Genomic characterization of carbapenem-resistant Acinetobacter baumannii from a specialized orthopaedic hospital in Southeast China, with phenotypic analysis of biofilm formation
Jul 2026· Frontiers in Cellular and Infection Microbiology· Vol 16· 0 citations· 51 references
Medicine
TL;DR
CRAB isolates in this orthopaedic specialty hospital are dominated by the ST2/KL3 clone, which carries multiple resistance and virulence genes, exhibits a remarkably strong biofilm-forming ability, and shows a capsular switch trend from KL2 to KL3.
Abstract
Background Carbapenem−resistant Acinetobacter baumannii (CRAB) is a major threat to hospitalised patients, particularly in intensive care units and orthopaedic wards where implant−associated infections are common. However, the genomic and biofilm characteristics of CRAB in orthopaedic specialty hospitals remain poorly understood. Methods A total of 97 non-duplicate CRAB isolates collected between 2024 and 2025 were included. Antimicrobial susceptibility testing was performed using the VITEK-2 system, and biofilm formation was quantitatively assessed by the crystal violet method. Whole-genome sequencing (WGS) was carried out on the Illumina platform to analyse multilocus sequence typing (MLST), capsular types, resistance genes and virulence genes. A phylogenetic tree was constructed based on single-nucleotide polymorphisms (SNPs). Results ST2 was the dominant clone (95.88%) among the 97 isolates, and KL3 was the most prevalent capsular type (83.51%). All isolates carried intrinsic blaOXA-51-like genes, predominantly blaOXA-66 (95.88%). The most common acquired carbapenemase gene was blaOXA-23 (98.97%), and two isolates carried metallo-β-lactamase (MBL) genes (blaNDM-1 and blaNDM-5, respectively). All isolates exhibited a multidrug-resistant phenotype, with low resistance rates to tigecycline (6.19%) and minocycline (7.22%), and all remained susceptible to colistin. Strong biofilm formers accounted for 91.75% of isolates, and the carriage rates of biofilm-associated genes (bap, csuABCDE, pgaABCD) exceeded 90%. Phylogenetic analysis grouped the isolates into three clonal clades, with the majority (88.66%) falling into Clade C (ST2/KL3). This clade had been circulating in China as an outbreak lineage since 2018, gradually replacing Clade B (ST2/KL2), and became the dominant clone in 2024–2025. Conclusion CRAB isolates in this orthopaedic specialty hospital are dominated by the ST2/KL3 clone, which carries multiple resistance and virulence genes, exhibits a remarkably strong biofilm-forming ability, and shows a capsular switch trend from KL2 to KL3. Enhanced molecular surveillance of this dominant clone and increased attention to anti-biofilm strategies for orthopaedic implant-related infections are strongly recommended.
Background/Objectives: Acinetobacter baumannii is a major cause of infections in Intensive Care Units (ICUs), driving mortality through high-level antimicrobial resistance. This study utilized whole-genome sequencing (WGS) to evaluate the phenotypic, genotypic and virulence features of carbapenem-resistant A. baumannii (CRAB), which has caused ventilator-associated pneumonia/tracheobronchitis (VAP/VAT) in the ICU of the University Hospital of Split, Croatia. Methods: Over 1 year, lower respiratory tract specimens from 79 VAP/VAT patients were analyzed. CRAB isolates were identified via MALDI-TOF MS and evaluated for antimicrobial susceptibility, and a representative subset underwent WGS and multilocus sequence typing (MLST). Results: Out of 106 specimens, 18 non-duplicate CRAB strains were isolated. Five isolates underwent genomic analysis, identifying two globally distributed, high-risk Pasteur lineages: ST2 and ST492. These lineages displayed distinct resistomes: ST2 carried blaOXA-23 and blaADC-73, while ST492 harbored plasmid-borne blaOXA-72 (Rep3-T1/AB082 cluster) and blaADC-30. All isolates shared aminoglycoside/macrolide-resistance genes, conserved efflux pumps, and virulence determinants (bau, bas, ent, bar) crucial for acinetobactin synthesis and respiratory colonization. Phylogenetic analysis confirmed regional circulation and genetic links to neighboring countries. Conclusions: This study highlights the evolutionary dynamics of endemic CRAB lineages in a Croatian ICU and their global dissemination, which poses a critical threat, demanding strict infection control and novel therapeutics.
Marija Čavka, Marija Kvesić Ivanković, Ana Maravić et al.· Antibiotics· 0 citations
The ICU environment was critical for CRAB control, and 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.
Yue Zhang, Yanru Liang, Yuanping Wang et al.· Frontiers in Cellular and In...· 0 citations
In Spain, CRAB dissemination is driven by interregional spread of isolates belonging to the ST218Oxf/ST2Pas clones, characterized by the blaOXA-23/blaOXA-66 genotype, the presence of armA, the KL7/OCL18 capsular profile and the presence of pS32-1 plasmid.
Jared Sotelo, B. Aracil, J. Arca-Suárez et al.· International Journal of Ant...· 0 citations
This study substantiates an escalated incidence of carbapenem-resistant, MDR A. baumannii in post-surgical infections in Pakistan, highlighting the exigency for strengthened antimicrobial stewardship and infection control strategies in the hospitals of the region.
Sana Gul, Nawab Ali, M. Qasim et al.· Antibiotics· 0 citations
OBJECTIVES
The numbers of infections caused by carbapenem-resistant Acinetobacter baumannii (CRAB) are increasing globally and present a significant burden on healthcare systems. This study describes the CRAB isolates received at the Swiss National Reference Centre for Emerging Antibiotic Resistance (NARA) over a 3-year period, from January 2022 to December 2025, and aimed to characterize the prevalence and mechanisms of FDC resistance.
METHODS
Two-hundred and thirty-four non-duplicate CRAB isolates were submitted to NARA over the study period from hospitals and laboratories across Switzerland. Susceptibility testing was performed by disk diffusion and broth microdilution, according to EUCAST methodology. Whole-genome sequencing was performed on 11 isolates. ADC alleles were cloned into vector pVRL1 and transformed into Escherichia coli Top10.
RESULTS
All isolates exhibited resistance to the carbapenems, and most were resistant to cephalosporins. Most isolates harboured an acquired class D carbapenemase, most frequently OXA-23 (181/234; 77.4%). One quarter of isolates were resistant to cefiderocol (FDC), exhibiting MICs ranging from 4->32 mg/L. Whole genome sequencing analyses, performed on 11 FDC-resistant isolates, identified that FDC resistance was due a combination of mechanisms including NDM and PER-production, mutations within the iron transporters, piuA and pirA, and the overexpression of ADC variants.
CONCLUSIONS
This study showed that OXA-23 was the dominant mechanism of carbapenem-resistance in CRAB in Switzerland. Almost one quarter of CRAB isolates were resistant to "last resort" antimicrobial, FDC. The mechanisms of FDC resistance identified in this study emphasise that resistance to this antimicrobial is often complex and multifactorial, requiring high-resolution methods, including WGS, to identify.
Unknown authors· Journal of Global Antimicrob...· 0 citations
It is indicated that blaOXA-23 is the predominant contributor to carbapenem resistance among A. baumannii isolates in Baghdad, while blaOXA-24 and blaOXA-58 are also increasingly prevalent.
A. A. Abdulhassan, Hiba Hazim Hamid, Sara Mahdi Al-Lami et al.· Cellular Physiology and Bioc...· 0 citations
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