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Genetic Characteristics of Acinetobacter baumannii Isolates Circulating in an Intensive Care Unit of an Infectious Diseases Hospital During the COVID-19 Pandemic

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04 September 2025

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05 September 2025

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Abstract
During the COVID-19 pandemic, a significant increase in the spread of healthcare-associated infections (HAIs) and antimicrobial resistance (AMR) was observed. Acinetobacter baumannii, particularly carbapenem-resistant strains, poses a serious threat in intensive care units (ICUs). This study aimed to genetically characterize A. baumannii isolates from the ICU of an infectious diseases hospital repurposed for COVID-19 patient treatment. Whole-genome sequencing (WGS) was performed on 56 A. baumannii isolates from patients and environmental surfaces using the Illumina MiSeq platform. Bioinformatic analysis included multi-locus sequence typing (MLST), core-genome MLST (cgMLST), phylogenetic analysis, and in silico detection of antimicrobial resistance genes. Three sequence types (STs) were identified: ST2 (35.7%), ST78 (30.4%), and ST19 (3.5%); while 30.4% of the isolates were non-typeable. Phylogenetic analysis revealed clustering of ST2 with isolates from East Africa, ST78 with European isolates, and ST19 with isolates from Germany and Spain. Resistance genes to eight classes of antimicrobials were detected. All isolates were resistant to aminoglycosides and β-lactams. The blaOXA-23 carbapenemase gene was present in all ST2 isolates. cgMLST analysis (cgST-1746) showed significant heterogeneity among ST2 isolates (24–583 allele differences), indicating microevolution within the hospital. A novel synonymous SNP (T2220G) in the rpoB gene was identified. Environmental sampling highlighted the role of contaminated personal protective equipment (PPE) in transmission, with 47.0% of ST2 and 64.3% of ST78 isolates found on PPE. The study underscores the high resolution of WGS and cgMLST for epidemiological surveillance and confirms the critical role of infection control measures in preventing the spread of multidrug-resistant A. baumannii.
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1. Introduction

The increasing threat of epidemic-prone infectious diseases is evident from recurrent global outbreaks of emerging viral infections, rising the incidence of healthcare-associated infections (HAIs), and the spread of antimicrobial-resistant (AMR) microorganisms [1]. The prevention of HAIs remains a pressing issue, requiring new approaches in the context of emerging biological threats. In the Russian Federation, the COVID-19 pandemic necessitated the rapid deployment of infectious disease hospitals with segregated "red" and "green" zones, which often led to disruptions in established HAI prevention protocols [2].
These hospitals created dynamic, closed ecosystems where patients underwent numerous invasive procedures, and received antimicrobial treatment, fostering the active circulation of pathogens, their adaptation, and the selection of resistant strains [3]. The spread of HAIs and AMR is a recognized contemporary biological threat, challenging patient safety, healthcare workers, and public health [4,5]. Environmental microorganisms can acquire resistance mechanisms and become clinically significant opportunistic pathogens (OP) upon entering hospital ecosystems [6,7].
Acinetobacter baumannii is a prime example—a ubiquitous environmental bacterium that has evolved into a significant OP in healthcare settings [8,9]. Carbapenem-resistant A. baumannii (CRAB) is a leading cause of nosocomial infections in ICUs [10,11]. The COVID-19 pandemic was associated with numerous hospital outbreaks of A. baumannii, posing a severe threat to patients [12,13].
Transmission routes in healthcare facilities are diverse, including direct contact, contaminated surfaces, medical devices, and notably, aerosols and personal protective equipment (PPE) [14,15]. A. baumannii sequence type 2 (ST2) is a successful, globally distributed clonal lineage associated with outbreaks and multidrug resistance. Classical MLST, based on seven housekeeping genes, lacks the resolution to track the microevolution of A. baumannii within a hospital [16].
High-throughput sequencing methods are essential for accurate epidemiological diagnostics, enabling high-resolution typing, relatedness assessment, and detection of resistance and virulence determinants [17,18,19]. This study aimed to provide a genetic characterization of A. baumannii isolates from an infectious diseases’ hospital ICU during the COVID-19 pandemic using whole-genome sequencing data.

