Acinetobacter Genomic Species 13TU Research Articles

Identification of Genomic Species of Acinetobacter Isolated from Burns of ICU Patients.

The worldwide emergence of multi-drug resistant (MDR) bacteria in recent years has caused many problems for hospitals and patients, especially intensive care unit patients. Among these clinically important MDR bacteria are Acinetobacter baumannii complex species (A. baumannii, Acinetobacter genomic species 3 and Acinetobacter genomic species 13TU) that cause a wide range of infections. The sequencing and bioinformatics analysis of a part of the Zone 1 of rpoB gene was performed for species identification of Acinetobacter isolates obtained from ICU patients with infected burns hospitalized in a hospital in Isfahan, Iran, over a 9-month period. Antibiotic sensitivity of Acinetobacter isolates was investigated using the disk diffusion method and different classes of antibiotics including amikacin, cefotaxime, ceftriaxone, ciprofloxacin, imipenem and piperacillin. Acinetobacter spp. were isolated from 10 of 80 (12.5%) investigated patients. All of the 10 Acinetobacter isolates were identified as Acinetobacter baumannii and multi-drug resistant according to antibiotic susceptibility tests. Of the Acinetobacter baumannii complex members, only A. baumannii species was identified among the isolates obtained from patients with infected burns in an Isfahan hospital over a 9-month period.

Molecular characteristics of carbapenem-resistant gram-negative bacteria in southern China.

A total of 368 nonreplicate gram-negative bacteria with resistance to imipenem or meropenem were collected to search for carbapenemase genes, class 1 integrons, and insertion sequence with common region 1 (ISCR1). The carbapenemase genes blaIMP-4, blaKPC-2, and blaNDM-1 were found in two Enterobacteriaceae and seven Pseudomonas aeruginosa isolates, nine Klebsiella pneumoniae isolates, and seven Enterobacteriaceae and two Acinetobacter spp. isolates. The class D OXA-type carbapenemase genes blaOXA-23-like, blaOXA-24-like, blaOXA-58, and blaOXA-51-like were detected in 59 (34.9%), 2 (1.2%), 16 (9.5%), and 126 (74.6%) Acinetobacter strains. This is the first description of blaNDM-1 in Enterobacter hormaechei and Acinetobacter genomic species 13TU. Of the integrase-positive strains, 135 (90.0%) Acinetobacter spp., 22 (61.1%) P. aeruginosa, and 14 (100%) Enterobacteriaceae isolates were identified by five, ten, and four different gene cassette arrays, respectively. Three novel gene cassette arrays aadB-aadA1, dfrA25, and dfrA16-aadA2 were reported for the first time in some species. Of the ISCR1-positive strains, the nonfermentative strains (102 Acinetobacter spp. and 13 P. aeruginosa. isolates) contained the same arrangement blaPER-1-putative glutathione-S-transferase-novel type ABC transporter, and three Enterobacteriaceae isolates harbored three different arrangements. Four distinct complex class 1 integron structures were observed. The complex class 1 integron detected in New Delhi, metallo-β-lactamase (NDM-1)-producing E. hormaechei, was found to coexist in the NDM-1-carrying plasmid. Our results suggested that we should pay more attention to the strict implementation of infection control measures and active antibiotic resistance surveillance to avoid the rapid spread or outbreak of carbapenemase-producing gram-negative bacteria.

Signature Motifs Identify an Acinetobacter Cif Virulence Factor with Epoxide Hydrolase Activity

Endocytic recycling of the cystic fibrosis transmembrane conductance regulator (CFTR) is blocked by the CFTR inhibitory factor (Cif). Originally discovered in Pseudomonas aeruginosa, Cif is a secreted epoxide hydrolase that is transcriptionally regulated by CifR, an epoxide-sensitive repressor. In this report, we investigate a homologous protein found in strains of the emerging nosocomial pathogens Acinetobacter nosocomialis and Acinetobacter baumannii ("aCif"). Like Cif, aCif is an epoxide hydrolase that carries an N-terminal secretion signal and can be purified from culture supernatants. When applied directly to polarized airway epithelial cells, mature aCif triggers a reduction in CFTR abundance at the apical membrane. Biochemical and crystallographic studies reveal a dimeric assembly with a stereochemically conserved active site, confirming our motif-based identification of candidate Cif-like pathogenic EH sequences. Furthermore, cif expression is transcriptionally repressed by a CifR homolog ("aCifR") and is induced in the presence of epoxides. Overall, this Acinetobacter protein recapitulates the essential attributes of the Pseudomonas Cif system and thus may facilitate airway colonization in nosocomial lung infections.

