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Article

Comparative Analysis of Clinical Characteristics and Antimicrobial Resistance Between Acinetobacter baumannii and Other Acinetobacter Species

by
Si-Ho Kim
1 and
Seok Jun Mun
2,3,*
1
Division of Infectious Diseases, Department of Medicine, Samsung Changwon Hospital, Sungkyunkwan University School of Medicine, Changwon 51353, Republic of Korea
2
Division of Infectious Diseases, Department of Internal Medicine, Inje University Busan Paik Hospital, Inje University College of Medicine, Busan 47392, Republic of Korea
3
Paik Institute for Clinical Research, Inje University College of Medicine, Busan 47392, Republic of Korea
*
Author to whom correspondence should be addressed.
Pathogens 2025, 14(1), 46; https://doi.org/10.3390/pathogens14010046
Submission received: 30 November 2024 / Revised: 22 December 2024 / Accepted: 7 January 2025 / Published: 8 January 2025
(This article belongs to the Section Epidemiology of Infectious Diseases)
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Abstract

:
Acinetobacter species are major pathogens responsible for hospital-acquired infections. This study aimed to compare the clinical characteristics, outcomes, and antimicrobial resistance between Acinetobacter baumannii (AB) and non-baumannii Acinetobacter (NBA) species. In this retrospective cohort study, we analyzed data from adult patients (aged 18 or older) with Acinetobacter bacteremia treated at two tertiary hospitals from July 2020 to November 2023. Among 260 cases of Acinetobacter bacteremia, 42 (16.2%) involved NBA species. The AB group exhibited higher antimicrobial resistance rates across all tested agents, except for minocycline. Female patients, younger patients, and those with catheter-related infections were more commonly observed in the NBA group than in the AB group, while pneumonia and septic shock were more prevalent in the AB group. In a multivariable analysis of 30-day mortality, factors associated with higher mortality included moderate to severe liver disease, chronic kidney disease, carbapenem resistance, septic shock, and higher Pitt Bacteremia Scores. When stratified by carbapenem resistance (CR) status, only CR-AB exhibited significantly lower 30-day survival rate (33.4%) compared to that of the other groups (non-CR-NBA, 77.3%; CR-NBA, 77.8%; non-CR-AB, 90.1%; p < 0.001). Our findings highlight distinct clinical differences between AB and NBA bacteremia cases; however, the mortality rate for non-CR-AB was comparable to that observed in NBA bacteremia.

1. Introduction

Acinetobacter, a complex bacterial genus, is a common cause of hospital-acquired infections (HAI), particularly pneumonia and catheter-associated infections [1]. Among the various species within the genus, Acinetobacter baumannii has been reported as the most common species associated with infections and exhibits the highest virulence, accounting for 60–90% of A. baumannii bacteremia cases [1,2,3,4]. Close relatives of A. baumannii—A. calcoaceticus, A. geminorum, A. lactucae (formerly also known as A. dijkshoorniae), A. nosocomialis, A. oleivorans, A. pittii, and A. seifertii—collectively form the Acinetobacter calcoaceticus–baumannii (ACB) complex. Although species within the ACB complex are nearly phenotypically indistinguishable, they exhibit substantial differences in ecology, pathogenicity, epidemiology, and antibiotic susceptibility [5]. These species also contribute to HAIs [1,4]. Additionally, other Acinetobacter species outside the ACB complex, such as A. lwoffii, have occasionally been reported as pathogens [1,6,7]. Since the adoption of matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry (MS) in clinical settings, Acinetobacter species have been reliably identified with over 97% accuracy [8,9]. Therefore, clinicians now have access to more accurate information on specific Acinetobacter species; however, only a few studies have described infections caused by species other than A. baumannii. Furthermore, no consensus has been established on the specific characteristics of infections caused by non-baumannii Acinetobacter (NBA) species in comparison to A. baumannii [2,3,4,10]. In this study, we describe the clinical characteristics and antimicrobial resistance profiles of bacteremia caused by NBA species and compare these to those of A. baumannii bacteremia.

2. Materials and Methods

2.1. Study Population, Definitions, and Design

This retrospective cohort study was conducted from July 2020 to November 2023 in two university-affiliated tertiary hospitals: Samsung Changwon Hospital (760 beds) and Inje University Busan Paik Hospital (818 beds). The inclusion criteria were adults (aged 18 or older) with Acinetobacter species bacteremia, which was isolated from one or more blood cultures. Patients were excluded if they (1) had polymicrobial bacteremia, (2) were lost to follow-up within 5 days, or (3) had Acinetobacter species isolated from only one blood culture bottle without any symptoms suggesting infection. Patient demographics and laboratory data were collected from electronic medical records. The updated Charlson Comorbidity Index was used to assess the degree of comorbidity, and the severity of bacteremia was evaluated using the Pitt Bacteremia Score (PBS) [11,12]. Intravenous catheter-related infection (CRI) is defined as an infection associated with peripheral intravascular catheters or central venous catheters [13]. The objectives of this study were to investigate the characteristics, antimicrobial resistance, and mortality of various Acinetobacter species. Therefore, the clinical characteristics and antimicrobial resistance were compared between A. baumannii and NBA species. Additionally, a subgroup analysis was conducted to compare the ACB complex (excluding A. baumannii) with the non-ACB complex within the NBA group. Patients included in this study were observed for 30 days after bacteremia, or until death or loss to follow-up. The survival rates of the A. baumannii and NBA groups were calculated, and factors associated with overall 30-day mortality were analyzed.

