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Frontiers in Cellular and Infection Microbiology logoLink to Frontiers in Cellular and Infection Microbiology
. 2026 Jul 31;16:1878371. doi: 10.3389/fcimb.2026.1878371

Comparative genomic insights into carbapenem-resistant versus susceptible Acinetobacter baumannii in Shanghai hospital settings: a multi-center molecular surveillance study

Yue Zhang 1,†, Yanru Liang 1,†, Yuanping Wang 1,†, Yiying Xu 1, Ye Qiu 1, Bing Zhao 1, Yifeng Shen 1,*, Xiao Wang 1,2,*
PMCID: PMC13472839  PMID: 42601925

Abstract

Background

Carbapenem-resistant Acinetobacter baumannii (CRAB) is priority pathogen for nosocomial infection control worldwide. This study aimed to elucidate differences in distribution, genotyping and antimicrobial resistance patterns between CRAB and carbapenem-susceptible Acinetobacter baumannii (CSAB) strains isolated from healthcare environments.

Materials and methods

A total of 1,812 environmental samples were collected from 10 medical institutions in Pudong New Area between June and December 2024 for the identification of A. baumannii. Antimicrobial susceptibility testing, whole-genome sequencing, and bioinformatic analysis were performed to reveal molecular characteristics of A. baumannii.

Results

A total of 81 A. baumannii strains were detected, with 39.51% CRAB (n = 32) and 60.49% CSAB (n = 49). CRAB strains were highly prevalent in intensive care units (ICUs, accounting for 83.33%) and patient-contact items, whereas CSAB were more evenly distributed. MLST analysis identified ST2 as dominant CRAB clone (78.13%), followed by ST164 (18.75%). CRAB isolates demonstrated 100% resistance to multiple antibiotics such as piperacillin/tazobactam and ciprofloxacin, whereas all CSAB isolates were susceptible to tested antibiotics except one ampicillin/sulbactam-resistant isolate. Carbapenem resistance in CRAB was predominantly mediated by class D carbapenemases, with carriage rate of the blaOXA-23 gene reaching 96.88%. Notably, six ST164 isolates co-harbored class B and class D carbapenemase genes, which may elevate resistance severity. Bioinformatic analysis indicated that 22.20% of resistance plasmids in CRAB were predicted to be conjugative. CRAB exhibited a more diverse and extensive virulence gene profile than CSAB strains.

Conclusions

The ICU environment was critical for CRAB control. ST2 and ST164 represented clones worthy of attention. CRAB exhibited stronger resistance, harbored more putatively conjugative plasmids and richer virulence-associated genes than CSAB, highlighting the need for targeted disinfection and surveillance of prevalent clones.

Keywords: antimicrobial resistance, Carbapenem-resistant Acinetobacter baumannii, medical institution environment, phylogeny, ST164

1. Introduction

Acinetobacter baumannii is an important nosocomial pathogen that can cause severe infections such as pneumonia, bloodstream infections, meningitis, and skin infections in individuals (Müller et al., 2023; Tamma et al., 2024). A. baumannii exhibited extremely strong viability-it could tolerate a broad range of temperatures and humidity, and survive on dry skin or object surfaces for months. This characteristic facilitates its transmission in healthcare environments, leading to infection epidemics and endemic persistence (Hassan et al., 2021; Müller et al., 2023). The increasingly severe drug resistance situation is another important reason for the continuous prevalence of A. baumannii. Reports indicate that A. baumannii is becoming more resistant to multiple antibiotics. With its high detection rate, strong adaptability, and severe drug resistance, A. baumannii has been listed as a priority drug-resistant pathogen by the World Health Organization (WHO), posing an urgent public health problem globally (Chen et al., 2025; Sati et al., 2025).

Carbapenems are key antibiotics for the clinical treatment of A. baumannii infections. However, with the irrational use of antibiotics, Carbapenem-resistant Acinetobacter baumannii (CRAB) has been constantly emerging. Studies have shown that the Centers for Disease Control and Prevention (CDC) of the United States has long classified CRAB as an “urgent threat,” the highest level in its risk classification (Watkins and Bonomo, 2023; Kubin et al., 2025). Among A. baumannii strains collected from three major hospitals in Jordan, 90.6% were resistant to carbapenems (Ababneh et al., 2021). The epidemic trend of CRAB in China is equally worrying. Among 77 intensive care unit (ICU) wards of hospitals in different provinces surveyed, 71.4% had CRAB prevalence, and clonal transmission of CRAB was found in 37.6% of ICUs. The resistance of these CRAB strains is mainly related to the production of carbapenemases, especially the class D β-lactamase encoded by blaOXA-23. blaOXA-23 can be vertically or horizontally transmitted among strains through chromosomes or plasmids, which is the reason for its wide distribution and transmission. It is worth noting that CRAB is often multidrug-resistant and carries more resistance genes and virulence genes compared with carbapenem-susceptible Acinetobacter baumannii (CSAB) (Chen et al., 2025). Clinical data also confirm that compared with CSAB infections, patients infected with CRAB have a significantly heavier disease burden and a higher risk of death (Pogue et al., 2022).

As a key site for the transmission and colonization of A. baumannii, medical institution environments-especially object surfaces such as medical devices and doctor-patient direct contact items-are important reservoirs of this bacterium. Studies have confirmed that A. baumannii in the environment can achieve nosocomial transmission through poor hand hygiene of medical staff and cross-contact of contaminated items, which is a core risk factor for nosocomial clustered infections or even outbreaks. At present, most studies on A. baumannii center on clinically isolated strains, and attention to strains in healthcare environments is gradually increasing. However, existing studies mostly focused on the single detection of CRAB and screening of resistance genes (Wong et al., 2022), lacking systematic comparative analysis of CRAB and CSAB in healthcare environments. Clarifying the distribution differences between CRAB and CSAB, and understanding the similarities and differences in drug resistance and epidemic sequence type (ST) between the two strains, can provide key evidence for tracing infection sources and determining transmission chains, thereby optimizing healthcare environment disinfection strategies and infection control measures. Based on this, this study selected 10 medical institutions in Pudong New Area as research objects, and systematically collected surface samples from different departments. The drug resistance and whole-genome sequence characteristics of isolated A. baumannii were analyzed, and the distribution characteristics, antimicrobial resistance, ST profiles, and plasmid carriage of CRAB and CSAB were compared, aiming to provide scientific basis for the environmental prevention and control of CRAB in regional medical institutions and help reduce the risk of nosocomial infections caused by A. baumannii.

2. Materials and methods

2.1. Sample source

According to the drug-resistant bacteria risk monitoring plan for medical institutions in Pudong New Area, all environmental samples were collected from different departments of 10 medical institutions in different geographical locations. The sampling frequency was one collection per quarter for each hospital. 1,812 environmental samples were obtained as test objects between June and December 2024. Detailed sampling quantities and departmental distributions were summarized in Supplementary Table 1. The specific on-site collection method was in accordance with GB 15982-2012 “Hygienic Standard for Hospital Disinfection.”

2.2. Identification of Acinetobacter baumannii

Samples were inoculated into double-strength TSB enrichment broth and cultured at 36 ± 1°C for 48h. The enrichment broth was inoculated on Acinetobacter chromogenic plates and blood plates, cultured at 36 ± 1°C for 24-48h, and suspected colonies were selected for Gram staining, oxidase, and other biochemical tests. Meanwhile, secondary confirmation was performed by mass spectrometry identification-colonies with a score >2.1 were identified as target strains. Pure colonies were preserved in 3% glycerol brain-heart infusion broth at -80°C for later use.

