Identification of bacteria in drinking water with Raman spectroscopy

Raman spectroscopy was used to discriminate between Legionella strains and between E. coli and coliform strains. The relationship between triplicate Raman spectra derived from Legionella bacteria was compared with that derived from a blind set of samples and amplified fragment length polymorphism (AFLP) data from the same strains. Triplicate Raman spectra of E. coli and coliform bacteria were compared with their 16S phylogeny. In all cases Raman spectra were reproducible and could be distinguished from spectra of other organisms down to the strain level. All samples in a blind fourth set were identified correctly. Raman spectra of organisms of the same coliform species clustered according to 16S rRNA gene phylogeny, except for Enterobacter spp. At higher taxonomic levels the relationship between species was less comparable. For Legionella strains the Raman spectra grouped according to AFLP groups, based on the dataset used in this study. Raman spectroscopy could correctly distinguish E. coli from other coliform bacteria and L. pneumophila from non-pneumophila strains. Incubation of Legionella strains in different types of drinking water at different temperatures over a period of one week introduced so little variation in the Raman spectra that only very closely related L. pneumophila strains could not be distinguished from each other. Temperature, ageing and water type did not influence the identification potency of Raman spectroscopy in all cases. Given the accuracy, speed and simplicity of the Raman spectroscopy technique this method seems a welcome addition to the current tools for identification of waterborne bacteria.