Clinical characteristics of Acinetobacter baumannii complex bacteremia in patients receiving total parenteral nutrition

BackgroundAcinetobacter baumannii complex (Abc) comprises at least three phenotypically undifferentiated species, including A baumannii, Acinetobacter genomic species 3 (AGS 3) and Acinetobacter genomic species 13TU (AGS 13TU). Abc bacteremia had rarely been described in patients receiving total parenteral nutrition (TPN). In this study, we aimed to determine any differences in the clinical features of patients having TPN and bacteremia due to A baumannii and those due to nonbaumannii Abc (including AGS 3 and AGS 13TU). MethodsThe data of patients who had received TPN and had Abc bacteremia in Taipei Veterans General Hospital between August 1998 and December 2007 were retrospectively reviewed. The Acinetobacter isolates were identified to genomic species level. ResultsA total of 23 patients with A baumannii and 23 patients with nonbaumannii Abc (15 AGS 13TU and 8 AGS 3) bacteremia were identified. The two groups of the patients were comparable regarding their gender, age and APACHE II score at the onset of bacteremia. However, several clinical features were different between the two groups of the patients in the univariate analysis. Furthermore, A baumannii isolates were resistant to more classes of antibiotics than nonbaumannii Abc isolates. The multivariate analysis showed that a higher number of patients with A baumannii bacteremia had received TPN for≥15 days before their onset of bacteremia [odds ratio (OR) 7.214, 95% confidence interval (CI) (1.108–46.989), p = 0.039]. Nevertheless, the 14-day (30.4% vs. 21.7%, p = 0.737) and all-cause in-hospital mortality rate (60.9% vs. 39.1%, p = 0.238) did not differ significantly between these two groups. ConclusionThe patients with A baumannii bacteremia demonstrated a longer timeframe in the treatment of TPN prior to the onset of bacteremia than those with nonbaumannii Abc bacteremia, however the clinical outcomes between the two groups of the patients did not differ significantly.

Molecular characterization of carbapenem-non-susceptible Acinetobacter spp. in Japan: predominance of multidrug-resistant Acinetobacter baumannii clonal complex 92 and IMP-type metallo-β-lactamase-producing non-baumannii Acinetobacter species

We conducted an epidemiological study concerning carbapenem-non-susceptible clinical isolates of Acinetobacter spp. in Japan by molecular procedures including carbapenemase gene identification and amplified ribosomal DNA restriction analysis. Among 598 clinically isolated Acinetobacter spp. in 2007, 27 (4.5%) were non-susceptible to carbapenems. Most carbapenem-non-susceptible Acinetobacter baumannii (13/14) belonged to clonal complex (CC) 92, harbored bla (OXA-51-like) genes, including novel bla (OXA-206), downstream of ISAba1, and were recovered mainly from the Kanto region. Carbapenem-non-susceptible A. baumannii CC92 isolates were further divided by pulsed-field gel electrophoresis into two groups, one of which was characterized by the presence of bla (OXA-23). One A. baumannii CC276 isolate carried bla (IMP-1) and bla (OXA-58). Almost all non-baumannii Acinetobacter isolates (12/13), including Acinetobacter pittii (formerly Acinetobacter genomic species 3) and Acinetobacter nosocomialis (formerly Acinetobacter genomic species 13TU), produced IMP-type metallo-β-lactamases, and were recovered from various regions in Japan. This is the first report describing the nationwide molecular epidemiology of carbapenem-non-susceptible Acinetobacter spp. with genomic species-level identification in Japan.

