Invest Clin 67(1): 108 - 124, 2026 https://doi.org/10.54817/IC.v67n1a08
Corresponding authors: Gege Fang Department of Pulmonary Medicine III, The Third People’s Hospital of Yichang
City, No. 23, Gangyao Road, Xiling District, Yichang City 443000, Hubei Province, China. Email: fgg2343@hotmail.
com. Wei Zhang. Department of Critical Care Medicine, The Third People’s Hospital of Yichang City, No. 23, Gan-
gyao Road, Xiling District, Yichang City, Hubei Province, China. Email: zw2390Z@hotmail.com
Treatment strategies and mortality risk
factors in patients with multidrug-resistant
Acinetobacter baumannii pneumonia:
A retrospective analysis.
Lili Liu#,1, Wen Lu#,2, Gege Fang3 and Wei Zhang2
1Infection Control Department, The Third People’s Hospital of Yichang City, No. 23,
Gangyao Road, Xiling District, Yichang City, Hubei Province, China.
2Department of Critical Care Medicine, The Third People’s Hospital of Yichang City,
No. 23, Gangyao Road, Xiling District, Yichang City, Hubei Province, China.
3Department of Pulmonary Medicine III, The Third People’s Hospital of Yichang City,
No. 23, Gangyao Road, Xiling District, Yichang City, Hubei Province, China.
#These authors contributed equally to this work as co-first authors.
Keywords: Acinetobacter baumannii; Pneumonia; Drug Resistance; Multiple;
Risk Factors; Tigecycline.
Abstract. This study aimed to investigate the determinants of drug resis-
tance risk factors, 30-day all-cause mortality risk factors, and related clinical
treatment strategies in patients with multidrug-resistant Acinetobacter bauman-
nii (MDRAB) pneumonia. This retrospective study analyzed data from 168 pa-
tients with MDRAB pneumonia and 141 patients with non-MDRAB pneumonia
between February 2022 and February 2025. On the second day of admission, the
severity of illness and use of carbapenems, tigecycline, etc., were higher in MDR-
AB pneumonia patients than in non-MDRAB pneumonia patients (p<0.05). The
risk factors significantly associated with MDRAB pneumonia included ICU stay
prior to AB infection (p<0.001), APACHE II score ≥ 18 (p=0.002), invasive pro-
cedures (p<0.001), septic shock (p=0.002), and drug abuse (p<0.001). Length
of ICU stay before culture, recent surgery, APACHE II score ≥18, tigecycline-
containing treatment, and the use of two or more antibiotic types (all p<0.05)
were significantly linked to 30-day mortality. In a cohort of 168 MDRAB patients,
the non-tigecycline treatment group (n=85) showed a significantly lower 30-day
mortality rate compared to the tigecycline treatment group (n=83) (p=0.003).
Among those receiving tigecycline, the incidence of gastrointestinal adverse re-
actions was significantly higher, while allergic reactions were less frequent (both
p<0.05). In conclusion, prior ICU admission, invasive procedures, and drug
abuse are risk factors for developing MDRAB. Severe pneumonia and tigecycline
treatment are strongly associated with higher mortality in MDRAB patients, and
tigecycline should be used cautiously.
Mortality risk factors in patients with resistant Acinetobacter baumannii pneumonia 109
Vol. 67(1): 108 - 124, 2026
Estrategias de tratamiento y factores de riesgo de mortalidad
en pacientes con neumonía por Acinetobacter baumannii
multirresistente: Un análisis retrospectivo.
Invest Clin 2026; 67 (1): 108 – 124
Palabras clave: Acinetobacter baumannii; Neumonía; Resistencia a Múltiples
Medicamentos; Factores de riesgo; Tigeciclina.
Resumen. El objetivo del trabajo fue explorar los factores de riesgo de
resistencia a múltiples medicamentos en pacientes con neumonía por Acine-
tobacter baumannii (MDRAB), los factores de riesgo de muerte por todas las
causas en 30 días y las estrategias de tratamiento. Este estudio retrospectivo
(febrero de 2022-febrero de 2025) analizó datos de 168 pacientes con neu-
monía por MDRAB y de 141 con neumonía por Non-MDRAB. Al segundo día,
los pacientes con neumonía por MDRAB presentaron mayor gravedad y ma-
yor uso de carbapenémicos y tigeciclina que los de Non-MDRAB (p<0,05). Los
factores de riesgo significativamente asociados con neumonía por MDRAB in-
cluyeron estancia en UCI previa a la infección por AB (p<0,001), puntuación
APACHE II≥18 (p=0,002), procedimientos invasivos (p<0,001), shock séptico
(p=0,002) y abuso de drogas (p<0,001). La estancia en UCI previa al cultivo,
cirugía reciente, puntaje APACHE II ≥ 18, tratamiento con tigeciclina y uso de
≥ 2 antibióticos (todos p<0,05) se asociaron significativamente con la mor-
talidad a 30 días. La cohorte de 168 pacientes con MDRAB mostró una tasa
de mortalidad a 30 días significativamente menor en el grupo sin tigeciclina
(n=85) que en el grupo con tigeciclina (n=83) (p=0,003). En el tratamiento
con tigeciclina, la incidencia de eventos adversos gastrointestinales fue mayor y
la de reacciones alérgicas, menor (ambas p<0,05). En conclusión, la admisión
previa en UCI, los procedimientos invasivos y el abuso de drogas son factores de
riesgo para el desarrollo de MDRAB. La enfermedad grave y el tratamiento con
tigeciclina se asocian significativamente con una alta mortalidad en pacientes
con MDRAB, por lo que debe usarse con precaución.
