Acinetobacter Seifertii Research Articles

Whole-plasmid analysis of NDM-1-producing Acinetobacter seifertii isolate and its fitness in several Acinetobacter species

ObjectivesThe aim of this study was to characterize an NDM-1-producing Acinetobacter seifertii isolates from a patient in South Korea. MethodsAntibiotic susceptibility testing and genotyping using multigene sequencing were performed and whole plasmid sequences were determined. ResultsThe genotype of A. seifertii was ST1899 and was resistant to ceftazidime, trimethoprim–sulfamethoxazole, and piperacillin–tazobactam, in addition to carbapenem. blaNDM-1 was surrounded by the ISAba125 insertion sequence within the structure of Tn125 in the 47 kb-sized plasmid. The plasmid exhibited a structure similar to that of other plasmids of diverse Acinetobacter sp. found worldwide. Transconjugation and the growth curve indicated that the plasmid was adapted to A. seifertii rather than other closely related Acinetobacter sp. ConclusionsAcquisition of carbapenem resistance by horizontal transfer of the blaNDM-1-carrying plasmid from another Acinetobacter species was found with no growth defect.

A bioinformatic approach to identify confirmed and probable CRISPR-Cas systems in the Acinetobacter calcoaceticus-Acinetobacter baumannii complex genomes.

The Acinetobacter calcoaceticus-Acinetobacter baumannii complex, or Acb complex, consists of six species: Acinetobacter baumannii, Acinetobacter calcoaceticus, Acinetobacter nosocomialis, Acinetobacter pittii, Acinetobacter seifertii, and Acinetobacter lactucae. A. baumannii is the most clinically significant of these species and is frequently related to healthcare-associated infections (HCAIs). Clustered regularly interspaced short palindromic repeat (CRISPR) arrays and associated genes (cas) constitute bacterial adaptive immune systems and function as variable genetic elements. This study aimed to conduct a genomic analysis of Acb complex genomes available in databases to describe and characterize CRISPR systems and cas genes. Acb complex genomes available in the NCBI and BV-BRC databases, the identification and characterization of CRISPR-Cas systems were performed using CRISPRCasFinder, CRISPRminer, and CRISPRDetect. Sequence types (STs) were determined using the Oxford scheme and ribosomal multilocus sequence typing (rMLST). Prophages were identified using PHASTER and Prophage Hunter. A total of 293 genomes representing six Acb species exhibited CRISPR-related sequences. These genomes originate from various sources, including clinical specimens, animals, medical devices, and environmental samples. Sequence typing identified 145 ribosomal multilocus sequence types (rSTs). CRISPR-Cas systems were confirmed in 26.3% of the genomes, classified as subtypes I-Fa, I-Fb and I-Fv. Probable CRISPR arrays and cas genes associated with CRISPR-Cas subtypes III-A, I-B, and III-B were also detected. Some of the CRISPR-Cas systems are associated with genomic regions related to Cap4 proteins, and toxin-antitoxin systems. Moreover, prophage sequences were prevalent in 68.9% of the genomes. Analysis revealed a connection between these prophages and CRISPR-Cas systems, indicating an ongoing arms race between the bacteria and their bacteriophages. Furthermore, proteins associated with anti-CRISPR systems, such as AcrF11 and AcrF7, were identified in the A. baumannii and A. pittii genomes. This study elucidates CRISPR-Cas systems and defense mechanisms within the Acb complex, highlighting their diverse distribution and interactions with prophages and other genetic elements. This study also provides valuable insights into the evolution and adaptation of these microorganisms in various environments and clinical settings.

Phylogenomics of Acinetobacter species and analysis of antimicrobial resistance genes.