Nosocomial bloodstream infections due to Acinetobacter baumannii, Acinetobacter pittii and Acinetobacter nosocomialis in the United States

To compare the clinical features and antimicrobial susceptibilities of the clinically most important Acinetobacter species Acinetobacter baumannii, Acinetobacter pittii (formerly Acinetobacter genomic species 3) and Acinetobacter nosocomialis (formerly Acinetobacter genomic species 13TU). 295 Acinetobacter isolates collected prospectively from patients with bloodstream infections (BSI) in 52 US hospitals were identified to species level. Clinical and microbiological features were compared between species. A. baumannii (63%) was the most prevalent species, followed by A. nosocomialis (21%), and A. pittii (8%). Intravascular catheters (15.3%) and the respiratory tract (12.9%) were the most frequent sources of BSI. A higher overall mortality was observed in patients with A. baumannii BSI than in patients with BSI caused by A. nosocomialis and A. pittii (36.9% vs. 16.4% and 13.0%, resp., p<0.001). The most active antimicrobial agents as determined by broth microdilution were tigecycline (99.6% of isolates susceptible), colistin (99.3%), amikacin (98.5%), and imipenem (95.2%). 27 isolates (10.0%) were multi-drug resistant, all but one of these were A. baumannii. About one third of Acinetobacter BSI in our study were caused by A. nosocomialis or A. pittii. Patients with A. baumannii BSI had a less favorable outcome.

Outbreak of imipenem-resistant Acinetobacter calcoaceticus–Acinetobacter baumannii complex harboring different carbapenemase gene-associated genetic structures in an intensive care unit

To investigate the clinical and molecular epidemiology of the imipenem-resistant Acinetobacter calcoaceticus-Acinetobacter baumannii (IRAcb) complex during an outbreak in an intensive care unit (ICU). Forty-six clinical and 11 environmental isolates of the IRAcb complex were collected from the ICU of Taipei Veterans General Hospital, Taiwan between December 2003 and March 2004. These isolates were genotyped using pulsed-field gel electrophoresis (PFGE). Carbapenemase genes and their associated genetic structures were analyzed using PCR. Clinical data obtained from the patients were also reviewed and analyzed. The isolates were identified at the genomic species level as A. baumannii (42 clinical and five environmental isolates) and Acinetobacter genomic species 13TU (four clinical and six environmental isolates). Both species were comprised of two pulsotypes, but those of A. baumannii were closely related (83% similar). IS1008-ΔISAba3-bla(OXA-58-like) and ISAba1-bla(OXA-51-like) were identified in 22 and 21 clinical isolates of A. baumannii, respectively (one isolate contained both). The ISAba3-bracketed bla(OXA-58-like) gene was detected in all isolates of Acinetobacter genomic species 13TU. Patient transfers between different sections of the ICU were important factors that contributed to the spread of the two pulsotypes of A. baumannii. However, among the A. baumannii isolates identified, only those carrying IS1008-ΔISAba3-bla(OXA-58-like) could be found in the environment, indicating an additional route of transmission. The prior use of carbapenem or cefepime was associated with the subsequent infection with A.baumannii carrying the ISAba1-bla(OXA-51-like) gene, while prior piperacillin/tazobactam use was associated with the subsequent infection with A. baumannii carrying the IS1008-ΔISAba3-bla(OXA-58-like) gene. A. baumannii isolates carrying different carbapenemase genes and their associated genetic structures might be transmitted or selected in different ways.

Amino acid substitutions of quinolone resistance determining regions in GyrA and ParC associated with quinolone resistance in Acinetobacter baumannii and Acinetobacter genomic species 13TU

Amino acid substitutions in GyrA and ParC are associated with resistance to quinolones in Acinetobacter baumannii (A baumannii), but this association is rarely elucidated in Acinetobacter genomic species (AGS) 13TU. This study aims to compare the association of amino acid substitutions in GyrA and ParC with quinolone resistance in A baumannii and AGS 13TU in Taiwan. Eleven representative strains of A baumannii and 13 strains of AGS 13TU were selected from 402 bacteremic isolates. The sequences of quinolone resistance determining regions of gyrA and parC were determined. Minimal inhibitory concentrations (MICs) of nalidixic acid, ciprofloxacin, levofloxacin and moxifloxacin were determined by agar dilution method. Ser83Leu substitution in GyrA in A baumannii (one strain) was associated with resistance to all tested quinolones. This substitution plus a Ser80Leu or Ser80Tyr in ParC in A baumannii (four strains) and AGS 13TU (two strains) were associated with higher MICs of all quinolones. All but one quinolone MICs of A baumannii (one strain) and AGS 13TU (two strains) carrying a single substitution Ser56Asn in ParC remained in the susceptibility breakpoint. The Ser83Leu substitution in GyrA, even with additional Ser56Asn substitution in ParC, was associated with resistance to only nalidixic acid, but not other newer quinolones in AGS 13TU (two strains). A baumannii and AGS 13TU possessed similar quinolone resistance associated with amino acid substitutions in GyrA and ParC. Further study with more strains is needed to determine whether a single Ser83Leu substitution in GyrA was associated with a high level of quinolone MIC only in A baumannii, but not in AGS 13TU.

