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Article

Bacteremia Outbreak Due to Achromobacter xylosoxidans in Hospitalized COVID-19 Patients

by
Magdalini Tsekoura
1,*,
Georgios Petridis
2,
Konstantinos Koutsouflianiotis
2,
Styliani Pappa
3,
Anna Papa
3,† and
Konstantina Kontopoulou
1,†
1
Laboratory of Clinical Microbiology, G. Gennimatas Tertiary Academic Hospital of Thessaloniki, 54635 Thessaloniki, Greece
2
Internal Medicine Clinic, G. Gennimatas Tertiary Academic Hospital of Thessaloniki, 54635 Thessaloniki, Greece
3
Department of Microbiology, Medical School, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece
*
Author to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Microbiol. Res. 2025, 16(7), 156; https://doi.org/10.3390/microbiolres16070156
Submission received: 31 May 2025 / Revised: 27 June 2025 / Accepted: 3 July 2025 / Published: 8 July 2025
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Abstract

Background: Hospitalized COVID-19 patients are particularly vulnerable to secondary bacterial infections, which can significantly worsen clinical outcomes. The aim of the study was to identify the cause of bacteremia in a group of hospitalized COVID-19 patients and find out the source of the outbreak to prevent further spread. Methods: Pathogen identification in blood cultures and sensitivity testing were carried out using the automated VITEK2 system. A total of 110 samples were tested; these were collected from patients’ colonization sites and from surfaces, materials and fluids used in the setting. Furthermore, multilocus sequence typing (MLST) and next-generation sequencing (NGS) were employed to characterize the isolates. Results: Achromobacter xylosoxidans was detected in the blood of nine hospitalized patients and in cotton used for disinfection; all isolates presented an identical antibiotic resistance pattern, and all carried the blaOXA-114 gene which is intrinsic to this species. Infection control measures were implemented promptly. With one exception, all patients recovered and were discharged in good health. Conclusions: This outbreak underscores the urgent need for investigation and control of hospital infections, as bacteremia is associated with increased morbidity, mortality, hospitalization time, and cost. It also highlights the importance of close collaboration among healthcare professionals.

1. Introduction

Healthcare-associated infections (HCAIs) are infections that occur while receiving healthcare in a hospital or other healthcare facility which first appear 48 or more hours after admission or within 30 days after having received healthcare [1]. HCAIs are the most common adverse events in healthcare. They affect patient safety as they increase morbidity, mortality, length of hospital stays, and cost [2]. Bacteremia (presence of viable bacteria circulating in the patients’ blood) is often caused as a result of HCAI. Bloodstream infections are diagnosed through blood culture testing; this is the gold-standard method, although multiple direct whole-blood pathogen detection methods exist. Detection of organisms in a patient’s blood culture has both diagnostic and prognostic significance, and is one of the most important functions of a diagnostic microbiology laboratory. Medical procedures that require direct contact with sterile tissues or patient vessels require thorough disinfection of equipment and the application of antiseptic to skin to minimize pathogen transmission risks [3,4]. Hospitalized COVID-19 patients are particularly susceptible to secondary bacterial infections due to their impaired immune system. Such infections often lead to clinical deterioration. Secondary bacterial infections, especially bacteremia, might be significant, though potentially treatable, contributors to disease severity among COVID-19 patients, raising challenges in both diagnosis and prognosis [5,6,7,8,9,10]. These coinfections pose a challenge for clinical management and outcome assessment [11].
Achromobacter spp. are obligately aerobic, motile, oxidase- and catalase-positive, indole-, urease-, and DNase-negative, non-lactose fermenting, Gram-negative bacteria belonging to the order Burkholderiales. They are commonly found in the environment and are now becoming an opportunistic pathogen, especially in immunocompromised hosts [12]. It is often associated with aquatic environments [13]. The pathogen was first described in 1971 by Yabuuchi and Ohyama, who isolated it from purulent ear discharge in patients with chronic otitis media [14]. Recently, it has been detected on a variety of surface and environmental samples in hospitals, often related to medical care and antiseptic solutions [15,16,17]. Achromobacter xylosoxidans leads to different clinical infections; these include meningitis, urinary tract infections, abscesses, osteomyelitis, corneal ulcers, prosthetic valve endocarditis, peritonitis, pneumonia, and wound infections. Immunocompromised patients are especially at risk, as Achromobacter xylosoxidans can survive in hospital environments and contaminate medical equipment [18]. Most Achromobacter infections are either hospital-acquired or healthcare-associated, often developing in relation to foreign devices [19]. Patients with devices (e.g., catheters and endotracheal tubes), underlying conditions (e.g., diabetes mellitus, chronic renal failure, chronic heart diseases), and current or previous hospitalization or healthcare exposure are all at risk [20,21]. Identification and management of A. xylosoxidans infection in immunocompromised patients is challenging. The early detection of Achromobacter spp. is important for correct therapeutic management and for the design of infection control measures [22]. The detection of beta-lactamase gene blaOXA-114c has been proposed for rapid and accurate A. xylosoxidans identification [23].
A. xylosoxidans exhibits intrinsic resistance to multiple antimicrobial agents, including aminoglycosides, cephalosporins (except ceftazidime), tetracyclines, fluoroquinolones, and aztreonam [24]. However, the intrinsic resistance mechanisms and associated genes are not yet fully understood. To date, two resistance-nodulation-cell division (RND)-type multidrug efflux pumps, AxyABM [8] and AxyXY-OprZ, as well as a chromosomally encoded narrow-spectrum class D β-lactamase, OXA-114, have been identified as being correlated with intrinsic resistance in A. xylosoxidans [25]. In addition, clinical isolates of A. xylosoxidans have exhibited acquired resistance beyond intrinsic resistance, especially to β-lactams. These acquired resistances are usually encoded by genes carried on mobile genetic elements (MGEs), such as integrons. Identified genes include IMP-type carbapenemase genes, VIM-type carbapenemase genes, and other metallo-β-lactamase genes [26]. Therefore, treatment of A. xylosoxidans infections is particularly challenging, especially in patients with severe underlying disease.
The aim of the present study was to investigate an outbreak of A. xylosoxidans infections among hospitalized COVID-19 patients and to identify the source of the infection in order to stop the further spread of the bacterium within the healthcare facilities.

