Targeting Outer Membrane Protein Component AdeC for the Discovery of Efflux Pump Inhibitor against AdeABC Efflux Pump of Multidrug Resistant <Emphasis Type="BoldItalic">Acinetobacter baumannii</Emphasis>

The structure and functioning of multidrug efflux systems provide us with a better understanding of the transport of various antibiotics, thus giving a path for the discovery of effective compounds for combating the multidrug resistance in Acinetobacter baumannii. In the present study, a number of computational techniques have been used to search for an inhibitor for the RND efflux pump, AdeABC, of A. baumannii targeting specifically its outermost component, i.e., AdeC. We have prepared the three-dimensional structure for AdeC using MODELLER v9.16 and identified its active binding site using SiteMap. Using high-throughput virtual screening, we identified compounds from a large library of biogenic compounds on the basis of their effective interaction at the binding site of AdeC. The validation of docking step was performed by plotting ROC curve (enrichment calculations). The docked complexes were further analyzed for their binding free energies by molecular mechanics using Generalized Born model and Solvent Accessibility (MMGBSA). The molecular dynamics simulation was performed for AdeC-ZINC77257599 complex using GROMACS. The present rational drug designing, molecular mechanics and molecular dynamics data provided an inhibitor, i.e, ZINC77257599 [(3R,4Z,6E,8E)-3-hydroxy-2,2,4-trimethyl-10-oxazol-5-yl-deca-4,6,8-trienamide], for the outer membrane protein component (AdeC) of efflux pump AdeABC of A. baumannii.     

In-silico interaction studies suggest RND efflux pump mediates polymyxin resistance in Acinetobacter baumannii

Bacterial efflux pumps have emerged as antibiotic resistance determinants and confers multi-drug resistance to a broad range of antimicrobials as well as non-antibiotic substances. A study about translocation of antibiotic molecules through the efflux transporter, will contribute in determining substrate specificity. In the present study, we have explored RND family efflux pump extensively found in Acinetobacter baumannii i.e. AdeABC. Besides, another well studied RND efflux pump, AcrAB-TolC together with a non-RND efflux pump, NorM was investigated for comparative analysis. We employed a series of computational techniques ranging from molecular docking to binding free energy estimation and molecular dynamics simulations to determine the binding affinity for different classes of drugs, namely aminoglycosides, polymyxins, β-lactams, tetracyclines, glycylcyclines, quinolones and metronidazole with AdeB, AcrB, and NorM efflux proteins. Our results revealed that class polymyxins has the highest binding affinity with the RND efflux pumps i.e. AcrAB-TolC and AdeABC as well as non-RND efflux pump, NorM. The experimental validation study demonstrated bigger zone of inhibition in presence of efflux pump inhibitor than polymyxin alone thus unveiling its specificity toward efflux pump. The reported experimental data comprising of minimum inhibitory concentration of antibiotics toward these efflux pumps also support our finding based on in silico approach. To recapitulate the outcome, polymyxins shows maximum specificity toward RND as well as non-RND efflux pump and may unlatch the way to rationally develop new potential antibacterial agents as well as efflux pump inhibitors in order to combat resistance.     

Screening of potential lead molecules against prioritised targets of multi-drug-resistant-Acinetobacter baumannii – insights from molecular docking,molecular dynamic simulations and in vitro assays

Acinetobacter baumannii, an opportunistic pathogen, has become multi-drug resistant (MDR) to major classes of antibacterial and poses grave threat to public health. The current study focused to screen novel phytotherapeutics against prioritised targets of Acinetobacter baumannii by computational investigation. Fourteen potential drug targets were screened based on their functional role in various biosynthetic pathways and the 3D structures of 9 targets were retrieved from Protein Data Bank and others were computationally predicted. By extensive literature survey, 104 molecules from 48 herbal sources were screened and subjected to virtual screening. Ten clinical isolates of A. baumannii were tested for antibiotic susceptibility towards clinafloxacin, imipenem and polymyxin-E. Computational screening suggested that Ajmalicine ((19α)-16, 17-didehydro-19-methyloxayohimban-16-carboxylic acid methyl ester from Rauwolfia serpentina), Strictamin (Akuammilan-17-oic acid methyl ester from Alstonia scholaris) and Limonin (7, 16-dioxo-7, 16-dideoxylimondiol from Citrus sps) exhibited promising binding towards multiple drug targets of A. baumannii in comparison with the binding between standard drugs and their targets. Limonin displayed promising binding potential (binding energy ?9.8 kcal/mol) towards diaminopimelate epimerase (DapF) and UDP-N-acetylglucosamine 1-carboxyvinyltransferase (MurA). Ajmalicine and Strictamin demonstrated good binding potential (?9.5, ?8.5 kcal/mol, respectively) towards MurA and shikimate dehydrogenase (?7.8 kcal/mol). Molecular dynamic simulations further validated the docking results. In vitro assay suggested that the tested isolates exhibited resistance to clinafloxacin, imipenem and polymyxin-E and the herbal preparations (crude extract) demonstrated a significant antibacterial potential (p ≤ .05). The study suggests that the aforementioned lead candidates and targets can be used for structure-based drug screening towards MDR A. baumannii.     