2.2. Microbiologic Methods

Blood samples were collected via a peripheral vein and/or central line, with two sets of blood culture bottles (aerobic and anaerobic, 8–10 cc each) prepared for incubation in either the Bactec-9240 system (Becton Dickinson, Sparks, MD, USA) or the BacT/Alert 3D system (bioMérieux, Marcy l’Etoile, France). All samples were cultured on blood agar and MacConkey agar plates in a 35 °C incubator for 24 h and identified by MALDI-TOF MS using the Vitek MS system (bioMérieux, Hazelwood, MI, USA). Antimicrobial susceptibility tests (ASTs) were conducted with the Vitek II automated system (bioMérieux, Marcy-l’Étoile, France). following the Clinical and Laboratory Standards Institute (CLSI) 2023 guidelines [14]. All procedures adhered to the manufacturers’ instructions.

2.3. Statistical Methods

The statistical analysis was conducted using IBM SPSS Statistics for Windows, version 25.0 (IBM Corp., 2018, Chicago, IL, USA), and R software, version 4.2.1 (R Foundation for Statistical Computing, Vienna, Austria). Continuous variables were analyzed with Student’s t-test or the Mann–Whitney U test, while categorical variables were compared using the chi-square test or Fisher’s exact test. The survival rate and curve were plotted using the Kaplan–Meier method and compared using the log-rank test. Risk factors for overall 30-day mortality were evaluated with a Cox regression model. Variables with p < 0.15 in the univariable analysis were included in the multivariable analysis using a forward stepwise Cox regression model. All p-values were two-tailed, and p < 0.05 was considered statistically significant.

2.4. Ethical Considerations

The study was approved by the Institutional Review Board of Samsung Medical Center (IRB file number: SCMC 2024-11-009) and Busan Paik Hospital (BPIRB 2024-11-024) with a waiver for informed consent. This waiver was granted as this was an observational retrospective study, and all patient data were analyzed anonymously.

3. Results

3.1. Study Population and Isolated Acinetobacter Species

A total of 260 patients with Acinetobacter bacteremia were included in this study. Of the 260 cases, 42 (16.2%) involved the NBA species (Figure 1). Among the NBA species, 22 cases were of the ACB complex, comprising 15 cases of A. nosocomialis and 7 cases of A. pittii. Of the 20 cases of non-ACB complex, A. ursingii (7 cases) was the most common species, followed by A. lwoffii (5 cases, Figure 2).

3.2. Clinical Characteristics and Antimicrobial Resistances in Each Acinetobacter Species Group

In comparing patients with A. baumannii bacteremia to those with NBA, the former group had a higher prevalence of male sex, diabetes with end-organ damage, end-stage renal disease, and carbapenem resistance. Pneumonia was also more frequent, and disease severity was more pronounced in the A. baumannii bacteremia group than in the NBA group. In contrast, patients with NBA bacteremia were younger, had a higher incidence of intravenous CRI, and received appropriate antibiotics earlier in the course of infection compared to those with A. baumannii (Table 1). When comparing antimicrobial resistance between the groups, A. baumannii isolates showed higher resistance rates to all antibiotics except minocycline (Table 2). In the subgroup analysis comparing the ACB complex (excluding A. baumannii) with the non-ACB complex, no statistically significant differences were observed, except for carbapenem and gentamicin resistance rates, which were higher in the ACB complex group (Supplementary Tables S1 and S2).

