Exploiting intrinsic fluorescence spectroscopy to discriminate between Acinetobacter calcoaceticus–Acinetobacter baumannii complex species

Abstract

Several spectroscopic techniques, such as infrared, Raman, fluorescence and mass spectrometry, have been tested in the context of bacterial typing. The degree of success is highly dependent on the taxonomic level. Intrinsic fluorescence spectroscopy, detecting natural bacterial fluorophores, has been claimed to be a reliable alternative to the standard typing methods, with some published works reporting its success. In this work we evaluate the ability of this technique to discriminate between four closely related species belonging to the so-called Acinetobacter calcoaceticus–Acinetobacter baumannii complex. Single-point and two-dimensional fluorescence spectral data were acquired at room temperature and 25 °C. Spectra were analysed by partial least squares discriminant analysis and soft independent modelling of class analogy. The percentages of correct species assignments, ranging from 4.2–97.7%, were highly dependent on the experimental conditions and the method of data analysis. It seems that the results benefit from strict temperature control being those achieved with two-dimensional data slightly better than with single-point data. Nevertheless, it was impossible to achieve a satisfactory percentage of correct assignments for the four species simultaneously, pointing to several limitations of this technique for such bacterial species typing purposes.