2. Materials and Methods

2.1. Materials and Definitions

Between December 2021 and January 2022, blood samples were taken from nine patients with suspected bacteremia who were hospitalized in the COVID-19 unit of the Internal Medicine Clinic of “G. Gennimatas” Tertiary Academic Hospital in Thessaloniki, Greece. All patients presented with signs and symptoms of bacteremia, such as chills, high fever (temperature > 38.6 °C), and tachycardia, without any other apparent focus of infection. Laboratory testing revealed high levels of white blood cells (>14.000/μL), and elevated levels of C-reactive protein (>0.5 mg/dL) and procalcitonin (>0.5 ng/mL).
Bacteremia due to Achromobacter spp. was defined when the bacterium was isolated from at least two blood cultures. The Hospital Infection Control Committee was informed following the recovery of the first three isolates from the blood cultures. The descriptive study of the outbreak, including the genetic characterization of A. xylosoxidans, was carried out retrospectively.

2.2. Blood Cultures

Blood culture aerobic vials (5–8 mL) were incubated in a BD BACTECTM FX instrument (Becton Dickinson, Sparks, MD, USA). In the event that they flagged positive for microbial growth, they were further cultured onto Brain Heart Infusion (BHI) agar and MacConkey agar plates to isolate the organisms. The colonies were tested by Gram staining to assess their morphology, and Gram-negative bacteria were subsequently tested for oxidase production. Identification and sensitivity testing of the isolates was carried out using the automated VITEK-2 system (bioMérieux, Marcy l’Etoile, France). Collection, processing, and interpretation of blood cultures was performed according to Clinical and Laboratory Standards Institute guidelines [27]. True bloodstream infections were confirmed based on clinical evaluation and the recovery of a second positive blood culture, which helped rule out contamination and confirmed the diagnosis of bacteremia.