3.3. Risk Factors for Overall 30-Day Mortality

The overall 30-day survival rates were 41.6% for patients with A. baumannii bacteremia and 77.4% for those with NBA bacteremia (p < 0.0001 by log-rank test, Figure 3A). In contrast, no significant differences were observed between the ACB complex (excluding A. baumannii) and the non-ACB complex bacteremia, with survival rates of 81.3% and 72.7%, respectively (p = 0.564, Supplementary Figure S1). Supplementary Table S3 details factors associated with 30-day mortality in the study population based on a Cox regression model. In the multivariable analysis, moderate to severe liver disease (adjusted hazard ratio [aHR] 2.092, 95% CI 1.159–3.775, p = 0.014), moderate to severe renal disease (aHR 1.951, 95% CI 1.245–3.059, p = 0.004), carbapenem resistance (aHR 2.145, 95% CI 1.057–4.351, p = 0.035), septic shock (aHR 2.450, 95% CI 1.353–4.437, p = 0.003), and PBS (aHR 1.200, 95% CI 1.121–1.284, p < 0.001) were associated with higher mortality. Conversely, appropriate antibiotic therapy (aHR 0.219, 95% CI 0.138–0.349, p < 0.001) was associated with lower mortality (Table 3). Since carbapenem resistance was an independent factor associated with mortality, the stratification of patients with Acinetobacter bacteremia by carbapenem resistance (CR) status revealed that only the CR-AB group had a significantly lower 30-day survival rate (33.4%) compared to the other groups (non-CR-NBA, 77.3%; CR-NBA, 77.8%; non-CR-AB, 90.1%; p < 0.001, Figure 3B).
Supplementary Table S4 presents a subgroup analysis of factors associated with 30-day mortality in patients who received appropriate antimicrobial therapy, using a Cox regression model. In the multivariable analysis, moderate to severe renal disease (aHR 3.986, 95% CI 1.817–8.743, p = 0.001), pneumonia (aHR 2.466, 95% CI 1.099–5.534, p = 0.029), and PBS (aHR 1.382, 95% CI 1.174–1.627, p < 0.001) were associated with higher mortality (Table 4).

4. Discussion

Our study revealed that approximately one in six cases of Acinetobacter bacteremia was caused by NBA. The ratio of ACB complex to non-ACB species among NBA cases was close to 1:1. The characteristics and antimicrobial resistance profiles were significantly different between A. baumannii and NBA cases. However, among NBA cases, carbapenem and gentamicin resistance rates were the only significant differences observed between the ACB complex and non-ACB species. Regarding the 30-day survival rates, patients with A. baumannii bacteremia showed significantly lower survival rates compared to those in the NBA group; however, when stratified by carbapenem resistance, only patients with CRAB bacteremia exhibited a significantly lower survival rate compared to other groups.
The genus name Acinetobacter, derived from the Greek word ακινητος (akinetos), meaning “nonmotile”, was first introduced in 1954 to distinguish nonmotile microorganisms from motile ones within the genus Achromobacter [15]. Subsequently, Baumann et al. conducted a comprehensive study and concluded that the various species mentioned above belonged to a single genus, which they proposed naming Acinetobacter; the group also reported that further subclassification into distinct species based on phenotypic characteristics was not feasible [16]. A significant advancement in the complex history of the Acinetobacter genus occurred in 1986 when Bouvet and Grimont used DNA–DNA hybridization studies to identify 12 DNA hybridization groups (or genospecies). Some of these groups were assigned formal species names, including A. baumannii [17]. Although species within Acinetobacter are difficult to classify based on phenotype, there are differences in the clinical characteristics and antimicrobial resistance patterns between A. baumannii and NBA [1]. First, A. baumannii has a higher virulence than do NBA species [1]. For example, A. baumannii strains demonstrated higher lethality toward wax moth larvae (Galleria mellonella) compared to strains of A. baylyi and A. lwoffii [18]. A study conducted in the United States, which analyzed Acinetobacter blood isolates collected between 1995 and 2003 from 52 hospitals, reported that A. baumannii (187/295) was the most prevalent species, followed by A. nosocomialis (61/295), A. pittii (23/295), and other NBA species (24/295). The mortality rates associated with these groups were 36.9%, 16.4%, 13.0%, and 4.2%, respectively, with statistically significant differences observed among the groups (p < 0.001) [2]. Second, both NBA species and A. baumannii are commonly found in wet environments and hospital settings. NBA species are frequently isolated from the skin of healthy individuals, whereas A. baumannii is rarely found on healthy skin and is primarily associated with hospital environments and immunocompromised patients [19,20]. In clinical studies involving hospitalized patients, those with NBA bacteremia were found to have fewer underlying conditions and lower disease severity than those with AB bacteremia. A study conducted in Korea further reported that patients with NBA bacteremia had lower rates of ICU admission (14.3% in the NBA group vs. 49.1% in the A. baumannii group, p < 0.001) and utilization of indwelling Foley catheters (21.4% vs. 60.7%, p < 0.001) and mechanical ventilation (3.6% vs. 40.2%, p < 0.001) [10]. Another study conducted on Korean children also revealed that malignancy was more common among patients infected with the ACB complex than it was in the non-ACB complex group [4]. Third, A. baumannii exhibited higher levels of antimicrobial resistance compared to the NBA species. While antimicrobial resistance varies greatly by geographic region, carbapenem resistance in A. baumannii has been reported to exceed 50% in Southern and Eastern Europe, reaching approximately 90% in the Republic of Korea [21,22]. However, carbapenem resistance in NBA species was reported to be approximately 10% or lower [2,3,4,22,23].
Our study findings were consistent with those reported in previous studies. The 30-day mortality rate of patients with A. baumannii bacteremia was more than two times higher than that of patients with NBA bacteremia. The most common portals of entry for bacteremia in each group were pneumonia and CRI, respectively. In addition, patients with A. baumannii bacteremia had higher rates of diabetes mellitus with end-organ damage and moderate to severe renal disease than those with NBA bacteremia. Furthermore, more patients with A. baumannii bacteremia had septic shock and had higher PBS than those with NBA bacteremia. Except for minocycline, resistance to all other antimicrobials was higher in A. baumannii isolates than in NBA isolates. The novelty of our study is that we classified Acinetobacter species not only into A. baumannii and NBA but also into ACB complex and non-ACB complex. Previous studies primarily compared the characteristics of various NBA species with A. baumannii [2,3,7] or overall non-ACB complex species with the ACB complex [4,10]. In contrast, our study included a subgroup analysis comparing the ACB complex (excluding A. baumannii) with the non-ACB complex, which revealed no significant differences in patient characteristics, clinical manifestations, or outcomes. However, carbapenem and gentamicin resistances were notably more common in the ACB complex group than in the NBA group. It is known that NBA species can exhibit carbapenem resistance [4,23,24], which is associated with beta-lactamase genes. However, to the best of our knowledge, this is the first study to report distinct antimicrobial resistance patterns between these two groups. In addition, analysis of factors associated with mortality revealed that carbapenem resistance was independently associated with higher mortality, regardless of whether the infection was caused by A. baumannii or NBA. This differs from a previous report from Thailand, which suggested that infection with CR-AB was associated with 30-day mortality (adjusted OR 2.50, 95% CI 1.03–6.25, p = 0.029), whereas infection with non-ACB complex species was associated with lower 30-day mortality (adjusted OR 0.09, 95% CI 0.02–0.41, p = 0.005) [3]. Therefore, further studies are needed to evaluate the contributions of specific Acinetobacter species and carbapenem resistance to patient outcomes.
Our study has several limitations. First, Acinetobacter species were identified using MALDI-TOF MS. Although MALDI-TOF MS demonstrates high accuracy (exceeding 97%) in identifying Acinetobacter species, including non-A. baumannii members of the ACB complex, the gold standard for species identification remains 16S rDNA and rpoB gene sequencing [8]. Second, this study was conducted in two medical centers in the Republic of Korea. Antimicrobial resistance patterns can vary significantly by period and geographic location. For example, in settings where the carbapenem resistance rate of A. baumannii is low, there might be no significant difference between A. baumannii and NBA isolates. However, even in the absence of differences in carbapenem resistance, other antimicrobial resistance tended to be higher in A. baumannii isolates [2,10]. Third, the disparity in sample sizes between the A. baumannii and NBA groups (particularly for carbapenem resistance in the NBA group) may have limited our ability to detect certain differences. Specifically, the relatively small sample size of the NBA group could have reduced the statistical power of the analysis.

