Towards Raman-based epidemiological typing of Pseudomonas aeruginosa

Raman spectra of bacteria can be used as highly specific fingerprints, enabling discrimination at strain level. Pseudomonas aeruginosa strains can be strongly pigmented, making it difficult to obtain high quality spectra of such isolates due to high fluorescent spectral backgrounds. Furthermore, the spectra that could be measured with acceptable quality often showed large spectral variations limiting the reproducibility required for strain level discrimination. P aeruginosa produces a characteristic yellowish green fluorescent pigment, called pyoverdin. Applying a washing procedure to reduce the amount of fluorescent pigment. enabled the highly pigmented isolates to be measured with sufficient spectral quality. Isolation of the pigment/pyoverdin spectral features, together with spectral scaling methods improved reproducibility. It will be important to analyze the range of the spectral variations that can occur and ensure the correction of all of these factors to obtain the highest reproducibility required for strain level typing. [GRAPHICS] Raman spectra showing the effect of multiple washing steps on the background, and pyoverdin levels in a sample.