Mapping Global Prevalence of Acinetobacter baumannii and Recent Vaccine Development to Tackle It

High-throughput single-cell analysis reveals Omp38-specific monoclonal antibodies that protect against Acinetobacter baumannii infection

Infections caused by Acinetobacter baumannii (A. baumannii) have emerged as a global public health concern because of high pathogenicity of this bacterium. Monoclonal antibodies (mAbs) have a lower likelihood of promoting drug resistance and offer targeted treatment, thereby reducing potential adverse effects; however, the therapeutic potential of mAbs targeting A. baumannii has not been fully characterized. In this study, mAbs against the outer membrane proteins (OMPs) of A. baumannii were isolated in a high-throughput manner. The ability of Omp38-specific mAbs to bind to A. baumannii strains from diverse sources was confirmed via enzyme-linked immunosorbent assay (ELISA). Intravenous administration of the Omp38-specific mAbs significantly improved the survival rate and reduced the bacterial load in a mouse model of lethal A. baumannii infection. Flow cytometry and ELISA confirmed that immune cell infiltration and cytokine production, respectively, decreased in a mouse model of sublethal A. baumannii infection. In addition, analysis of the Omp38-mAb C3 binding conformation revealed the potential mechanism of broad-spectrum binding activity of this mAb against A. baumannii. Taken together, these findings indicate that mAbs against Omp38 facilitate bacterial clearance from host, minimize inflammatory mediator release and reduce host damage, highlighting the potential of Omp38-specific mAbs in the clinical treatment of A. baumannii infection.

Systematic review and meta-analysis on the prevalence of extended-spectrum β-lactamases-producing Acinetobacter baumannii in Iran: Evaluation of TEM, PER, SHV, CTX-M, VEB and GES

Acinetobacter baumannii's resistance to antibiotics restricts treatment ways, and has enhanced its mortality rates approaching 35%. Resistance to β-lactams in Acinetobacter baumannii, related to extended-spectrum β-lactamases (ESBLs), has become a worldwide concern. This study aimed to assess the prevalence of Extended-Spectrum Beta-Lactamase-Producing Acinetobacter baumannii in Iran. Important databases (PubMed, Scopus, Wily Online Library, ScienceDirect and Google Scholar) were searched for related literature published from January 2010 to April 2024. The inclusion criteria were predefined based on PRISMA guidelines. A random-effects model was used according to the heterogeneity test. Publication bias was specified using Egger's weighted regression and Begg's rank correlation methods. The statistical analyses were carried out relying on the Comprehensive Meta-Analysis Software (CMA). Among 2409 articles identified, 15 papers met the eligibility criteria. Among encoding genes of ESBLs, TEM, PER, SHV, CTX-M, VEB and GES were found with the prevalence of 25.0% (95% CI: 15.9-37.1%), 16.1% (95% CI: 7.4-31.5%), 14.3% (95% CI: 6.3-29.4%), 11.1% (95% CI: 4.3-25.8%), 9.9% (95% CI: 5.2-18.1%) and 8.5% (95% CI: 1.4-37.2%), respectively. A subgroup analysis based on province showed some differences in TEM prevalence. The evaluated pooled prevalence of TEM was highest in Ilam (53.4%; 95% CI: 42.0-64.5%), however, it was based only on one study. It was 51.1% (95% CI: 33.7-68.3%) in Tehran. The present studies demonstrate a high prevalence of ESBL in Acinetobacter Baumannii in Iran which poses a serious concern in critically ill patients. As well as these findings can assist our conception of the real prevalence of ESBL to work on new strategies for the control and prevention of infection.