5. Conclusions

In conclusion, our study suggested that a significant portion of NBA species contribute to clinical infections among Acinetobacter species. In addition to A. baumannii, other species within the ACB complex should also be monitored for antimicrobial resistance. Although patients with A. baumannii bacteremia exhibited higher mortality than those with NBA bacteremia, this difference may be attributable to carbapenem resistance rather than to the intrinsic virulence of A. baumannii. Further large-scale and prospective studies are needed to evaluate the clinical characteristics and burden of infections caused by NBA species.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/pathogens14010046/s1, Supplementary Table S1. Clinical characteristics of patients with ACB complex (excluding A. baumannii) and non-ACB complex bacteremia. Supplementary Table S2. Antibiotic resistance rate of ACB complex (excluding A. baumannii) and non-ACB complex bacteremia. Supplementary Table S3. Univariable analyses for overall 30-day in-hospital mortality in patients with Acinetobacter bacteremia. Supplementary Table S4. Univariable analyses for overall 30-day mortality in patients with Acinetobacter bacteremia who received appropriate antibiotic therapy. Supplementary Figure S1. The survival curve illustrates outcomes among patients with ACB complex (excluding A. baumannii) and non-ACB complex bacteremia.

Author Contributions

Conceptualization, S.J.M.; methodology, S.-H.K.; software, S.-H.K.; validation, S.J.M. and S.-H.K.; formal analysis, S.J.M. and S.-H.K.; investigation, S.J.M. and S.-H.K.; resources, S.J.M. and S.-H.K.; data curation, S.J.M. and S.-H.K.; writing—original draft preparation, S.J.M. and S.-H.K.; writing—review and editing, S.J.M. and S.-H.K.; visualization, S.-H.K.; supervision, S.J.M.; project administration, S.J.M. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

This study was conducted in accordance with the Declaration of Helsinki and approved by the Institutional Review Board of Samsung Changwon Hospital (SCMC 2024-11-009 and 18 November 2024) and Busan Paik Hospital (BPIRB 2024-11-024, and 27 November 2024).