2.3. Antimicrobial susceptibility testing

AST Panel For Aerobic Gram Negative bacilli (Fosun Diagnostics Technology Co, Shanghai, China) was used to determine the resistance profile of A. baumannii. Antimicrobial susceptibility testing detected minimum inhibitory concentrations (MICs) values of 16 types of antibiotics, including Piperacillin/Tazobactam, Ampicillin/Sulbactam, Cefoperazone/Sulbactam, Cefotaxime, Ceftazidime, Cefepime, Imipenem, Meropenem, Minocycline, Tigecycline, Gentamicin, Amikacin, Trimethoprim/, Sulfamethoxazole, Polymyxin B, Ciprofloxacin and Levofloxacin. The E. coli ATCC®25922TM strain was employed as the quality control strain. Results were categorized as susceptible (S), intermediate (I), or resistant (R) based on the Clinical and Laboratory Standards Institute (CLSI) standards.

2.4. Whole genome sequencing

A. baumannii strains were retrieved and purified by streaking on blood agar plates. Genomic nucleic was extracted using BG-Nege-96 fully automatic nucleic acid extraction instrument and its corresponding proprietary reagents (Shanghai Bojie Medical Technology Co., Ltd, China).The sequence was performed on the DNA library generated by Whole-genome DNA Library Construction Kit (Shanghai Bojie Medical Technology Co., Ltd, China) using MGISEQ-T7 platform (MGI Tech Co., Ltd, China). Raw data from each sample were filtered using Fastp software (version 0.23.2) to trim adapter sequences and discard low-quality reads. SPAdes software (version v3.15.5) was performed for reference-free assembly of bacterial samples. Kraken (version 2.1.2) was employed to annotate the assembled data and non-target bacterial sequences were filtered out. All sequencing data have been uploaded to the NCBI database under BioProject ID: PRJNA1390075.

2.5. Bioinformatics analysis

Multilocus Sequence Typing (MLST) of A. baumannii were obtained based on the PubMLST platform (2025, https://pubmlst.org/). The 7 housekeeping genes used for MLST analysis based on the Pasteur scheme were cpn60, fusA, gltA, pyrG, recA, rplB and rpoB, while those based on the Oxford scheme were gltA, gyrB, gdhB, recA, cpn60, gpi and rpoD. Based on MLST, Grapetree was used to generate and display minimum-spanning trees (MST) of study data. The ABRIcate (v1.0.1) tool (https://github.com/tseemann/abricate) was used to identify resistance genes and virulence genes of strains based on the ResFinder database and VFDB database, respectively. Core-genome alignment was executed with Snippy (v4.6.0), using A. baumannii ATCC 19606 (GenBank accession No. GCF_009035845.1) as the reference genome. Snp-dists (v0.8.2) was utilized to calculate pairwise allelic single-nucleotide polymorphism (SNP) distances from this matrix. A maximum-likelihood phylogenetic tree was reconstructed based on core-genome single-nucleotide polymorphisms (core-SNPs), which was visualized through the Chiplot online platform (https://www.chiplot.online/tvbot.html) (Xie et al., 2023). MOB-Suite (v3.19) software was used to identify and reconstruct plasmid sequences from genome assembly data, and the conjugative transfer ability of plasmids was predicted via the MOB-typer module. All analytical parameters were set to default values.

2.6. Statistical analysis

Comprehensive statistical analyses were performed with the aid of SPSS statistical software (Version 22) and GraphPad Prism (Version 11.0). For the analysis of categorical variables, either Pearson’s chi-square test or Fisher’s exact test was selected based on the sample size and expected cell frequencies. The consistency between resistance phenotypes and resistance genes was evaluated using Cohen’s kappa statistics. The Kolmogorov-Smirnov test was implemented to evaluate whether the continuous data followed a normal distribution. In the case of two-group comparisons, the parametric unpaired t-test was applied for normally distributed data, whereas the nonparametric Mann-Whitney U test was used for data that deviated from normality. Two-sided and P < 0.05 was considered to be statistically significant.

3. Results

3.1. Distribution of Acinetobacter baumannii

The overall detection rate of A. baumannii was 4.47% (81/1812), and the recovered isolates displayed distinct distribution across different hospitals. Hospital I had the highest proportion at 17.28%, whereas Hospital A presented the lowest proportion of only 4.94%. By department, the proportion of A. baumannii isolates was the highest in Internal Medicine (27.16%), compared with merely 8.64% in Surgery. Spatial distribution analysis demonstrated that A. baumannii was widely present in shared items, items directly contacted by patients, and hands/nasal cavities of medical staff (Figure 1A). Among them, water taps, pillows and bed linen, and medical staff’s hands were hotspots of A. baumannii contamination (Figure 1B).

Figure 1.

Panel A presents a Sankey diagram showing the distribution of sample sources from hospitals, through departments, to object types. Panel B is a vertical bar chart displaying proportions of different object types and locations where samples were collected. Panels C, D, and E are horizontal bar charts comparing the proportions of CRAB and CSAB strains across hospitals, departments, and object categories, respectively, using distinct color coding for each strain.

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Distribution of A. baumannii isolates in the medical institutions environment. (A) The Sankey diagram depicts the distribution profile of all 81 A. baumannii strains across 10 medical institutions, 5 departments, and 6 Objects. The thickness of each line is proportional to the quantity (B) Distribution of 81 A. baumannii strains in specific sampling sites (The top three sites are marked with red dashed boxes); (C) Comparison of the proportions of CRAB and CSAB among different medical institutions; (D) Comparison of the proportions of CRAB and CSAB among different departments; (E) Comparison of the proportions of CRAB and CSAB among different objects.

Among the 81 A. baumannii strains, CRAB accounted for 39.51% (n = 32) and CSAB accounted for 60.49% (n = 49). The two also showed marked disparities in their distribution across medical institutes, departments, and objects (Table 1). With regard to institutional distribution, Hospital H recorded the highest proportion of CRAB isolates at 21.88%, whereas Hospitals I and J shared the highest proportion of CSAB isolates at 16.33% each. Among A. baumannii strains in Hospital C, CRAB isolates accounted for more than 85%, while no CRAB was detected in Hospitals A and B (Figure 1C). For departmental distribution, CRAB isolates were predominantly present in ICUs (46.88%), while CSAB isolates were relatively evenly distributed in other departments such as Internal Medicine. A key finding was that among all A. baumannii strains in ICU environments, CRAB accounted for as high as 83.33%, which was significantly higher than CSAB (16.67%). In other departments such as Surgery, CSAB was more numerous than CRAB (Figure 1D). In terms of objects, CRAB isolates were concentrated in items directly contacted by patients, while CSAB was primarily found on shared items, etc. The proportion of CRAB isolates in diagnostic-therapeutic items and items directly contacted by patients was significantly higher than that of CSAB. Most A. baumannii strains detected in hands/nasal cavities of medical staff and items directly contacted by medical staff were CSAB (Figure 1E).

Table 1.

Multidimensional distribution of CRAB and CSAB in the medical institutions environment.