Received: 24-09-2025 Accepted: 30-12-2025
INTRODUCTION
Acinetobacter baumannii (A. baumannii
or AB) is an aerobic, Gram-negative oppor-
tunistic pathogen. As a significant pathogen
in hospital-acquired infections worldwide, it
accounts for approximately 20% of intensive
care unit (ICU) infections 1-3. The bacteria
demonstrate strong environmental adapt-
ability, can survive and reproduce across var-
ious pH levels and temperatures, and can ad-
here to surfaces of medical equipment such
as surgical instruments, ventilators, cath-
eters, and respiratory measuring devices
to form biofilms and continue spreading4,5.
Because A. baumannii closely resembles
other strains, phenotypic and biochemical
classification methods often misidentify it,
resulting in an underestimation of its role in
nosocomial infections. A. baumannii causes
various hospital-associated infections, in-
cluding ventilator-associated pneumonia and
110 Liu et al.
Investigación Clínica 67(1): 2026
bloodstream infections 6,7. As a multidrug-
resistant pathogen that has garnered global
attention, infections caused by A. baumannii
are associated with higher mortality rates,
ranging from 7.8% to 43%. The risk of death
is particularly high among ICU patients. It
is the second most common Gram-negative
pathogen in hospital-acquired pneumonia,
responsible for about 3% to 5% of such cas-
es, with associated mortality rates reaching
30% to 75%.
Recently, the overuse of antibiotics,
frequent cross-infections among hospital-
ized patients, and the horizontal trans-
fer of drug-resistant genes have led to the
emergence of multidrug-resistant (MDR),
extensively drug-resistant (XDR), and even
pan-drug-resistant (PDR) strains of A. bau-
mannii. This has severely limited options for
clinical anti-infective therapy. Globally, the
multidrug resistance rate of A. baumannii
remains high, at approximately 45%. Cur-
rently, mainstream strains show extensive
resistance to multiple antibiotics, especially
carbapenems. In Asia, bacterial suscepti-
bility to carbapenems is even lower than
27%8,9. Many guidelines at home and abroad
recommend treating pneumonia caused by
MDRAB with polymyxin, tigecycline, and sul-
bactam, combined with other antibiotics.
However, regional differences in bacterial
sensitivity to specific drugs necessitate the
development of individualized drug combi-
nation strategies based on local resistance
profiles and current guidelines 10. Polymyxin
and tigecycline remain the effective first-line
treatments for infections caused by MDR
strains. With MDRAB infections, treatment
options are extremely limited, mainly rely-
ing on a few classes such as polymyxin and ti-
gecycline. Unfortunately, strains resistant to
polymyxin are emerging, and tigecycline re-
sistance is also increasing in A. baumannii,
further intensifying treatment difficulties.
Tigecycline is a broad-spectrum semi-
synthetic glycopeptide antibiotic derived
from minocycline. The drug has strong in
vitro activity against a variety of MDR bac-
teria (e.g., A. baumannii), but is ineffective
against P. aeruginosa and Shigella 11. The
structural design of tigecycline enables it to
avoid the common tetracycline resistance
mechanism, thus showing good applica-
tion potential in dealing with multi-drug
resistant bacteria infection 12. In general,
tigecycline alone is not recommended when
other effective antibiotics are available. The
combination of tigecycline and sulbactam is
one of the common strategies for the treat-
ment of hospital-acquired MDRAB infection.
For pulmonary and systemic carbapenem-
resistant A. baumannii infection, high-dose
tigecycline regimen is often given priority
because of its high drug concentration in
plasma and lung tissue, which shows bet-
ter efficacy than conventional doses in ret-
rospective studies13. Despite demonstrating
in vitro susceptibility against MDRAB, the
clinical efficacy of tigecycline is controver-
sial. Evidence suggests that its antibacte-
rial activity fails to translate into significant
clinical benefit, offering little improvement
in patient prognosis 14.
This study investigated the risk factors
for drug resistance and the determinants of
30-day all-cause mortality in patients with
MDRAB pneumonia, and related clinical
treatment strategies. At the same time, the
safety evaluation of the adverse reactions of
Radical Antimicrobial Regimens was carried
out to provide evidence-based basis for early
identification of high-risk patients, optimi-
zation of treatment strategies and improve-
ment of prognosis.
MATERIAL AND METHODS
Study design
This retrospective, single-center, obser-
vational study included 343 patients with AB
pneumonia treated at the Third People’s Hos-
pital of Yichang City, China, between Febru-
ary 2022 and February 2025. After applying
exclusion criteria, 168 patients had MDRAB
pneumonia, and 141 had non-MDRAB pneu-
monia. Their basic characteristics, in vitro
Mortality risk factors in patients with resistant Acinetobacter baumannii pneumonia 111
Vol. 67(1): 108 - 124, 2026
antimicrobial susceptibility testing, treat-
ment strategies on the second day of admis-
sion, and survival curves of Radical Antimi-
crobial Regimens were analyzed. Potential
risk factors for drug resistance and 30-day
all-cause mortality were evaluated using uni-
variate and multivariate logistic regression
analyses. The process flow is shown in Fig. 1.
Inclusion criteria
(1) diagnosed as pneumonia; (2) The
culture of blood and respiratory tract was
AB positive; (3) Age greater than 18 years
old; (4) Complete clinical data.
Exclusion criteria
(1) transfer, death, or treatment aban-
donment within 24 hours of admission; (2)
Incomplete clinical data; (3) Lactating wom-
en during pregnancy; (4) No clinical mani-
festations of infection.