Antimicrobial Resistance Determinants in Imipenem-nonsusceptible Acinetobacter calcoaceticus-baumannii Complex Isolated in Daejeon, Korea

BackgroundMembers of the Acinetobacter calcoaceticus-baumannii (Acb) complex are important opportunistic bacterial pathogens and present significant therapeutic challenges in the treatment of nosocomial infections. In the present study, we investigated the integrons and various genes involved in resistance to carbapenems, aminoglycosides, and fluoroquinolones in 56 imipenem-nonsusceptible Acb complex isolates.MethodsThis study included 44 imipenem-nonsusceptible A. baumannii, 10 Acinetobacter genomic species 3, and 2 Acinetobacter genomic species 13TU strains isolated in Daejeon, Korea. The minimum inhibitory concentrations (MICs) were determined by Etest. PCR and DNA sequencing were used to identify the genes that potentially contribute to each resistance phenotype.ResultsAll A. baumannii isolates harbored the blaOXA-51-like gene, and 21 isolates (47.7%) co-produced OXA-23. However, isolates of Acinetobacter genomic species 3 and 13TU only contained blaIMP-1 or blaVIM-2. Most Acb complex isolates (94.6%) harbored class 1 integrons, armA, and/or aminoglycoside-modifying enzymes (AMEs). Of particular note was the fact that armA and aph(3')-Ia were only detected in A. baumannii isolates, which were highly resistant to amikacin (MIC50≥256) and gentamicin (MIC50≥1,024). In all 44 A. baumannii isolates, resistance to fluoroquinolones was conferred by sense mutations in the gyrA and parC. However, sense mutations in parC were not found in Acinetobacter genomic species 3 or 13TU isolates.ConclusionsSeveral differences in carbapenem, aminoglycoside, and fluoroquinolone resistance gene content were detected among Acb complex isolates. However, most Acb complex isolates (87.5%) possessed integrons, carbapenemases, AMEs, and mutations in gyrA. The co-occurrence of several resistance determinants may present a significant threat.

Changes in antimicrobial susceptibility and major clones of Acinetobacter calcoaceticus–baumannii complex isolates from a single hospital in Korea over 7 years

Acinetobacter species have emerged as opportunistic nosocomial pathogens in intensive care units. Epidemic spread and outbreaks of multidrug-resistant or carbapenem-resistant Acinetobacter baumannii infections have been described worldwide. Species distribution, antimicrobial resistance and genotypes were investigated for Acinetobacter species isolates collected from a single institution in Korea over 7 years. Two hundred and eighty-seven Acinetobacter species isolates were collected from patients with bloodstream infections in one Korean hospital from 2003 to 2010. Most of them belonged to the Acinetobacter calcoaceticus-baumannii complex (94.4 %). The most frequently isolated species was A. baumannii (44.2 %), followed by Acinetobacter nosocomialis (formerly Acinetobacter genomic species 13TU) (34.1 %). The proportion of A. baumannii increased significantly from 2008 to 2010 (40.4 to 50.0 %). From 2008, imipenem and meropenem resistance rates increased significantly compared with 2003-2007 (12.9 % and 20.5 %, respectively, to 41.4 % and 41.5 %, respectively). An increased carbapenem resistance rate between the two periods was identified more clearly amongst A. baumannii isolates. Polymyxin-resistant A. baumannii isolates emerged in 2008-2010, despite the availability of few isolates. The increase of carbapenem resistance in A. baumannii might be due to the substitution of main clones. Although ST92 and ST69 were the most prevalent clones amongst A. baumannii in 2003-2007 (47.8 % and 15.9 %, respectively), ST75 and ST138 had increased in 2008-2010 (39.7 % and 25.9 %, respectively). Although ST92 showed moderate resistance to carbapenems, most ST75 and ST138 isolates were resistant to carbapenems. All ST75 and ST138 isolates, but only one ST92 isolate, contained the bla(OXA-23-like) gene. Increased carbapenem resistance in Acinetobacter species and A. baumannii isolates might be due to the expansion of specific carbapenem-resistant clones.