Non-baumannii Acinetobacter species are increasingly isolated in the clinical setting and the environment. The aim of the present study was to analyze a genome database of 837 Acinetobacter spp. isolates, which included 798 non-baumannii Acinetobacter genomes, in order to define the concordance of classification and discriminatory power of 7-gene MLST, 53-gene MLST, and single-nucleotide polymorphism (SNPs) phylogenies. Phylogenies were performed on Pasteur Multilocus Sequence Typing (MLST) or ribosomal Multilocus Sequence Typing (rMLST) concatenated alleles, or SNPs extracted from core genome alignment. The Pasteur MLST scheme was able to identify and genotype 72 species in the Acinetobacter genus, with classification results concordant with the ribosomal MLST scheme. The discriminatory power and genotyping reliability of the Pasteur MLST scheme were assessed in comparison to genome-wide SNP phylogeny on 535 non-baumannii Acinetobacter genomes assigned to Acinetobacter pittii, Acinetobacter nosocomialis, Acinetobacter seifertii, and Acinetobacter lactucae (heterotypic synonym of Acinetobacter dijkshoorniae), which were the most clinically relevant non-baumannii species of the A. baumannii group. The Pasteur MLST and SNP phylogenies were congruent at Robinson-Fould and Matching cluster tests and grouped genomes into four and three clusters in A. pittii, respectively, and one each in A. seifertii. Furthermore, A. lactucae genomes were grouped into one cluster within A. pittii genomes. The SNP phylogeny of A. nosocomialis genomes showed a heterogeneous population and did not correspond to the Pasteur MLST phylogeny, which identified two recombinant clusters. The antimicrobial resistance genes belonging to at least three different antimicrobial classes were identified in 91 isolates assigned to 17 distinct species in the Acinetobacter genus. Moreover, the presence of a class D oxacillinase, which is a naturally occurring enzyme in several Acinetobacter species, was found in 503 isolates assigned to 35 Acinetobacter species. In conclusion, Pasteur MLST phylogeny of non-baumannii Acinetobacter isolates coupled with in silico detection of antimicrobial resistance makes it important to study the population structure and epidemiology of Acinetobacter spp. isolates.

Genome sequence of a tigecycline-resistant Acinetobacter seifertii recovered in human bloodstream infection in China

The phylogenetic characteristics of Acinetobacter seifertii clinical strain are not well-studied. Here, we reported one tigecycline-resistant ST1612PasteurA. seifertii isolated from bloodstream infections (BSI) in China. Antimicrobial susceptibility tests were conducted via broth microdilution. Whole-genome sequencing (WGS) was performed and annotation was conducted using rapid annotations subsystems technology (RAST) server. Multilocus sequence typing (MLST), Capsular polysaccharide (KL) and lipoolygosaccharide (OCL) were analyzed using PubMLST and Kaptive. Resistance genes, virulence factors and comparative genomics analysis were performed. Cloning, mutations of efflux pump related genes and expression level were further investigated. The draft genome sequence of A. seifertii ASTCM strain is made up of 109 contigs with a total length of 4,074,640 bp. Based on the RAST results, 3,923 genes that belonged to 310 subsystems were annotated. A. seifertii ASTCM was ST1612Pasteur with KL26 and OCL4, respectively. It was resistant to gentamicin and tigecycline. ASTCM harbored tet(39), sul2 and msr(E)-mph(E) and one amino acid mutation in Tet(39) (T175A) was further identified. Nevertheless, the signal mutation failed to contribute to susceptibility change of tigecycline. Of note, several amino acid substitutions were identified in AdeRS, AdeN, AdeL and Trm, which could lead to overexpression of adeB, adeG, and adeJ efflux pump genes and further possibly lead to tigecycline resistance. Phylogenetic analysis showed a huge diversity was observed among A. seifertii strains based on 27-52,193 SNPs difference. In summary, we reported a tigecycline-resistant ST1612PasteurA. seifertii in China. Early detection is recommended to prevent their further spread in the clinical setting.

Paclobutrazol Biodegradation of Native Bacteria in Mango Orchards in Mekong Delta, Vietnam

Background: Paclobutrazol (PBZ), a plant growth regulator, is usually used to promote off-season flowering in mango orchards in the Mekong Delta, Vietnam. Several studies demonstrated that PBZ degradation in the soil takes several months and its residue effects to the soil environment and consequently to the plants and microorganism community. The objective of this study was to identify native bacteria that can biodegrade PBZ in the soil of mango orchards. Methods: Soil samples were collected in thirty mango orchards in Vietnam’s Mekong Delta. One gram of soil was mixed with distilled water and injected into a PBZ culture medium. After culturing, bacterial colonies were isolated and transferred onto the TSA medium in order to characterize morphological and biochemical assays and to evaluate PBZ biodegradation ability. Four strains of bacteria, which had high PBZ biodegradation, were identified and evaluated PBZ biodegradation ability. Additionally, 16S rDNA region was sequenced. Result: The results of identification indicated that the four high PBZ biodegradation bacterial strains related to Pseudomonas fluorescens, Pseudomonas nitroreducens, Burkholderia cepacia, Acinetobacter seifertii. After 30 days, the content of paclobutrazol biodegradable by these bacteria was 36.51%, 36.23%, 34.19% and 33.56%, respectively, at an initial concentration of 60 ppm.

