Clinical Isolates Of Acinetobacter Research Articles

Structure of a short-chain dehydrogenase/reductase (SDR) within a genomic island from a clinical strain of Acinetobacter baumannii.

Over 15% of the genome of an Australian clinical isolate of Acinetobacter baumannii occurs within genomic islands. An uncharacterized protein encoded within one island feature common to this and other International Clone II strains has been studied by X-ray crystallography. The 2.4 Å resolution structure of SDR-WM99c reveals it to be a new member of the classical short-chain dehydrogenase/reductase (SDR) superfamily. The enzyme contains a nucleotide-binding domain and, like many other SDRs, is tetrameric in form. The active site contains a catalytic tetrad (Asn117, Ser146, Tyr159 and Lys163) and water molecules occupying the presumed NADP cofactor-binding pocket. An adjacent cleft is capped by a relatively mobile helical subdomain, which is well positioned to control substrate access.

Species distribution of clinical Acinetobacter isolates revealed by different identification techniques.

A total of 2582 non-duplicate clinical Acinetobacter spp. isolates were collected to evaluate the performance of four identification methods because it is important to identify Acinetobacter spp. accurately and survey the species distribution to determine the appropriate antimicrobial treatment. Phenotyping (VITEK 2 and VITEK MS) and genotyping (16S rRNA and rpoB gene sequencing) methods were applied for species identification, and antimicrobial susceptibility test of imipenem and meropenem was performed with a disk diffusion assay. Generally, the phenotypic identification results were quite different from the genotyping results, and their discrimination ability was unsatisfactory, whereas 16S rRNA and rpoB gene sequencing showed consistent typing results, with different resolution. Additionally, A. pittii, A. calcoaceticus and A. nosocomialis, which were phylogenetically close to A. baumannii, accounted for 85.5% of the non-A. baumannii isolates. One group, which could not be clustered with any reference strains, consisted of 11 isolates and constituted a novel Acinetobacter species that was entitled genomic species 33YU. None of the non-A. baumannii isolates harbored a bla OXA-51-like gene, and this gene was disrupted by ISAba19 in only one isolate; it continues to be appropriate as a genetic marker for A. baumannii identification. The resistance rate of non-A. baumannii isolates to imipenem and/or meropenem was only 2.6%, which was significantly lower than that of A. baumannii. Overall, rpoB gene sequencing was the most accurate identification method for Acinetobacter species. Except for A. baumannii, the most frequently isolated species from the nosocomial setting were A. pittii, A. calcoaceticus and A. nosocomialis.

In vitro antibacterial activity of beta lactam-beta lactamase inhibitor combinations against clinical Isolates of acinetobacter

In vitro antibacterial activity of beta lactam-beta lactamase inhibitor combinations against clinical Isolates of acinetobacter

Identification of Acinetobacter clinical isolates by polymerase chain reaction analysis of 16S-23S ribosomal ribonucleic acid internal transcribed spacer

Background: The genus Acinetobacter is a diverse group of Gram-negative bacteria involve at least 33 species using the molecular methods. Although the genus Acinetobacter comprises a number of definite bacterial species, some of these species are of clinical importance. Therefore, it is of vital importance to use a method which is able to reliably and efficiently differentiate the numerous Acinetobacter species. Objectives: This study aims to identify Acinetobacter of clinical isolates from Assir region to the species level by 16S-23S intergenic spacers internal transcribed spacer (ITS) of ribosomal ribonucleic acid (rRNA). Materials and Methods: Deoxyribonucleic acid extraction, polymerase chain reaction amplification of 16S-23S intergenic spacer sequences (ITS) was performed using the bacterium-specific universal primers. Results: Based on the 16S-23S intergenic spacers (ITS) of rRNA sequences, all isolates tested were identified as Acinetobacter baumannii. The isolates shared a common ancestral lineage with the prototypes A. baumannii U60279 and U60280 with 99% sequence similarities. Conclusion: These findings confirmed 16S-23S rRNA ITS for the identification of A. baumannii of different genotypes among patients.