Sample size calculation
The mortality rate of A. baumannii in
hospital-acquired pneumonia ranges from
30% to 75% 15. This study assumed that the
mortality rate could be reduced by 30% with
tigecycline treatment. A bilateral test was
used to set the significance level α at 0.05,
with a test power (1-β) of 0.8. After esti-
mating and adjusting the sample size, the
minimum total sample size was 142. Overall,
309 patients were included in this study, of
whom 83 with MDRAB infection received a
comprehensive treatment regimen contain-
ing tigecycline, meeting the preset sample
size requirements and providing sufficient
statistical power for the research conclu-
sions.
Ethical statement
The study protocol was approved by our
hospital’s research ethics committee and
strictly adhered to the ethical guidelines
and norms established by the ‘Helsinki Dec-
laration’ (latest revision) 16. It prioritizes the
rights, safety, and well-being of the subjects
and ensures all research activities follow in-
ternational ethical standards. We have ef-
Fig. 1. Case identification flow chart.
112 Liu et al.
Investigación Clínica 67(1): 2026
fectively protected the legitimate rights and
interests of all participants by implementing
a thorough informed consent process, safe-
guarding the privacy and confidentiality of
subjects, and adhering to principles of fair
benefit and risk reduction.
Basic information collection
Clinical data of patients with AB pneu-
monia were retrieved from the Hospital Infor-
mation System (HIS) database. The collected
data include age, gender, hospitalization his-
tory, past medical history, surgical history,
disease diagnosis, clinical outcomes, antibi-
otic use history, and microbiological data.
Disease severity was assessed at the onset of
AB using the SOFA and APACHE II scores. All-
cause 30-day mortality following the onset of
AB pneumonia was the primary clinical out-
come. All antibiotic regimens were adminis-
tered in accordance with the instructions and
clinical medication protocols.
Antimicrobial susceptibilities
In this study, the VITEK 2 Compact sys-
tem (bioMérieux, France) and its support-
ing MALDI-TOF MS mass spectrometry were
used to identify the strains of A.baumannii
isolates. The drug sensitivity test was per-
formed by the VITEK-2 Compact system
combined with the AST-GN16 drug sensitiv-
ity card (bioMérieux). Tigecycline suscepti-
bility was determined per FDA breakpoints.
For all other antibiotics, susceptibility was
interpreted according to the latest CLSI
guidelines 17,18.
Adverse reactions
During the treatment, adverse reactions
such as nausea and vomiting, Diarrhea, oto-
toxicity, allergic reactions, liver injury, and
kidney injury were observed and recorded.
Definitions
(1) Blood and respiratory cultures
should be collected within the first 48 hours of
hospitalization. AB isolates were categorized
as S (sensitive), I (intermediate), or R (resis-
tant). For this analysis, I and R were consid-
ered non-sensitive. MDRAB was defined as any
AB resistant to at least one of three or more
classes of antimicrobial agents. (2) Complica-
tions included cerebrovascular disease, liver
disease, chronic lung disease, renal failure,
etc. (3) The simultaneous administration of
two or more different antibacterial agents is
called combination antibacterial therapy. (4)
Invasive procedures included tracheotomy,
catheterization, abdominal puncture, ventila-
tor use, etc.
Statistical analysis
Continuous and categorical data were
expressed as mean ± standard deviation and
number (percentage), respectively. For com-
parisons of mean values between groups, the
independent t-test was used under the nor-
mality assumption, and categorical data were
evaluated using the chi-square test. Statisti-
cal analysis was conducted using SPSS version
26. GraphPad Prism was used for plotting.
p<0.05 indicated statistical significance of
each test. Univariate and multivariate logis-
tic regression models were used to examine
associations between independent variables
and dichotomous outcomes, including MDR-
AB infection and 30-day mortality.
RESULTS
Antibiotic resistance characteristics
of Acinetobacter baumannii pneumonia
The drug-sensitivity test results showed
that the AB strain was most sensitive to poly-
myxin and tigecycline, followed by minocy-
cline, cefoperazone/sulbactam, and levofloxa-
cin. Resistance rates to other antibiotics were
more than 45%, particularly carbapenems,
and resistance to carbapenems was more
than 75%. By comparing the antimicrobial
susceptibility spectra, we found significant
differences in the susceptibility of carbapen-
ems, cephalosporins, quinolones, aminogly-
cosides, tigecycline, and combination drugs
between the MDRAB and Non-MDRAB groups
(p<0.05). In the MDRAB group, in addi-
Mortality risk factors in patients with resistant Acinetobacter baumannii pneumonia 113
Vol. 67(1): 108 - 124, 2026
tion to tigecycline, polymyxin, minocycline,
cefoperazone/sulbactam, and levofloxacin
(6.20%, 3.52%, 45.53%, 49.43%, and 63.40%,
respectively), the resistance rates to other an-
tibiotics exceeded 75% (Table 1).
Treatment of Acinetobacter baumannii
pneumonia
By day 2, MDRAB patients exhibited
greater disease severity, with higher ICU ad-
mission rates (70.8% vs. 18.4%, p<0.001)
and mechanical ventilation rates (54.2%
vs. 36.2%, p=0.002). The use of carbapen-
ems, extended-spectrum cephalosporins,
aminoglycosides, and tigecycline was more
frequent than in the Non-MDRAB group
(p<0.05). This indicates that MDRAB pneu-
monia patients have fewer clinical options,
which complicates treatment and increases
the risk of side effects (Table 2).
Table 1. Antibiotic Resistance characteristics of Acinetobacter baumannii pneumonia.