The Interaction between Intratumoral Microbiome and Immunity Is Related to the Prognosis of Ovarian Cancer.

Microbiota can influence the occurrence, development, and therapeutic response of a wide variety of cancer types by modulating immune responses to tumors. Recent studies have demonstrated the existence of intratumor bacteria inside ovarian cancer (OV). However, whether intratumor microbes are associated with tumor microenvironment (TME) and prognosis of OV still remains unknown. The RNA-sequencing data and clinical and survival data of 373 patients with OV in The Cancer Genome Atlas (TCGA) were collected and downloaded. According to the knowledge-based functional gene expression signatures (Fges), OV was classified into two subtypes, termed immune-enriched and immune-deficient subtypes. The immune-enriched subtype, which had higher immune infiltration enriched with CD8+ T cells and the M1 type of macrophages (M1) and higher tumor mutational burden, exhibited a better prognosis. Based on the Kraken2 pipeline, the microbiome profiles were explored and found to be significantly different between the two subtypes. A prediction model consisting of 32 microbial signatures was constructed using the Cox proportional-hazard model and showed great prognostic value for OV patients. The prognostic microbial signatures were strongly associated with the hosts' immune factors. Especially, M1 was strongly associated with five species (Achromobacter deleyi and Microcella alkaliphila, Devosia sp. strain LEGU1, Ancylobacter pratisalsi, and Acinetobacter seifertii). Cell experiments demonstrated that Acinetobacter seifertii can inhibit macrophage migration. Our study demonstrated that OV could be classified into immune-enriched and immune-deficient subtypes and that the intratumoral microbiota profiles were different between the two subtypes. Furthermore, the intratumoral microbiome was closely associated with the tumor immune microenvironment and OV prognosis. IMPORTANCE Recent studies have demonstrated the existence of intratumoral microorganisms. However, the role of intratumoral microbes in the development of ovarian cancer and their interaction with the tumor microenvironment are largely unknown. Our study demonstrated that OV could be classified into immune-enriched and -deficient subtypes and that the immune enrichment subtype had a better prognosis. Microbiome analysis showed that intratumor microbiota profiles were different between the two subtypes. Furthermore, the intratumor microbiome was an independent predictor of OV prognosis that could interact with immune gene expression. Especially, M1 was closely associated with intratumoral microbes, and Acinetobacter seifertii could inhibit macrophage migration. Together, the findings of our study highlight the important roles of intratumoral microbes in the TME and prognosis of OV, paving the way for further investigation into its underlying mechanisms.

High poly ε-caprolactone biodegradation activity by a new Acinetobacter seifertii isolate.

Poly(ε-caprolactone; PCL) is an attractive biodegradable polymer that has been increasingly used to solve environmental problems caused by plastic wastes. In the present study, 468 bacterial isolates were recovered from soil samples and screened for PCL degradation activity. Of the isolates, 37 (7.9%) showed PCL depolymerase activity on PCL agar medium, with the highest activity being by isolate S22 which was identified using 16S rRNA and rpoB gene sequencing as Acinetobacter seifertii. Scanning electron microscopy and Fourier transform infrared spectroscopy confirmed the degradation of PCL films after treatment with A. seifertii S22. The PCL depolymerase activity of A. seifertii S22 relied on the activity of esterase which occurred at an optimum temperature of 30-40°C. The highest PCL depolymerase activity (35.5 ± 0.7 U/mL) was achieved after culturing A. seifertii S22 for 6h in mineral salt medium (MSM) containing 0.1% Tween 20 and 0.02% ammonium sulfate as the carbon and nitrogen sources, respectively, which was approximately 20-fold higher than for cultivation in MSM supplemented with 0.1% PCL as sole carbon source. The results suggested that A. seifertii S22 or its enzymes could be used for PCL bioplastic degradation.