Discovery of multidrug efflux pump inhibitors with a novel chemical scaffold

Multidrug efflux is a major contributor to antibiotic resistance in Gram-negative bacterial pathogens. Inhibition of multidrug efflux pumps is a promising approach for reviving the efficacy of existing antibiotics. Previously, inhibitors targeting both the efflux transporter AcrB and the membrane fusion protein AcrA in the Escherichia coli AcrAB-TolC efflux pump were identified. Here we use existing physicochemical property guidelines to generate a filtered library of compounds for computational docking. We then experimentally test the top candidate coumpounds using in vitro binding assays and in vivo potentiation assays in bacterial strains with controllable permeability barriers. We thus identify a new class of inhibitors of E. coli AcrAB-TolC. Six molecules with a shared scaffold were found to potentiate the antimicrobial activity of erythromycin and novobiocin in hyperporinated E. coli cells. Importantly, these six molecules were also active in wild-type strains of both Acinetobacter baumannii and Klebsiella pneumoniae, potentiating the activity of erythromycin and novobiocin up to 8-fold.     

Identification of Natural Compound Inhibitors for Multidrug Efflux Pumps of Escherichia coli and Pseudomonas aeruginosa Using In Silico High-Throughput Virtual Screening and In Vitro Validation

Pseudomonas aeruginosa and Escherichia coli are resistant to wide range of antibiotics rendering the treatment of infections very difficult. A main mechanism attributed to the resistance is the function of efflux pumps. MexAB-OprM and AcrAB-TolC are the tripartite efflux pump assemblies, responsible for multidrug resistance in P. aeruginosa and E. coli respectively. Substrates that are more susceptible for efflux are predicted to have a common pharmacophore feature map. In this study, a new criterion of excluding compounds with efflux substrate-like features was used, thereby refining the selection process and enriching the inhibitor identification process. An in-house database of phytochemicals was created and screened using high-throughput virtual screening against AcrB and MexB proteins and filtered by matching with the common pharmacophore models (AADHR, ADHNR, AAHNR, AADHN, AADNR, AAADN, AAADR, AAANR, AAAHN, AAADD and AAADH) generated using known efflux substrates. Phytochemical hits that matched with any one or more of the efflux substrate models were excluded from the study. Hits that do not have features similar to the efflux substrate models were docked using XP docking against the AcrB and MexB proteins. The best hits of the XP docking were validated by checkerboard synergy assay and ethidium bromide accumulation assay for their efflux inhibition potency. Lanatoside C and diadzein were filtered based on the synergistic potential and validated for their efflux inhibition potency using ethidium bromide accumulation study. These compounds exhibited the ability to increase the accumulation of ethidium bromide inside the bacterial cell as evidenced by these increase in fluorescence in the presence of the compounds. With this good correlation between in silico screening and positive efflux inhibitory activity in vitro, the two compounds, lanatoside C and diadzein could be promising efflux pump inhibitors and effective to use in combination therapy against drug resistant strains of P. aeruginosa and E. coli.     

Attaching NorA efflux pump inhibitors to methylene blue enhances antimicrobial photodynamic inactivation of Escherichia coli and Acinetobacter baumannii in vitro and in vivo

