Applications of Raman Spectroscopy to Virology and Microbial Analysis - Emerging Raman Applications and Techniques in Biomedical and Pharmaceutical Fields - page 447

Fig. 19.4. UVRR spectrum of a bacterial bulk layer with genotypic information
due to enhanced DNA and protein signals compared with a micro-Raman spectrum
of a bacterial cell for phenotypic characterization since all subcellular components
DNA, protein, carbohydrates, and lipids contribute to the Raman spectrum
by phenylalanine 1001 cm − 1 , tryptophan 1602 cm − 1 , and tryptophan and
tyrosine 1615 cm − 1 . The Raman signals from amide I 1650-1680 cm − 1
and amide III 1230-1295 cm − 1 are only present in the non-resonant Raman
spectrum. Moreover, the Raman signals from carbohydrates located in the
1030-1130 cm − 1 region are missing in the UVRR spectrum.
In biological studies, 244 nm is one of the most commonly applied exci-
tation wavelengths in the ultra-violet region yielding Raman spectra exhibit-
ing signals from nucleic acids and from aromatic amino acids. Javis et al.
used 244 nm and showed the capability to distinguish between various uri-
nary tract bacteria [78]. Lopez-Diez and Goodacre analyzed different Bacillus
species and compared these results with those obtained by 16S rDNA gene
sequencing. Here, a good agreement between both Raman identification and
16S rDNA sequencing was noticed [80]. The influence of cultivation condi-
tions on the identification of different lactic acid bacteria was investigated by
Gaus et al. [81]. The results indicate that the variation of cultivation condi-
tions does not influence the identification results for UVRR measurements.
Grun et al. employed a new approach for bacterial identification, measuring
two-dimensional resonant Raman spectra [82]. In this approach, the Raman
spectra are recorded for 30 excitation wavelengths between 210 and 280 nm.
The wavelength-dependent changes are found to be characteristic for the dif-
ferent species.