Tricuspid valve endocarditis following over-the-counter intravenous injection of skin-whitening products

Intravenous drug use, central catheters and intracardiac devices are known predispositions to right-sided infective endocarditis (IE). We report a case of tricuspid IE caused by Acinetobacter seifertii and Enterobacter bugandensis as a result of intravenous use of skin-whitening products bought online. Clinical implications and pharmaceutical regulations are briefly discussed.

Inhibitory Effects of Ternary Mixtures of Sodium Dodecyl Sulfate and Heavy Metals to Acinetobacter seifertii from Otamiri River Sediment in Southeastern Nigeria

Toxicities of sodium dodecyl sulfate (SDS) and heavy metals, Pb(II), Cd(II), Ni(II), Zn(II) and Co(II), as individuals and ternary mixtures of two heavy metals and SDS to Acinetobacter seifertii isolated as preponderant bacterium from Otamiri river sediment, were assessed, using inhibition of dehydrogenase activity as end point. Among the individual toxicants, the EC50S observed ranged from 0.011 ± 0.000 mM for Cd(II) to 2.810 ± 0.140 mM for SDS. The EC50S of the toxicants were statistically different from one another and the order of increasing toxicities were SDS > Ni(II) > Pb(II) > Zn(II) > Co(II) >Cd(II). The responses of the bacterium were concentration -dependent. Arbitrary (ABCR) and EC50 equieffect (EECR) fixed ratio mixtures were used to evaluate the combined toxicities of the toxicants. The concentration-response relationships of all mixtures and individual toxicants were sigmoidal and fitted with logistic function. The observed toxicities (EC50S) were compared with toxicities predicted from concentration addition (CA) and independent action (IA) models. In ABCR1 and ABCR3 mixture ratios of SDS+Ni(II)+Cd(II) and SDS+Co(II)+Cd(II) ternary mixtures, both CA- and IA-predicted EC50S were not statistically different from each other. Furthermore, in all ternary mixtures, both models underestimated the mixture toxicities to A. seifertii, except in ABCR1 of SDS+Ni(II)+Cd(II) mixture, where both models almost correctly predicted the toxicities. Basically, synergistic interaction of the mixture components observed against A. seifertii, indicates their possible toxicological effects on the bacterial population of the aquatic ecosystems.

Plasmids Carrying blaVIM-2 in Acinetobacter nosocomialis and A. seifertii Isolates from South Korea.

We identified nine Verona integron-encoded metallo-β-lactamase-2 (VIM-2)-producing Acinetobacter nosocomialis (n = 8) and Acinetobacter seifertii (n = 1) isolates from South Korea and performed whole-plasmid sequencing for two A. nosocomialis isolates and one A. seifertii isolate. Genotyping, antibiotic resistance profiles, and whole plasmid sequences indicated clonal dissemination of the eight VIM-2-producing A. nosocomialis isolates. The plasmid-bearing blaVIM-2 in the A. seifertii isolate differed from those in the A. nosocomialis isolates.

The Identification of Acinetobacter baumannii Blood Isolates by MALDI-TOF MS, ARDRA and blaOXA-51-like Gene-Specific Real-Time PCR