2.3. DNA Extraction

Bacterial DNA from three representative isolates was extracted from fresh colonies grown overnight on BHI agar at 37 °C using the Qiagen DNA mini kit (Qiagen, Hilden, Germany) according to the manufacturer’s instructions. Colonies were selected using a sterile loop. The selected colonies were transferred to a 1.5 mL Eppendorf tube containing 180 μL ATL buffer and stirred until the bacteria were thoroughly suspended. A quantity of 20 μL proteinase K was added. The tube was then vortexed until mixed well, then placed on a heater block at 56 °C until complete homogenization was achieved. A quantity of 200 μL AL buffer was added to the mixture and incubated at 70 °C on a heater block for 10 min, followed by the addition of 200 μL absolute ethanol. The mixture was added into the DNA mini spin columns (in 2 mL collection tubes). Two wash steps were followed using 500 μL of Wash Buffer 1 and 2 to wash out impurities. Elution buffer was then added to elute the DNA. DNA concentration (sample starting concentration between 10–100 ng/μL) was assessed by Qubit 2.0 (Thermo Fisher Scientific, Waltham, MA, USA) using a double-strand DNA HS assay kit (Life Technologies Corporation, Grand Island, NY, USA).

2.4. Next-Generation Sequencing and Bioinformatic Analysis

Next-generation sequencing (NGS) was applied to the extracted DNA on an Ion Torrent PGM Platform. DNA libraries were prepared using the Ion XpressTM plus Fragment Library Kit with the protocol adjusted to obtain 200 bp fragments. All procedures regarding purification, ligation, barcoding, library preparation, emulsion PCR, and enrichment were carried out according to the manufacturer’s instructions. Quantified libraries (Ion Library TaqMan® Quantification kit) were mixed in equimolar concentrations and subjected to emulsion PCR-based template preparation using the Ion OneTouchTM 2 system. Sequencing was performed on an Ion PGM bench-top sequencer with the Hi-Q View Sequencing Kit. The final library (single end) was loaded on an Ion-316™ chip. All reagents were obtained from Life Technologies Corporation (Grand Island, NY, USA).
For pathogen identification, the sequences were analyzed with the Basic Local Alignment Search Tool (BLAST) from the National Center for Biotechnology Information (NCBI) [28] and the Kmer Finder Tool (version 3.2) from the Center of Genomic Epidemiology [29]. The Kmer Resistance tool was used for detection of the resistance genes [29,30]. The Comprehensive Antibiotic Resistance Database (CARD) was used, with the selection criteria for hits set to perfect (100%) and strict (>95%) identity to a reference sequence [31]. Multilocus sequence typing (MLST) was based on the analysis of the allelic profiles of the seven housekeeping genes (nusA, rpoB, eno, gltB, lepA, nuoL, and nrdA) against the PubMLST database [32,33].

2.5. Outbreak Investigation

Upon detection of the first three Achromobacter-positive blood cultures (patients 1, 2, and 3), an outbreak investigation team was formed. This included the hospital infection control team, infectious diseases specialists, a clinical microbiologist, a clinical services leader, and a lead nurse, who worked together to identify all cases of Achromobacter bacteremia and collect clinical details both retrospectively and prospectively until the end of the outbreak.
Environmental sampling was performed to identify the source of the outbreak and to implement an infection control intervention. A total of 130 swab samples were collected from each patient’s room, as well as from medication-preparation rooms and nearby offices. Specifically, 22 samples were taken from various surfaces in the Internal Medicine Clinic (room furniture and floors, sinks, taps, door handles, windows, refrigerators, WC ceiling, telephones, cabinet buttons, and other surfaces), 31 from various materials and devices (high-flow devices, blood pressure devices, oxygen flow meters, 3-way systems, cotton, bandages, unused sterile PIVCs, gloves, and syringes), 37 from liquid solutions (liquid hand soaps, soap dispensers, IV water solutions, IV drugs, disinfectants, betadine solutions, chlorhexidine gluconate 4%, and polyvinylpyrrolidone iodine 9.6%), and 20 from nasopharyngeal and rectal swabs obtained from patients for colonization screening. Hand cultures from health care workers were also obtained (20 samples) (Figure 1).
All samples were inoculated on BHI and MacConkey agar plates and placed into thioglycolate broths, which were incubated at 37 °C for 10 days. The broths were sub-cultured to BHI and MacConkey agar plates. As above, the identification and sensitivity testing of the isolates were conducted using the automated VITEK-2 system. Furthermore, samples from the chlorhexidine, betadine, and other disinfectants that were used for patients were cultured in BACTEC vials. Incubation was carried out for 5 days to rule out the possibility of a false negative result. Prior to inoculation, a two-fold dilution of the samples was performed using sterile human plasma. The final inoculation volume was 5 mL (2.5 mL of antiseptic solution and 2.5 mL of human plasma).