Antimicrobial Total
(N=309)
MDRAB
(N=168)
Non-MDRAB
(N=141) χ2p
Carbapenem antibiotic
Meropenem 77.35% (239/309) 91.07% (153/168) 60.99%(86/141) 37.885 <0.001
Imipenem 82.85% (256/309) 95.83% (161/168) 67.38% (95/141) 41.708 <0.001
Cephalosporins
Cefepime 52.10%(161/309) 91.07%(153/168) 5.67%(8/141) 220.61 <0.001
Ceftriaxone 53.21%(141/265) 97.83%(135/138) 4.27%(6/127) 175.9 <0.001
Ceftazidime 54.50%(109/200) 90.27%(102/113) 8.05%(7/87) 101.93 <0.001
Aminoglycosides
Gentamicin 53.36% (135/253) 94.20%(130/138) 4%(5/125) 168.992 <0.001
Amikacin 50.19% (133/265) 97.73%(129/132) 3.01% (4/133) 171.457 <0.001
Tobramycin 48.51%(129/268) 84.21%(128/152) 1.72%(2/116) 175.136 <0.001
Quinolones
Ciprofloxacin 56.30%(152/270) 96.58%(141/156) 8.87%(11/124) 177.794 <0.001
Levofloxacin 35.03%(103/294) 63.40%(97/153) 4.26%(6/141) 99.579 <0.001
Tetracycline
Tigecycline 3.29%(8/243) 6.20%(8/129) 0%(0/114) 5.133 0.024
Minocycline 25.38%(66/260) 45.53%(56/123) 7.30%(10/137) 31.447 0.011
Others
Colistin 1.87%(5/268) 3.52%(5/142) 0%(0/126) 5.133 0.092
Combined medication
Trimethoprim/
sulfamethoxazole 54.58%(149/273) 93.06%(134/144) 11.63%(15/129) 146.218 <0.001
Piperacillin/
tazobactam 54.64%(100/183) 97.96%(96/98) 4.71%(4/85) 103.26 <0.001
Cefoperazone/
sulbactam 26.47%(45/170) 49.43%(43/87) 2.41%(2/83) 35.978 <0.001
Data expressed as % (n). MDRAB: multidrug-resistant Acinetobacter baumannii; Non-MDRAB: no multidrug-resis-
tant. Comparisons of mean values between groups, was performed by independent χ2 test.
114 Liu et al.
Investigación Clínica 67(1): 2026
Baseline characteristics of Acinetobacter
baumannii pneumonia
Data on 309 patients with AB pneumo-
nia were collected, and their characteristics
were analyzed. Patients with MDRAB pneumo-
nia were older (64.72 ± 10.19 years vs 60.72
± 10.71 years, p = 0.001), and the propor-
tion of males in both groups exceeded 55%.
The incidence of AB infection in hospitals
was above 90%, and 82.14% of MDRAB pneu-
monia patients were diagnosed in the ICU.
Complications were common in patients with
MDRAB pneumonia, among which hypopro-
teinemia (76.19%) and septic shock (32.14%)
were the most common. The APACHE II and
SOFA scores of patients with MDRAB pneu-
monia were higher than those of patients with
Non-MDRAB pneumonia. In addition, alcohol
abuse and drug abuse also have a greater im-
pact on patients with MDRAB pneumonia.
Detailed data are shown in Table 3.
Risk Factors for patients with
Acinetobacter baumannii pneumonia
Univariate analysis showed that age, ICU
stay prior to AB infection, hospital stay over
30 days before AB infection, hemodialysis,
immunosuppressive status, APACHE II score
of 18 or higher, SOFA score of 10 or higher,
invasive procedures, hypoproteinemia, septic
shock, alcohol abuse, and drug abuse were
associated with MDRAB. After adjusting for
confounders, multivariate logistic regres-
sion revealed that ICU stay prior to AB infec-
tion [p<0.001; OR(95% CI): 17.855 (9.764-
32.650)], APACHE II score ≥ 18 [p = 0.002;
OR(95% CI): 4.002 (1.658-9.662)], invasive
procedures [p<0.001; OR(95% CI): 5.707
(2.933-11.104)], septic shock [p = 0.002;
OR(95% CI): 5.059 (1.834-13.956)], and
drug abuse [p<0.001; OR(95% CI): 5.092
(2.351-11.024)] were independent risk fac-
tors for MDRAB resistance (Table 4).
Risk factors for death within 30 days in
patients with Acinetobacter baumannii
pneumonia
The 30-day all-cause mortality of 168
MDRAB patients was 48.21% (81). Univari-
ate analysis showed that the length of ICU
stay prior to culture, recent surgery, immu-
nocompromised status, endotracheal tube,
fiberoptic bronchoscopy, and a SOFA score
≥ 10 were associated with culture positivity.
Table 2. Treatment of Acinetobacter baumannii pneumonia.
Treatment MDRAB
(N=168)
Non-MDRAB
(N=141) χ² p
Illness severity measured by day 2
ICU admission 119(70.83%) 26(18.44%) 84.399 < 0.001
Mechanical ventilation 91(54.17%) 51(36.17%) 9.909 0.002
Antibiotics administered by day 2
Extended-spectrum cephalosporins 58(34.52%) 29(20.57%) 7.386 0.007
Fluoroquinolones 63(37.5%) 46(32.627%) 0.783 0.376
Carbapenems 97(57.74%) 31(22%) 40.247 < 0.001
Aminoglycosides 42(25%) 16(11.35%) 9.376 0.002
Combined medication 46(27.38%) 20(14.18%) 7.942 0.005
Tetracyclines 14(8.33%) 6(4.26%) 13.341 < 0.001
Polymyxins 7(4.17%) 0(0%) 6.024 0.014
Data expressed as n (%). MDRAB: multidrug-resistant Acinetobacter baumannii; Non-MDRAB: no multidrug-resis-
tant. Comparisons of mean values between groups, was performed by independent χ2 test.