Effect of Multipurpose Solutions against Acinetobacter Carrying QAC Genes

Acinetobacter has low virulence but causes infections in subjects with reduced immunity. It has been reported in ocular infections including those of patients using contact lenses. Treatment is difficult because Acinetobacter is frequently multidrug resistant. Antibiotic-resistant strains frequently also harbor genes for antiseptic resistance (quaternary ammonium compound [QAC]) genes. Because Acinetobacter is part of the normal flora, it may contaminate contact lens and accessories. This study aims to investigate carriage rates of QAC genes in household and clinical isolates of Acinetobacter and to determine the effectiveness of two multipurpose solutions (MPSs) for soft lenses against organisms carrying QAC genes. DNA was extracted from 11 bathroom isolates and 15 clinical isolates and amplified by polymerase chain reaction to determine the presence of qacEΔ1. Gene-positive and gene-negative control strains were used to challenge the two MPSs, and minimum inhibitory concentrations (MICs) of these organisms to benzalkonium chloride and chlorhexidine gluconate were determined. More than 90% of isolates carried qacEΔ1. The MICs of clinical isolates were higher than those of isolates of bathrooms. Both MPSs were able to produce a 3-log reduction in the numbers of all isolates. Although most isolates carried qacEΔ1 and elevated MICs to benzalkonium chloride and chlorhexidine gluconate were observed, all were susceptible to both MPSs tested. However, if there were to be poor compliance with care procedures, it is probable that such organisms could survive in the presence of diluted or expired solutions.

Co-production of ESBL and AmpC β-Lactamases in Clinical Isolates of A. baumannii and A. lwoffii in a Tertiary Care Hospital From Northern India.

Acinetobacter baumannii is an important cause of health care associated infections which are difficult to control and treat, because of widespread antimicrobial resistance which is possessed by this organism. The aim of the present study was to know the prevalence of ESBLs and AmpC β-lactamases in clinical isolates of Acinetobacter spp. which were cultured from various clinical specimens by using different phenotypic methods. Study was conducted over a period of one year at the Microbiology Department of a tertiary care teaching hospital. A total of 100 consecutive, non-duplicate strains of Acinetobacter species which were isolated from various clinical samples were included. All the isolates were identified by standard microbiological procedures and antimicrobial susceptibility testing was done by Kirby-Bauer disc diffusion technique. Isolates which showed reduced susceptibilities to third generation cephalosporins were tested for ESBL production by CLSI double disc synergy method and also by using sulbactam as an inhibitory agent. Isolates which showed reduced susceptibilities to cefoxitin were tested for AmpC detection by doing AmpC disc test. SPSS, version 17 was used to calculate p-value. If the p-value was <0.05, it was considered to be significant. Out of 100 isolates, 82 were Acinetobacter baumannii and 18 were Acinetobacter lwoffii. ESBL were mentioned in 4% of the Acinetobacter isolates and in 77% of the isolates by using clavulanic acid and sulbactam as inhibitory agents respectively. AmpC β-lactamase production was detected in 60% isolates of Acinetobacter spp. Co-production of both ESBL and AmpC enzymes were seen in 29% of the Acinetobacter strains. Failure in detecting β-lactamases contributes to their uncontrolled spread and therapeutic failures. Hence, these β-lactamases should be detected routinely and they should be reported to clinicians in time, so that inappropriate use of antibiotics can be stopped in time.

Draft Genome Sequence of the Clinical Isolate Acinetobacter nosocomialis Strain M2

We report the 3.78-Mbp high-quality draft assembly of the genome from a clinical isolate of Acinetobacter nosocomialis called strain M2 (previously known as Acinetobacter baumannii strain M2).

Comparison of rpoB gene sequencing, 16S rRNA gene sequencing, gyrB multiplex PCR, and the VITEK2 system for identification of Acinetobacter clinical isolates

Since accurate identification of species is necessary for proper treatment of Acinetobacter infections, we compared the performances of 4 bacterial identification methods using 167 Acinetobacter clinical isolates to identify the best identification method. To secure more non-baumannii Acinetobacter (NBA) strains as target strains, we first identified Acinetobacter baumannii in a total of 495 Acinetobacter clinical isolates identified using the VITEK 2 system. Because 371 of 495 strains were identified as A. baumannii using gyrB multiplex 1 PCR and blaOXA51-like PCR, we performed rpoB gene sequencing and 16S rRNA gene sequencing on remaining 124 strains belonging to NBA and 52 strains of A. baumannii. For identification of Acinetobacter at the species level, the accuracy rates of rpoB gene sequencing, 16S rRNA gene sequencing, gyrB multiplex PCR, and the VITEK 2 were 98.2%, 93.4%, 77.2%, and 35.9%, respectively. The gyrB multiplex PCR seems to be very useful for the detection of ACB complex because its concordance rates to the final identification of strains of ACB complex were 100%. Both the rpoB gene sequencing and the 16S rRNA gene sequencing may be useful in identifying Acinetobacter.