Items Number (%) X2 P value
CRAB (n = 32) CSAB (n = 49)
Hospital A 0 (0.00) 4 (8.16) 18.435 0.030*
B 0 (0.00) 6 (12.24)
C 6 (18.75) 1 (2.04)
D 1 (3.13) 5 (10.20)
E 2 (6.25) 4 (8.16)
F 4 (12.50) 6 (12.24)
G 2 (6.25) 4 (8.16)
H 7 (21.88) 3 (6.12)
I 6 (18.75) 8 (16.33)
J 4 (12.50) 8 (16.33)
Department ICU 15 (46.88) 3 (6.12) 19.336 0.001*
Internal Medicine 7 (21.88) 15 (30.61)
Surgery 1 (3.13) 6 (12.24)
General Practice Ward 4 (12.50) 10 (20.41)
Other departments 5 (15.63) 15 (30.61)
Object Items directly contacted by patients 10 (31.25) 8 (16.33) 10.276 0.068
Diagnostic-therapeutic items 9 (28.13) 5 (10.20)
Shared items 7 (21.88) 15 (30.61)
Hands and nasal cavities of medical staff 3 (9.38) 13 (26.53)
Sanitation supplies 2 (6.25) 3 (6.12)
Items directly contacted by medical staff 1 (3.13) 5 (10.20)
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*Bold value, P < 0.05. ICU, intensive care unit.

3.2. MLST typing of Acinetobacter baumannii

The Pasteur and Oxford schemes were used to analyze the MLST of the whole-genome sequences of 81 A. baumannii strains. Typing results based on the Pasteur scheme showed that the 81 A. baumannii strains were assigned to 32 distinct sequence types (STs). The 32 CRAB strains fell into only 3 types, with the ST2 clone accounting for the highest proportion (78.13%), consistent with the dominant clone type worldwide. Six strains (18.75%) belonged to ST164, and only 1 strain was classified as ST412. Compared with CRAB, CSAB exhibited a substantially broader ST distribution, encompassing a total of 29 distinct STs. ST132 was the most prevalent type, accounting for 12.24% of all CSAB strains (Figure 2A).

Figure 2.

Two network diagrams labeled A and B show circles of varying sizes connected by lines with numbers indicating relationships. Green circles labeled CSAB and orange circles labeled CRAB represent different types, with a legend in the top center of each diagram. Circle size corresponds to the number of items in each type, and some circles are labeled “untyped.”.

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MLST typing of A. baumannii isolates. (A) Minimum Spanning Tree of CRAB and CSAB based on Pasteur MLST Scheme; MLST types are labeled inside circles; circle size corresponds to the number of isolates for each MLST type, with larger circles indicating higher counts. (B) Minimum Spanning Tree of CRAB and CSAB based on Oxford MLST Scheme; MLST types are labeled inside circles; circle size corresponds to the number of isolates for each MLST type, with larger circles indicating higher counts.

Based on the Oxford scheme, typing results showed that the 81 A. baumannii strains belonged to 37 STs. There were no overlapping types between CRAB and CSAB. CRAB isolates were restricted to 7 of these types, with ST540 and ST369 as the dominant types, accounting for 28.13% and 25.00% respectively. Nodes such as ST540, ST369, ST195, ST1791, and ST136 on the right were closely connected. ST1418 and ST3609 were positioned on distinct distantly related clades. Similar to the Pasteur typing results, CSAB covered multiple genetic branches of the MST with scattered STs, indicating high genetic diversity (Figure 2B).

3.3. Clustering analysis of Acinetobacter baumannii

To characterize the genomic profiles of the 32 CRAB isolates collected in this study within local and global phylogenetic contexts, a total of 46 publicly available whole-genome sequences of A. baumannii recovered from 19 countries were incorporated for comparative analysis. Phylogenetic reconstruction of the combined dataset consisting of 78 A. baumannii genomes resolved four different clades (Clade IV designated as the reference group). Lineage I constituted the largest clade, all isolates of which belonged to ST2. This lineage encompassed strains isolated from 8 medical institutions, 5 departments, and 6 categories of object surfaces in the local region. Notably, isolate CRAB-21 recovered from healthcare workers in Hospital I exhibited close phylogenetic relatedness to CRAB-22 cultured from diagnostic-therapeutic items of the same hospital, with only a single SNP distinguishing their core genomes. A comparable pattern was observed in Hospital H: CRAB-14 derived from medical staff shared merely 0~6 core-genome SNPs with five environmental CRAB isolates (CRAB-09 to CRAB-13) collected from the same facility. Moreover, local strains within Clade I displayed tight genetic relatedness to isolates retrieved from the USA, as well as domestic strains from Guangdong and Zhejiang Provinces of China (Figure 3; Supplementary Table 2).

Figure 3.

Phylogenetic tree diagram showing relationships among bacterial isolates, with columns visualizing metadata including clade, sequence type, hospital, department, object, country, and province. Color-coded legends for each attribute and bootstrap values are provided for interpretation.

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Phylogeny tree of A. baumannii isolates from 19 countries. Strains in bold represent the 32 CRAB isolates in this study, and the remaining strains were retrieved from public databases. The strain labeled “Reference” is the reference strain ATCC 19606. Circles indicate the bootstrap support values of each phylogenetic clade, with darker red corresponding to higher support values.

Clade III contained 26 A. baumannii isolates originating from 11 countries, all of which were assigned to ST164. Phylogenetic analysis revealed that the six ST164-type CRAB isolates recovered in the present study shared extremely close genetic relatedness. These strains also exhibited tight phylogenetic clustering with isolates from Jiangsu, Zhejiang and Jiangxi Provinces in China, with core-genome SNP differences ranging from 24 to 54. In contrast, they were genetically distant from strains isolated from the USA, Thailand and other foreign regions (Figure 3; Supplementary Table 2).

3.4. Antimicrobial resistance of Acinetobacter baumannii

The drug resistance results showed that in addition to being fully resistant to carbapenem antibiotics, the 32 CRAB strains were also 100% resistant to piperacillin/tazobactam, cefotaxime, ceftazidime, and ciprofloxacin. Meanwhile, CRAB strains also showed varying degrees of resistance to ampicillin/sulbactam, cefoperazone/sulbactam, cefepime, minocycline, gentamicin, amikacin, srimethoprim/sulfamethoxazole, and levofloxacin (Figure 4). However, CSAB strains were almost fully sensitive to the above antibiotics (only one isolate exhibited resistance to ampicillin/sulbactam). These results confirmed the significant difference in drug resistance profiles between CRAB and CSAB strains, and the potential hazard of CRAB’s multidrug resistance (Table 2). Importantly, no A. baumannii strains resistant to tigecycline or polymyxin B were found in this study.

Figure 4.

Bar and line chart showing resistance rates in percentage of a microorganism to various antibiotics. Resistance is highest for most drugs except tigecycline, minocycline, and polymyxin B, which show low resistance.

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Antimicrobial resistance phenotypes of A. baumannii isolates. The bar chart shows the resistance rates of 32 CRAB strains against 16 antimicrobial agents.

Table 2.

Antimicrobial resistance of CRAB and CSAB to various antimicrobial agents.

Antimicrobial family Antimicrobial agents Number of resistant isolates (%) X2 P value
CRAB (n = 32) CSAB (n = 49)
Penicillins Piperacillin/tazobactam 32 (100.00) 0 (0.00) 81.000 <0.001*
Ampicillin/sulbactam 28 (87.50) 1 (2.04) 61.510 <0.001*
Cephalosporins Cefoperazone/sulbactam 13 (40.63) 0 (0.00) 23.712 <0.001*
Cefotaxime 32 (100.00) 0 (0.00) 81.000 <0.001*
Ceftazidime 32 (100.00) 0 (0.00) 81.000 <0.001*
Cefepime 24 (75.00) 0 (0.00) 52.224 <0.001*
Carbapenems Imipenem 32 (100.00) 0 (0.00) 81.000 <0.001*
Meropenem 32 (100.00) 0 (0.00) 81.000 <0.001*
Tetracyclines Minocycline 3 (9.38) 0 (0.00) / 0.058
Tigecycline 0 (0.00) 0 (0.00) – –
Aminoglycosides Gentamicin 25 (78.13) 0 (0.00) 55.371 <0.001*
Amikacin 24 (75.00) 0 (0.00) 52.224 <0.001*
Sulfonamides Trimethoprim/
sulfamethoxazole		 18 (56.25) 0 (0.00) 35.438 <0.001*
Polymyxins Polymyxin B 0 (0.00) 0 (0.00) – –
Quinolones Ciprofloxacin 32 (100.00) 0 (0.00) 81.000 <0.001*
Levofloxacin 20 (62.50) 0 (0.00) 40.666 <0.001*
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/, Fisher’s exact test (no X2 value); -, no comparison for identical resistance rates; *Bold value, P < 0.05.