3. Results

3.1. Patient Demographics and Clinical Presentation

A total of nine COVID-19 patients (5 males and 4 females) aged 55–87 years (median 70 years) developed bacteremia 4–19 days (median 11 days) post-admission. All patients had peripheral intravenous catheters (PIVCs). Their anonymized demographic characteristics, COVID-19 vaccination history, and underlying health conditions, as well as the numbers of days between their admission to the hospital and detection of A. xylosoxidans, are shown in Table 1. Hypertension and dyslipidemia were the most common comorbidities [three cases (33.3%)], while two patients had no comorbidities. All patients were COVID-19 PCR-positive and had received oxygen during their hospitalization.
An epidemic curve was created to visualize the temporal pattern of cases of A. xylosoxidans infection including the first case (Figure 2).

3.2. Microbial Identification and Antibiotic Resistance Profile

The environmental samples did not reveal colonization by Achromobacter spp. on surfaces in medication preparation rooms or patient rooms or doctors’ offices. The chlorhexidine-alcohol skin disinfectant used for hand disinfection, as well as the solutions used for pre-procedure skin disinfection (betadine solutions, polyvinylpyrrolidone iodine) were found to be sterile. Water solutions and IV medications administered to patients prior to blood culture collection showed no microbial growth. Similarly, environmental samples collected from work surfaces showed no contamination. All materials and devices tested were sterile, except for the cotton, which tested culture-positive for A. xylosoxidans. Furthermore, A. xylosoxidans was isolated from blood cultures of the nine COVID-19 patients, as well as from the cotton used during their care (Table 2). Therefore, contaminated cotton used during the maintenance of PIVCs and during phlebotomy for skin disinfection before needle insertion was considered to be the source of the Achromobacter spp. bacteremia outbreak. Following the identification of the source, the outbreak investigation team instructed that the specific batch of cotton be withdrawn from all clinical areas. After this action, no new cases of Achromobacter bacteremia were reported.
After overnight incubation on blood agar, smooth, pinpoint, and non-hemolytic colonies measuring approximately 1 mm in diameter were observed; MacConkey agar showed non-lactose fermenting, pale-colored, and low convex colonies. Antimicrobial susceptibility testing revealed identical resistance profiles across all isolates. All nine isolates displayed resistance to amikacin, gentamicin, tobramycin, aztreonam, cefotaxime, cefoxitin, ceftazidime, and ciprofloxacin. Susceptibility was retained to colistin, carbapenems, trimethoprim/sulfamethoxazole, and piperacillin/tazobactam (Table 3). Based on susceptibility results, all patients were treated with appropriate antimicrobial therapy, with the majority receiving piperacillin/tazobactam. Follow-up blood cultures collected 5 to 10 days after initiation of antibiotic treatment were negative. Clinical resolution was achieved in all patients, except for one severely immunocompromised patient with multiple comorbidities who passed away.

3.3. Molecular Characterization of A. xylosoxidans

BLAST analysis of the NGS results showed that all three sequenced isolates showed >99.5% identity with A. xylosoxidans strains (e.g., strain GN050, GenBank Accession number NZ_CP053617). A similar result was obtained using the Kmer Resistance tool, and it was shown that the isolates carried the blaOXA-114 gene which is intrinsic to this species. The CARD analysis detected the resistance-nodulation-cell division (RND) antibiotic efflux pump genes adeF, AxyY, and OprZ, which confer resistance to fluoroquinolone, tetracycline, macrolide, aminoglycoside, and cephalosporin antibiotics, as well as the chloramphenicol acetyltransferase (CAT) B3 gene which inactivates phenicol. Regarding the seven housekeeping genes related to MLST, all three isolates presented an identical allelic profile: nusA 14, eno_2, gltB_4, lepA_59, nuoL_4, and nrdA_4. However, the rpoB gene differed by one amino acid (G48A), which was closest to rpoB_80, suggesting that the isolates belong to a novel MLST type.

3.4. Investigation of the Source of the Outbreak

Investigations showed that sterile cotton was removed from its original sterile packaging and stored in a plastic container which was exposed to the environment in a room with high humidity. In addition, the healthcare workers wore double gloves, and only removed their outer gloves after patient contact, leaving the inner gloves in place. This practice led to the accumulation of moisture between the two pairs of gloves. This moisture was then transferred to the cotton upon contact, increasing its humidity and potentially allowing microorganisms to proliferate. As a result of these factors, the cotton used for antiseptic application during patient care became contaminated. Following the identification of the outbreak source, we concluded that the patients became contaminated either during the phlebotomy procedure or during care of PIVCs, in either case as a result of contaminated cotton being used for antisepsis.