Resistance of bacteria to antibiotics is a public health concern worldwide due to the increasing failure of standard antibiotic therapies. Antimicrobial photodynamic inactivation (aPDI) is a promising non-antibiotic alternative for treating localized bacterial infections that uses non-toxic photosensitizers and harmless visible light to produce reactive oxygen species and kill microbes. Phenothiazinium photosensitizers like methylene blue (MB) and toluidine blue O are hydrophobic cations that are naturally expelled from bacterial cells by multidrug efflux pumps, which reduces their effectiveness. We recently reported the discovery of a NorA efflux pump inhibitor-methylene blue (EPI-MB) hybrid compound INF55-(Ac)en–MB that shows enhanced photodynamic inactivation of the Gram-positive bacterium methicillin-resistant Staphylococcus aureus (MRSA) relative to MB, both in vitro and in vivo. Here, we report the surprising observation that INF55-(Ac)en–MB and two related hybrids bearing the NorA efflux pump inhibitors INF55 and INF271 also show enhanced aPDI activity in vitro (relative to MB) against the Gram-negative bacteria Escherichia coli and Acinetobacter baumannii, despite neither species expressing the NorA pump. Two of the hybrids showed superior effects to MB in murine aPDI infection models. The findings motivate wider exploration of aPDI with EPI-MB hybrids against Gram-negative pathogens and more detailed studies into the molecular mechanisms underpinning their activity.     

A Truncated AdeS Kinase Protein Generated by ISAba1 Insertion Correlates with Tigecycline Resistance in Acinetobacter baumannii

Over-expression of AdeABC efflux pump stimulated continuously by the mutated AdeRS two component system has been found to result in antimicrobial resistance, even tigecycline (TGC) resistance, in multidrug-resistant Acinetobacter baumannii (MRAB). Although the insertion sequence, ISAba1, contributes to one of the AdeRS mutations, the detail mechanism remains unclear. In the present study we collected 130 TGC-resistant isolates from 317 carbapenem resistant MRAB (MRAB-C) isolates, and 38 of them were characterized with ISAba1 insertion in the adeS gene. The relationship between the expression of AdeABC efflux pump and TGC resistant was verified indirectly by successfully reducing TGC resistance with NMP, an efflux pump inhibitor. Further analysis showed that the remaining gene following the ISAba1 insertion was still transcribed to generate a truncated AdeS protein by the Pout promoter on ISAba1 instead of frame shift or pre-termination. Through introducing a series of recombinant adeRS constructs into a adeRS knockout strain, we demonstrated the truncated AdeS protein was constitutively produced and stimulating the expression of AdeABC efflux pump via interaction with AdeR. Our findings suggest a mechanism of antimicrobial resistance induced by an aberrant cytoplasmic sensor derived from an insertion element.     

Effect of 1-(1-Naphtylmethyl)-piperazine,an Efflux Pump Inhibitor,on Antimicrobial Drug Susceptibilities of Clinical <Emphasis Type="Italic">Acinetobacter baumannii</Emphasis> Isolates

In this study, the effects of 1-(1-naphtylmethyl)-piperazine (NMP), an efflux pump inhibitor, on antimicrobial drug susceptibilities of 42 clinical Acinetobacter baumannii isolates were investigated by the disc diffusion method. The inhibition zone diameters of antibiotic discs were tested in the presence and absence of NMP and then these zone diameters were compared. Presence of NMP restored ciprofloxacin susceptibility in 15 intermediate and 2 resistant isolates. One ciprofloxacin resistant isolate became intermediate in the presence of NMP. One isolate resistant to gentamicin became intermediate with NMP. Interestingly, one isolate susceptible to meropenem became resistant in the presence of NMP. Although NMP increased the inhibition zone diameters of some of the tested antibiotics against the resistant isolates, the increase was not enough to restore susceptibility. In conclusion, the presence of NMP increases the zone diameters of ciprofloxacin and levofloxacin. Intermediate strains become susceptible but the resistant isolates do not.     

Structure-activity relationship-based screening of antibiotics against Gram-negative Acinetobacter baumannii

To discover potent antibiotics against the Gram-negative bacteria, we performed a structure-activity relationship (SAR) study of YKsa-6, which was the most potent inhibitor of Staphylococcus aureus β-ketoacyl acyl carrier protein III in our previous study. We identified and selected 11 candidates, and finally screened two active compounds, YKab-4 (4-[(3-chloro-4-methylphenyl)aminoiminomethyl]benzene-1,3-diol) and YKab-6 (4-[[3-(trifluoromethyl)phenyl]aminoiminomethyl]phenol) as inhibitors of Acinetobacter baumannii KAS III (abKAS III). They showed potent antimicrobial activities at 2 or 8 μg/mL, specifically against Acinetobacter baumannii and a strong binding affinity for abKAS III. From the homology modeling, we defined the three-dimensional (3D) structure of abKAS III for the first time and found that it had an extra loop region compared with common Gram-negative bacteria derived KAS IIIs. The docking study revealed that the hydroxyl groups of inhibitors formed extensive hydrogen bonds and the complicated hydrophobic and cation-stacking interactions are important to binding with abKAS III. We confirmed that the hydrophobicity of these compounds might be the essential factor for their antimicrobial activities against Gram-negative bacteria as well as their structural rigidity, a cooperative feature for retaining the hydrophobic interactions between abKAS III and its inhibitors. This study may provide an insight developing strategies for potent antibiotics against A. baumannii.     