To further elucidate the molecular mechanisms underlying antimicrobial resistance in A. baumannii, the carriage of resistance genes was characterized. As shown in Figure 5A and Supplementary Table 3, a total of 62 types of resistance genes were identified in the 81 A. baumannii isolates. The average number of resistance genes carried by CRAB isolates was significantly higher than that of CSAB (P < 0.05) (Figure 5B). Meanwhile, evident differences were observed in the composition of both acquired resistance genes and intrinsic determinants between the two groups. The carriage rates of the acquired carbapenem resistance genes blaOXA-23 reached 96.88% in CRAB isolates. Combined with MLST analysis, CRAB isolates belonging to ST2 simultaneously possessed blaOXA-23 and its corresponding lineage-specific intrinsic oxacillinase gene, blaOXA-66. Critically, six CRAB strains co-carrying blaOXA-23, the acquired carbapenemases blaNDM-1 and the intrinsic blaOXA-91 gene all belonged to ST164. CRAB isolates also harbored a variety of acquired resistance genes related to aminoglycoside, tetracycline, macrolide, and sulfonamide antibiotics, with carriage rates of APH(3’’)-Ib (78.13%), APH(6)-Id (78.13%), armA (53.13%), APH(3’)-Ia (40.63%), mphE (46.88%), msrE (46.88%), tet(B) (75%), and sul2 (31.25%) respectively. Instead, CSAB isolates lacked all the aforementioned genes. In addition to the universally shared efflux pump genes (abeM, amvA, and adeF), CSAB isolates specifically presented with the intrinsic resistance determinants blaOXA-120 and blaADC-2.

Figure 5.

Panel A shows a heatmap with dendrogram clustering, displaying the presence or absence of resistance genes across CRAB and CSAB isolates, with sample and resistance gene identifiers labeled along axes. Panel B presents a violin plot comparing the number of resistance genes between CRAB and CSAB groups, demonstrating significantly higher gene counts in CRAB isolates.

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Distribution of resistance genes in A. baumannii isolates. (A) The clustered heatmap shows the carriage of resistance genes in CRAB and CSAB isolates. Orange squares indicate the presence of resistance genes, while green squares indicate their absence; (B) The violin plot compares the average number of resistance genes carried by CRAB and CSAB isolates. ****P < 0.0001.

A concordance analysis between resistance phenotypes and genotypes was performed for the 81 A. baumannii isolates. The drug classes included in this analysis were β-lactams, tetracyclines, aminoglycosides, and sulfonamides. The kappa coefficients for blaOXA-23 with piperacillin/tazobactam, ampicillin/sulbactam, cefotaxime, ceftazidime, cefepime, imipenem, and meropenem were all greater than 0.8, demonstrating near-perfect agreement. APH(3’)-Ia and armA with aminoglycosides, and sul2 with trimethoprim/sulfamethoxazole showed substantial agreement, with kappa coefficients ranging between 0.6 and 0.8. In contrast, poor concordance was observed between tet(B) and minocycline, yielding a kappa coefficient below 0.2 (Supplementary Table 4).

3.5. Plasmid prediction of Acinetobacter baumannii

The study further characterized the carriage of key plasmids across all A. baumannii isolates via bioinformatic analysis. In silico prediction showed that the number of plasmids carrying resistance genes in CRAB was significantly higher than that in CSAB (P < 0.05) (Figure 6A), with marked differences in plasmid profiles between the two groups. Among the plasmids in CRAB, 75.30% were putatively non-mobile plasmids, 22.20% were putatively conjugative plasmids, and 2.50% were classified as mobilizable plasmids, while all CSAB plasmids were predicted non-mobilizable (Figure 6B). The carriage of resistance genes in CRAB plasmids was inferred via bioinformatic tools. Prediction results indicated that blaOXA-23 gene was likely located on conjugative or mobilizable plasmids in 68.00% (17/25) of strains within Clade I. In contrast, blaNDM-1 gene carried by all ST164-type strains may reside on non-mobile plasmids. Notably, the study also found that the plasmid of CRAB-08 was predicted to simultaneously carried the sulfonamide resistance gene sul1 and the quaternary ammonium compound disinfectant resistance gene qacEdelta1, both of which were putatively located on conjugative plasmids (Figure 6C).

Figure 6.

Panel A shows a violin plot comparing the number of resistance plasmids in CRAB (n equals thirty-two) and CSAB (n equals fifty-nine) groups, with CRAB having significantly more. Panel B presents two donut charts comparing the mobility types of resistance plasmids, showing all CSAB plasmids as non-mobilizable, while CRAB plasmids include non-mobilizable, mobilizable, and conjugative types with respective percentages labeled. Panel C displays a circular phylogenetic tree of CRAB strains labeled by clade and annotated with colored outer rings denoting plasmid cluster ID, replication type, plasmid mobility, and resistance genes, with a corresponding legend.

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Plasmid prediction in A. baumannii isolates. (A) The violin plot compares the average number of predicted plasmids carrying resistance genes between CRAB and CSAB, **P < 0.01; (B) The two donut charts separately show the proportions of resistance gene-carrying plasmids with distinct mobility features in CSAB (left) and CRAB (right) isolates based on bioinformatic analyses; (C) The phylogenetic tree illustrates some of predicted plasmids and matching antimicrobial resistance gene profiles identified in 32 CRAB isolates. The annotations are (from inner to outer ring): Plasmid cluster ID, Rep_type, Predicted_mobility and Resistance gene of CRAB isolates. Clades I–III are distinguished by branches in distinct colors. Circles indicate the bootstrap support values of each phylogenetic clade, with darker red corresponding to higher support values.

3.6. Virulence genes in Acinetobacter baumannii

The virulence genes of CRAB and CSAB that exert virulence through different mechanisms were characterized. The results showed that the average number of virulence genes carried by CRAB was significantly greater than that by CSAB, with an average of 116 and 96, respectively (Figure 7A). Comparing virulence genes involved in various biological functions, the carriage rates of genes related to iron uptake (bauA), biofilm formation (csu operon, abaI/R system), secretion system (tssA/B), and adhesion (pilA) in CRAB were all significantly higher than those in CSAB (P < 0.05) (Table 3 and Figure 7).

Figure 7.

Violin plot on the left compares the number of virulence genes in CRAB (carbapenem-resistant) versus CSAB (carbapenem-susceptible) bacterial isolates, showing a significantly higher median in CRAB. Heatmap on the right displays the presence (orange) or absence (white) of specific virulence genes across individual CRAB and CSAB isolates, with genes and sample names labeled on axes, and a legend explaining color coding by type and gene presence.

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Distribution of virulence genes in A. baumannii isolates. (A) The violin plot compares the average number of virulence genes carried by CRAB and CSAB isolates. ****P < 0.0001 (B) The clustered heatmap shows the carriage of virulence genes in CRAB and CSAB isolates. Orange squares indicate the presence of virulence genes, while white squares indicate their absence.

Table 3.

Virulence gene carriage and functional classification of CRAB and CSAB.