3.5. Control Measures and Outcome

The specific batch of cotton was removed from the hospital to halt the ongoing outbreak. In addition, it was recommended that a sterile gauze be used instead of cotton during venipuncture procedures to reduce the risk of future infections. All basic infection prevention practices, such as hand hygiene and isolation, were strictly followed, ensuring that all healthcare personnel were compliant with proper practices.
All patients were diagnosed with true bloodstream infections because all of them developed symptoms of bacteremia. As a result, contamination during the peripheral blood culture collection in the vials was ruled out, along with the pseudoepidemic hypothesis. The patients received piperacillin/tazobactam treatment and most of them were discharged in good condition, except for one patient who had a fatal outcome.

4. Discussion

Between December 2021 and January 2022, we had nine cases of A. xylosoxidans bacteremia in the COVID-19 unit of our hospital, prompting an urgent outbreak investigation. One patient developed bacteremia within four days after admission, while the rest developed the disease after the 10th day of hospitalization, suggesting an HCAI source.
Blood culture is an essential diagnostic tool for detecting live bacteria in the bloodstream [34]. Any contaminated agent that comes into direct contact with blood can potentially cause bacteremia in a short period. Procedures involving contact with sterile tissues or blood vessels of patients can increase the risk of pathogen transmission. Therefore, thorough disinfection of equipment and proper antiseptic procedures on the skin are essential. However, false positive results can also occur when microorganisms from the skin or the surrounding environment are introduced into vials during the blood collection process, and this may influence the physician’s decision to initiate empirical antimicrobial therapy [35,36,37]. Outbreaks and pseudo-outbreaks in healthcare settings can be complex and their differentiation challenging; therefore, they should be systematically investigated using epidemiologic tools. Laboratory testing plays an important role in the evaluation of such outbreaks. In our study, the possibility of pseudo-bacteremia due to contamination of blood culture during venipuncture, culture media preparation, or laboratory processing of the culture was also considered; however, all patients developed clinical signs of bacteremia which were confirmed by laboratory findings, including positive blood cultures and increased procalcitonin levels.
According to the definition provided in the guideline for the control of HCAI outbreaks (WS/T 524-2016), this incident was suspected to be a hospital infection outbreak. Subsequently, an outbreak investigation was initiated, and a multi-modal infection control program implemented. Nosocomial infections are associated with increased morbidity, mortality, and medical costs in patients, and they also contribute to antimicrobial resistance.
During the COVID-19 pandemic, broad-spectrum antibiotics were often misused, with many patients taking them without proper indication or prescription [38]. This inappropriate use not only reflects poor compliance but also raises concerns about accelerating antimicrobial resistance in the community. In patients with COVID-19, secondary bacterial infections and bacterial coinfections have been identified as the major causes of mortality and morbidity [6,39]. Achromobacter spp. are increasingly recognized as important emerging nosocomial pathogens, mainly in immunocompromised hosts, as well as in patients with cystic fibrosis [17].
Research on A. xylosoxidans transmissibility has mostly focused on specific loci, ranging from near-incident-level variation to extremely endemic. Incubators and humidifiers, contaminated soaps, well water, and fluids (intravenous, hemodialysis, irrigation, and mouthwash) have all been linked to hospital-acquired infections. Another frequent cause of bacteremia is the introduction of A. xylosoxidans through inadequately sanitized equipment. A further pathway of infection is provided by the resistance of certain strains to sterilizing drugs (such as chlorhexidine) which can act as extra reservoirs. Although patient-to-patient transmission has been documented, environmental sources seem to account for the majority of A. xylosoxidans infections [15,40,41,42]. Furthermore, biofilm formation, which seems to be a natural ability in the majority of strains, adds to virulence and resistance to antibiotics [43].
Cotton is a highly hydrophilic material [44]. Although this characteristic can be beneficial in certain medical practices [45], it may also raise the risk of infection if cotton comes into contact with contaminated fluids. Cotton balls that are immersed in benzalkonium chloride solution have a tendency to be contaminated, according to a study by Oie et al., who investigated the microbiological contamination of antiseptics used in hospital settings [46]. The cotton used in these settings was not soaked in any antiseptic; however, it may have absorbed enough moisture to enable the growth of pathogenic bacteria on its surface. It has been reported that cotton can even release an extracellular matrix to create bacterial plaques or biofilms which can pose a risk to human health [47]. In this study, the source of the Achromobacter spp. bacteremia outbreak was identified as contaminated cotton used for antiseptic purposes during phlebotomy or PIVC care. As a result, the infection control team recommended replacing cotton with sterile gauze for application of pressure at puncture sites.
The effective treatment of A. xylosoxidans infection is challenging due to its intrinsic resistance to a variety of antibiotics; therefore, alternative or combined antibiotic therapy may be required [48]. The rise of antimicrobial resistance requires precise, innovative strategies. The Trojan horse technique uses bacterial iron uptake to deliver antibiotics linked to siderophores, bypassing defenses and improving drug entry. Targeting bacterial metallophores, vital for metal ion acquisition and virulence, also disrupts pathogen survival. These targeted approaches are key to developing effective treatments against resistant bacteria by overcoming barriers and limiting resistance [49,50,51].
The application of new technology such as NGS provides additional insight into the genetic characterization of strains, and increases knowledge of the underlying mechanisms of the intrinsic antibiotic resistance of the bacterium. The detection of a common distinct (not determined) ST in the isolates of the present study suggests a clonal similarity among A. xylosoxidans isolates. Molecular studies are needed to identify novel alleles and sequence types which will enrich the MLST database and enable studies on the association of specific STs with virulence properties [52].
Treating infections caused by Achromobacter spp. is challenging because of their innate or acquired resistance to several medicines [25,53]. Good sanitation and strict infection control practices are fundamental in healthcare facilities to decrease the risk of infections in hospitalized patients. Medical supplies such as cotton require proper storage in clean, dry conditions, as moisture accumulation can promote bacterial growth. In our setting, the immediate removal of the contaminated cotton effectively halted the further spread of the pathogen. Regular training for healthcare workers on proper handling techniques and hygiene practices is also crucial. Furthermore, molecular approaches were critical in achieving accurate species identification and for assessing clonal relationships among the isolates. Finally, continuous communication between laboratory staff and clinical doctors is necessary to promptly identify the potential source of any infection, as demonstrated in our study with the identification of A. xylosoxidans, and to prevent the spread of pathogens. The importance of multidisciplinary collaboration among clinical microbiologists, infectious disease specialists, epidemiologists, and nurses in infection control should be strongly emphasized when elucidating an epidemiological situation.