The Acinetobacter calcoaceticus-Acinetobacter baumannii (Acb) complex consists of phenotypically very similar nosocomial species; A.baumannii, Acinetobacter nosocomialis, Acinetobacter pittii, Acinetobacter seifertii and Acinetobacter djikshoorniae and one environmental species A.calcoaceticus. The rapid and accurate identification of the members of Acb complex is critical as these nosocomial pathogens can show differences in antimicrobial susceptibility and clinical outcomes. The conventional phenotypic methods are slow, unreliable and less efficient for the differentiation of Acb complex species, including the A.baumannii species within the Acb complex. Although various molecular methods are available, such as amplified ribosomal DNA restriction analysis (ARDRA) and blaOXA-51-like gene specific PCR, they are usually inconvenient for the routine diagnostic laboratories. Recently, matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) offers an opportunity for rapid, cost-effective and convenient bacterial identification in routine diagnostic procedures conducted in clinical laboratory. In this study, we aimed to evaluate the diagnosis performance of MALDI-TOF MS system to identify blood isolates of A.baumannii. A total of 180 nonduplicate carbapenem resistant Acb complex (strain numbers; TR1-TR60) and A.baumannii (TR61-TR180) blood isolates were collected from the intensive care units of the three university hospitals in Turkey from January 2016 to December 2016. All isolates were evaluated by using blaOXA-51-like gene specific real time (Rt-PCR) analysis, ARDRA (restriction enzymes-AluI, CfoI, MboI, MspI, RsaI) method and MALDI-TOF MS (VITEK® MS, bioMérieux, France) system. All the strains except TR10, TR31, TR35 and TR52 were identified as A.baumannii by ARDRA method. Out of 177 of all the isolates, presence of blaOXA-51-like gene was found except for TR10, TR31 and TR52 isolates. However, TR31 without the presence of blaOXA-51-like gene was identified as A.pittii using the ARDRA. Totally 176 isolates which were identified as A.baumannii by both of the methods, ARDRA and Rt-PCR- blaOXA-51-like, were accepted as a reference for the evaluation of the diagnosis performance capacity of the MALDI-TOF MS. Overall, for all 176 isolates tested, the sensitivity obtained with the MALDI-TOF MS were 99.4% with 75% specificity. The accuracy value of the method was determined as 98.9% for the identification of A.baumannii to the species level. MALDI-TOF MS is increasingly used in diagnostic microbiology for the routine identification of bacteria to the genus, species or subspecies level with high rates of sensitivity and specificity. In future, by expanding the database, MALDI-TOF MS system would possibly become the ideal method for routine diagnostic laboratories that could potentially identify more species and even determine some characteristics of antimicrobial resistance and virulence determinants.

Physicochemical and Bacteriological Qualities of Otamiri River Water and Sediment in South Eastern Nigeria

The bacteriological, physicochemical and anionic surfactants qualities of Otamiri river water and sediment were analysed, using standard techniques. The bacteriological analyses revealed the presence of Serratia marcescens (SerEW01) (33.33%), Staphylococcus (22.20%), Streptococcus (22.20%), Enterobacter (11.11%), Escherichia coli (11.11%) in Otamiri river water as well as Acinetobacter seifertii (42.10%), Bacillus (15.80%), Escherichia coli (15.80%), Klebsiella (10.53%) and Streptococcus species (5.30%), in the sediment. Some of these bacteria are indicators of fecal contamination of the river water. Iron recorded the highest value among the heavy metals (1.972 mg/l), in the river water while Co was not detected. Also, Pb, Cd, Ni, Hg, electrical conductivity and turbidity recorded values higher than WHO standards for drinking water. In the sediment, Fe and Cd had the highest and least values 19.82 and 0.025 mg/kg respectively. The pH of the river and sediment were 6.42 and 5.40. Similarly, among the anionic surfactants, sodium dodecyl sulfate (SDS) was the highest in both Otamiri river water (0.100 mg/l) and sediment (0.453 mg/kg), while perfluorobutane sulfate was not detected in the river water. These results imply that the quality of Otamiri river water and possibly the sediment are below the WHO recommendations for drinking water. People using the river water for drinking and other domestic activities should therefore purify it adequately to avert possible health hazards.

Characterization of an Environmental Multidrug-Resistant Acinetobacter seifertii and Comparative Genomic Analysis Reveals Co-occurrence of Antimicrobial Resistance and Metal Tolerance Determinants.

Acinetobacter calcoaceticus-Acinetobacter baumannii complex is considered one of the main causes of hospital-acquired infections. Acinetobacter seifertii was recently characterized within this complex and it has been described as an emergent pathogen associated with bacteremia. The emergence of multidrug-resistant (MDR) bacteria, including Acinetobacter sp., is considered a global public health threat and an environmental problem because MDR bacteria have been spreading from several sources. Therefore, this study aimed to characterize an environmental MDR A. seifertii isolate (SAb133) using whole genome sequencing and a comparative genomic analysis was performed with A. seifertii strains recovered from various sources. The SAb133 isolate was obtained from soil of a corn crop field and presented high MICs for antimicrobials and metals. The comparative genomic analyses revealed ANI values higher than 95% of relatedness with other A. seifertii strains than A. calcoaceticus-A. baumannii complex. Resistome and virulome analyses were also performed and showed different antimicrobial resistance determinants and metal tolerance genes as well as virulence genes related to A. baumannii known virulence genes. In addition, genomic islands, IS elements, plasmids and prophage-related sequences were detected. Comparative genomic analysis showed that MDR A. seifertii SAb133 had a high amount of determinants related to antimicrobial resistance and tolerance to metals, besides the presence of virulence genes. To the best of our knowledge, this is the first report of a whole genome sequence of a MDR A. seifertii isolated from soil. Therefore, this study contributed to a better understanding of the genetic relationship among the few known A. seifertii strains worldwide distributed.

