Discrimination of the Acinetobacter calcoaceticus-Acinetobacter baumannii complex species by Fourier transform infrared spectroscopy

The main goal of this work was to assess the ability of Fourier transform infrared spectroscopy with attenuated total reflectance (FTIR-ATR) to discriminate between the species of the Acinetobacter calcoaceticus- Acinetobacter baumannii (Acb) complex, i.e. A. baumannii, A. nosocomialis, A. pittii, A. calcoaceticus, genomic species "Between 1 and 3" and genomic species "Close to 13TU". A total of 122 clinical isolates of the Acb complex previously identified by rpoB sequencing were studied. FTIR-ATR spectra was analysed by partial least squares discriminant analysis (PLSDA) and the model scores were presented in a dendrogram form. This spectroscopic technique proved to be effective in the discrimination of the Acb complex species, with sensitivities from 90 to 100 %. Moreover, a flowchart aiming to help with species identification was developed and tested with 100 % correct predictions for A. baumannii, A. nosocomialis and A. pittii test isolates. This rapid, low cost and environmentally friendly technique proved to be a reliable alternative for the identification of these closely related Acinetobacter species that share many clinical and epidemiological characteristics and are often difficult to distinguish. Its validation towards application on a routine basis could revolutionise high-throughput bacterial identification.