Prevalence and Antibiogram Pattern of Acinetobacter baumannii from 2013 to 2023 in a Tertiary Care Hospital in the Western Region of Saudi Arabia

Acinetobacter baumannii is pathogen of global concern. It causes infection, especially among immunocompromised individuals in intensive care units, due to its ability to survive for long periods on hard surfaces and under a wide range of environmental conditions and become resistant to almost all the available antibiotics used in clinical practice. Objectives: This study aims to address the gap in A. baumannii surveillance in Saudi Arabia by tracking the prevalence, patterns, and trends of acquired A. baumannii resistance at a healthcare facility in the western part of Saudi Arabia over eleven years. Methods: The study was conducted in a tertiary care hospital in the western region of Saudi Arabia, from January 2013 to December 2023. Results: Our data indicated that A. baumannii infections were predominantly observed in inpatients admitted to the hospital (96%) compared to those treated as outpatients in the emergency clinic (4%). The mean of annual A. baumannii infections isolated from inpatients is 503.3, whereas the mean for outpatients is 21, indicating a statistically significant difference with a p-value of <0.0001. The analysis of the antimicrobial susceptibility profile of A. baumannii demonstrated a variable levels of resistance to the evaluated antibiotics. The lowest resistance rate was for colistin. Conclusions: In conclusion, the incidence patterns of A. baumannii isolates peaked in 2013, then declined, and have recently shown an increase, underscoring the necessity for proactive interventions to curtail its dissemination, notwithstanding initial decreases in infection rates and resistance.

Prevalence, antimicrobial resistance profiles, and determinants of Acinetobacter baumannii and Pseudomonas aeruginosa isolates among nosocomial infection--suspected patients in the northwestern region of Ethiopia

BACKGROUND

Pseudomonas aeruginosa and Acinetobacter baumannii are common causes of nosocomial infections. Furthermore, antimicrobial resistance is frequently observed in these pathogens, posing significant challenges to treatment.

OBJECTIVE

This study aimed to determine the prevalence, antimicrobial resistance profiles, and determinants of A baumannii and P aeruginosa isolates among nosocomial infection--suspected patients at Debre Markos Comprehensive Specialized Hospital.

METHODS

An institutional-based cross-sectional study was conducted from March 01, 2021 to May 30, 2021. A consecutive convenient sampling technique was applied to select 200 nosocomial infection--suspected patients. Clinical samples were collected and inoculated on MacConkey agar, blood agar, and Tryptic Soy broth. Testing for antibiotic susceptibility was done on Mueller Hinton agar.

RESULTS

The overall prevalence of A baumannii and P aeruginosa isolates among nosocomial infection--suspected patients was 11.5%. All isolates of P aeruginosa and A baumannii were 100% resistant to cefepime and piperacillin. Prolonged hospitalization and antibiotics use were significant determinants of P aeruginosa and A baumannii--induced nosocomial infection (adjusted odds ratio: 5.691, 95% CI: 1.069-7.296, P<.050 and adjusted odds ratio: 4.199, 95% CI: 0.997-6.675, P<.042, respectively).

CONCLUSIONS

The prevalence of A baumannii and P aeruginosa isolates was high in the study area. Therefore, there should be serious attention to control the spread of drug-resistant nosocomial infections in the study area.

In silico screening and molecular dynamics analysis of natural DHPS enzyme inhibitors targeting Acinetobacter baumannii

Over time, antimicrobial agents are losing their credibility in curbing infections due to the development of resistant pathogen strains. The resistant strains have proven to invade living beings and cause various diseases, leading to deaths at an alarming rate. Acinetobacter baumannii is one such pathogen, and to target it through enzyme inhibition, Dihydropteroate synthase enzyme's active site is virtually screened for antimicrobial agents against in-house libraries of natural molecules from medicinally important plants and Agaricus spp. fungus. Two ligands (MSID_000725 and CID_291096) are found to be suitable candidate inhibitors after various screening through Lipinski's based drug-like parameters, pharmacokinetic parameters, toxicity parameters and structural parameters which comprised of estimated free energy of binding, ligand efficiency and interaction analysis. DHPS enzyme catalyses the condensation reaction of hydroxymethyl-7, 8-dihydropterin pyrophosphate and para-aminobenzoic acid in the folic acid synthesis pathway in bacterial cells. The Complexes of the DHPS enzyme and ligands are validated through in silico studies, including MD simulations and MM/PBSA based binding free energy studies. The Complex DHPS-MSID_000725 and DHPS-CID_291096 were analysed for global dynamics attributes such as RMSD, RMSF, Rg, SASA and essential dynamics through PCA. The complexes were subjected to MM/PBSA based binding free energy analysis and were found to have binding free energy of -25.18 kcal/mol (DHPS-MSID_000725) and - 4.90 kcal/mol (DHPS-CID_291096).