Identification of Acinetobacter seifertii isolated from Bolivian hospitals.

Acinetobacter seifertii is a recently described species that belongs to the Acinetobacter calcoaceticus-Acinetobacter baumannii complex. It has been recovered from clinical samples and is sometimes associated with antimicrobial resistance determinants. We present here the case of three A. seifertii clinical isolates which were initially identified as Acinetobacter sp. by phenotypic methods but no identification at the species level was achieved using semi-automated identification methods. The isolates were further analysed by whole genome sequencing and identified as A. seifertii. Due to the fact that A. seifertii has been isolated from serious infections such as respiratory tract and bloodstream infections, we emphasize the importance of correctly identifying isolates of the genus Acinetobacter at the species level to gain a deeper knowledge of their prevalence and clinical impact.

Lettuce and fruits as a source of multidrug resistant Acinetobacter spp.

The role of ready-to-eat products as a reservoir of pathogenic species of Acinetobacter remains unclear. The objective of the present study was to evaluate the presence of Acinetobacter species in lettuces and fruits marketed in Portugal, and their susceptibility to antimicrobials. Acinetobacter spp. were isolated from 77.9% of the samples and these microorganisms were also found as endophytes (i.e. present within the plant tissue) in 12 of 20 samples of lettuces analysed. Among 253 isolates that were identified as belonging to this genus, 181 presented different PFGE profiles, representing different strains. Based on the analysis of the partial sequence of rpoB, 175 strains were identified as members of eighteen distinct species and the remaining six strains may represent five new candidate species since their rpoB sequence similarities with type strains were less than 95%. Acinetobacter calcoaceticus and Acinetobacter johnsonii were the most common species, both with the frequency of 26.5%; and 11% of the strains belong to the Acinetobacter baumannii group (i.e. A. baumannii, Acinetobacter pittii, Acinetobacter seifertii and Acinetobacter nosocomialis), which is most frequently associated with nosocomial infections.Overall, the strains were least susceptible to piperacillin (80.1%), piperacillin-tazobactam (64.1%), ceftazidime (43.1%), ciprofloxacin (16.6%), trimethoprim-sulfamethoxazole (14.9%), imipenem (14.4%) and colistin (13.3%). The most active antimicrobials were minocycline and tetracycline, with 0.6% and 3.9% of strains resistant, respectively. About 29.8% of the strains were classified as multidrug-resistant (MDR), 4.4% as extensively drug-resistant (XDR) and the prevalence of MDR strains within the A. baumannii group (25%) was similar to other species (30.4%). The presence of clinically important species as well as MDR strains in lettuces and fruits may be a threat to public health considering that they may transmit these pathogens to environments such as the community and hospital settings.

The first cases of human bacteremia caused by Acinetobacter seifertii in Japan

Acinetobacter seifertii, a novel species of Acinetobacter, was first reported in 2015. A.seifertii strains were isolated from human clinical specimens (blood, respiratory tract, and ulcer) and hospital environments. Here, we report the first cases of bacteremia caused by A.seifertii in patients with catheter-related bloodstream infection in Japan. The patients favorably recovered, without any complications, after removal of the peripheral intravenous catheters and administration of antibiotics. The pathogens were initially identified as Acinetobacter baumannii, using phenotypic methods and the MicroScan Walkaway System; however, rpoB gene sequence analysis indicated 99.54% similarity to A.seifertii. Moreover, antimicrobial susceptibility testing revealed that one of the strains was not susceptible to gentamicin and ceftazidime. Our report shows that Acinetobacter species other than A.baumannii can also cause nosocomial infections and that accurate methods for the identification of causative agents should be developed.

Acinetobacter seifertii sp. nov., a member of the Acinetobacter calcoaceticus-Acinetobacter baumannii complex isolated from human clinical specimens.

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 well-supported 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) ( = CIP 110471(T) = CCUG 34785(T) = CCM 8535(T)).