Impaired Virulence and Fitness of a Colistin-Resistant Clinical Isolate of Acinetobacter baumannii in a Rat Model of Pneumonia

We compared the fitness and lung pathogenicity of two isogenic clinical isolates of Acinetobacter baumannii, one resistant (ABCR) and the other susceptible (ABCS) to colistin. In vitro, ABCR exhibited slower growth kinetics than ABCS. In a rat model of pneumonia, ABCR was associated with less pronounced signs of infection (lung bacterial count, systemic dissemination, and lung damage) and a better outcome (ABCR and ABCS mortality rates, 20 and 50%, respectively [P = 0.03]).

In Vivo -Validated Essential Genes Identified in Acinetobacter baumannii by Using Human Ascites Overlap Poorly with Essential Genes Detected on Laboratory Media

ABSTRACTA critical feature of a potential antimicrobial target is the characteristic of being essential for growth and survival during host infection. For bacteria, genome-wide essentiality screens are usually performed on rich laboratory media. This study addressed whether genes detected in that manner were optimal for the identification of antimicrobial targets since the in vivo milieu is fundamentally different. Mutant derivatives of a clinical isolate of Acinetobacter baumannii were screened for growth on human ascites, an ex vivo medium that reflects the infection environment. A subset of 34 mutants with unique gene disruptions that demonstrated little to no growth on ascites underwent evaluation in a rat subcutaneous abscess model, establishing 18 (53%) of these genes as in vivo essential. The putative gene products all had annotated biological functions, represented unrecognized or underexploited antimicrobial targets, and could be grouped into five functional categories: metabolic, two-component signaling systems, DNA/RNA synthesis and regulation, protein transport, and structural. These A. baumannii in vivo essential genes overlapped poorly with the sets of essential genes from other Gram-negative bacteria catalogued in the Database of Essential Genes (DEG), including those of Acinetobacter baylyi, a closely related species. However, this finding was not due to the absence of orthologs. None of the 18 in vivo essential genes identified in this study, or their putative gene products, were targets of FDA-approved drugs or drugs in the developmental pipeline, indicating that a significant portion of the available target space within pathogenic Gram-negative bacteria is currently neglected.

Detection of Quorum Sensing Signal Molecules and Identification of an Autoinducer Synthase Gene among Biofilm Forming Clinical Isolates of Acinetobacter spp.

BackgroundQuorum sensing is a term that describes an environmental sensing system that allows bacteria to monitor their own population density which contributes significantly to the size and development of the biofilm. Many gram negative bacteria use N-acyl-homoserine lactones as quorum sensing signal molecules. In this study, we sought to find out if the biofilm formation among clinical isolates of Acinetobacter spp. is under the control of autoinducing quorum sensing molecules.Methodology/Principal FindingsBiofilm formation among clinical isolates of Acinetobacter spp. was assessed and the production of signal molecules were detected with Chromobacterium violaceum CV026 biosensor system. Characterisation of autoinducers was carried out by mass spectrometric analysis. We have also reported the identification of an autoinducer synthase gene, abaΙ among the isolates that produce quorum sensing signal molecules and have reported that the mutation in the abaI gene influences their biofilm forming capabilities. Using a microtitre-plate assay it was shown that 60% of the 50 Acinetobacter spp. isolates significantly formed biofilms. Further detection with the biosensor strain showed that some of these isolates produced long chain signal molecules. Mass spectrometric analysis revealed that five of these isolates produced N-decanoyl homoserine lactone and two isolates produced acyl-homoserine lactone with a chain length equal to C12. The abaΙ gene was identified and a tetracycline mutant of the abaΙ gene was created and the inhibition in biofilm formation in the mutant was shown.Conclusions/SignificanceThese data are of great significance as the signal molecules aid in biofilm formation which in turn confer various properties of pathogenicity to the clinical isolates including drug resistance. The use of quorum sensing signal blockers to attenuate bacterial pathogenicity is therefore highly attractive, particularly with respect to the emergence of multi antibiotic resistant bacteria.