Genotypic and phenotypic characterization of the Acinetobacter calcoaceticus– Acinetobacter baumannii complex with the proposal of Acinetobacter pittii sp. nov. (formerly Acinetobacter genomic species 3) and Acinetobacter nosocomialis sp. nov. (formerly Acinetobacter genomic species 13TU)

Acinetobacter genomic species (gen. sp.) 3 and gen. sp. 13TU are increasingly recognized as clinically important taxa within the Acinetobacter calcoaceticus- Acinetobacter baumannii (ACB) complex. To define the taxonomic position of these genomic species, we investigated 80 strains representing the known diversity of the ACB complex. All strains were characterized by AFLP analysis, amplified rDNA restriction analysis and nutritional or physiological testing, while selected strains were studied by 16S rRNA and rpoB gene sequence analysis, multilocus sequence analysis and whole-genome comparison. Results supported the genomic distinctness and monophyly of the individual species of the ACB complex. Despite the high phenotypic similarity among these species, some degree of differentiation between them could be made on the basis of growth at different temperatures and of assimilation of malonate, l-tartrate levulinate or citraconate. Considering the medical relevance of gen. sp. 3 and gen. sp. 13TU, we propose the formal names Acinetobacter pittii sp. nov. and Acinetobacter nosocomialis sp. nov. for these taxa, respectively. The type strain of A. pittii sp. nov. is LMG 1035 T (=CIP 70.29 T) and that of A. nosocomialis sp. nov. is LMG 10619 T (=CCM 7791 T).

Difference in imipenem, meropenem, sulbactam, and colistin nonsusceptibility trends among three phenotypically undifferentiated Acinetobacter baumannii complex in a medical center in Taiwan, 1997–2007

To determine whether the susceptibilities and the trends of nonsusceptibility of imipenem, meropenem, sulbactam, and colistin differed among Acinetobacter baumannii, Acinetobacter genomic species 3 (AGS 3), and Acinetobacter genomic species 13TU (AGS 13TU) over 11 years. A total of 1,039 nonduplicate blood isolates of A baumannii complex from bacteremic patients between 1997 and 2007 were collected at Taipei Veterans General Hospital and were identified to the species level using a multiplex polymerase chain reaction method and sequence analysis of 16S-23S intergenic spacer. The minimal inhibitory concentrations of antibiotics were determined by the agar dilution method. The nonsusceptibility rates of carbepenems and sulbactam were highest in A baumannii, which also showed a trend toward increasing rate of carbapenems nonsusceptibility over the 11-year period of the study. AGS 13TU had the highest nonsusceptible rate to colistin, comparably increasing trend of carbapenem nonsusceptiblity as that of A baumannii, and is the only species with increasing sulbactam nonsusceptibility. AGS 3 had the lowest rate of nonsusceptibility to all four antimicrobial agents. Although A baumannii had the highest nonsusceptibility rate to imipenem, meropenem, and sulbactam over the years, the higher rate of colistin nonsusceptibility and the emergence of nonsusceptibility of carbapenems and sulbactam in AGS 13TU suggested that this species might cause a great problem in the near future.

Species identification and molecular characterization of Acinetobacter spp. blood culture isolates from Norway