2. Materials and Methods

2.1. Sampling and Bacterial Isolation

From 2022 to 2023, biological and environmental samples were collected from the infectious diseases hospital for treating COVID-19 patients for the presence of OP. These samples were collected in accordance with a scheme for surface swabs patented by the authors, which was developed for simultaneous assessment of both viral and bacterial contamination [20]. The samples were collected using two swabs pre-moistened in sterile, deionized water simultaneously for three days every four hours at 20 sampling points from environmental surfaces grouped into three blocks: PPE of medical workers (the outer surface of the doctor’s/nurse’s/orderly’s PPE suit, the outer surface of the upper pair of medical gloves: doctor/nurse/orderly), patient care environment (the surface of medical manipulation table, the outer surface of the medical syringe dispenser, handrails and adjustment levers on an ICU bed, the outer surface of the ventilator), general hospital sampling points (The outer surface of the suction unit, dispensers for liquid soap and hand sanitizer, ICU door handles, oxygen pipeline valves, ICU electric light switches, clinical doctor’s workspace) (Figure 1).

2.2. DNA Extraction and Whole-Genome Sequencing

DNA extraction was performed using the «RIBO-prep» reagent kit (FBIS CRIE, Moscow) following the manufacturer’s protocol. Samples preparation for whole-genome sequencing was conducted in accordance with the Illumina DNA Prep Reference Guide (document #1000000025416 v10) and the LMN DNA LP (M) Tagmentation Kit (Illumina, Singapore). Briefly, DNA libraries were fragmented, and tagged using the transposome included in the kit, with unique indices (DNA/RNA UD Indexes Set A, Tagmentation, Singapore), added to each sample. Samples were normalized, pooled, and subjected to paired-end sequencing on an Illumina MiSeq system with a MiSeq V2 cartridge (300 cycles). Sample preparation and sequencing was done following the manufacturer’s protocol.

2.3. Bioinformatic Analysis

Sequencing data quality was assessed using FastQC, evaluating read counts, maximum/minimum read lengths, GC content, and ambiguous nucleotide proportions for forward and reverse reads.
De novo genome assembly was performed via scaffolding using SPAdes 3.15.5 [21] on the Galaxy server, based on paired-end reads. Taxonomic analysis of scaffolds was conducted using Galaxy’s FCS GX tool [22] to confirm species identity and remove contaminants. All isolates were confirmed as A. baumannii.
Assembled A. baumannii sequences were cleaned of residual adapters using NCBI VecScreen: FCS Adaptor [22] and filtered by scaffold length with Trim.seqs 1.39.5 [23].
Typing was performed via multilocus sequence typing (MLST) and core-genome MLST (cgMLST) using the PubMLST database (https://pubmlst.org/).
Multiple sequence alignment and neighbor-joining (NJ) phylogenetic tree construction were performed in Mauve 2.4.0 [24] using the Progressive Mauve algorithm (default parameters: Full Alignment, Sum-of-pairs LCB scoring, HOXD matrix). Scaffolds were aligned to the NCBI reference sequence GCF_009035845.1 (https://www.ncbi.nlm.nih.gov/datasets/genome/GCF_009035845.1/).
In silico detection of antimicrobial resistance (AMR) determinants was conducted using ResFinder 4.6.0 [25] (default thresholds: ≥90% identity, ≥60% coverage). Input data consisted of fastq files (paired-end reads).
Genome annotation was performed via the NCBI Prokaryotic Genome Annotation Pipeline. MLST gene alignment and analysis were conducted in MEGA X using the MUSCLE algorithm. The whole genome sequences obtained in this study were submitted to GenBank under accession numbers JBHYBP000000000–JBHYCK000000000, JBITPW000000000–JBITRA000000000.

3. Results

3.1. Isolate Collection and Sequence Types

A total of 56 A. baumannii isolates were obtained. MLST analysis successfully typed 39 isolates, revealing ST2 (n=20, 35.7%), ST78 (n=17, 30.4%), and ST19 (n=2, 3.5%). While seventeen isolates (30.4%) were non-typeable (n/d).
ST2 isolates were obtained from patients (15.0%, n=3) and hospital environmental surfaces (85.0%, n=17), with the majority from PPE (47.0%) and patient care environment (41.2%). ST78 isolates were also predominantly isolated from the environmental samples (82.3%, n=14), with most found on PPE (64.3%). Both ST19 isolates were identified in a patient and on PPE.