Mortality risk factors in patients with resistant Acinetobacter baumannii pneumonia 115
Vol. 67(1): 108 - 124, 2026
Table 3. Baseline characteristics of Acinetobacter baumannii pneumonia.
Baseline characteristics MDRAB (N=168) Non-MDRAB (N=141) χ²/t p
Age(years) 63.64±10.55 60.92±8.17 2.492 0.013
Gender
Male 94(56.95%) 82(58.16%) 0.145 0.703
Female 74(44.05%) 59(41.84%)
Infection
Nosocomial infection 157(93.45%) 129(91.49%) 0.406 0.524
Community infections 11(6.55%) 12(8.51%)
Hospital exposure
ICU stay prior to AB infection 138(82.14%) 31(21.99%) 111.956 <0.001
Hospital stay >30 days prior to AB infection 15(8.93%) 4(2.84%) 4.922 0.027
Operation 64(38.10%) 52(36.88%) 0.048 0.826
Hemodialysis 26(15.48%) 8(5.67%) 7.521 0.006
Illness severity at time of AB
APACHE II 24.36±8.39 20.31±7.36 4.479 <0.001
SOFA 8.03±5.16 4.11±2.89 7.998 <0.001
Invasive procedures 82(48.81%) 25(17.73%) 32.7 <0.001
Comorbid conditions
Cerebrovascular diseases 36(21.43%) 27(19.15%) 0.245 0.621
Liver disease 40(23.81%) 31(21.99%) 0.144 0.704
Chronic pulmonary disease 16(9.52%) 14(9.93%) 0.015 0.903
Renal failure 27(16.07%) 16(11.35%) 1.428 0.232
Malignant tumor 32(19.05%) 28(19.86%) 0.032 0.858
Diabetes 28(16.67%) 21(14.89%) 0.181 0.67
Hypoproteinemia 128(76.19%) 89(63.12%) 6.214 0.013
Septic shock 54(32.14%) 11(7.80%) 27.34 <0.001
Immunocompromised status 30(17.86%) 6(4.26%) 13.788 <0.001
Coagulopathy 31(18.45%) 15(10.64%) 3.694 0.055
Paralysis 29(17.26%) 22(15.60%) 0.165 0.684
Gastrointestinal bleeding 20(11.90%) 14(9.93%) 0.305 0.581
Other factors
Obesity 32(19.05%) 26(18.44%) 0.019 0.891
Weight loss 34(20.24%) 39(27.66%) 2.33 0.127
Fluid and electrolyte disorders 92(54.76%) 79(56.03%) 0.044 0.834
Anemia 64(38.1%) 61(43.26%) 0.85 0.357
Alcohol abuse 28(16.67%) 9(6.38%) 7.723 0.005
Drug abuse 66(39.29%) 18(12.77%) 27.257 <0.001
Mental disorders diseases 31(18.45%) 27(19.15%) 0.024 0.877
Hypertension 102(60.71%) 95(67.38%) 1.451 0.228
Outcome
30-day mortality 81(48.21%) 10(7.09%) 62.393 <0.001
Data expressed as n (%) or mean ± SD. MDRAB: multidrug-resistant Acinetobacter baumannii; Non-MDRAB: no
multidrug-resistant. Comparisons of mean values between groups, was performed by independent t-test or χ2.
116 Liu et al.
Investigación Clínica 67(1): 2026
APACHE II ≥ 18 and invasive interventions
(n > = 3 types) were significantly associated
with 30-day mortality. Multivariate logistic
regression showed that independent risk fac-
tors included length of ICU stay prior to cul-
ture [p = 0.012, OR (95% CI): 0.327 (0.137-
0.778)], recent surgery [p = 0.001, OR
(95% CI): 0.063 (0.012-0.338)], APACHE II
≥ 18 [p<0.001, OR (95% CI): 0.104 (0.034-
0.321)], which were significantly associated
with 30-day mortality (Table 5).
The effect of radical antimicrobial
regimens on the 30-day mortality of
patients with Acinetobacter baumannii
pneumonia
In this study, 83 MDRAB pneumonia
patients received radical treatment con-
taining tigecycline, of which 57 patients
(68.67%) died within 30 days. Univariate
analysis showed that radical treatment, in-
cluding tigecycline, polymyxin, and ≥2 an-
tibiotic agents, was significantly associated
with 30-day mortality. Multivariate logistic
regression analysis showed that Tigecycline
+ Other drugs, ≥ 2 types of antibiotics, were
independent risk factors for 30-day mortality.
168 patients with MDRAB were divided into
Non-tigecycline treatment group (n = 85),
and tigecycline treatment group (n = 83).
The 30-day mortality of the Non-tigecycline
group was lower than that of the tigecycline
group (p= 0.003) (Table 6 and Fig. 2). This
suggests that physicians should select a regi-
men containing tigecycline to treat MDRAB
infection with discretion and prioritize other
treatment strategies that may be more effec-
tive or safer.
Adverse reaction of radical antimicrobial
regimens
The incidence of gastrointestinal ad-
verse reactions, including nausea and vom-
iting (p = 0.044) and diarrhea (p = 0.035),
Table 4. Risk factors for death within 30 days in patients with MDRAB.