Function Virulence genes Number of strains carrying virulence genes (%) X2 P value
CRAB (n = 32) CSAB (n = 49)
Iron uptake hemO 23 (71.88) 25 (51.02) 3.487 0.062
bauA 25 (78.13) 0 (0.00) 55.371 <0.001*
bauB, bauC, bauD, bauE 32 (100.00) 49 (100.00) – –
Biofilm formation abaI 32 (100.00) 29 (59.18) 17.344 <0.001*
bfmR, bfmS 32 (100.00) 49 (100.00) – –
csuA 32 (100.00) 40 (81.63) / 0.010*
csuA/B 32 (100.00) 36 (73.47) 10.113 0.001*
csuB 32 (100.00) 37 (75.51) / 0.002*
csuC 32 (100.00) 45 (91.84) / 0.149
csuD 32 (100.00) 43 (87.76) / 0.076
csuE 32 (100.00) 44 (89.80) / 0.151
abaR 32 (100.00) 12 (24.49) 44.482 <0.001*
Immune evasion ACICU_RS00395 26 (81.25) 11 (22.45) 26.974 <0.001*
ACICU_RS00400 26 (81.25) 11 (22.45) 26.974 <0.001*
ACICU_RS00405 26 (81.25) 11 (22.45) 26.974 <0.001*
ACICU_RS00445 1 (3.13) 2 (4.08) / 1.000
ACICU_RS00450 1 (3.13) 3 (6.12) / 1.000
Secretion System tssA 26 (81.25) 4 (8.16) 44.342 <0.001*
tssB 25 (78.13) 2 (4.08) 47.758 <0.001*
tagX 25 (78.13) 5 (10.20) 38.295 <0.001*
Adherence pilA 26 (81.25) 4 (8.16) 44.342 <0.001*
Open in a new tab

/, Fisher’s exact test (no X2 value); -, no comparison for identical carriage rates; *Bold value, P < 0.05.

4. Discussion

Since the discovery of A. baumannii, its detection rate in medical institutions has been increasing. Coupled with its significant resistance to multiple antibiotics, this bacterium has gradually evolved into an important pathogen threatening public health security (Sharma and LakhanpalAcinetobacter, 2025). As a key representative of carbapenem-resistant bacteria, CRAB strains poses an urgent global public health challenge, with its transmission being particularly prominent in medical institutions (Liu H. et al., 2024; Karakonstantis et al., 2025). CRAB strains exhibit high prevalence in nosocomial infections, attributed to its strong environmental adaptability—it can colonize various medical supplies and survive on dry surfaces for months, and a prior CRAB colonization history increases the subsequent infection risk by 8-fold (Medioli et al., 2022). Of note, CRAB strains infection leads to more severe clinical outcomes compared with CSAB strains. Thus, clarifying the distribution, drug resistance characteristics, and transmission patterns of CRAB and CSAB isolates in medical institutions is essential to guide the prevention and control of A. baumannii, especially CRAB isolates. This study systematically analyzed the distribution, ST molecular typing, drug resistance profile, plasmid carriage, and virulence gene characteristics of CRAB and CSAB strains in 10 medical institutions in Pudong New Area, providing targeted scientific evidence for healthcare-associated infection control in this region.

This study demonstrated significant differences in the distribution of CRAB and CSAB strains across medical institutions, departments, and sampling objects. CRAB isolates were highly concentrated in ICU, predominantly isolated from patient-direct contact items and diagnostic-therapeutic equipment. In contrast, CSAB isolates were evenly distributed in other departments, with shared items and medical staff’s hands/nasal cavities serving as the main reservoirs. These findings confirm that the ICU is a high-risk area for CRAB isolates colonization, and patient-direct contact items are likely core vehicles for the spread of environmental CRAB (Ng et al., 2018; Doughty et al., 2023; Liu L. et al., 2024; Wang B. et al., 2025). As a specialized unit for critically ill patients, ICUs feature immunocompromised individuals, frequent invasive procedures, and high-intensity antimicrobial use—collectively fostering a microenvironment conducive to CRAB strains colonization and persistence. Furthermore, the detection rates of CRAB isolates varied significantly among different hospitals, which may be closely related to disinfection methods, implementation intensity of infection control measures, and management level of antimicrobial use in each hospital. Additionally, A. baumannii detection rates were relatively high on surfaces of faucets, pillows, and bedding-items with high-frequency contact and easy neglect in cleaning/disinfection—further verifying that hospital environmental surfaces serve as key A. baumannii reservoirs. Based on these differences, targeted prevention and control strategies were warranted: (1) Conduct intensive disinfection for ICUs and patient-contact items; (2) Optimize infection control procedures in hospitals with high CRAB detection rates; (3) Improve hand hygiene training for medical staff to reduce the circulation of CSAB and remain alert to potential dissemination of CRAB between humans and environmental surfaces.

ST2 CRAB strains have been well-documented as the predominant clonal lineage driving global CRAB infection outbreaks, largely due to its robust environmental adaptability and enhanced resistance gene-carrying capacity (Nawfal Dagher et al., 2019; Yu et al., 2021; Brek et al., 2025; Zhang et al., 2025). In this study, CRAB isolates were restricted to 3 STs, with ST2 accounting for 78.13%, which is consistent with the globally dominant CRAB epidemic clone (Valcek et al., 2022; Mat Ghani et al., 2025). Phylogenetic analysis revealed that ST2 strains from 8 hospitals and 5 departments belonged to the same evolutionary clade. This high genetic relatedness suggests the possibility of inter-hospital and intra-hospital clonal dissemination of CRAB strains, whereas definitive transmission chains need further analysis combined with epidemiological data. It is noteworthy that CRAB isolates detected from medical staff’s hands/nasal cavities shared close genetic proximity with strains from items directly contacted by patients and diagnostic-therapeutic items. This evolutionary characteristic implies the potential transmission routes of CRAB between healthcare personnel and the medical environment, underscoring the previous conclusion that “hand hygiene is a crucial measure to interrupt the potential nosocomial transmission of A. baumannii.” (Garnacho-Montero et al., 2015; Weinberg et al., 2020). In addition, the phylogenetic tree integrated with public database genomes displayed that the local ST2 strains showed low core-genome SNP distances to domestic isolates from high-prevalence provinces (Guangdong and Zhejiang) and tight genomic clustering with the USA isolates, which may imply the potential transregional mobility of ST2. Intriguingly, although the ST164-type CRAB isolates co-harboring two carbapenemase genes in this study exhibited substantial genetic differentiation from overseas strains, they shared high genetic relatedness with isolates from neighboring provinces. This reminds us that routine surveillance should not only guard against the persistent threat of international clones like ST2, but also continuously monitor ST164 clones with significant resistance potential to prevent their dissemination.