3.2. Phylogenetic Analysis

Phylogenetic analysis using the PubMLST database (2013–2024) showed that ST2 isolates clustered with samples from East Africa, with sporadic relatedness to Northern and Southern European isolates, suggesting potential introductions to the Russian Federation. ST78 isolates showed relatedness to isolates from Greece, Germany, Finland, Denmark, and Belarus. ST19 isolates were similar to isolates from Germany and Spain (Figure 2).
Within the hospital, clear clustering was observed between patient and environmental isolates. For example, a patient isolate (4-II_S19) clustered with isolates from bed rails, from an orderly's PPE, from and door handles. Another large cluster included isolates from various surfaces (ventilator, PPE of doctors/nurses/orderlies, and manipulation table), underscoring the role of healthcare workers in transmission.

3.3. Antimicrobial Resistance Determinants

Resistance genes to eight antimicrobial classes were identified: aminoglycosides, β-lactams, macrolides, streptogramin B, amphenicols, rifamycins, antifolates, and tetracyclines.All STs showed 100% prevalence of resistance genes to aminoglycosides and β-lactams.
  • ST2: Characteristic profile: armA, aph(6)-Id, aph(3')-Ia, aph(3'')-Ib, blaOXA-23, msr(E), mph(E). The blaOXA-23 carbapenemase was present in 100% of isolates.
  • ST78: Characteristic profile: armA, blaOXA-72, blaOXA-90, msr(E), mph(E). blaOXA-23 was absent.
  • ST19: Profile included aph(3')-VIa, blaOXA-69, blaADC-25, catA1, sul2, tet(B).
The n/d group's resistance profile resembled ST2, suggesting possible genetic relatedness or horizontal gene transfer.
When analyzing genetic profiles, isolates were divided into two groups: 1 – patients (Appendix A.2); 2 – environmental surfaces (Appendix A.3). Isolates from both groups represented all detected ST (Figure 3). All ST, including n/d group, showed 100% presence of resistance determinants to aminoglycosides and β-lactams, with presumed multidrug resistance (resistance to 4–5 antimicrobial classes) across all groups.

3.4. Microevolution and SNP Analysis

Analysis of classical MLST genes for ST2 revealed complete identity with reference sequences. However, cgMLST analysis assigned most isolates to a common cgST-1746 but revealed significant heterogeneity, with allele mismatches ranging from 24 to 583 (Table 1). Isolate 188-II_S28 had the highest number of mismatches (583) and contained a unique synonymous SNP (T2220G) in the rpoB gene, not previously reported in databases.