The study investigated the species distribution, antibiotic susceptibility patterns and genotypic resistance characteristics of 113 consecutive blood culture isolates of Acinetobacter species collected between 2005 and 2007 throughout Norway. Species identification was performed by partial rpoB sequence analysis, and verified by 16S rDNA and recA sequence analyses. Susceptibility testing was performed by agar disc diffusion and Etest. Distribution of OXA carbapenemase genes and epidemic clonality of Acinetobacter baumannii isolates were detected by PCR assays. Analyses of blaOXA-51-like variants and quinolone resistance-determining regions (QRDRs) were done by sequencing. The most prevalent species in the collection were Acinetobacter genomic species (gen. sp.) 13TU (46.9%) and Acinetobacter gen. sp. 3 (19.5%), followed by A. baumannii (8.8%) and Acinetobacter lwoffii/Acinetobacter gen. sp. 9 (7.1%). Carbapenem resistance was observed in one blaOXA-23-like-positive A. baumannii isolate. Quinolone resistance was detected in five isolates from the Acinetobacter calcoaceticus-A. baumannii complex, of which two had point mutations in the QRDRs, including one novel ParC mutation. None of the A. baumannii isolates belonged to European/international clones I, II or III. Six blaOXA-51-like variants, including two novel variants, were identified. Acinetobacter gen. sp. 13TU and Acinetobacter gen. sp. 3 were predominant in Norwegian blood cultures, in contrast to in other countries where A. baumannii has dominated. The study demonstrated the importance of genotypic identification to determine the exact epidemiology of non-baumannii Acinetobacter species.

A Single Clone of Acinetobacter baumannii, ST22, Is Responsible for High Antimicrobial Resistance Rates of Acinetobacter Spp. Isolates That Cause Bacteremia and Urinary Tract Infections in Korea

We investigated the characteristics of a total of 96 Acinetobacter spp. isolates that were shown to cause bacteremia and urinary tract infections (UTIs) from 10 university hospitals located in various regions of Korea from November 2006 to August 2007. The antimicrobial susceptibilities of these isolates were determined using a broth microdilution method, and the species were identified using molecular identification. In addition, we performed multilocus sequence typing for Acinetobacter baumannii subgroup A isolates. A. baumannii subgroup A was the most prevalent in patients with both bacteremia (32 isolates, 53.3%) and UTIs (20 isolates, 55.6%), followed by Acinetobacter genomic species 13TU (15.0% and 27.8% in bacteremia and UTIs, respectively). A. baumannii subgroup B and Acinetobacter junii were found exclusively in isolates causing bacteremia (seven and five isolates, respectively). Among 96 Acinetobacter spp. isolates, 19.8% were resistant to imipenem and 25.0% were resistant to meropenem. Most carbapenem-resistant A. baumannii isolates contained PER or oxacillinase-23-like enzymes (65.2% and 78.3%, respectively). In addition, 13.5% were resistant to polymyxin B and 17.7% were resistant to colistin. A. baumannii subgroup A isolates (52 isolates, 54.2%) showed higher resistance rates to most antimicrobial agents than other species, but not to colistin. Among A. baumannii subgroup A isolates, ST22 was the most prevalent genotype (33 isolates, 63.5%) and showed higher resistance rates to all antimicrobial agents than the other genotypes. In addition, four out of five polymyxin-resistant A. baumannii group A isolates belonged to ST22. Thus, dissemination of the main clone of A. baumannii, ST22, may contribute to the high resistance rates of Acinetobacter isolates to antimicrobials, including carbapenems, in Korea.

Contribution of a Plasmid-Borne bla OXA-58 Gene with Its Hybrid Promoter Provided by IS 1006 and an IS Aba3 -Like Element to β-Lactam Resistance in Acinetobacter Genomic Species 13TU

The contribution of the blaOXA-58 gene and its promoter to beta-lactam resistance has not been validated in Acinetobacter spp. other than Acinetobacter baumannii. We identified a multidrug-resistant (including carbapenem resistance) Acinetobacter genomic species 13TU in which blaOXA-58 was the only detected carbapenemase gene. The blaOXA-58 gene was plasmid located, flanked by ISAba3 (downstream) and an ISAba3-like element (upstream). An IS1006 element was inserted into ISAba3-like (IS1006-DeltaISAba3-like) to generate a hybrid promoter for blaOXA-58, with a -35 promoter located in IS1006 and a -10 promoter in ISAba3-like. The reference strain of Acinetobacter genomic species 13TU, ATCC 17903, revealed higher MICs of amoxicillin, ticarcillin, and piperacillin and heteroresistance to imipenem and meropenem when it was transformed with a shuttle vector containing a fragment encompassing DeltaISAba3-like-blaOXA-58, compared to the same host containing only blaOXA-58. When the fragment was changed from DeltaISAba3-like-blaOXA-58 to IS1006-DeltaISAba3-like-blaOXA-58, the ATCC 17903 transformant revealed a markedly higher level of blaOXA-58 transcription (12-fold), increased cefuroxime and piperacillin-tazobactam MICs, and homoresistance to imipenem and meropenem. Different roles of the insertion elements preceding the blaOXA-58 gene in Acinetobacter genomic species 13TU are demonstrated. The ISAba3-like--blaOXA-58 construct can mediate resistance to penicillin derivatives but only heteroresistance to carbapenems. The insertion of IS1006 into ISAba3-like, generating a hybrid promoter, could further enhance the transcription of blaOXA-58 and mediate homoresistance to carbapenems and also enhanced resistance to piperacillin-tazobactam.