Baseline
characteristics
Univariable Analysis
OR (95% CI) pMultivariable Analysis
OR (95% CI) p
Age(years) 0.970(0.947-0.994) 0.015
Hospital exposure
ICU stay prior to AB infection 16.323(9.314-28.604) <0.001 17.855(9.764-32.650) <0.001
Hospital stay >30 days prior
to AB infection
3.358(1.088-10.361)
0.035
1.364(0.278-6.683)
0.702
Hemodialysis 3.044(1.331-6.960) 0.008 0.565(0.165-1.931) 0.362
Illness severity at time of AB
APACHE II≥18 2.327(1.460-3.708) <0.001 4.002(1.658-9.662) 0.002
SOFA≥10 1.619(1.031-2.541) 0.036 0.527(0.2221.254) 0.148
Invasive procedures 4.424(2.611-7.498) <0.001 5.707(2.933-11.104) <0.001
Comorbid conditions
Hypoproteinemia 1.870(1.142-3.061) 0.013 1.233(0.733-2.076) 0.43
Septic shock 5.598(2.793-11.222) <0.001 5.059(1.834-13.956) 0.002
Immunocompromised status 4.891(1.973-12.128) 0.001 1.042(0.238-3.832) 0.951
Other factors
Alcohol abuse 2.933(1.334-6.449) 0.007 0.737(0.259-2.059) 0.567
Drug abuse 4.422(2.467-7.925) <0.001 5.092(2.351-11.024) <0.001
MDRAB: multidrug-resistant Acinetobacter baumannii. Data expressed as n (%). OR(95% CI): Odds Ratio (OR) with
a 95% Confidence Interval.
Mortality risk factors in patients with resistant Acinetobacter baumannii pneumonia 117
Vol. 67(1): 108 - 124, 2026
Table 5. Risk factors for mortality of patients with Acinetobacter baumannii pneumonia.
Risk factors Survival
(N=87)
Mortality
(N=81)
Univariable Analysis
OR (95% CI) pMultivariable
Analysis OR (95% CI) p
Age >60 years
51(58.62%)
49(60.49%)
0.833
(0.448-1.550)
0.565
Male
43(49.43%)
51(62.96%)
0.575
(0.310-1.065)
0.078
ICU length of stay before
AB culture (d)
21(24.14%)
38(46.91%)
0.360
(0.187-0.694)
0.002
0.327
(0.137-0.778)
0.012
Recent surgery
(within 1 month)
12(13.79%)
36(44.44%)
0.200
(0.094-0.424)
<0.001
0.063
(0.012-0.338)
0.001
Immunocompromised
status
8(9.20%)
22(27.16%)
0.272
(0.113-0.653)
0.004
1.273
(0.322-5.032)
0.731
Endotracheal tube
34(39.08%)
47(58.02%)
0.464
(0.250-0.860)
0.015
0.740
(0.269-2.037)
0.56
Fiberoptic bronchoscopy
25(28.74%)
38(46.91%)
0.448
(0.239-0.839)
0.012
3.872
(0.857-17.507)
0.079
SOFA≥10
39(44.83%)
55(67.90%)
0.367
(0.195-0.688)
0.002
1.579
(0.593-4.206)
0.361
APACHE II≥18
41(51.72%)
39(87.65%)
0.151
(0.069-0.331)
<0.001
0.104
(0.034-0.321)
<0.001
Invasive interventions
(n > = 3 types)
11(12.64%)
21(25.93%)
0.414(0.185-0.924) 0.031 0.786(0.280-2.206) 0.647
Data expressed as n (%). OR(95% CI): Odds Ratio (OR) with a 95% Confidence Interval.
Table 6. The Effect of Radical Antimicrobial Regimens on the 30-Day mortality
of patients with Acinetobacter baumannii pneumonia.
Antimicrobial
Regimen
Survival
(N=87)
Mortality
(N=81)
Univariable
Analysis
OR (95% CI)
p
Multivariable
Analysis
OR (95% CI)
p
Containing Tigecycline 26(29.89%) 57(70.37%)
Tigecycline
2(2.30%)
5(6.17%)
0.294
(0.058-1.501)
0.012
0.697
(0.130-3.736)
0.673
Tigecycline+Other drugs
24(27.59%)
52(64.20%)
0.212
(0.110-0.408)
<0.001
0.220
(0.112-0.431)
<0.001
Not containing Tigecycline 61(70.11%) 24(29.63%)
Polymyxins
2(2.30%)
8(9.88%)
0.215
(0.044-0.215)
0.056
0.225
(0.044-1.153)
0.074
Cefoperazone/sulbactam
32(36.78%)
35(43.21%)
0.765
(0.412-1.420)
0.396
1.579
(0.721-3.459)
0.254
≥2 types of antibiotic
51(58.62%)
62(76.54%)
0.434
(0.223-0.847)
0.014
0.371
(0.166-0.833)
0.016
Data expressed as n (%). OR(95% CI): Odds Ratio (OR) with a 95% Confidence Interval.
118 Liu et al.
Investigación Clínica 67(1): 2026
was significantly higher in regimens con-
taining tigecycline than in regimens with-
out it. In contrast, the occurrence of aller-
gic reactions was lower with the tigecycline
treatment (p = 0.04). Additionally, there
was no significant difference in adverse
reactions such as ototoxicity, liver injury,
and kidney injury between the two groups.
This indicates that clinicians and patients
should pay close attention to, and proac-
tively manage, gastrointestinal adverse re-
actions when using tigecycline in clinical
practice. The risk of allergy caused by tige-
cycline is relatively low, making it a poten-
tially favorable option for patients allergic
to other antibiotics (Table 7).
DISCUSSION
Pneumonia poses a major burden on
global health, and its high morbidity and
mortality make it one of the main causes of
in-hospital death in hospitalized patients19.
A. baumannii is a notable opportunistic
pathogen responsible for severe nosocomial
infections, especially in critically ill patients,
which often leads to serious complications
such as ventilator-associated pneumonia.