5. Conclusions

Achromobacter spp. was previously considered a rare pathogen. However, in recent years, the incidence of Achromobacter spp. infections has increased, mainly due to the growing number of immunocompromised patients. The results of the current study showed that the source of an A. xylosoxidans outbreak among hospitalized COVID-19 patients was contaminated cotton used for antisepsis application. The early identification of the source enabled the successful application of infection control measures which prevented further spread of the infection in the healthcare setting. The findings reported here highlights the need for enhanced awareness, continuous surveillance, and collaboration among healthcare professionals.

Author Contributions

Conceptualization, K.K. (Konstantina Kontopoulou) and M.T.; Methodology, K.K. (Konstantina Kontopoulou), M.T. and S.P.; Formal Analysis, K.K. (Konstantina Kontopoulou), M.T. and A.P.; Investigation, K.K. (Konstantina Kontopoulou), G.P., K.K. (Konstantinos Koutsouflianiotis), M.T. and A.P.; Resources, G.P. and K.K. (Konstantinos Koutsouflianiotis); Data Curation, K.K. (Konstantina Kontopoulou), M.T. and A.P.; Writing—Review and Editing, M.T., K.K. (Konstantina Kontopoulou) and A.P.; Visualization, M.T., K.K. (Konstantina Kontopoulou) and A.P.; Supervision, K.K. (Konstantina Kontopoulou), A.P. and M.T. All authors have read and agreed to the published version of the manuscript.

Funding

The molecular part of the study was funded by the DURABLE project. The DURABLE project has been co-funded by the European Union under the EU4Health Programme (EU4H), project no. 101102733. Views and opinions expressed are, however, those of the author only and do not necessarily reflect those of the European Union or the European Health and Digital Executive Agency. Neither the European Union nor the granting authority can be held responsible for them.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Informed consent statements were not required for this study as it involved a retrospective analysis of medical records and microbiological samples collected during routine diagnostic procedures for suspected bacteremia. The research aimed to investigate an infection outbreak, not to intervene in patient care, and no additional experimental interventions were conducted.