First Identification of blaOXA-51-like in Non-baumannii Acinetobacter spp.

blaOXA-51-like, the intrinsic carbapenemase gene in Acinetobacter baumannii previously found only in this species, was detected in a clinical isolate of Acinetobacter genomic species 13TU. This study aimed to characterize this gene in the isolate. Genomic species identification was confirmed by amplified ribosomal DNA restriction analysis and sequence analysis of 16S-23S ribosomal DNA intergenic spacer, rpoB and recA. The blaOXA-51-like gene, with an upstream ISAba1 insertion, was plasmid-encoded and the surrounding sequences suggested that its origin was from A. baumannii. Transformation of Acinetobacter genomic species 13TU ATCC 17903 with recombinant plas-mid bearing ISAba1-blaOXA-51-like from the isolate increased the minimum inhibitory concentrations (MICs) of meropenem and imipenem 256-fold. This is the first reportof blaOXA-51-like in an organism other than A. baumannii. This plasmid-borne blaOXA-51-like gene with an upstream ISAba1 insertion confers a high level of carbapenem resistance to Acinetobacter genomic species 13TU

Genetic basis of resistance to aminoglycosides in Acinetobacter spp. and spread of armA in Acinetobacter baumannii sequence group 1 in Korean hospitals

A total of 75 Acinetobacter isolates resistant to all available aminoglycosides obtained from 2 Korean hospitals were studied for the genetic basis of resistance to aminoglycosides. The MIC 50 and MIC 90 of Acinetobacter baumannii isolates ( n = 61) to amikacin, gentamicin, isepamycin spectinomycin, streptomycin, and tobramycin were higher than those of Acinetobacter genomic species 13TU isolates ( n = 14). Genes encoding aminoglycoside-modifying enzymes, ant(3″)-Ia, aac(6′)-Ib, aph(3′)-1a, aac(3)-Ia, and aph(3′)-VI, and 16S ribosomal RNA (rRNA) methylase armA were detected. ant(3″)-Ia and aac(6′)-Ib were commonly detected in both Acinetobacter spp., but armA and aph(3″)-Ia were only detected in A. baumannii. armA was located on the plasmids. A. baumannii isolates carrying armA were classified into 7 pulsotypes but belonged to sequence group 1. The combination of aminoglycoside-modifying enzymes is responsible for the moderate-level resistance to aminoglycosides in Acinetobacter genomic species 13TU, whereas armA is responsible for the high-level resistance to aminoglycosides in A. baumannii sequence group 1.

Identification of Acinetobacter Genomic Species 13TU by Sequence Analysis of the 16S-23S rRNA Gene Spacer Region