Molecular epidemiology of carbapenem-non-susceptible Acinetobacter baumannii in Japan

Acinetobacter baumannii presents a clinical challenge when it is non-susceptible to carbapenems. The prevalence of carbapenem-non-susceptible A. baumannii in Japan is unclear, as previous studies have been limited in scope. We investigated the spread of carbapenem-non-susceptible A. baumannii in Japan and performed a comparison with findings from overseas. A total of 305 non-duplicate clinical isolates of Acinetobacter spp. from 176 medical facilities in all geographical regions of Japan were tested for susceptibility to antimicrobial agents by the agar dilution method. Isolates with MICs of imipenem ≥ 4 mg/L underwent PCR analysis of OXA-type β-lactamase gene clusters and metallo-β-lactamase genes. These isolates were further analysed by sequencing of OXA-type β-lactamases and by multilocus sequence typing (MLST). Fifty-five of the 305 clinical isolates had MICs of imipenem ≥ 4 mg/L. The OXA-51-like carbapenemase gene was detected in 52 of these 55 isolates. Within the OXA-51-like gene cluster, OXA-66 was found in 43 (82.7%) of the 52 isolates. MLST identified the following sequence types (STs): ST74, ST76, ST92, ST106, ST188 and ST195 in 2 (3.8%), 2 (3.8%), 40 (76.9%), 5 (9.6%), 2 (3.8%) and 1 (1.9%) of the isolates, respectively. In particular, ST92 was found in 31 (91.2%) of the 34 A. baumannii isolates with MICs of imipenem ≥ 16 mg/L. This is the first report on the molecular epidemiology of A. baumannii with MICs of imipenem ≥ 4 mg/L in Japan. OXA-66 and ST92 were dominant among these isolates.

Identification of Acinetobacter species: Is Bruker biotyper MALDI-TOF mass spectrometry a good alternative to molecular techniques?

Acinetobacter spp. has become a leading cause of nosocomial infection in recent years. Phenotypic similarities between the species in the genus have made it difficult to identify them clearly using routine diagnostic methods. Consequently, more relevant species have been grouped together as Acinetobacter calcoaceticus–Acinetobacter baumannii complex (A. baumannii, A. calcoaceticus, Acinetobacter genospecies 3 and A. genospecies 13TU). However, there are other species that may also have clinical significance.The aims of this study were to establish the usefulness of matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) for the identification of Acinetobacter species by comparison with two molecular techniques, as well as determine the role of species other than A. baumannii play in nosocomial infections.The study sample comprised 109 clinical isolates of Acinetobacter. They were all identified using MALDI-TOF MS. Thirty-one isolates of these were also tested using comparator amplification of blaOXA51-like and sequencing of the rpoB gene. Different score values in MALDI-TOF MS revealed 87 A. baumannii, 19 A. genospecies 3, 1 Acinetobacter junii, 1 Acinetobacter baylyi and 1 Acinetobacter tjernbergiae. Amplification of blaOXA-51-like showed products in 85 isolates. Sequencing of the rpoB gene allowed us to identify all the 31 isolates analyzed: 16 were consistent with the results of spectrometry and 15 were not. This work showed that molecular techniques are still needed to identify the different species of clinical interest within the genus Acinetobacter. Although, MALDI-TOF MS could be useful to identify A. baumannii but not other species in the genus.

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.