In silico screening of anti-inflammatory compounds from Lichen by targeting cyclooxygenase-2

Abstract

Non-steroidal anti-inflammatory drugs (NSAID) targeting cyclooxygenase-2 are clinically effective. However, they lack anti-thrombotic activity resulting in incidences of adverse effects like myocardial infarction, gastrointestinal and abdominal discomfort which necessitate for discovering new drug candidates with improved therapeutic effects and tolerability. Various recent researches have suggested that many lichens offer a vast reservoir for anti-inflammatory drug candidates which are natural as well as safe for human consumption. Drug discovery is a very complex and time-consuming process; however, in silico techniques can make this process simple and economic. Hence to find out natural anti-inflammatory compounds, we have carried out the virtual screening of 412 lichen compounds by molecular docking with human Cox-2 enzyme and validated the docking score by X-Score followed by ADMET and Drug-likeness analysis. The resulting 6 top-scored compounds were subjected to Molecular dynamics simulation (MDS) to analyze the stability of docked protein-ligand complex, to assess the fluctuation and conformational changes during protein-ligand interaction. The values of RMSD, Rg, and interaction energy after 30?ns of MDS revealed the good stability of these Lichen compounds in the active site pocket of Cox-2 in compare to reference, JMS. Additionally, we have done the pharmacophore analysis which found many common pharmacophore features between Lichen compounds and well known anti-inflammatory compounds. Our result shows that these lichen compounds are potential anti-inflammatory candidates and could be further modified and evaluated to develop more effective anti-inflammatory drugs with fewer side effects for the treatment of inflammatory diseases.

Communicated by Ramaswamy H. Sarma     

Improvement of MALDI-TOF MS profiling for the differentiation of species within the Acinetobacter calcoaceticus—Acinetobacter baumannii complex

MALDI-TOF MS is currently becoming the method of choice for rapid identification of bacterial species in routine diagnostics. Yet, this method suffers from the inability to differentiate reliably between some closely related bacterial species including those of the Acinetobacter calcoaceticus–Acinetobacter baumannii (ACB) complex, namely A. baumannii and Acinetobacter nosocomialis. In the present study, we evaluated a protocol which was different from that used in the Bruker Daltonics identification system (MALDI BioTyper) to improve species identification using a taxonomically precisely defined set of 105 strains representing the four validly named species of the ACB complex. The novel protocol is based on the change in matrix composition from alpha-cyano-4-hydroxycinnamic acid (saturated solution in water:acetonitrile:trifluoroacetic acid, 47.5:50:2.5, v/v) to ferulic acid (12.5 mg ml⁻¹ solution in water:acetonitrile:formic acid 50:33:17, v/v), while the other steps of sample processing remain unchanged. Compared to the standard protocol, the novel one extended the range of detected compounds towards higher molecular weight, produced signals with better mass resolution, and allowed the detection of species-specific signals. As a result, differentiation of A. nosocomialis and A. baumannii strains by cluster analysis was improved and 13 A. nosocomialis strains, assigned erroneously or ambiguously by using the standard protocol, were correctly identified.     

Evolution of antimicrobial resistance of Acinetobacter baumannii in a university hospital

Aims: To investigate the susceptibility pattern and the molecular epidemiology of Acinetobacter baumannii isolates in two periods (1994–1996 and 2004–2007) in Londrina University Hospital. Methods and Results: Antimicrobial susceptibility of 150 A. baumannii isolates was assessed by disc diffusion and agar dilution methods. Genetic similarity amongst the isolates was evaluated by ERIC–PCR. Resistance of A. baumannii to carbapenems increased from 2% (1994–1996) to 73% (2004–2007). Thirty‐eight clones were detected. Conclusions: The results of the study suggest that the high prevalence of carbapenem resistance amongst Acinetobacter baumannii organisms in this institution is not caused by the spread of a predominant clone. Significance and Impact of the Study: This work reinforces the importance monitoring antimicrobial susceptibility rates.     

