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Strains of the genusAcinetobacter, classified as genomic species 13BJ/14TU have been previously associated with human infections and resistance to colistin. To clarify the taxonomy of this provisional group, we investigated 24 strains that have been isolated from humans since the 1960s in 10 countries. The genus-wide analysis of the rpoB and gyrB sequences of all strains and whole-genome sequences of strains representing different rpoB/gyrB genotypes showed that the 24 strains formed a distinct monophyletic group within the so-called haemolytic clade of the genus Acinetobacter. The distinctness of the group at the species level was supported by the results of the cluster analysis of the whole-cell protein fingerprints generated by matrix-assisted laser desorption ionization-time-of-flight MS. The 24 strains had very similar metabolic features and could be distinguished from other members of the genus by the combination of strong haemolytic and proteolytic activities and the ability to oxidize d-glucose and grow on phenylacetate and/or l-phenylalanine. The minimum inhibitory concentrations of the 24 strains to colistin and polymyxin B ranged from 16 to 64 mgl-1 and from 4 to 32 mgl-1, respectively, so uniformly reaching the current clinical resistance breakpoint (4 mg l-1) for these drugs. Genus-wide comparison revealed that such a consistently high level of resistance to polymyxins is a unique feature among species of the genus Acinetobacter,which occur in humans. We conclude that genomic species 13BJ/14TU represents a biologically meaningful and medically relevant species, for which the name Acinetobacter colistiniresistens sp. nov. is proposed. The type strain is NIPH 2036T (=CCM 8641T=CIP 110478T=CCUG 67966T=CNCTC 7573T).

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This study aimed to define the taxonomic status of a novel, phenetically distinct group of seven strains belonging to the genus Acinetobacter, which were isolated from environmental soil and water samples collected in Central Bohemia, Czech Republic. Comparative sequence analyses of the 16S rRNA, gyrB and rpoB genes showed that all these strains formed respective tight clusters (intracluster sequence similarities of ≥99.8, ≥98.1 and ≥98.3 %, respectively), which were distant from all known Acinetobacter species (≤98.2, ≤84.0 and ≤88.9 %, respectively). The average nucleotide identity and digital DNA-DNA hybridization values (≤83.5 and ≤27.4 %, respectively) between the whole-genome sequence of a group representative (strain ANC 4149T) and those of known taxa were far below the thresholds used to discriminate between bacterial species. The seven strains also formed a tight and distinct cluster based on the genus-wide comparison of whole-cell mass fingerprints generated by matrix-assisted laser desorption/ionization time-of-flight MS and could be distinguished from all other members of the genus Acinetobacter by the combination of their ability to assimilate glutarate and l-tartrate and inability to grow at 37 °C and on l-aspartate. It is concluded that the seven strains represent a novel species for which the name Acinetobacter pragensis sp. nov. is proposed. The type strain is ANC 4149T (=CCM 8637T=CCUG 67962T=CNCTC 7530T).