4. Discussion

One of the most prevalent nosocomial pathogens in modern healthcare settings is A. baumannii, which can cause urinary tract infections, bacteremia, meningitis, pneumonia, and catheter-associated infections [26,27]. Immunocompromised systems, particularly those with burn injuries or those admitted to ICU, are at highest risk of infection. The recent COVID-19 pandemic was associated with an increased incidence of ventilator-associated nosocomial secondary infections, for which A. baumannii served as a primary etiological agent [28,29].
According to the 2019 Global Antimicrobial Resistance and Use Surveillance System (GLASS) report, 132,000 A. baumannii infections directly contributing to patient mortality were resistant to at least one clinically important antibiotic, with 57,700 fatal cases demonstrating carbapenem resistance [30].
The global prevalence of CRAB continues to rise relentlessly, severely limiting treatment options and exacerbating morbidity and mortality rates associated with these infections.
Key mechanisms of carbapenem resistance in A. baumannii include enzymatic inactivation, porin modifications, efflux pump upregulation, and β-lactamase production. Among the four known β-lactamase classes (A–D), classes B and D are primarily responsible for carbapenem resistance.
OXA-type carbapenemases (Class D) represent the most prevalent carbapenemases in A. baumannii, particularly blaOXA-23-like enzymes. These enzymes are typically plasmid-encoded, facilitating horizontal gene transfer and dissemination within bacterial populations, especially in the hospital environment. The blaOXA-23-like carbapenemase was the first OXA-type carbapenemase identified in CRAB and remains the most globally widespread variant [31]. Consequently, it represents a critical target for molecular surveillance, whose integration into HAIs epidemiological monitoring systems is imperative.
In this study, we showed that ST2 is the predominant lineage in the ICU, with isolates from 3 patients and 17 environmental surfaces (8 from PPE, 7 from patient care areas, and 2 from general hospital sampling points). The prevalence of ST2 reflects the evolutionary success of this clonal lineage (CC2), which accounts for the majority of sequenced genomes globally. The characteristic multidrug resistance profile of ST2 lineage, coupled with limited therapeutic options, ensures its continued prevalence in healthcare facilities [32].
cgMLST analysis revealed a single prevalence cgST-1746 for most isolates. Isolate 104-II_S26 exhibited both cgST-1746 and cgST-11006, while isolate 188-II_S28 (max mismatches=583) contained a unique rpoB SNP, potentially indicating accelerated evolutionary adaptation. The mismatch distribution showed no temporal correlation with sampling chronology. The observed cgMLST heterogeneity despite conserved cgST is characteristic of long-term hospital-adapted populations and reflects the remarkable genomic plasticity of A. baumannii.
ST78 represented the second most frequently detected ST, with 3 patient isolates and 14 environmental isolates (9 from PPE, 3 from patient care environment and 2 from hospital sampling points).
ST19 isolates were sporadically detected and did not significantly impact the epidemiological landscape of the COVID-19 ICU.
Beyond antimicrobial resistance mechanisms, A. baumannii pathogenicity is mediated by diverse virulence factors. Although virulence determinants remain incompletely characterized, key factors facilitating successful infection include genes encoding outer membrane proteins, biofilm formation machinery, secretion systems, and micronutrient acquisition systems – all warranting further investigation.
Phylogenetic analysis incorporating isolates from the PubMLST international database revealed clustering patterns associated with specific geographic regions, suggesting potential pathogen introductions.
Within the infectious disease hospital, distinct clustering was observed between isolates from patients, medical workers’ PPE, and patient environment surfaces. For the two predominant lineages (ST2 and ST78), PPE represented the most contaminated sites (47.0% and 64.3% of isolates, respectively), underscoring the critical importance of strict infection control measures and hygiene practices in healthcare facilities to prevent the spread of antibiotic-resistant bacteria.
In silico analysis identified resistance determinants to eight antimicrobial classes in all A. baumannii isolates. Each sequence type exhibited a characteristic resistance profile. All ST2 samples are characterized by a genetic profile of resistance that includes armA, aph(6)-Id, aph(3’)-Ia, aph(3”)-Ib, blaOXA-23, and msrI genes. While, all ST78 samples have a genetic profile of resistance that includes the same resistance genes as ST2, as well as blaOXA-72 and blaOXA-90. Separate resistance genes for various AMR classes have been found in ST19 isolates.
Notably, all ST2 isolates carried the blaOXA-23 carbapenemase, confirming their CRAB status, while this determinant was absent in ST78 and ST19 lineages. The results are very similar to results published during the same COVID-19 period in Croatia, where A. baumannii isolates carrying blaOXA-23 carbapenemase were identified in ICU patients and air conditioners [33]. This finding is consistent with reports from another Croatian hospital, where CRAB was isolated from hospital surfaces [34], highlighting the role of the contaminated hospital environment in the persistence and spread of these pathogens. Similar results of an A. baumannii producing blaOXA-23 carbapenemase outbreak in Basel, Switzerland were reported in an ICU [35].
One study reported an increased incidence of ventilator-associated pneumonia caused by A. baumannii during the pandemic in Mexico. An increase in resistance to aminoglycosides, carbapenems, folate inhibitors and other antibiotics was also observed [36]. Furthermore, the detection of genetic determinants of resistance to these antibiotic classes in our samples is consistent with the observed phenotype of multidrug resistance in A. baumannii strains described during the pandemic period.
WGS and cgMLST emerged as the most informative bioinformatics tools, offering superior resolution for HAIs epidemiological surveillance compared to classical MLST approaches.
This study was also only limited to samples collected from one center and from a single ICU. However, the obtained results still emphasize the significance of high-throughput sequencing techniques in studying the biological features of current pathogens. By determining the degree of similarity among isolated strains, identifying their resistance and virulence determinants, and investigating the epidemiological connections between pathogens, we can more accurately identify the key factors contributing to nosocomial infections. These findings will be valuable for developing more efficient strategies to prevent and control infections caused by A. baumannii in hospital settings.

5. Conclusions

In conclusion, the ICU environment during the COVID-19 pandemic was dominated by MDR A. baumannii ST2, harboring the armA 16S rRNA methylstransferase and the blaOXA-23 carbapenemase. The study demonstrates the critical role of contaminated environmental surfaces, especially PPE, in the transmission chain. The high resolution of WGS and cgMLST is essential for effective epidemiological surveillance and outbreak investigation. These findings emphasize the need for reinforced infection prevention and control measures in healthcare settings managing vulnerable patient populations.