Novel antibacterial agents and emerging therapies in the fight against multidrug-resistant Acinetobacter baumannii

Acinetobacter baumannii, a multidrug-resistant pathogen, poses a critical challenge in healthcare settings due to its adaptability and limited treatment options. The global rise in antimicrobial resistance (AMR) has underscored the urgent need for novel therapeutic strategies to combat infections caused by extensively drug-resistant (EDR) and pan-drug-resistant (PDR) A. baumannii. Traditional antibiotic discovery methods, such as whole-cell screening, have fallen short, consistently identifying drugs prone to resistance. This review explores the discovery of new anti-bacterial agents targeting A. baumannii, focusing on emerging therapeutic approaches, including nanoparticle-based therapies, antimicrobial peptides, and antibiotic combination therapies. Nanoparticle-based approaches, leveraging enhanced penetration and multi-mechanistic action, show promise in overcoming resistance, though challenges such as toxicity and biocompatibility persist. Additionally, combination therapies, such as polymyxins with carbapenems, have demonstrated efficacy in clinical settings. This review also highlights the limitations of current therapies, the mechanisms of bacterial resistance, and the role of alternative strategies like bacteriophage therapy. Emphasis is placed on the need for further research into overcoming cross-resistance and enhancing therapeutic efficacy against A. baumannii. The review concludes by discussing the importance of advancing research into novel agents, optimizing dosage strategies, and addressing the challenges posed by toxicity to ensure the effective treatment of A. baumannii infections in both hospital and community settings.

Intrahospital dissemination of multidrug-resistant Acinetobacter baumannii at a teaching hospital in Northeast of Mexico

Background

Acinetobacter baumannii is an opportunistic drug-resistant Gram-negative coccobacillus associated with nosocomial infections, representing a worldwide public health problem.

Aim

The aim of this study was to analyse the dissemination of A. baumannii in two hospital buildings in Mexico through phenotypic and genotypic characterization of clinical isolates obtained for three years.

Methods

Clinical strains were collected from two buildings in a tertiary-care hospital in Monterrey, Mexico. After species identification by MALDI-TOF MS and PCR, antimicrobial susceptibility was determined by disk diffusion and microdilution methods, carbapenemase-encoding genes (OXA-23, -24, -51, and -58) were searched, and clonal diversity was analysed by PFGE and MLST.

Findings

Among 204 specimens, 87.3% and 50.5% of the isolates were classified as multidrug-resistant (MDR) and difficult-to-treat-resistant (DTR), respectively. The OXA-24 gene was detected in 95% of the isolates. Most isolates (n=181) were grouped into 15 clones, four which predominated and disseminated after five months. Among ST detected (ST1694, ST758, ST124, and ST490), ST124, which belongs to the high-risk CC636 clonal complex, is reported for the first time in Mexico.

Conclusions

Long-term persistence and dissemination of A. baumannii clones were observed in specific hospital wards from two buildings in a tertiary-care hospital in Mexico. High antimicrobial resistance, such as MDR and DTR, were observed in this hospital. DTR surveillance and early recognition of MDR A. baumannii clones should be performed routinely to prevent their dissemination.

