ARTICLE Discrimination of the Acinetobacter calcoaceticus–Acinetobacter baumannii complex species by Fourier transform infrared spectroscopy C. Sousa & L. Silva & F. Grosso & A. Nemec & J. Lopes & L. Peixe Received: 17 December 2013 /Accepted: 31 January 2014 # Springer-Verlag Berlin Heidelberg 2014 Abstract 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 discrimi- nation 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 tech- nique 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. Introduction The genus Acinetobacter currently comprises 29 distinct species with valid names (http://www.bacterio.cict.fr/a/ acinetobacter.html) and a number of taxa which include either genomic species (gen. sp.) delineated by DNA–DNA hybridisation [1] or species with effectively (but not validly) published names. Some of these species are difficult to identify using current methods available in routine clinical laboratories, in particular those belonging to the Acinetobacter calcoaceticus–Acinetobacter baumannii (Acb) complex, which encompasses four phenotypically and geno- typically related species with valid names, i.e. A. baumannii, A. nosocomialis, A. pittii an A. calcoaceticus, and two provi- sional gen. sp., i.e. the so-called “Between 1 and 3” and “Close to 13TU” [2]. Among the members of the Acb complex, A. baumannii is the most clinically important species, which is frequently involved in nosocomial infections including serious outbreaks and associated with increasing reports of multidrug- and pandrug-resistant strains, as well as with higher mortality rates and poorer outcomes when compared with the related species [3, 4]. Moreover, we have assisted to increasing reports of noso- comial infections of non-A. baumannii species of the Acb complex [5]. These species differ from A. baumannii in char- acteristics regarding infectious potential, antimicrobial sus- ceptibility and mortality rates, which dictates the need for precise identification to guide the therapy and improve the clinical outcome [4]. A number of genotypic methods have been proposed for Acinetobacter species identification [1]. The most widely used identification approaches include polymerase chain reaction (PCR) amplification and sequencing of species- specific DNA regions (e.g. the intrinsic oxacillinases from C. Sousa : L. Silva : F. Grosso : L. Peixe (*) REQUIMTE, Laboratório de Microbiologia, Departamento de Ciências Biológicas, Faculdade de Farmácia, Universidade do Porto, Rua de Jorge Viterbo Ferreira, 228, 4050-313 Porto, Portugal e-mail: lpeixe@gmail.com A. Nemec Laboratory of Bacterial Genetics, National Institute of Public Health, Šrobárova 48, 100 42 Prague, Czech Republic J. Lopes REQUIMTE, Laboratório de Química Aplicada, Departamento de Ciências Químicas, Faculdade de Farmácia, Universidade do Porto, Rua de Jorge Viterbo Ferreira, 228, 4050-313 Porto, Portugal Eur J Clin Microbiol Infect Dis DOI 10.1007/s10096-014-2078-y