Author Contributions

Conceptualization, S.S.S. and N.N.Z.; methodology, S.S.S., D.D.A. and T.M.I.; software, D.D.A.; validation, Y.S.S. and N.N.Z.; formal analysis, D.D.A.; investigation, S.S.S., Y.S.S., N.N.Z. and T.M.I.; resources, M.V.H.; data curation, D.D.A.; writing—original draft preparation, D.D.A. and S.S.S.; writing—review and editing, all authors; visualization, D.D.A.; supervision, S.S.S.; project administration, S.S.S.; funding acquisition, S.S.S. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Russian scientific project “Study of the epidemic process and prevention of viral healthcare-associated infections”, Reg. No. 121040500099-5.

Institutional Review Board Statement

The study was conducted in accordance with the Declaration of Helsinki and approved by the Local Ethics Committee of the State Scientific Center of Virology and Biotechnology “Vector” (protocol code № 3, date of approval 24 June 2022).

Informed Consent Statement

Patient consent was waived due to the retrospective nature of the study and the use of anonymized bacterial isolates obtained as part of routine clinical microbiological surveillance.

Data Availability Statement

The raw sequencing data generated in this study have been deposited in the NCBI SRA database under BioProject accession number PRJNA1165946.

Acknowledgments

The authors thank the staff of the Nizhny Tagil City Infectious Diseases Hospital for their assistance in sample collection.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

AMR Antimicrobial resistance
CRAB Carbapenem-resistant A. baumannii
cgMLST Core-genome MLST
ICUs Intensive care units
HAIs Healthcare-associated infections
OP Opportunistic pathogen
MLST Multi-locus sequence typing
PPE Personal protective equipment
ST Sequence type
WGS Whole-genome sequencing
PCE Patient care environment
GHP General hospital point
AMI Aminoglicoside
BL Beta-lactam
MKL Macrolide
SGB Streptogramin b
AP Amphenicol
RF Rifamycin
AF Antifolates
TET Tetracycline

Appendix A

Appendix A.1

Sample ID Selection group Selection point
5-2-III_S1 PPE The outer surface of the upper pair of medical gloves (orderly)
6-2-III_S35 PPE The outer surface of the orderly’s PPE suit
7-II_S40 PCE The surface of medical manipulation table
13-2-II_S41 PCE The outer surface of the medical syringe dispenser
21-II_S42 PPE The outer surface of the upper pair of medical gloves (doctor)
22-II_S43 PPE The outer surface of the upper pair of medical gloves (nurse)
25-II_S45 PPE The outer surface of the orderly’s PPE suit
26-II_S36 PPE The outer surface of the doctor’s PPE suit
26-III_S22 PPE The outer surface of the orderly’s PPE suit
27-III_S34 PCE The surface of medical manipulation table
28-II_S46 PCE Handrails and adjustment levers on an ICU bed
33-II_S47 PCE The outer surface of the medical syringe dispenser
38-II_S48 GHP ICU door handles
42-III_S7 PPE The outer surface of the doctor’s PPE suit
44-2-III_S6 PPE The outer surface of the nurse’s PPE suit
48-2-III_S4 PCE Handrails and adjustment levers on an ICU bed
48-II_S49 PCE The surface of medical manipulation table
49-II_S50 PCE Handrails and adjustment levers on an ICU bed
50-2-III_S11 PCE The outer surface of the ventilator
51-II_S51 PCE The outer surface of the ventilator
53-II_S27 PCE Handrails and adjustment levers on an ICU bed
55-II_S52 PCE The outer surface of the ventilator
61-II_S53 PPE The outer surface of the upper pair of medical gloves (orderly)
63-II_S54 PPE The outer surface of the upper pair of medical gloves (nurse)
64-II_S55 PPE The outer surface of the nurse’s PPE suit
66-II_S56 PPE The outer surface of the doctor’s PPE suit
69-II_S57 PCE Handrails and adjustment levers on an ICU bed
72-III_S10 PCE Handrails and adjustment levers on an ICU bed
87-II_S58 PCE The surface of medical manipulation table
89-II_S59 PCE Handrails and adjustment levers on an ICU bed
96-II_S23 GHP The outer surface of the suction unit
100-II_S24 GHP Dispensers for liquid soap and hand sanitizer
102-II_S25 PPE The outer surface of the nurse’s PPE suit
104-II_S26 PPE The outer surface of the orderly’s PPE suit
108-2-III_S9 PCE Handrails and adjustment levers on an ICU bed
188-II_S28 PCE Handrails and adjustment levers on an ICU bed
198-II_S29 GHP ICU door handles
221-II_S30 PPE The outer surface of the upper pair of medical gloves (doctor)
284-2-III_S18 PPE The outer surface of the nurse’s PPE suit
285-III_S17 PPE The outer surface of the upper pair of medical gloves (orderly)
286-III_S15 PPE The outer surface of the orderly’s PPE suit
306-III_S14 PPE The outer surface of the orderly’s PPE suit
307-1-II_S32 PCE The surface of medical manipulation table
331-II_S12 PCE The surface of medical manipulation table
344-III_S20 PPE The outer surface of the nurse’s PPE suit
346-II_S33 PPE The outer surface of the orderly’s PPE suit
224-2_S15 PPE The outer surface of the doctor’s PPE suit
Notes: PPE – personal protective equipment, PCE – patient care environment, GHP – general hospital point.