Carbapenem-ResistantAcinetobacter baumannii

Clinical isolates of Acinetobacter spp. in Korea exhibit higher antimicrobial resistance rates than in foreign countries and frequently show multi-drug resistance. Approximately 67% (272/405) of Acinetobacter baumannii isolates collected from 19 hospitals in Korea in 2008 exhibited intermediate susceptibility or resistance to imipenem and/or meropenem. The most important mechanisms in acquiring carbapenem resistance in A. baumannii in Korea are production of OXA-23 and overproduction of OXA-51, while that in non-baumannii Acinetobacter is the production of metallo-β-lactamases. All the carbapenem-resistant A. baumannii isolates were identified as clonal complex 92 and belonged to worldwide clone 2. (Korean J Clin Microbiol 2012;15:1-8)

Molecular characterization of clinical multiresistant isolates of Acinetobacter sp. from hospitals in Porto Alegre, State of Rio Grande do Sul, Brazil

Hospitals around the world have presented multiresistant Acinetobacter sp. outbreaks. The spread of these isolates that harbor an increasing variety of resistance genes makes the treatment of these infections and their control within the hospital environment more difficult. This study aimed to evaluate the occurrence and dissemination of Acinetobacter sp. multiresistant isolates and to identify acquired resistance genes. We analyzed 274 clinical isolates of Acinetobacter sp. from five hospitals in Porto Alegre, RS, Brazil. We evaluated the susceptibility to antimicrobial, acquired resistance genes from Ambler's classes B and D, and performed molecular typing of the isolates using enterobacterial repetitive intergenic consensus-polymerase chain reaction (ERIC-PCR) technique. A high (68%) percentage of multiresistant isolates of Acinetobacter sp. was observed, and 69% were resistant to carbapenems. We identified 84% of isolates belonging to species A. baumannii because they presented the gene blaOXA-51. The gene blaOXA-23 was detected in 62% of the isolates, and among these, 98% were resistant to carbapenems. Using the ERIC-PCR technique, we identified clones of Acinetobacter sp. spread among the four hospitals analyzed during the sampling period. The data indicate the dissemination of Acinetobacter sp. isolates among hospitals and their permanence in the hospital after one year.

Phenotypic and Molecular Characterization of Acinetobacter Clinical Isolates Obtained from Inmates of California Correctional Facilities

Acinetobacter spp. increasingly have been wreaking havoc in hospitals and communities worldwide. Although much has been reported regarding Acinetobacter isolates responsible for nosocomial infections, little is known about these organisms in correctional facilities. In this study, we performed species identification, examined the antibiotic resistance profiles, and determined the mechanisms of resistance and clonal relationships of 123 Acinetobacter isolates obtained from inmates of 20 California correctional facilities (CCFs). We found that 57.7% of the isolates belong to A. baumannii, followed by isolates of Acinetobacter genomic species 3 (gen. sp. 3; 23.6%) and of Acinetobacter gen. sp. 13TU (10.6%). Multidrug-resistant (MDR) CCF isolates were found in only six CCFs. Additionally, DNA sequences of gyrA and parC genes were consistent with fluoroquinolone (FQ) susceptibility phenotypes. Furthermore, the presence of class 1 integrons was detected in 15 CCF isolates, all of which are MDR. Integron-associated gene cassettes encode several aminoglycoside modification enzymes, which correlate with most of the aminoglycoside-resistant phenotypes. Antimicrobial susceptibility testing in the presence of Phe-Arg-β-naphthylamide dihydrochloride and 1-(1-naphthylmethyl)-piperazine indicated the involvement of efflux pumps in the FQ resistance of only a few CCF isolates. Finally, genetic profiling showed that there was no evidence of A. baumannii outbreaks in CCFs. Instead, our analyses revealed only limited clonal dissemination of mostly non-MDR A. baumannii strains in a few facilities. This study represents the first report to characterize phenotypic and molecular features of Acinetobacter isolates in correctional facilities, which provides a baseline for monitoring the antimicrobial resistance changes and dissemination patterns of these organisms in such specialized institutions.

