli cells was visualized with principal component analysis (PCA).The exposure of bacterial cells to Cefazolin and Penicillin/Streptomycin at the end of the exponential growth phase, resulted in differences in the time dependence of several Raman intensities. In addition, a shift of the spectral position of the adenine ring-breathing mode, associated with normal growth, was not observed for either of the two antibiotic drug exposures. The time dependence of the amide I Raman band intensity changed for Penicillin/Streptomycin exposure compared to normal growth, but not for Cefazolin treatment. This suggests that Raman spectroscopic markers of cellular response may differ between antibiotics or drug classes.