Appendix A.2

Genetic determinants profiles of resistance of patient’s A. baumannii isolates
Sample ID MLST AMI BL MKL SGB AP RF AF TET
armA aph(6)-Id (strB) aph(3')-Ia aph(3')-VIa aph(3'')-Ib aph(3')-VIb aadA1 aac(6')-lb3 blaOXA-23 blaADC-25 blaPER-7 blaOXA-66 blaCTX-M-124 blaOXA-72 blaOXA-90 blaTEM-1D blaCARB-14 msr(E) mph(E) catB8 cmlA1 floR catA1 ARR-2 sul1 sul2 tet(B)
2-II_S37 n/d 1 1 1 0 1 0 1 0 1 1 1 0 0 0 0 0 0 1 1 1 1 0 0 1 1 1 0
4-II_S19 ST2 1 1 1 0 1 0 1 1 1 1 1 1 0 0 0 0 0 1 1 1 0 0 0 1 0 0 0
6-531-2-III_S5 ST2 1 1 1 0 1 0 1 1 1 1 0 1 0 0 0 0 0 1 1 1 0 0 0 0 0 1 0
7-555-III_S3 ST78 1 0 0 0 0 0 0 0 0 1 0 0 1 1 1 0 0 1 1 0 0 0 1 0 0 0 0
13-II_S38 ST19 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 1 1
14-II_S21 n/d 1 1 1 0 1 1 0 0 1 0 0 0 0 0 0 1 1 1 1 0 0 1 0 0 0 0 1
16-II_S39 ST78 1 0 0 0 0 0 0 0 0 1 0 0 1 1 1 0 0 1 1 0 0 0 1 0 0 0 0
17-II_S13 ST78 1 0 0 0 0 0 0 0 0 1 0 0 0 1 1 0 0 1 1 0 0 0 0 0 0 0 0
19-II_S16 ST2 1 1 1 0 1 0 1 1 1 1 0 1 0 0 0 0 0 1 1 1 1 0 0 1 1 1 0
Notes: AMI – aminoglicoside; BL – beta-lactam; MKL – macrolide; SGB – streptogramin b; AP – amphenicol; RF – rifamycin; AF – antifolates; TET – tetracycline; 1 – is available; 0 – absent.

