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The emergence of Acinetobacter carbapenem resistance in the Czech Republic is associated with the spread of A. baumannii strains of EU clone II. The variation in susceptibility in these strains is likely to result from both the horizontal spread of resistance genes and differential expression of intrinsic genes.

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Acinetobacter genospecies (genomic species) 10 and 11 were described by Bouvet and Grimont in 1986 on the basis of DNA–DNA reassociation studies and comprehensive phenotypic analysis. In the present study, the names Acinetobacter bereziniae sp. nov. and Acinetobacter guillouiae sp. nov., respectively, are proposed for these genomic species based on the congruence of results of polyphasic analysis of 33 strains (16 and 17 strains of genomic species 10 and 11, respectively). All strains were investigated by selective restriction fragment amplification (i.e. AFLP) analysis rpoB sequence analysis, amplified rDNA restriction analysis and tDNA intergenic length polymorphism analysis, and their nutritional and physiological properties were determined. Subsets of the strains were studied by 16S rRNA gene sequence analysis and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) MS or had been classified previously by DNA–DNA reassociation. Results indicate that A. bereziniae and A. guillouiae represent two phenetically and phylogenetically distinct groups within the genus Acinetobacter. Based on the comparative analysis of housekeeping genes (16S rRNA and rpoB genes), these species together represent a monophyletic branch within the genus. Despite their overall phenotypic similarity, the ability to oxidize d-glucose and to grow at 38 °C can be used in the presumptive differentiation of these two species from each other: with the exception of three strains that were positive for only one test, A. bereziniae strains were positive for both tests, whereas A. guillouiae strains were negative in these tests. The strains of A. bereziniae originated mainly from human clinical specimens, whereas A. guillouiae strains were isolated from different environmental sources in addition to human specimens. The type strain of A. bereziniae sp. nov. is LMG 1003T (=CIP 70.12T =ATCC 17924T) and that of A. guillouiae sp. nov. is LMG 988T (=CIP 63.46T =ATCC 11171T =CCUG 2491T).

This study aimed to define the taxonomic status of a phenetically distinct group of 16 strains that corresponds to Acinetobacter genomic species 'close to 13TU', a provisional genomic species of the Acinetobacter calcoaceticus-Acinetobacter baumannii (ACB) complex recognized by Gerner-Smidt and Tjernberg in 1993. These strains have been isolated in different countries since the early 1990s and were mostly recovered from human clinical specimens. They were compared with 45 reference strains representing the known taxa of the ACB complex using taxonomic methods relevant to the genus Acinetobacter. Based on sequence analysis of the concatenated partial sequences (2976 bp) of seven housekeeping genes, the 16 strains formed a tight and wellsupported cluster (intracluster sequence identity of ¢98.4 %) that was clearly separated from the other members of the ACB complex (¡94.7 %). The species status of the group was supported by average nucleotide identity values of ¡91.7 % between the whole genome sequence of representative strain NIPH 973 T (NCBI accession no. APOO00000000) and those of the other species. In addition, whole-cell matrix-assisted laser desorption ionization-time-of-flight (MALDI-TOF) MS analyses indicated the distinctness of the group at the protein level. Metabolic and physiological tests revealed several typical features of the group, although they did not allow its reliable differentiation from the other members of the ACB complex. We conclude that the 16 strains represent a distinct novel species, for which we propose the name Acinetobacter seifertii sp. nov. The type strain is NIPH 973 T (5CIP 110471 T 5CCUG 34785 T 5CCM 8535 T). The term 'Acinetobacter calcoaceticus-Acinetobacter baumannii (ACB) complex' was coined by Gerner-Smidt et al. (1991) for a group of four phenotypically similar species. These included A. calcoaceticus, A. baumannii and genomic species (gen. sp.) 3 and gen. sp. 13 sensu Tjernberg & Ursing (1989), which were later named Acinetobacter pittii and Acinetobacter nosocomialis, respectively (Nemec et al., 2011). Early taxonomic studies based on DNA-DNA hybridization suggested that the species of the ACB complex were genomically more related to each other than to the other species of the genus Acinetobacter (Bouvet & Grimont, 1986; Tjernberg & Ursing, 1989). Recent studies Abbreviations: ACB complex, Acinetobacter calcoaceticus-Acinetobacter baumannii complex; ANIb, average nucleotide identity based on BLAST; MALDI-TOF, matrix-assisted laser desorption ionization-time-of-flight; MLSA, multilocus sequence analysis. The GenBank/EMBL/DDBJ accession numbers for the rpoB gene sequences determined in this study are KJ956425, KJ956427, KJ956428, KJ956430, KJ956437, KJ956440, KJ956442, KJ956443, KJ956447-KJ956457 and KJ956459-KJ956466. The partial sequences of the seven genes used for MLSA are available from the Institut Pasteur MLST website (http://www.pasteur.fr/mlst) under the sequence type codes listed in Table 1. Two supplementary figures and three supplementary tables are available ...