主动外排机制在鲍曼不动杆菌耐药性中的作用

目的探讨细菌主动外排机制在临床分离的鲍曼不动杆菌耐药性中的作用。方法琼脂稀释法检测临床分离的鲍曼不动杆菌对常用抗生素的耐药性,测定经外排泵抑制剂碳酰氰基-对-氯苯腙（CCCP）处理前后鲍曼不动杆菌对抗生素最小抑菌浓度（MIC）的变化,以聚合酶链反应（PCR）、逆转录-聚合酶链反应（RT-PCR）检测多重耐药主动外排基因以出及其表达水平。结果临床分离的鲍曼不动杆菌对常用抗生素耐药率高且具有多重耐药性,并存在药物的主动外排。所有临床分离的菌株均能检测到adeB基因,但多重耐药株表达水平明显高于敏感株（P〈0．01）。结论临床分离的鲍曼不动杆菌的耐药性尤其是多重耐药性与外排泵介导的耐药机制密切相关。     

Proteomic analysis of <Emphasis Type="Italic">Acinetobacter baumannii</Emphasis> in biofilm and planktonic growth mode

Recently, multidrug-resistant clinical isolates of Acinetobacter baumannii have been found to have a high capacity to form biofilm. It is well known that bacterial cells within biofilms are highly resistant to antibiotics, UV light, acid exposure, dehydration, and phagocytosis in comparison to their planktonic counterparts, which suggests that the cells in a biofilm have altered metabolic activity. To determine which proteins are up-regulated in A. baumannii biofilm cells, we performed a proteomic analysis. A clinical isolate of A. baumannii 1656-2, which was characterized to have a high biofilm forming ability, was cultivated under biofilm and planktonic conditions. Outer membrane enriched A. baumannii 1656-2 proteins were separated by two-dimensional (2-D) gel electrophoresis and the differentially expressed proteins were identified by MALDI-TOF mass spectrometry. The proteins up-regulated or expressed only in biofilm cells of A. baumannii are categorized as follows: (i) proteins processing environmental information such as the outer membrane receptor protein involved in mostly Fe transport, a sensor histidine kinase/response regulator, and diguanylate cyclase (PAS-GGEDF-EAL domain); (ii) proteins involved in metabolism such as NAD-linked malate dehydrogenase, nucleoside-diphosphate sugar epimerase, putative GalE, ProFAR isomerase, and N-acetylmuramoyl-l-alanine amidase; (iii) bacterial antibiotic resistance related proteins; and (iv) proteins related to gene repair such as exodeoxyribonuclease III and GidA. This proteomic analysis provides a fundamental platform for further studies to reveal the role of biofilm in the persistence and tolerance of A. baumannii.     

头孢地尔:新型铁载体头孢菌素抗多重耐药革兰阴性杆菌感染北大核心CSCD

抗菌药物耐药是目前全世界面临的重要公共卫生问题之一,亟需开发有效的广谱抗菌药物以应对多重耐药革兰阴性杆菌的感染。头孢地尔是日本Shionogi公司开发的新型铁载体头孢菌素类抗菌药物。该药物对碳青霉烯耐药的肠杆菌目细菌(carbapenem resistant Enterobacterales,CRE)、铜绿假单胞菌、鲍曼不动杆菌和嗜麦芽窄食单胞菌等具有广谱强效的抗菌活性。该药物克服了革兰阴性杆菌因外膜孔道蛋白表达量下调和主动外排泵表达量上调产生的耐药性,并对丝氨酸酶和金属碳青霉烯酶具有较好的稳定性。该药可用于治疗由革兰阴性杆菌引起的复杂性尿路感染(包括肾盂肾炎)、院内获得性肺炎和呼吸机相关性肺炎。文中通过汇总头孢地尔的化学结构、抗菌作用机制、体外抗菌活性、药代动力学、药效学和临床治疗等信息,展现头孢地尔作为新型铁载体头孢菌素在治疗多重耐药革兰阴性杆菌感染中的应用前景。     

Effect of Carvacrol and Thymol on NorA efflux pump inhibition in multidrug-resistant (MDR) Staphylococcus aureus strains