Antimicrobial susceptibility testing showed typical multidrug resistance in CRAB strains, whereas CSAB strains were sensitive to most tested antibiotics. This disparity appeared to be closely associated with the distinct resistance gene patterns. In this study, the carriage rate of the acquired carbapenemase blaOXA-23 in CRAB was as high as 96.88%, which is the core gene mediating A. baumannii resistance to carbapenem antibiotics (Sharma et al., 2022; Ababneh et al., 2025; Mat Ghani et al., 2025). The β-lactamase encoded by blaOXA-23 can effectively hydrolyze carbapenem antibiotics, which is the main molecular mechanism for the prevalence of CRAB strains (Liu et al., 2022). More alarmingly, as mentioned above, six ST164 CRAB strains simultaneously harboring blaOXA-23, blaNDM-1 and the chromosome-encoded intrinsic oxacillinase blaOXA-91.While blaOXA-91 represents an intrinsic background marker for ST164, the horizontal co-acquisition of the exogenous class D (blaOXA-23) and class B (blaNDM-1) carbapenemases amplifies the resistance potential. Liu et al. reported that ST164 isolates had higher MIC50/MIC90 values for carbapenem antibiotics than global clone 2. A comparison of genomes from 26 countries revealed that ST164 has independently evolved carbapenem resistance multiple times (Liu H. et al., 2024). In addition, a study by Wang et al. demonstrated that ST164 CRAB isolates exhibited a significantly stronger biofilm-forming capacity in vitro than ST2 isolates (Wang et al., 2026). Existing research also revealed that ST164 strains produce pyomelanin to achieve substantially elevated survival under UV irradiation (Zhao et al., 2022). Collectively, these studies provide stronger evidence that CRAB strains belonging to ST164 represent a clone with potential risks, warranting global attention and focused surveillance (Liu H. et al., 2024; Wang K. et al., 2025). No A. baumannii strains resistant to tigecycline or polymyxin B were found, and this near-zero resistance conclusion is consistent with the research results of Hou, Hu, and others (Hu et al., 2024; Chen et al., 2025; Hou et al., 2025). Tigecycline and polymyxin B remain important clinical drugs for the treatment of CRAB strains infections, providing certain guarantees for the selection of clinical treatment regimens. Nevertheless, vigilance is required to monitor the emergence of resistance driven by the long-term clinical use of these agents.

As pivotal carriers mediating horizontal transfer of resistance genes, plasmids directly affect the transmission risk of drug-resistant bacteria (Acman et al., 2022; Kilbas et al., 2023). Theoretically, conjugative plasmids achieve horizontal transfer through direct bacteria-to-bacteria contact, serving as a key vehicle for the rapid dissemination of resistance genes. This notion aligns with the view proposed by Ying et al. that. “horizontal transmission of the blaOXA-23 gene is an important driver of CRAB nosocomial epidemics” (Liu et al., 2015; Ying et al., 2025). Our bioinformatic analyses also suggested that nearly 70.00% of CRAB strains harbored the blaOXA-23 gene on predicted conjugative or mobilizable plasmids, which raised the possibility of horizontal spread of this gene via mobile genetic elements. Furthermore, a unique feature was identified in strain CRAB-08: its putatively conjugative plasmid likely co-carries the sulfonamide resistance gene sul1 and the quaternary ammonium compound disinfectant resistance gene qacEdelta1. This genomic feature predicts the potential for both “therapeutic resistance” and “environmental tolerance” capabilities in this strain. Quaternary ammonium compound disinfectants were widely used in hospital environmental disinfection. Carriage of the qacEdelta1 gene may potentially reduce the bactericidal efficacy of disinfectants against A. baumannii, thereby enhancing its colonization and transmission probability within healthcare settings. Naturally, further phenotypic assays targeting disinfectant resistance are required to verify this speculation. Nevertheless, this finding still reminds us that long-term exclusive use of a certain type of disinfectant may induce selective pressure on drug-resistant strains, highlighting the need to optimize hospital disinfection protocols to avoid the development of disinfectant resistance.

This study has several limitations that should be acknowledged. First, the sample collection period was relatively short, resulting in a relatively small number of strains. Second, no clinical infection case data were integrated, making it impossible to clarify the direct association between the characteristics of environmental CRAB and CSAB and clinical infections. Third, epidemiological information regarding patient movement and layout was unavailable, preventing further verification of the speculated transmission chains. Fourth, no assays including gene expression quantification, biofilm formation detection, animal infection models or other virulence phenotypic validations were performed in this study, so present results only demonstrated differences in the carriage abundance of virulence-associated genes among isolates.

5. Conclusions

In summary, this study systematically clarified the significant differences between CRAB and CSAB strains in healthcare institution environments across multiple dimensions. ICU environments and items directly contacted by patients were identified as key high-risk links for CRAB prevention and control. ST2 and ST164 were the clones of CRAB isolates that deserve the greatest attention. CRAB strains exhibited stronger multidrug-resistant phenotypes compared to CSAB strains. Bioinformatic evidence suggested the co-occurrence of antimicrobial-resistance and disinfectant-resistance-associated genes in some CRAB isolates, which may increase their persistence and dissemination potential. In conclusion, it’s critical for blocking the potential transmission routes of drug-resistant A. baumannii to strengthen the disinfection and management of high-frequency contact surfaces in hospitals and conduct precise monitoring of dominant clones.

Funding Statement

The author(s) declared that financial support was received for this work and/or its publication. This work was supported by The Young Medical Talents Training Program of Shanghai Pudong New Area Health Commission (PWRq2026-10); The Medical Discipline Construction Program of Shanghai Pudong New Area Health Commission (the Public Health Disciplines Program) (PWGw2025-05); The Young Medical Talents Training Program of Shanghai Pudong New Area Health Commission (PWRq2025-03); Pudong New Area Science and Technology Development Innovation fund (grant no: PKJ2024-Y78).

Footnotes

Edited by: Nasib Singh, Eternal University, India

Reviewed by: Humberto Barrios Camacho, National Institute of Public Health (Mexico), Mexico

Dong Chan Moon, Korea National Institute of Health, Republic of Korea

Data availability statement

The datasets presented in this study can be found in online repositories. The names of the repository/repositories and accession number(s) can be found below: https://www.ncbi.nlm.nih.gov/, PRJNA1390075.

Ethics statement

The studies involving humans were approved by Medical Ethics Committee of Shanghai Pudong New Area Center for Disease Control and Prevention. The studies were conducted in accordance with the local legislation and institutional requirements. The ethics committee/institutional review board waived the requirement of written informed consent for participation from the participants or the participants’ legal guardians/next of kin because The studies involved in this research were approved by the Ethics Committee of Shanghai Pudong New Area Center for Disease Control and Prevention (Shanghai Pudong New Area Health Supervision Institute). The studies were conducted in accordance with local legislation and institutional requirements. The ethics committee/institutional review board waived the requirement of written informed consent for participation from the participants or their legal guardians/next of kin because no additional samples were collected specifically for this study. Only residual specimens preserved from routine surveillance were utilized. Therefore, individual informed consent was not sought, and the informed consent waiver was formally approved by the Ethics Committee of Shanghai Pudong New Area Center for Disease Control and Prevention (Shanghai Pudong New Area Health Supervision Institute).

Author contributions

YZ: Conceptualization, Investigation, Visualization, Writing – original draft, Writing – review & editing. YL: Investigation, Software, Writing – original draft. YW: Investigation, Visualization, Writing – review & editing. YX: Supervision, Writing – original draft. YQ: Software, Writing – review & editing. BZ: Supervision, Writing – review & editing. YS: Conceptualization, Writing – review & editing. XW: Conceptualization, Writing – original draft.

Conflict of interest

The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Generative AI statement

The author(s) declared that generative AI was not used in the creation of this manuscript.