Informed Consent Statement

Patient consent was waived because this was an observational retrospective study, and all patient data were analyzed anonymously.

Data Availability Statement

The raw data supporting the conclusions of this article will be made available by the authors upon request.

Acknowledgments

This study was supported by “Inje University Busan Paik Hospital”.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Wong, D.; Nielsen, T.B.; Bonomo, R.A.; Pantapalangkoor, P.; Luna, B.; Spellberg, B. Clinical and Pathophysiological Overview of Acinetobacter Infections: A Century of Challenges. Clin. Microbiol. Rev. 2017, 30, 409–447. [Google Scholar] [CrossRef] [PubMed]
  2. Wisplinghoff, H.; Paulus, T.; Lugenheim, M.; Stefanik, D.; Higgins, P.G.; Edmond, M.B.; Wenzel, R.P.; Seifert, H. Nosocomial bloodstream infections due to Acinetobacter baumannii, Acinetobacter pittii and Acinetobacter nosocomialis in the United States. J. Infect. 2012, 64, 282–290. [Google Scholar] [CrossRef] [PubMed]
  3. Chusri, S.; Chongsuvivatwong, V.; Rivera Jesabel, I.; Silpapojakul, K.; Singkhamanan, K.; McNeil, E.; Doi, Y. Clinical Outcomes of Hospital-Acquired Infection with Acinetobacter nosocomialis and Acinetobacter pittii. Antimicrob. Agents Chemother. 2014, 58, 4172–4179. [Google Scholar] [CrossRef]
  4. Kang, H.M.; Kim, K.R.; Kim, G.; Lee, D.-g.; Kim, Y.J.; Choi, E.H.; Lee, J.; Yun, K.W. Antimicrobial resistance genes harbored in invasive Acinetobacter calcoaceticus-baumannii complex isolated from Korean children during the pre-COVID-19 pandemic periods, 2015–2020. Front. Cell. Infect. Microbiol. 2024, 14, 1410997. [Google Scholar] [CrossRef] [PubMed]
  5. Nemec, A.; Krizova, L.; Maixnerova, M.; van der Reijden, T.J.K.; Deschaght, P.; Passet, V.; Vaneechoutte, M.; Brisse, S.; Dijkshoorn, L. Genotypic and phenotypic characterization of the Acinetobacter calcoaceticus–Acinetobacter baumannii complex with the proposal of Acinetobacter pittii sp. nov. (formerly Acinetobacter genomic species 3) and Acinetobacter nosocomialis sp. nov. (formerly Acinetobacter genomic species 13TU). Res. Microbiol. 2011, 162, 393–404. [Google Scholar] [CrossRef]
  6. Ku, S.; Hsueh, P.; Yang, P.; Luh, K. Clinical and microbiological characteristics of bacteremia caused by Acinetobacter lwoffii. Eur. J. Clin. Microbiol. Infect. Dis. 2000, 19, 501–505. [Google Scholar] [CrossRef]
  7. Koizumi, Y.; Sakanashi, D.; Ohno, T.; Yamada, A.; Shiota, A.; Kato, H.; Hagihara, M.; Watanabe, H.; Asai, N.; Watarai, M.; et al. The clinical characteristics of Acinetobacter bacteremia differ among genomospecies: A hospital-based retrospective comparative analysis of genotypically identified strains. J. Microbiol. Immunol. Infect. 2019, 52, 966–972. [Google Scholar] [CrossRef] [PubMed]
  8. Li, X.; Tang, Y.; Lu, X. Insight into Identification of Acinetobacter Species by Matrix-Assisted Laser Desorption/Ionization Time of Flight Mass Spectrometry (MALDI-TOF MS) in the Clinical Laboratory. J. Am. Soc. Mass Spectrom. 2018, 29, 1546–1553. [Google Scholar] [CrossRef]
  9. Espinal, P.; Seifert, H.; Dijkshoorn, L.; Vila, J.; Roca, I. Rapid and accurate identification of genomic species from the Acinetobacter baumannii (Ab) group by MALDI-TOF MS. Clin. Microbiol. Infect. 2012, 18, 1097–1103. [Google Scholar] [CrossRef]
  10. Choi, S.-H.; Kim, M.-Y.; Jun, J.-B.; Kim, N.J.; Jeong, J.-Y.; Kim, Y.S.; Woo, J.H.; Choo, E.J.; Kwak, Y.G.; Kim, M.-N. Clinical characteristics and outcomes of bacteremia caused by Acinetobacter species other than A. baumannii: Comparison with A. baumannii bacteremia. J. Infect. Chemother. 2006, 12, 380–386. [Google Scholar] [CrossRef] [PubMed]
