Identification of coryneform bacteria and related taxa by Fourier-transform infrared (FT-IR) spectroscopy.

An extensive Fourier-transform infrared (FT-IR) spectroscopy database for the identification of bacteria from the two suborders Micrococcineae and Corynebacterineae (Actinomycetales, Actinobacteria) as well as other morphologically similar genera was established. The database consists of averaged IR spectra from 730 reference strains, covering 220 different species out of 46 genera. A total of 192 species are represented by type strains. The identity of 352 reference strains was determined by comparative 16S rDNA sequence analysis and, if necessary, strains were reclassified accordingly. FT-IR frequency ranges, weights and reproducibility levels were optimized for this section of high-G+C gram-positive bacteria. In an internal validation, 98.1% of 208 strains were correctly identified at the species level. A simulated external validation which was carried out using 544 strains from 54 species out of 16 genera resulted in a correct identification of 87.3% at the species level and 95.4% at the genus level. The performance of this identification system is well within the range of those having been reported in the literature for the identification of coryneform bacteria by phenotypical methods. Coryneform and related taxa display a certain degree of overlapping distribution of different taxonomical markers, leading to a limited differentiation capacity of non-genotypical identification methods in general. However, easy handling, rapid identification within 25 h starting from a single colony, a satisfactory differentiation capacity and low cost, render FT-IR technology clearly superior over other routine methods for the identification of coryneform bacteria and related taxa.