Data Availability Statement

Data and materials are available on request.

Conflicts of Interest

The authors confirm that there are no known conflicts of interest associated with this publication.

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Figure 1. Proportions of samples collected and tested during the achromobacter outbreak investigation (n = 130).
Figure 1. Proportions of samples collected and tested during the achromobacter outbreak investigation (n = 130).
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Figure 2. Epidemic curve of cases of A. xylosoxidans infection per day, including the first case of infection.
Figure 2. Epidemic curve of cases of A. xylosoxidans infection per day, including the first case of infection.
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Table 1. Characteristics of COVID-19 patients who presented A. xylosoxidans bacteremia.
Table 1. Characteristics of COVID-19 patients who presented A. xylosoxidans bacteremia.
AgeSexCOVID-19 Vaccine DosesDays Between Admission and Detection of A. xylosoxidans Underlying Diseases
55Male04-
61Female011Hypothyroidism
59Male010-
61Female117Asthma
70Male311Myocardial infarction,
dyslipidemia
87Female319Hypertension, gastroesophageal reflux disease
76Male212Hypertension,
dyslipidemia
71Male011Hypertension,
dyslipidemia,
diabetes
83Female212Breast cancer, Alzheimer’s
Table 2. Numbers of A. xylosoxidans isolates detected from environmental samples and patient cultures.
Table 2. Numbers of A. xylosoxidans isolates detected from environmental samples and patient cultures.
Sample TypeNumber (n = 140)Culture ResultOrganism Detected
Environmental surfaces 22No growth—
Liquid and disinfectant solutions37No growth—
Materials and devices 31No growth—
Colonization screening samples20No growth—
Hand cultures20No growth—
Cotton1PositiveAchromobacter xylosoxidans
Blood cultures9PositiveAchromobacter xylosoxidans
Table 3. In vitro antimicrobial resistance profiles of nine Achromobacter xylosoxidans isolates.
Table 3. In vitro antimicrobial resistance profiles of nine Achromobacter xylosoxidans isolates.
Antimicrobial AgentNumber of Isolates (n = 9)
Number of Resistant IsolatesResistance Rate (%)Interpretation
Amikacin9100Resistant
Gentamicin9100Resistant
Tobramycin9100Resistant
Aztreonam9100Resistant
Cefotaxime9100Resistant
Cefoxitin9100Resistant
Ceftazidime9100Resistant
Ciprofloxacin9100Resistant
Colistin00Susceptible
Imipenem00Susceptible
Meropenem00Susceptible
Trimethoprim/Sulfamethoxazole00Susceptible
Piperacillin/Tazobactam00Susceptible
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Tsekoura, M.; Petridis, G.; Koutsouflianiotis, K.; Pappa, S.; Papa, A.; Kontopoulou, K. Bacteremia Outbreak Due to Achromobacter xylosoxidans in Hospitalized COVID-19 Patients. Microbiol. Res. 2025, 16, 156. https://doi.org/10.3390/microbiolres16070156

AMA Style

Tsekoura M, Petridis G, Koutsouflianiotis K, Pappa S, Papa A, Kontopoulou K. Bacteremia Outbreak Due to Achromobacter xylosoxidans in Hospitalized COVID-19 Patients. Microbiology Research. 2025; 16(7):156. https://doi.org/10.3390/microbiolres16070156

Chicago/Turabian Style

Tsekoura, Magdalini, Georgios Petridis, Konstantinos Koutsouflianiotis, Styliani Pappa, Anna Papa, and Konstantina Kontopoulou. 2025. "Bacteremia Outbreak Due to Achromobacter xylosoxidans in Hospitalized COVID-19 Patients" Microbiology Research 16, no. 7: 156. https://doi.org/10.3390/microbiolres16070156

APA Style

Tsekoura, M., Petridis, G., Koutsouflianiotis, K., Pappa, S., Papa, A., & Kontopoulou, K. (2025). Bacteremia Outbreak Due to Achromobacter xylosoxidans in Hospitalized COVID-19 Patients. Microbiology Research, 16(7), 156. https://doi.org/10.3390/microbiolres16070156

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