  11. Quan, H.; Li, B.; Couris, C.M.; Fushimi, K.; Graham, P.; Hider, P.; Januel, J.-M.; Sundararajan, V. Updating and Validating the Charlson Comorbidity Index and Score for Risk Adjustment in Hospital Discharge Abstracts Using Data From 6 Countries. Am. J. Epidemiol. 2011, 173, 676–682. [Google Scholar] [CrossRef]
  12. Chow, J.W.; Yu, V.L. Combination antibiotic therapy versus monotherapy for gram-negative bacteraemia: A commentary. Int. J. Antimicrob. Agents 1999, 11, 7–12. [Google Scholar] [CrossRef]
  13. CDC Guidelines for the Prevention of Intravascular Catheter-Related Infections. 2011. Available online: https://www.cdc.gov/infection-control/media/pdfs/Guideline-BSI-H.pdf (accessed on 5 November 2024).
  14. Clinical and Laboratory Standards Institute (CLSI). Performance Standards for Antimicrobial Susceptibility Testing: Twenty-First Informational Supplement: CLSI Document M100, 33rd ed.; Clinical and Laboratory Standards Institute: Wayne, PA, USA, 2023. [Google Scholar]
  15. Brisou, J.; Prevot, A.R. Studies on bacterial taxonomy. X. The revision of species under Acromobacter group. Ann. Inst. Pasteur. 1954, 86, 722–728. [Google Scholar]
  16. Baumann, P.; Doudoroff, M.; Stanier, R.Y. A study of the Moraxella group. II. Oxidative-negative species (genus Acinetobacter). J. Bacteriol. 1968, 95, 1520–1541. [Google Scholar] [CrossRef] [PubMed]
  17. Bouvet, P.; Grimont, P. Taxonomy of the Genus Acinetobacter with the Recognition of Acinetobacter baumannii sp. nov. Acinetobacter haemolyticus sp. nov. Acinetobacter johnsonii sp. nov. and Acinetobacter junii sp. nov. and Emended Descriptions of Acinetobacter calcoaceticus and Acinetobacter lwofii. Int. J. Syst. Bacteriol. 1986, 36, 228–240. [Google Scholar] [CrossRef]
  18. Peleg Anton, Y.; Jara, S.; Monga, D.; Eliopoulos George, M.; Moellering Robert, C.; Mylonakis, E. Galleria mellonella as a Model System To Study Acinetobacter baumannii Pathogenesis and Therapeutics. Antimicrob. Agents Chemother. 2009, 53, 2605–2609. [Google Scholar] [CrossRef]
  19. Al Atrouni, A.; Joly-Guillou, M.-L.; Hamze, M.; Kempf, M. Reservoirs of Non-baumannii Acinetobacter Species. Front. Microbiol. 2016, 7, 49. [Google Scholar] [CrossRef]
  20. Dijkshoorn, L.; van Aken, E.; Shunburne, L.; van der Reijden, T.J.K.; Bernards, A.T.; Nemec, A.; Towner, K.J. Prevalence of Acinetobacter baumannii and other Acinetobacter spp. in faecal samples from non-hospitalised individuals. Clin. Microbiol. Infect. 2005, 11, 329–332. [Google Scholar] [CrossRef] [PubMed]
  21. Antimicrobial Resistance Surveillance in Europe 2023–2021 Data; European Centre for Disease Prevention and Control and World Health Organization: Stockholm, Sweden, 2023.
  22. Kim, D.; Yoon, E.-J.; Hong, J.S.; Choi, M.H.; Kim, H.S.; Kim, Y.R.; Kim, Y.A.; Uh, Y.; Shin, K.S.; Shin, J.H.; et al. Major Bloodstream Infection-Causing Bacterial Pathogens and Their Antimicrobial Resistance in South Korea, 2017–2019: Phase I Report From Kor-GLASS. Front. Microbiol. 2022, 12, 799084. [Google Scholar] [CrossRef] [PubMed]
  23. Park, Y.K.; Jung, S.-I.; Park, K.-H.; Kim, S.H.; Ko, K.S. Characteristics of carbapenem-resistant Acinetobacter spp. other than Acinetobacter baumannii in South Korea. Int. J. Antimicrob. Agents 2012, 39, 81–85. [Google Scholar] [CrossRef] [PubMed]
  24. Chen, P.K.; Lee, Y.-T.; Liu, C.-Y.; Thuy, T.T.D.; Anh, K.; Wu, J.-J.; Liao, C.-H.; Huang, Y.-T.; Chen, Y.-C.; Kao, C.-Y. A 19-year longitudinal study to characterize carbapenem-nonsusceptible Acinetobacter isolated from patients with bloodstream infections and the contribution of conjugative plasmids to carbapenem resistance and virulence. J. Microbiol. Immunol. Infect. 2024, 57, 288–299. [Google Scholar] [CrossRef] [PubMed]
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Figure 1. Study population.
Figure 1. Study population.