Appendix A.3

Genetic determinants profiles of resistance of environmental objects’ A. baumannii isolates
Sample ID MLST AMI BL MKL SGB AP RF AF TET
armA aph(6)-Id (strB) aph(3')-Ia aph(3')-VIa aph(3'')-Ib aph(3')-Vib aadA1 aac(6')-lb3 blaOXA-23 blaADC-25 blaPER-7 blaOXA-66 blaCTX-M-124 blaOXA-72 blaOXA-90 blaTEM-1D blaCARB-14 msr(E) mph(E) catB8 cmlA1 floR catA1 ARR-2 sul1 sul2 tet(B)
5-2-III_S1 ST2 1 1 1 0 1 0 1 1 1 1 0 1 0 0 0 0 0 1 1 1 1 0 0 1 1 1 0
6-2-III_S35 n/d 1 1 1 0 1 0 1 1 1 1 0 0 0 0 0 0 0 1 1 1 1 0 0 1 1 1 0
7-II_S40 n/d 1 1 1 0 1 0 1 1 1 1 1 1 0 0 0 0 0 1 1 1 1 0 0 1 1 1 0
13-2-II_S41 n/d 1 0 0 0 0 0 0 0 0 0 0 0 1 1 1 0 0 1 1 0 0 0 1 0 0 0 0
21-II_S42 n/d 0 0 0 1 0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 1 0 0 1 1
22-II_S43 ST78 1 0 0 0 0 0 0 0 0 1 0 0 1 1 1 0 0 1 1 0 0 0 1 0 0 0 0
25-II_S45 n/d 1 0 0 0 0 0 0 0 0 0 0 0 1 1 1 0 0 1 1 0 0 0 1 0 0 0 0
26-II_S36 ST78 1 0 0 0 0 0 0 0 0 1 0 0 1 1 1 0 0 1 1 0 0 0 1 0 0 0 0
26-III_S22 ST2 1 1 1 0 1 0 1 1 1 1 0 1 0 0 0 0 0 1 1 1 1 0 0 1 1 1 0
27-III_S34 ST2 1 1 1 0 1 0 1 1 1 1 0 1 0 0 0 0 0 1 1 1 1 0 0 1 1 1 0
28-II_S46 n/d 1 1 1 0 1 0 1 1 1 1 1 0 0 0 0 0 0 1 1 1 1 0 0 1 1 1 0
33-II_S47 n/d 1 1 1 0 1 0 1 1 1 0 1 0 0 0 0 0 0 1 1 1 1 0 0 1 1 1 0
38-II_S48 ST78 1 0 0 0 0 0 0 0 0 1 0 0 1 1 1 0 0 1 1 0 0 0 1 0 0 0 0
42-III_S7 ST2 1 1 1 0 1 0 1 1 1 1 0 1 0 0 0 0 0 1 1 1 1 0 0 1 1 1 0
44-2-III_S6 ST2 1 1 1 0 1 0 1 1 1 1 0 0 0 0 0 0 0 1 1 1 1 0 0 1 1 1 0
48-2-III_S4 n/d 1 1 1 0 1 0 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 0 0 1 1 1 0
48-II_S49 n/d 1 1 1 0 1 0 0 1 1 1 1 1 0 0 0 0 0 1 1 1 1 0 0 1 0 1 0
49-II_S50 n/d 1 1 1 0 1 0 1 1 1 0 1 0 0 0 0 0 0 1 1 1 1 0 0 1 1 1 0
50-2-III_S11 ST2 1 1 1 0 1 0 1 1 1 1 0 1 0 0 0 0 0 1 1 1 1 0 0 1 0 0 0
51-II_S51 n/d 1 1 1 0 1 0 1 1 1 0 1 0 0 0 0 0 0 1 1 1 1 0 0 1 0 0 0
53-II_S27 ST78 1 0 0 0 0 0 0 0 0 1 0 0 1 1 1 0 0 1 1 0 0 0 1 0 0 0 0
55-II_S52 ST2 1 1 1 0 1 0 1 1 1 1 1 1 0 0 0 0 0 1 1 1 1 0 0 1 1 1 0
61-II_S53 ST2 1 1 1 0 1 0 1 1 1 1 1 1 0 0 0 0 0 1 1 1 1 0 0 1 1 1 0
63-II_S54 ST2 1 1 1 0 1 0 1 1 1 1 1 1 0 0 0 0 0 1 1 1 1 0 0 1 1 1 0
64-II_S55 n/d 1 1 1 0 1 0 1 1 1 0 1 0 0 0 0 0 0 1 1 1 1 0 0 1 1 1 0
66-II_S56 ST78 1 0 0 0 0 0 0 0 0 1 0 0 0 1 1 0 0 1 1 0 0 0 0 0 0 0 0
69-II_S57 ST2 1 1 1 0 1 0 1 1 1 1 1 1 0 0 0 0 0 1 1 1 1 0 0 1 1 1 0
72-III_S10 ST2 1 1 1 0 1 0 1 1 1 1 0 1 0 0 0 0 0 1 1 1 1 0 0 1 1 1 0
87-II_S58 ST78 1 0 0 0 0 0 0 0 0 1 0 0 1 1 1 0 0 1 1 0 0 0 1 0 0 0 0
89-II_S59 ST78 1 0 0 0 0 0 0 0 0 1 0 0 1 1 1 0 0 1 1 0 0 0 1 0 0 0 0
96-II_S23 ST78 1 0 0 0 0 0 0 0 0 1 0 0 1 1 1 0 0 1 1 0 0 0 1 0 0 0 0
100-II_S24 ST2 1 1 1 0 1 1 0 0 1 1 0 1 0 0 0 1 1 1 1 0 0 1 0 0 0 1 1
102-II_S25 ST19 0 0 0 1 0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 1 0 0 1 1
104-II_S26 ST2 1 1 1 0 1 0 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 0 0 1 1 1 0
108-2-III_S9 ST2 1 1 1 0 1 0 1 1 1 1 0 1 0 0 0 0 0 1 1 1 1 0 0 1 1 1 0
188-II_S28 ST2 1 1 1 0 1 0 1 1 1 0 1 0 0 0 0 0 0 1 1 1 1 0 0 1 1 1 0
198-II_S29 ST2 1 1 1 0 1 0 1 1 1 1 1 1 0 0 0 0 0 1 1 1 1 0 0 1 1 1 0
221-II_S30 ST78 1 0 0 0 0 0 0 0 0 1 0 0 1 1 1 0 0 1 1 0 0 0 1 0 0 0 0
284-2-III_S18 ST78 1 0 0 0 0 0 0 0 0 0 0 0 1 1 1 0 0 1 1 0 0 0 1 0 0 0 0
285-III_S17 ST78 1 0 0 0 0 0 0 0 0 1 0 0 1 1 1 0 0 1 1 0 0 0 1 0 0 0 0
286-III_S15 ST78 1 0 0 0 0 0 0 0 0 1 0 0 1 1 1 0 0 1 1 0 0 0 1 0 0 0 0
306-III_S14 ST78 1 0 0 0 0 0 0 0 0 1 0 0 1 1 1 0 0 1 1 0 0 0 1 0 0 0 0
307-1-II_S32 n/d 1 1 1 0 1 1 1 0 1 1 1 0 0 0 0 0 0 1 1 1 1 0 0 1 1 1 0
331-II_S12 n/d 1 0 0 0 0 0 0 0 0 1 0 0 1 1 1 0 0 1 1 0 0 0 1 0 0 0 0
344-III_S20 ST78 1 0 0 0 0 0 0 0 0 1 0 0 1 1 1 0 0 1 1 0 0 0 1 0 0 0 0
346-II_S33 ST2 1 1 1 0 1 0 1 1 1 1 1 1 0 0 0 0 0 1 1 1 1 0 0 1 1 1 0
224-2_S15 n/d 1 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 1 1 0 0 0 1 0 0 0 0
Notes: AMI – aminoglicoside; BL – beta-lactam; MKL – macrolide; SGB – streptogramin b; AP – amphenicol; RF – rifamycin; AF – antifolates; TET – tetracycline; 1 – is available; 0 – absent.