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Supplementary material

The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fcimb.2026.1878371/full#supplementary-material

Table1.xlsx (10.3KB, xlsx)
Table2.xlsx (44.2KB, xlsx)
Table3.xlsx (28.4KB, xlsx)
Table4.xlsx (11.5KB, xlsx)

References

  1. Ababneh Q., Aldaken N., Jaradat Z., Al-Rousan E., Inaya Z., Alsaleh D., et al. (2025). Predominance of extensively-drug resistant Acinetobacter baumannii carrying bla OXA-23 in Jordanian patients admitted to the intensive care units. PloS One 20, e0317798. doi:  10.1371/journal.pone.0317798 [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Ababneh Q., Aldaken N., Jaradat Z., Al Sbei S., Alawneh D., Al-Zoubi E., et al. (2021). Molecular epidemiology of carbapenem-resistant Acinetobacter baumannii isolated from three major hospitals in Jordan. Int. J. Clin. Pract. 75, e14998. doi:  10.1111/ijcp.14998 [DOI] [PubMed] [Google Scholar]
  3. Acman M., Wang R., van Dorp L., Shaw L. P., Wang Q., Luhmann N., et al. (2022). Role of mobile genetic elements in the global dissemination of the carbapenem resistance gene bla(NDM). Nat. Commun. 13, 1131. doi:  10.1038/s41467-022-28819-2 [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Brek T. M., Muhajir A. A., Alkuwaity K. K., Haddad M. A., Alattas E. M., Eisa Z. M., et al. (2025). Genomic insights of predominant international high-risk clone ST2 Acinetobacter baumannii isolates in Saudi Arabia. J. Glob. Antimicrob. Resist. 42, 243–252. doi:  10.1016/j.jgar.2025.03.012 [DOI] [PubMed] [Google Scholar]
  5. Chen X., Tu Y., Wang F., Li H., Zhao Y., Jiang M., et al. (2025). Molecular characterization of carbapenem-resistant and carbapenem-sensitive Acinetobacter baumannii isolates from an intensive care unit in Ningbo, China. Front. Microbiol. 16, 1646319. doi:  10.3389/fmicb.2025.1646319 [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. Doughty E. L., Liu H., Moran R. A., Hua X., Ba X., Guo F., et al. (2023). Endemicity and diversification of carbapenem-resistant Acinetobacter baumannii in an intensive care unit. Lancet Reg Health West Pac 37, 100780. doi:  10.1016/j.lanwpc.2023.100780 [DOI] [PMC free article] [PubMed] [Google Scholar]
  7. Garnacho-Montero J., Dimopoulos G., Poulakou G., Akova M., Cisneros J. M., De Waele J., et al. (2015). Task force on management and prevention of Acinetobacter baumannii infections in the ICU. Intensive Care Med. 41, 2057–2075. doi:  10.1007/s00134-015-4079-4 [DOI] [PubMed] [Google Scholar]
  8. Hassan R. M., Salem S. T., Hassan S. I. M., Hegab A. S., Elkholy Y. S. (2021). Molecular characterization of carbapenem-resistant Acinetobacter baumannii clinical isolates from Egyptian patients. PloS One 16, e0251508. doi:  10.21203/rs.3.rs-123397/v1 [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Hou B., Niu X., Yu Q., Wang W. (2025). Epidemiological trends and drug resistance patterns of carbapenem-resistant gram-negative bacteria: a retrospective study in a tertiary hospital in China (2019-2024). Infect. Drug Resist. 18, 2867–2880. doi:  10.2147/idr.s518461 [DOI] [PMC free article] [PubMed] [Google Scholar]
  10. Hu M., Sun H., Xu Y., Xu X. (2024). Antimicrobial susceptibility and genetic characteristics of multi-drug resistant Acinetobacter baumannii isolates in Northwest China. Front. Microbiol. 15, 1293725. doi:  10.3389/fmicb.2024.1293725 [DOI] [PMC free article] [PubMed] [Google Scholar]
  11. Karakonstantis S., Kritsotakis E. I., Tziolos R. N., Vassilopoulou L., Loukaki M., Kypraiou D., et al. (2025). Mortality due to carbapenem-resistant Acinetobacter baumannii bacteraemia: a 5-year cohort study in intensive care patients. Clin. Microbiol. Infect. 31, 1033–1039. doi:  10.1016/j.cmi.2025.02.018 [DOI] [PubMed] [Google Scholar]
  12. Kilbas E. P. K., Kilbas I., CiftciMolecular I. H. (2023). Molecular epidemiology of carbapenem-resistant Acinetobacter baumannii isolates in Turkiye: systematic review. North Clin. Istanb 10, 531–539. doi:  10.14744/nci.2022.17003 [DOI] [PMC free article] [PubMed] [Google Scholar]
  13. Kubin C. J., Garzia C., UhlemannAcinetobacter A. C. (2025). Acinetobacter baumannii treatment strategies: a review of therapeutic challenges and considerations. Antimicrob. Agents Chemother. 69, e0106324. doi:  10.1128/aac.01063-24 [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. Liu C., Chen K., Wu Y., Huang L., Fang Y., Lu J., et al. (2022). Epidemiological and genetic characteristics of clinical carbapenem-resistant Acinetobacter baumannii strains collected countrywide from hospital intensive care units (ICUs) in China. Emerg. Microbes Infect. 11, 1730–1741. doi:  10.1080/22221751.2022.2093134 [DOI] [PMC free article] [PubMed] [Google Scholar]
  15. Liu L., Huang Y., Wang Y., Jiang Y., Liu K., Pei Z., et al. (2024). Molecular epidemiology and genetic characterization of carbapenem-resistant Acinetobacter baumannii isolates from the ICU of a tertiary hospital in East China. Infect. Drug Resist. 17, 5925–5945. doi:  10.2147/idr.s491858 [DOI] [PMC free article] [PubMed] [Google Scholar]
  16. Liu L. L., Ji S. J., Ruan Z., Fu Y., Fu Y. Q., Wang Y. F., et al. (2015). Dissemination of blaOXA-23 in Acinetobacter spp. in China: main roles of conjugative plasmid pAZJ221 and transposon Tn2009. Antimicrob. Agents Chemother. 59, 1998–2005. doi:  10.1128/aac.04574-14 [DOI] [PMC free article] [PubMed] [Google Scholar]
  17. Liu H., Moran R. A., Doughty E. L., Hua X., Snaith A. E., Zhang L., et al. (2024). Longitudinal genomics reveals carbapenem-resistant Acinetobacter baumannii population changes with emergence of highly resistant ST164 clone. Nat. Commun. 15, 9483. doi:  10.1038/s41467-024-53817-x [DOI] [PMC free article] [PubMed] [Google Scholar]
  18. Mat Ghani N., Hong K. W., Liew Y. J. M., Lau Y. Y., Yong H. S., Tee K. K., et al. (2025). Whole genome analysis revealed the role of bla(OXA-23) and bla(OXA-66) genes in carbapenem resistance of Acinetobacter baumannii strains. Pathog. Glob. Health 119, 10–21. doi:  10.1080/20477724.2024.2442194 [DOI] [PMC free article] [PubMed] [Google Scholar]
  19. Medioli F., Bacca E., Faltoni M., Burastero G. J., Volpi S., Menozzi M., et al. (2022). Is it possible to eradicate carbapenem-resistant Acinetobacter baumannii (CRAB) from endemic hospitals? Antibiotics (Basel) 11, 1015. doi:  10.3390/antibiotics11081015 [DOI] [PMC free article] [PubMed] [Google Scholar]
  20. Müller C., Reuter S., Wille J., Xanthopoulou K., Stefanik D., Grundmann H., et al. (2023). A global view on carbapenem-resistant Acinetobacter baumannii. mBio 14, e0226023. doi:  10.1128/mbio.02260-23 [DOI] [PMC free article] [PubMed] [Google Scholar]