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Figure 2. Distribution of isolated Acinetobacter species in the study population.
Figure 2. Distribution of isolated Acinetobacter species in the study population.
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Figure 3. The survival curve illustrates outcomes among patients with different Acinetobacter species bacteremia (A) Comparison of survival between patients with A. baumannii bacteremia and NBA bacteremia. (B) Comparison of survival among patients with Acinetobacter bacteremia, stratified by species and carbapenem resistance status (post hoc analysis: CRAB vs. non-CRAB [p < 0.001], CRAB vs. CR-NAB [p = 0.041], CRAB vs. non-CR- NAB [p < 0.001]). NBA, non-baumannii Acinetobacter; CR, carbapenem resistance; AB, A. baumannii.
Figure 3. The survival curve illustrates outcomes among patients with different Acinetobacter species bacteremia (A) Comparison of survival between patients with A. baumannii bacteremia and NBA bacteremia. (B) Comparison of survival among patients with Acinetobacter bacteremia, stratified by species and carbapenem resistance status (post hoc analysis: CRAB vs. non-CRAB [p < 0.001], CRAB vs. CR-NAB [p = 0.041], CRAB vs. non-CR- NAB [p < 0.001]). NBA, non-baumannii Acinetobacter; CR, carbapenem resistance; AB, A. baumannii.
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Table 1. Clinical characteristics of patient with Acinetobacter bacteremia.
Table 1. Clinical characteristics of patient with Acinetobacter bacteremia.
CharacteristicsOverall
(n = 260)		Non-baumannii Acinetobacter Bacteremia (n = 42)A. baumannii Bacteremia (n = 218)p Value
Male154 (59.2)17 (40.5)137 (62.8)0.007
Age, years, median (IQR)70 (61.25–77)65.5 (51–75)71 (63–77)0.031
Comorbidities
 Updated CCI, median (IQR)2 (1–4)2 (1–5)2 (1–4)0.717
 Hypertension 114 (43.8)22 (52.4)92 (42.2)0.224
 DM with end-organ damage43 (16.5)2 (4.8)41 (18.8)0.025
 Moderate to severe liver disease17 (6.5)1 (2.4)16 (7.3)0.323
 Moderate to severe renal disease33 (12.7)1 (2.4)32 (14.7)0.028
 Metastatic solid tumor37 (14.2)8 (19.1)29 (13.3)0.329
Carbapenem resistance195 (75.0)9 (21.4)186 (85.3)<0.001
Focus of bacteremia
 Primary bacteremia26 (10)7 (16.7)19 (8.7)0.155
 Intravascular catheter-related infection78 (30.0)29 (69.1)49 (22.5)<0.001
 Pneumonia126 (48.5)2 (4.8)124 (56.9)<0.001
 Intra-abdominal infections12 (4.6)2 (4.8)10 (4.6)>0.999
 SSTI5 (1.9)0 (0.0)5 (2.3)>0.999
 UTI10 (3.8)2 (4.8)8 (3.7)0.667
 Other infections4 (1.5)0 (0.0)4 (1.8)>0.999
Initial severity
 Septic shock144 (55.4)17 (40.5)127 (58.3)0.034
 Pitt bacteremia score4 (1–7)2 (1–3)5 (1–8)0.002
 Renal replacement therapy44 (16.9)4 (9.5)40 (18.4)0.163
Antibiotic therapy
 AAT146 (56.2)37 (88.1)109 (50.0)<0.001
 Time to AAT, days, median (IQR)1 (0–3)1 (0–2)2 (0–3)0.009
 Colistin containing regimen
(n = 146)		75 (51.4)7 (18.9)68 (62.4)<0.001
 Tetracycline containing regimen
(n = 146)		46 (31.5)3 (8.1)43 (39.5)0.004
 Carbapenem containing regimen
(n = 146)		71 (48.6)21 (56.8)50 (45.9)0.252
 Ampicillin-sulbactam containing
regimen (n = 146)		11 (7.5)3 (8.1)8 (7.3)>0.999
 Combination therapy a (n = 146)31 (21.2)8 (21.6)23 (21.1)0.947
Data are presented as numbers (%) unless otherwise indicated. a Combination therapy was defined as the administration of two or more effective antibiotics. Abbreviations: AAT, appropriate antibiotic therapy; CCI, Charlson Comorbidity Index; CKD, chronic kidney disease; CRI, catheter-related infections; DM, diabetes mellitus; IQR, interquartile range; SSTI, skin and soft tissue infections; UTI, urinary tract infections.
Table 2. Antibiotic resistance rate of Acinetobacter isolates.
Table 2. Antibiotic resistance rate of Acinetobacter isolates.
AntibioticsNon-baumannii Acinetobacter Species
(n = 42)		A. baumannii (n = 218)p Value
Ampicillin-sulbactam5 (11.9)169 (77.5)<0.001