Prevalence of OXA-type carbapenemase genes and genetic heterogeneity in clinical isolates of Acinetobacter spp. from Mangalore, India

The prevalence of OXA-type carbapenemase genes, ISAba1 insertion sequence, carbapenem resistance, biofilm forming ability and genetic heterogeneity in clinical isolates of Acinetobacter spp. from hospitals in Mangalore, South India was studied. Based on the presence of the bla(OXA-51) -like gene, the 62 isolates of Acinetobacter spp. were identified as 48 A. baumannii and 14 other Acinetobacter spp. The prevalence of bla(OXA-23) -like, bla(OXA-24) -like and bla(OXA-58) -like genes in A. baumannii was 47.9%, 22.9% and 4.2%, while in other Acinetobacter spp. it was 28.5%, 64.3% and 35.7% respectively. Several A. baumannii isolates (16/48) harbored the insertion sequence ISAba1 in the upstream region of the bla(OXA-23) -like gene. Resistance to meropenem was seen in 39.6% and 14.2% of A. baumannii and other Acinetobacter spp. isolates, respectively. The ability to form biofilm was observed to be higher among A. baumannii in comparison to other Acinetobacter spp. The present study shows that bla(OXA-23) -like genes are more common in A. baumannii,whereas bla(OXA-24) -like genes are common to other Acinetobacter spp. The study revealed genetic heterogeneity among the isolates, indicating multiple sources in the hospitals.

Distribution of Intrinsic Plasmid Replicase Genes and Their Association with Carbapenem-Hydrolyzing Class D β-Lactamase Genes in European Clinical Isolates of Acinetobacter baumannii

Ninety-six genetically diverse multidrug-resistant clinical isolates of Acinetobacter baumannii from 25 hospitals in 17 European countries were screened by PCR for specific carbapenemase-hydrolyzing class D β-lactamase (CHDL) genes and by PCR-based replicon typing for the presence of 19 different plasmid replicase (rep) gene homology groups (GRs). Results were confirmed by DNA sequencing where necessary. All 96 isolates contained at least 1 (with a maximum of 4) of the 19 groups of rep genes. Groups detected were GR6 (repAci6; 93 isolates), GR2 (including repAci1 [67 isolates] and repAci2 [3 isolates]), GR16 (repApAB49; 12 isolates), GR12 (p2ABSDF0001; 10 isolates), GR3 (repAci3; 4 isolates), GR4 (repAci4; 3 isolates), GR10 (repAciX; 1 isolate), and GR14 (repp4AYE; 1 isolate). Variations in rep gene content were observed even among epidemiologically related isolates. Genes encoding OXA-58-like CHDLs (22 isolates) were associated with carriage of the repAci1, repAci3, repAci4, and repAciX genes, genes encoding OXA-40-like CHDLs (6 isolates) were associated with repAci2 and p2ABSDF0001, and genes encoding OXA-23-like CHDLs (8 isolates) were associated with repAci1. Most intrinsic Acinetobacter plasmids are non-self-transferable, but the almost ubiquitous repAci6 gene was strongly associated with a potential tra locus that could serve as a general system for plasmid mobilization and consequent horizontal transmission of plasmids and their associated antibiotic resistance genes among strains of A. baumannii.

Carbapenem-non-susceptible Acinetobacter baumannii of sequence type 92 or its single-locus variants with a G428T substitution in zone 2 of the rpoB gene

to investigate the epidemiological traits of carbapenem-non-susceptible Acinetobacter baumannii (CNSAB) and the usefulness of phylogenetic grouping based on partial rpoB gene sequencing in defining the epidemiological traits of CNSAB. a total of 547 non-duplicate clinical isolates of Acinetobacter spp. were collected from 19 hospitals in Korea in 2008. Detection of genes encoding OXA carbapenemases and metallo-β-lactamases was performed by PCR. The epidemiological relationships of the isolates were investigated by multilocus sequence typing and repetitive-sequence-based PCR. The 450 bp sequence (zone 2) of the rpoB gene was amplified and sequenced. molecular characterization of the 272 CNSAB isolates identified five sequence types (STs): ST92, ST75, ST137, ST138 and ST69. The first four of these STs were clustered into clonal complex (CC) 92, sharing alleles at six of seven housekeeping gene loci; ST69 shared alleles at five of seven loci. CNSAB of CC92 carried the bla(OXA-23) gene (n = 169), the bla(OXA-51)-like gene preceded by ISAba1 (n = 89) or both (n = 14). Notably, all CNSAB isolates carried a G428T substitution in zone 2 of the rpoB gene. CNSAB isolates of CC92 with the G428T substitution in zone 2 of the rpoB gene are disseminated nationwide in Korea. A. baumannii with the single nucleotide substitution may be more likely to acquire carbapenem resistance than are other isolates.