Genotypic and Phenotypic Resistance Profiles of Invasive Acinetobacter baumannii Isolates at Bulgarian University Hospital

Molecular Characterization of OXA Carbapenemase Genes in Acinetobacter Baumannii Isolated from Different Clinical Samples.

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.

Genetic diversity and ERIC-PCR-based relationships of Acinetobacter baumannii isolates from hospitals

Antimicrobial resistance and genes profiles of Acinetobacter baumannii isolated from University Teaching Hospital of Kigali

INTRODUCTION: Antimicrobial resistance is a growing global threat, with carbapenem-resistant A. baumannii (CRAB) identified by World Health Organisation (WHO) as a top-priority pathogen. In Rwanda, data on resistance patterns and underlying genetic determinants in A. baumannii remains limited. This study aims to assess phenotypic resistance profile and detect key resistance genes to support infection prevention and control (IPC) and antimicrobial stewardship interventions. METHODS: A cross-sectional study was conducted from February to July 2025.Acinetobacter baumannii isolates were identified and tested for antimicrobial susceptibility using the disk diffusion method. Polymerase chain reaction (PCR) was used to detect selected resistance genes. Data on patient demographics, sample types, and hospital wards were collected and analysed. RESULTS: Of 1746 clinical isolates, 3.2% (n=56) were confirmed Acinetobacter baumannnii. Most isolates were recovered from male Intensive Care Unit (ICU) patients aged 19–40. All isolates showed 100% resistance to key beta-lactams, high resistance to ciprofloxacin with 87.0%, gentamicin 78.3%, while complete susceptibility to imipenem at 100% was observed. Resistance genes; blaOXA-23 and blaCTX-M were detected in 60.9% and 52.2% of isolates respectively, confirming the genetic basis for carbapenem and ESBL resistance. CONCLUSION: The study revealed a significant burden of multidrug-resistant Acinetobacter baumannii infections, particularly among ICU patients. The high resistance of blaOXA-23 and blaCTX-M highlights the complexity of managing these infections and underscores the need for strengthened IPC measures, routine molecular surveillance, and targeted AMS strategies.

Mechanisms of cefiderocol resistance in carbapenem-resistant Acinetobacter baumannii: a Swiss 2023-2025 collection.

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.

Antimicrobial Resistance and Virulence of Acinetobacter baumannii; A Whole-Genome Sequencing Perspective from a Croatian Intensive Care Unit

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.

Characterization of blaNDM-1 and blaOXA-23-Type Carbapenemases in Acinetobacter baumannii Isolated from Post-Surgical Patients

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.