  21. Nawfal Dagher T., Al-Bayssari C., Chabou S., Antar N., Diene S. M., Azar E., et al. (2019). Investigation of multidrug-resistant ST2 Acinetobacter baumannii isolated from Saint George hospital in Lebanon. BMC Microbiol. 19, 29. doi:  10.1186/s12866-019-1401-2 [DOI] [PMC free article] [PubMed] [Google Scholar]
  22. Ng D. H. L., Marimuthu K., Lee J. J., Khong W. X., Ng O. T., Zhang W., et al. (2018). Environmental colonization and onward clonal transmission of carbapenem-resistant Acinetobacter baumannii (CRAB) in a medical intensive care unit: the case for environmental hygiene. Antimicrob. Resist. Infect. Ctrl 7, 51. doi:  10.1186/s13756-018-0343-z [DOI] [PMC free article] [PubMed] [Google Scholar]
  23. Pogue J. M., Zhou Y., Kanakamedala H., Cai B. (2022). Burden of illness in carbapenem-resistant Acinetobacter baumannii infections in US hospitals between 2014 and 2019. BMC Infect. Dis. 22, 36. doi:  10.1186/s12879-021-07024-4 [DOI] [PMC free article] [PubMed] [Google Scholar]
  24. Sati H., Carrara E., Savoldi A., Hansen P., Garlasco J., Campagnaro E., et al. (2025). The WHO bacterial priority pathogens list 2024: a prioritisation study to guide research, development, and public health strategies against antimicrobial resistance. Lancet Infect. Dis. 25, 1033–1043 doi:  10.1016/s1473-3099(25)00118-5 [DOI] [PMC free article] [PubMed] [Google Scholar]
  25. Sharma S., Banerjee T., Yadav G., Kumar A. (2022). Susceptibility profile of bla (OXA-23) and metallo-β-lactamases co-harbouring isolates of carbapenem resistant Acinetobacter baumannii (CRAB) against standard drugs and combinations. Front. Cell. Infect. Microbiol. 12, 1068840. doi:  10.3389/fcimb.2022.1068840 [DOI] [PMC free article] [PubMed] [Google Scholar]
  26. Sharma R., LakhanpalAcinetobacter D. (2025). Acinetobacter baumannii: a comprehensive review of global epidemiology, clinical implications, host interactions, mechanisms of antimicrobial resistance and mitigation strategies. Microb. Pathog. 204, 107605. doi:  10.1016/j.micpath.2025.107605 [DOI] [PubMed] [Google Scholar]
  27. Tamma P. D., Immel S., Karaba S. M., Soto C. L., Conzemius R., Gisriel E., et al. (2024). Successful treatment of carbapenem-resistant Acinetobacter baumannii meningitis with sulbactam-durlobactam. Clin. Infect. Dis. 79, 819–825. doi:  10.1093/cid/ciae210 [DOI] [PMC free article] [PubMed] [Google Scholar]
  28. Valcek A., Nesporova K., Whiteway C., De Pooter T., De Coster W., Strazisar M., et al. (2022). Genomic analysis of a strain collection containing multidrug-, extensively drug-, pandrug-, and carbapenem-resistant modern clinical isolates of Acinetobacter baumannii. Antimicrob. Agents Chemother. 66, e0089222. doi:  10.1128/aac.00892-22 [DOI] [PMC free article] [PubMed] [Google Scholar]
  29. Wang B., Wang W., Lu M., Jin H. (2025). Genomic characterization of carbapenem-resistant Acinetobacter baumannii in ICU environments: mobile genetic elements, efflux pumps, and resistance mechanism. Infect. Drug Resist. 18, 5577–5587. doi:  10.2147/idr.s543138 [DOI] [PMC free article] [PubMed] [Google Scholar]
  30. Wang X., Xu T., Zhang Y., Qiu Y., Liang Y., Feng J., et al. (2026). Comparative genomic and resistance characterization of ST2 and ST164 carbapenem-resistant Acinetobacter baumannii from hospital environments and clinical specimens. Microb. Genom. 12, 001679. doi:  10.1099/mgen.0.001679 [DOI] [PMC free article] [PubMed] [Google Scholar]
  31. Wang K., Zhu W., Gong L., Yang X., Ye H., Lou Z.. (2025). Genomic and phenotypic insights into ST164 bla(NDM-1)-positive Acinetobacter baumannii from intestinal colonization in China. BMC Microbiol. 25, 272. doi:  10.1186/s12866-025-03979-5 [DOI] [PMC free article] [PubMed] [Google Scholar]
  32. Watkins R. R., Bonomo R. A. (2023). Sulbactam-durlobactam: a step forward in treating carbapenem-resistant Acinetobacter baumannii (CRAB) infections. Clin. Infect. Dis. 76 (Suppl 2), S163–S165. doi:  10.1093/cid/ciad093 [DOI] [PMC free article] [PubMed] [Google Scholar]
  33. Weinberg S. E., Villedieu A., Bagdasarian N., Karah N., Teare L., Elamin W. F.. (2020). Control and management of multidrug resistant Acinetobacter baumannii: a review of the evidence and proposal of novel approaches. Infect. Prev. Pract. 2, 100077. doi:  10.1016/j.infpip.2020.100077 [DOI] [PMC free article] [PubMed] [Google Scholar]
  34. Wong S. C., Chau P. H., So S. Y., Lam G. K., Chan V. W., Yuen L. L., et al. (2022). Control of healthcare-associated carbapenem-resistant Acinetobacter baumannii by enhancement of infection control measures. Antibiotics (Basel) 11, 1076. doi:  10.3390/antibiotics11081076 [DOI] [PMC free article] [PubMed] [Google Scholar]
  35. Xie J., Chen Y., Cai G., Cai R., Hu Z., Wang H.. (2023). Tree visualization by one table (tvBOT): a web application for visualizing, modifying and annotating phylogenetic trees. Nucleic Acids Res. 51, W587–W592. doi:  10.1093/nar/gkad359 [DOI] [PMC free article] [PubMed] [Google Scholar]
  36. Ying S., Zhang Z., XiangMetagenomic R. (2025). Metagenomic and whole-genome characterization of carbapenem-resistant Acinetobacter baumannii carrying bla(OXA-23) gene within the Tn2006 transposon among ICU patients. J. Glob. Antimicrob. Resist. 44, 180–185. doi:  10.1016/j.jgar.2025.06.009 [DOI] [PubMed] [Google Scholar]
  37. Yu K., Zeng W., Xu Y., Liao W., Xu W., Zhou T., et al. (2021). Bloodstream infections caused by ST2 Acinetobacter baumannii: risk factors, antibiotic regimens, and virulence over 6 years period in China. Antimicrob. Resist. Infect. Ctrl 10, 16. doi:  10.1186/s13756-020-00876-6 [DOI] [PMC free article] [PubMed] [Google Scholar]
  38. Zhang G., Zhou Y., Yan B., Wu C., Yang Y., Qiu T., et al. (2025). The evolution of the multidrug-resistant and globally distributed ST2 Acinetobacter baumannii in China. BMC Microbiol. 25, 618. doi:  10.1186/s12866-025-04346-0 [DOI] [PMC free article] [PubMed] [Google Scholar]
  39. Zhao F., Liu H., Yao Y., Zhang L., Zhou Z., Leptihn S., et al. (2022). Description of a rare pyomelanin-producing carbapenem-resistant Acinetobacter baumannii strain coharboring chromosomal OXA-23 and NDM-1. Microbiol. Spectr 10, e0214422. doi:  10.1128/spectrum.02144-22 [DOI] [PMC free article] [PubMed] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

Table1.xlsx (10.3KB, xlsx)
Table2.xlsx (44.2KB, xlsx)
Table3.xlsx (28.4KB, xlsx)
Table4.xlsx (11.5KB, xlsx)

Data Availability Statement

The datasets presented in this study can be found in online repositories. The names of the repository/repositories and accession number(s) can be found below: https://www.ncbi.nlm.nih.gov/, PRJNA1390075.

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