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Figure 1. Study design and sampling scheme from patients and the hospital environment.
Figure 1. Study design and sampling scheme from patients and the hospital environment.
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Figure 2. Neighbor-joining phylogenetic tree of A. baumannii clinical isolates and reference sequences from the PubMLST database. Colored clades: red (ST2), purple (ST78), yellow (ST19). Blue: study isolates; Black: PubMLST database; Green: GenBank reference.
Figure 2. Neighbor-joining phylogenetic tree of A. baumannii clinical isolates and reference sequences from the PubMLST database. Colored clades: red (ST2), purple (ST78), yellow (ST19). Blue: study isolates; Black: PubMLST database; Green: GenBank reference.
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Figure 3. Distribution of A. baumannii ST isolated from patients and environmental samples.
Figure 3. Distribution of A. baumannii ST isolated from patients and environmental samples.
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Table 1. Comparative analysis of A. baumannii ST2 isolates according to the cgMLST scheme.
Table 1. Comparative analysis of A. baumannii ST2 isolates according to the cgMLST scheme.
Sample ID Closest cgST Mismatches, n Loci matched, %
6-531-2-III_S5 1746 24 98,9
108-2-III_S9 1746 110 94,8
50-2-III_S11 1746 115 95,6
61-II_S53 1746 115 94,6
72-III_S10 1746 117 94,5
42-III_S7 1746 121 94,3
26-III_S22 1746 129 94,0
55-II_S52 1746 138 93,5
19-II_S16 1746 156 92,7
27-III_S34 1746 171 92,0
346-II_S33 1746 186 91,3
63-II_S54 1746 202 90,5
44-2-III_S6 1746 211 90,1
4-II_S19 1746 222 89,6
69-II_S57 1746 228 89,3
198-II_S29 1746 232 89,1
100-II_S24 1746 258 87,9
104-II_S26 1746, 11006 461 78,4
188-II_S28 1746 583 72,7
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