Undue exposure to antimicrobials has led to the acquisition and development of sophisticated bacterial resistance mechanisms, such as efflux pumps, which are able to expel or reduce the intracellular concentration of various antibiotics, making them ineffective. Therefore, inhibiting this mechanism is a promising way to minimize the phenomenon of resistance in bacteria. In this sense, the present study sought to evaluate the activity of the Carvacrol (CAR) and Thymol (THY) terpenes as possible Efflux Pump Inhibitors (EPIs), by determining the Minimum Inhibitory Concentration (MIC) and the association of these compounds in subinhibitory concentrations with the antibiotic Norfloxacin and with Ethidium Bromide (EtBr) against strains SA-1199 (wild-type) and SA-1199B (overexpresses NorA) of Staphylococcus aureus. In order to verify the interaction of the terpenes with the NorA efflux protein, an in silico molecular modeling study was carried out. The assays used to obtain the MIC of CAR and THY were performed by broth microdilution, while the Efflux Pump inhibitory test was performed by the MIC modification method of the antibiotic Norfloxacin and EtBr. docking was performed using the Molegro Virtual Docker (MVD) program. The results of the study revealed that CAR and THY have moderate bacterial activity and are capable of reducing the MIC of Norfloxacin antibiotic and EtBr in strains of S. aureus carrying the NorA efflux pump. The docking results showed that these terpenes act as possible competitive NorA inhibitors and can be investigated as adjuvants in combined therapies aimed at reducing antibiotic resistance.

     

Synthesis of amides from (E)-3-(1-chloro-3,4-dihydronaphthalen-2-yl)acrylic acid and substituted amino acid esters as NorA efflux pump inhibitors of Staphylococcus aureus

Inhibitors for NorA efflux pump of Staphylococcus aureus have attracted the attention of many researchers towards the discovery and development of novel efflux pump inhibitors (EPIs). In an attempt to find specific potent inhibitors of NorA efflux pump of S. aureus, a total of 15 amino acid conjugates of 3-(1-chloro-3,4-dihydronaphthalen-2-yl)acrylic acid (4–18) were synthesized using a simple convenient synthetic approach and bioevaluated against NorA efflux pump. Two compounds 7 and 8 (each having MEC of 1.56?µg/mL) were found to restore the activity of ciprofloxacin through reduction of the MIC elucidated by comparing the ethidium bromide efflux in dose dependent manner in addition to ethidium bromide efflux inhibition and accumulation study using NorA overexpressing strain SA-1199B. Most potent compounds among these were able to restore the antibacterial activity of ciprofloxacin completely against SA-1199B. Structure activity relationship (SAR) studies and docking study of potent compounds 7 and 8 could elucidate the structural requirements necessary for interaction with the NorA efflux pumps. On the whole, compounds 7 and 8 have ability to reverse the NorA efflux mediated resistance and could be further optimized for development of potent efflux pump inhibitors.     

Dissemination of ceftazidime-resistant Acinetobacter baumannii clonal complex 92 in Korea

Aims: This study was performed to describe the epidemiological traits of ceftazidime‐resistant Acinetobacter baumannii clinical isolates from Korea. Methods and Results: Antimicrobial susceptibilities were determined by disk diffusion assay. PCR experiments were performed to detect genes encoding extended‐spectrum β‐lactamases and metallo‐β‐lactamases. Detection of ISAba1 upstream of the bla_ADC gene was also performed by PCR amplification. The genetic organization of the bla_PER‐1 gene was investigated by PCR mapping and sequencing of the regions surrounding the gene. Multilocus sequence typing was performed using seven housekeeping genes. A. baumannii isolates of clonal complex (CC) 92 exhibited a higher resistance rate (286/289, 99%) against ceftazidime compared to A. baumannii isolates of non‐CC92 (7/87, 8%). Amongst 286 ceftazidime‐resistant isolates of CC92, 100 (35%) isolates carried the bla_PER‐1 gene, while none of the 87 isolates of non‐CC92 carried the gene. The bla_ADC gene associated with an ISAba1 element was detected in 98% (281/286) of ceftazidime‐resistant isolates of CC92 and in all seven ceftazidime‐resistant isolates of non‐CC92. The bla_PER‐1 gene was located on a transposon, Tn1213 (ISPa12‐bla_PER‐1‐Δgst‐ISPa13), in 95 isolates and on a complex class 1 integron (orf513‐bla_PER‐1‐putative ABC transporter gene) in five isolates. Southern blot experiments confirmed the chromosomal location of the bla_PER‐1 gene. Conclusions: Acinetobacter baumannii CC92 which has acquired ceftazidime resistance by the production of PER‐1 extended‐spectrum β‐lactamases and/or the overproduction of Acinetobacter‐derived cephalosporinase is widely disseminated in Korea. Significance and Impact of the Study: This study shows the mechanisms of acquiring ceftazidime resistance in A. baumannii and the epidemiological traits of ceftazidime‐resistant A. baumannii isolates from Korea.