The genus Acinetobacter currently contains up to 32 described named and unnamed (genomic) species (3). Acinetobacter baumannii, genomic species 3, and 13TU, three of the most clinically relevant species, are genetically and phenotypically very similar to an environmental species, Acinetobacter calcoaceticus, and are therefore grouped together into the so-called A. calcoaceticus-A. baumannii (Acb) complex (3). Because phenotypic identification of Acinetobacter isolates to the species level has proven to be insufficient, several genotypic methods have been developed for genomic species identification (1, 3, 4). In the last 3 years, our laboratory has routinely used the 16S-23S rRNA gene intergenic spacer (ITS) sequence-based method described by Chang et al. (1) to delineate isolates belonging to the Acb complex to the genomic species level. We found the procedure accurate and easy to perform. However, we have recently encountered a discrepancy during the characterization of Acinetobacter strain 74510 isolated originally from a clinical source at the Prince of Wales Hospital, Hong Kong, in 1995 (2). Strain 74510 was previously identified as genomic species 13TU by restriction analysis of amplified ribosomal DNA (2, 4). However, examination of the single PCR amplicon of the ITS region of strain 74510 (GenBank accession no. {type:entrez-nucleotide,attrs:{text:FJ360743,term_id:210063372,term_text:FJ360743}}FJ360743) revealed an ITS sequence length of 607 bp, as opposed to the 615 bp reported by Chang et al. for the genomic species 13TU reference strain BCRC 15417 (1). On the other hand, DNA sequence analysis of this 607-bp ITS of strain 74510 showed an identity of 0.9561 to that of strain BCRC 15417 (Table ​(Table1).1). Upon further analysis of nucleotide sequences in GenBank, the strain 74510 ITS sequence was also found to share increasing identity (0.9950 to 0.9967) with three other genomic species 13TU strains, namely, v104-2, 00574, and DR25612/96 (Table ​(Table1).1). Interestingly, the ITS length (607 bp) of these three genomic species 13TU strains was also 607 bp, identical to that of strain 74510 (Table ​(Table1).1). In addition, the ITS sequences of these genomic species 13TU strains 74510, v104-2, 00574, and DR25612/96 appeared to be more closely related to the A. baumannii (genomic species 2) strain BCRC 10591T than to the 13TU reference strain BCRC 15417 (0.9538 to 0.9588 versus 0.9171 identity) (Table ​(Table1),1), which reinforces the notion that genetic similarity among A. baumannii and genomic species 13TU is high (3) and perhaps suggests that BCRC 15417 may not be as representative for genomic species 13TU. TABLE 1. ITS sequence similarity between A. baumannii and genomic species 13TUa Acinetobacter genomic species 13TU is the second most clinically relevant species in the Acb complex (3, 5, 6). Therefore, we believe that it is important to extend the number of Acinetobacter genomic species 13TU ITS sequences in the ITS sequence database for more-accurate genomic species identification. Also, we would suggest that the reference ITS sequence length for genomic species 13TU be 607 bp long and that strain 74510 could be considered as the “type” strain for genomic species 13TU.

Molecular epidemiology of clinical Acinetobacter baumannii and Acinetobacter genomic species 13TU isolates using a multilocus sequencing typing scheme

To further expand the limited multilocus sequence typing (MLST) database for Acinetobacter baumannii, 53 clinical isolates from various outbreaks in Europe and the USA, collected between 1991 and 2004, plus the A. baumannii reference strain ATCC 19606(T) and 20 clinical Acinetobacter genomic species 13TU isolates from the same period, were analyzed using a new MLST scheme based on fragments of the gltA, gyrB, gdhB, recA, cpn60, gpi and rpoD genes. Data were compared with typing results generated using pulsed-field gel electrophoresis (PFGE) and randomly amplified polymorphic DNA (RAPD)-PCR. In total, 50 sequence types (STs) were distinguished among the A. baumannii isolates investigated, and the MLST data were in high concordance with the PFGE and RAPD-PCR results. Only five clonal complexes were identified by eBURST analysis, including the 21 STs listed in a previous study, suggesting high diversity among the A. baumannii isolates. With one exception, there was no relatedness among isolates from outbreaks in different countries (Europe) or regions (USA). No intercontinental spread was revealed. Acinetobacter genomic species 13TU isolates could also be analyzed using the A. baumannii MLST scheme (18 different STs) and could be distinguished from A. baumannii isolates according to characteristic sequences. It was concluded that the MLST scheme provides a high level of resolution and is a promising tool for studying the epidemiology of A. baumannii and Acinetobacter genomic species 13TU.

A PCR-based method to differentiate between Acinetobacter baumannii and Acinetobacter genomic species 13TU

A new PCR-based method that exploits differences in gyrB gene sequences was developed to distinguish between Acinetobacter baumannii and Acinetobacter genomic sp. 13TU. Among 118 clinical and reference Acinetobacter strains, 102 of which were previously speciated by amplified rDNA restriction analysis as belonging to the Acinetobacter calcoaceticus-A. baumannii complex, the method correctly identified 31 A. baumannii and 54 Acinetobacter genomic sp. 13TU isolates to the species level. The method was rapid, specific and easy to interpret.