Due to its significant drug resistance and
susceptibility to clonal transmission, the pre-
vention and control of this bacterium have
become a major challenge for global health-
care systems 20. Recently, the resistance rate
of A. baumannii to a variety of commonly
used antibiotics, including carbapenems,
has continued to rise. Therefore, A. bauman-
nii has been listed as a ‘first-class’ key patho-
gen by the WHO. It is urgent to develop new
or more effective antibiotic treatment pro-
grams 21. The emergence of MDRAB has not
only increased the morbidity and mortality of
patients, but also become one of the core ob-
jectives of hospital infection prevention and
control, which further highlights the urgent
need for effective treatment strategies for
MDRAB 22. Currently, sulbactam-containing
combinations, polymyxins, and tigecycline
are recommended as standard combination
therapies for the treatment of A. baumannii
infections. However, global reports of drug
resistance to these drugs are gradually in-
creasing 23. Through retrospective analysis,
this study summarized the clinical char-
acteristics of patients with AB pneumonia,
identified risk factors for MDRAB pneumo-
nia, further evaluated the predictive factors
for 30-day mortality in patients with MDRAB
Fig. 2. Kaplan–Meier survival estimates among pa-
tients with MDRAB.
MDRAB: multidrug-resistant Acinetobacter baumannii.
Table 7. Adverse Reaction of Radical Antimicrobial Regimens.
Variables Containing
Tigecycline(n=83)
Not containing
Tigecycline(n=85) χ2p
Nausea and vomiting 22(26.51%) 11(12.94%) 4.074 0.044
Diarrhea 20(24.10%) 9(10.59%) 4.461 0.035
Allergic reactions 5(6.02%) 14(16.47%) 4.24 0.04
Ototoxicity 2(2.41%) 4(4.71%) 0.149 0.699
Liver injury 7(8.43%) 9(10.59%) 0.045 0.832
renal injury 6(7.23%) 8(9.41%) 0.054 0.816
Other 9(10.84%) 13(15.29%) 0.392 0.531
Data expressed as n (%). Comparison of mean values between groups was performed by the χ2 test.
Mortality risk factors in patients with resistant Acinetobacter baumannii pneumonia 119
Vol. 67(1): 108 - 124, 2026
pneumonia, and assessed the efficacy and
safety of different eradication regimens. It
is expected to provide infection control and
clinical care for MDRAB.
The emergence of MDRAB has be-
come a major global healthcare challenge,
severely compromising treatment options.
Numerous studies have demonstrated this
pathogen’s resistance to a wide range of an-
timicrobial agents, including carbapenems,
cephalosporins, tigecycline, quinolones,
aminoglycosides, and sulbactam-containing
compounds 24,25. Several studies have shown
that AB strains are highly sensitive to poly-
myxins and tigecycline and exhibit high
resistance to other antimicrobial agents,
particularly carbapenems. In the MDRAB
group, except for tigecycline, polymyxin,
minocycline, cefoperazone/sulbactam, and
levofloxacin, the other antibacterial drugs
had higher resistance rates, consistent with
the trend observed in this study 15,18,26. How-
ever, it has also been reported that there is
a high resistance to myxobacterial polyanti-
bodies 27, this difference may be related to
factors such as the source and type of the
selected sample and the underlying disease
of the patient. In addition, the severity of
disease in patients with MDRAB pneumonia
is significantly higher than that in patients
with non-MDRAB pneumonia. This further
complicates treatment and increases the
risk of adverse drug events. Compared with
the Non-MDRAB group, the frequency of
carbapenem, extended-spectrum cephalo-
sporin, aminoglycoside, and tigecycline use
in patients with MDRAB pneumonia was
higher, indicating that, under the pressure
of multidrug-resistant infections, the clinic
has to rely more on these drugs, which have
certain toxicities and side effects.
In terms of clinical impact, drug-resis-
tant strains were associated with previous ad-
mission to ICU, APACHE II score ≥ 18, inva-
sive procedures, septic shock, and drug abuse.
The most common risk factors for obtaining
MDRAB included age, previous admission to
ICU, length of hospital stay before AB infec-
tion more than 30 days, hemodialysis, immu-
nosuppressive status, APACHE II score ≥ 18,
SOFA score ≥ 10, invasive procedures, hypo-
proteinemia, septic shock, alcohol abuse, and
drug abuse28-30, which were basically consis-
tent with the conclusions of this study. This
result may be attributed to AB biofilm for-
mation, which enables bacteria to survive in
the hospital environment (especially on the
surfaces of medical equipment) for extended
periods 31. The occurrence of MDRAB pneu-
monia is often due to invasive procedures or
certain surgeries that disrupt the patient’s
skin and mucosal barriers, thereby creating a
pathway for bacterial invasion 32. In addition,
prolonged hospitalization, ICU admission,
and hemodialysis showed that the patients
were in a serious condition and their immune
function was impaired. These patients further
deteriorated after infection with MDRAB,
and they had higher APACHE II and SOFA
scores. Septic shock and drug abuse are the
most common risk factors for MDRAB infec-
tion. ICU patients are mostly in a critic al
state and generally have immunosuppression.
If they are combined with septic shock and
have received multiple drug treatments, their
susceptibility to MDRAB will be further in-
creased. It is worth noting that interactions
among these factors may attenuate their in-
dependent effects. In addition, other studies
have reported additional relevant factors, but
are limited by specific conditions; this study
does not cover all of them.