Ceftazidime20 (47.6)192 (88.1)<0.001
Piperacillin-tazobactam12 (28.6)190 (87.2)<0.001
Meropenem9 (21.4)186 (85.3)<0.001
Imipenem8 (19.1)185 (84.9)<0.001
Minocycline0 (0.0)10 (4.6)0.377
Trimethoprim-sulfamethoxazole3 (7.1)157 (72.0)<0.001
Gentamicin12 (28.6)145 (66.5)<0.001
Data are presented as numbers (%).
Table 3. Univariable and multivariable analyses for overall 30-day mortality in patients with Acinetobacter bacteremia.
Table 3. Univariable and multivariable analyses for overall 30-day mortality in patients with Acinetobacter bacteremia.
VariableHR (95% CI)p ValueAdjusted HR (95% CI)p Value
A. baumannii bacteremia3.707 (1.882–7.302)<0.001
Male1.429 (0.999–2.043)0.051
Age (per 1 year)1.016 (1.001–1.031)0.031
DM with end-organ damage1.775 (1.186–2.658)0.005
Moderate to severe liver disease2.265 (1.276–4.019)0.0052.092 (1.159–3.775)0.014
Moderate to severe renal disease1.958 (1.273–3.011)0.0021.951 (1.245–3.059)0.004
Carbapenem resistance6.075 (3.182–11.597)<0.0012.145 (1.057–4.351)0.035
Intravascular CRI0.405 (0.260–0.630)<0.001
Pneumonia3.822 (2.617–5.582)<0.001
Intra-abdominal infections0.276 (0.068–1.116)0.071
Urinary tract infection0.294 (0.073–1.186)0.085
Septic shock7.684 (4.820–12.249)<0.0012.450 (1.353–4.437)0.003
PBS (per 1 point)1.383 (1.312–1.457)<0.0011.200 (1.121–1.284) <0.001
Renal replacement therapy2.486 (1.693–3.649)<0.001
AAT0.131 (0.089–0.194)<0.0010.219 (0.138–0.349)<0.001
HR, hazard ratio; DM, diabetes mellitus; CI, confidence interval; CRI, catheter-related infections; PBS, Pitt Bacteremia Score; AAT, appropriate antibiotic therapy.
Table 4. Univariable and multivariable analyses for 30-day in-hospital mortality in patients with Acinetobacter bacteremia who received appropriate antibiotic therapy.
Table 4. Univariable and multivariable analyses for 30-day in-hospital mortality in patients with Acinetobacter bacteremia who received appropriate antibiotic therapy.
VariableHR (95% CI)p ValueAdjusted HR (95% CI)p Value
DM with end-organ damage2.674 (1.334–5.362)0.006
Moderate to severe CKD2.989 (1.420–6.291)0.0043.986 (1.817–8.743)0.001
Carbapenem resistance1.950 (0.953–3.989)0.068
Intravascular CRI0.267 (0.118–0.603)0.002
Pneumonia5.600 (2.838–11.050)<0.0012.466 (1.099–5.534)0.029
Septic shock4.739 (2.464–9.116)<0.001
PBS (per 1 point)1.472 (1.287–1.683)<0.0011.382 (1.174–1.627)<0.001
Renal replacement therapy5.278 (2.725–10.225)<0.001 c
Colistin containing regimen2.270 (1.170–4.404)0.015
Carbapenem containing regimen2.213 (1.155–4.241)0.017
CCI, Charlson Comorbidity Index; CI, confidence interval; CKD, chronic kidney disease; CRI, catheter-related infections; DM, diabetes mellitus; HR, hazard ratio; PBS, Pitt Bacteremia Score.
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Kim, S.-H.; Mun, S.J. Comparative Analysis of Clinical Characteristics and Antimicrobial Resistance Between Acinetobacter baumannii and Other Acinetobacter Species. Pathogens 2025, 14, 46. https://doi.org/10.3390/pathogens14010046

AMA Style

Kim S-H, Mun SJ. Comparative Analysis of Clinical Characteristics and Antimicrobial Resistance Between Acinetobacter baumannii and Other Acinetobacter Species. Pathogens. 2025; 14(1):46. https://doi.org/10.3390/pathogens14010046

Chicago/Turabian Style

Kim, Si-Ho, and Seok Jun Mun. 2025. "Comparative Analysis of Clinical Characteristics and Antimicrobial Resistance Between Acinetobacter baumannii and Other Acinetobacter Species" Pathogens 14, no. 1: 46. https://doi.org/10.3390/pathogens14010046

APA Style

Kim, S.-H., & Mun, S. J. (2025). Comparative Analysis of Clinical Characteristics and Antimicrobial Resistance Between Acinetobacter baumannii and Other Acinetobacter Species. Pathogens, 14(1), 46. https://doi.org/10.3390/pathogens14010046

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