The mortality rate of infection caused
by MDRAB can be as high as 30% -75%, pos-
ing a serious threat to human health 33. Pre-
vious studies have explored a variety of fac-
tors as potential predictors of mortality risk
in patients with MDRAB pneumonia: such
as length of ICU stay before AB culture, re-
cent surgical history, immunocompromised
status, tracheal intubation, fiberoptic bron-
choscopy, SOFA score, APACHE II score ≥
18 points, and the number of invasive inter-
ventions (≥ 3 types)34-37, which is consistent
with the results of this study. Although ti-
gecycline can reach a high concentration in
120 Liu et al.
Investigación Clínica 67(1): 2026
multiple tissues (such as the concentration
in lung tissue can reach twice that in se-
rum)38, this study divided 168 patients with
MDRAB into a non-tigecycline group and a ti-
gecycline group according to the treatment
method, and found that the 30-day mortality
of the former was lower than that of the lat-
ter. This result is consistent with many re-
ports that tigecycline-containing treatment
regimens are associated with higher AB in-
fection mortality 39-41.
The limited choice of therapeutic drugs
for patients with MDRAB pneumonia not
only increases the difficulty of clinical treat-
ment but also increases the risk of drug-
related side effects. In the treatment regi-
men containing tigecycline, the incidence of
gastrointestinal adverse events such as nau-
sea, vomiting, and diarrhea was significantly
higher than that of the non-tigecycline regi-
men, which was consistent with the existing
research results 42. In contrast, the incidence
of allergic reactions in the tigecycline treat-
ment group was lower. In addition, there was
no significant difference in adverse reactions
such as ototoxicity, liver injury, and kidney
injury between the two groups. The lower
allergenicity of tigecycline may make it a
better choice for patients allergic to other
antibiotics. These findings suggest that ti-
gecycline should be used with caution, and
that alternative regimens may yield safer
and more effective outcomes.
This study explored risk factors for
drug resistance, 30-day all-cause mortality,
and associated clinical treatment strate-
gies in patients with MDRAB pneumonia. It
provides a new clinical basis for treatment
strategies and mortality risk factors in pa-
tients with MDRAB pneumonia and has im-
portant implications for optimizing clinical
prevention and treatment. It is suggested
that clinicians should be cautious when pre-
scribing tigecycline for MDRAB pneumonia,
as its use may be associated with increased
mortality. However, this study also has some
limitations. First, because the cases in this
study are all from a single center, there are
limitations to the representativeness of the
sample. Therefore, the extrapolation of the
research conclusions may be limited and
should not be directly extended to other
regions or populations. Furthermore, the
study was a retrospective design. Although it
can provide clinical reference to a certain ex-
tent, there are still unavoidable information
biases and confounding factors, which may
affect the accuracy of the results. Finally, a
limitation of this study is its small sample
size, which may limit statistical power and
increase uncertainty in some results. There-
fore, the current conclusions should be
treated as a preliminary reference only. It is
recommended that more prospective, mul-
ticenter, large-sample studies be conducted
in the future, particularly covering patient
groups across different institutions and geo-
graphical regions, to further verify the risk
factors for MDRAB pneumonia and the ef-
fectiveness and safety of treatment strate-
gies. Provide a higher level of evidence-based
medical evidence for MDRAB pneumonia, so
as to optimize clinical practice and improve
the prognosis of patients. At the same time,
it is necessary to strengthen research on the
molecular epidemiology and mechanisms of
drug resistance in MDRAB infection, thereby
laying a scientific foundation for the devel-
opment of new antibacterial drugs and pre-
cise treatment strategies. Through various
efforts, a systematic and efficient compre-
hensive prevention and control system was
ultimately established to address this seri-
ous public health challenge.
In summary, the occurrence of MDRAB
pneumonia was closely related to the history
of ICU hospitalization, APACHE II score ≥
18, invasive operation, septic shock, and drug
abuse. After the diagnosis of MDRAB pneu-
monia, Severe and tigecycline treatment
were significantly associated with patient
mortality. Patients with MDRAB pneumonia
should be cautious about using tigecycline
when receiving treatment. Although there
are some limitations, the results of this
study still provide an important reference
Mortality risk factors in patients with resistant Acinetobacter baumannii pneumonia 121
Vol. 67(1): 108 - 124, 2026
for the clinical prevention and treatment
of MDRAB pneumonia. In the future, more
rigorous methodological research is needed
to systematically explore treatment strate-
gies and associated mortality risk factors in
MDRAB pneumonia, to further improve clini-
cal prevention and treatment.
Acknowledgment
None
Funding
None
Consent to publish
The manuscript has not been published
before and is not under review by any other
journal. All authors have approved the con-
tent of the paper.
Consent to participate
We have effectively protected the legal
rights and interests of all participants by
carrying out a thorough informed consent
process.
Ethic approval
The study protocol was approved by
the research ethics committee of The Third
People’s Hospital of Yichang City and strictly
adhered to the ethical guidelines and norms
established by the ‘Helsinki Declaration’
(latest revision).
Data availability statement
The data supporting the findings of this
study are available from the corresponding
author upon request.
ORCID numbers of authors
• Lili Liu (LL):
0009-0005-0283-3094
• Wen Lu (WL):
0009-0000-1845-3962
• Gege Fang (GF):
0009-0004-5947-6131
• Wei Zhang (WZ):
0009-0003-4892-0973
Author contribution
LL, WL: Conceived and designed the re-
search, and analyzed data. Drafted and criti-
cally revised the manuscript for important
intellectual content. GF, WZ: Contributed
to data acquisition, analysis, and interpreta-
tion. Provided substantial intellectual input
during manuscript drafting and revision.
GF, WZ: Contributed to the study’s concep-
tion and design. Played a vital role in data
interpretation and manuscript writing. All
authors have reviewed and approved the final
version of the manuscript.
Conflicts of interest
The authors state that they have no fi-
nancial conflicts of interest.
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