Blue benzoquinone from scorpion venom shows bactericidal activity against drug-resistant strains of the priority pathogen Acinetobacter baumannii

Antibiotic-resistant bacteria pose a significant global health threat, particularly pathogens resistant to last-resort antibiotics, such as those listed as priority pathogens by the World Health Organization. Addressing this challenge requires the development of novel antimicrobial agents. Previously, we identified a blue 1,4-benzoquinone isolated from the venom of the Mexican scorpion Diplocentrus melici as a potent antimicrobial compound effective against Staphylococcus aureus and Mycobacterium tuberculosis. Moreover, we devised a cost-effective synthetic route for its production. In this study, we demonstrate that the blue benzoquinone exhibits antibacterial activity against additional pathogens, including the priority pathogen Acinetobacter baumannii. Notably, the compound effectively killed clinical strains of A. baumannii resistant to multiple antibiotics, including carbapenem and colistin. Furthermore, A. baumannii did not develop resistance to the benzoquinone even after multiple growth cycles under sub-inhibitory concentrations, unlike the tested antibiotics. These findings underscore the potential of this blue benzoquinone as a lead compound for the development of a new class of antibiotics targeting multidrug-resistant bacteria.

Sub-minimum inhibitory concentrations in ceftazidime exacerbate the formation of Acinetobacter baumannii biofilms

Associated with nosocomial infections, the environmental Gram-negative coccobacillus A. baumannii leads to various kinds of high mortality-rate infections among which pneumonias mainly in immune-compromised people from health-care facilities. A critical component of the current antibiotic resistance problem is the presence of antibiotics sub-minimum inhibitory concentrations (sub-MICs) in a variety of natural settings including drinking water, sewage water, rivers, lakes, and natural sludge. In India, third-generation cephalosporins such as ceftazidime (CAZ) count among the most often prescribed β-lactams to treat infections by A. baumannii. In this study, we showed that CAZ sub-MICs 1/reduce adhesion to lung epithelial cells and slow down the growth of the A. baumannii KSK1 strain, which nevertheless quickly resumes its growth; 2/alter the morphology of A. baumannii KSK1 planktonic cells and induce the formation of bacterial aggregates that resemble biofilms; 3/increase the in vitro formation of biofilms by A. baumannii KSK1 bacterial cells. Our findings underscore the importance of considering sub-MICs in antibiotic therapy and environmental contamination as the antibiotics sub-MICs potentially found in wastewater may contribute to the selection causing antibiotic resistance and persistence of antibiotic-resistant strains.

Analysis of the genome data of Acinetobacter baumannii UOL-KIMZ-24, exhibiting multiple drug resistance through efflux pumps

Acinetobacter baumannii is a well-known opportunistic pathogen, responsible for various nosocomial infections. A. baumannii UOL-KIMZ-24 was previously isolated from a clinical specimen, collected from Lahore General Hospital, Lahore (LGH), Pakistan, dated 3rd March, 2022. During the initial screening for antimicrobial susceptibility, the UOL-KIMZ-24 was found a multiple drug resistant (MDR) strain. However, the detailed genomic insights for genes e.g. responsible for exhibiting antibiotic resistance via efflux pumps, have not yet been reported from A. baumannii strains, recovered from LGH. The current research to fills this gap by isolating, whole genome sequencing and subsequent post-sequencing analysis for addressing and identifying the efflux pumps associated genes, responsible for multiple drug resistant in A. baumannii. In a hybrid approach, short reads were processed through Illumina platform, while long reads were sequenced by MinION MK1B sequencing technique. The assembled and annotated genome of the UOL-KIMZ-24 revealed that it has 4048631 bp genome size with 179 contigs, 38.9 % GC content, 3628 protein coding sequences, 80 tRNA and 7 rRNA. The analysis of antibiotic-resistance genes (AMR) depicted 27 genes. where the genes encoding efflux pumps such as adeABC, adeRS, adeJK, and adeMN were the more prominent. In addition, sequence typing (ST) study showed that UOL-KIMZ-24 strain lies in ST2, six prophage sequences and 73 virulence factors were also identified in the studied UOL-KIMZ-24. Such an all-inclusive study uncovered the genetic flexibility of UOL-KIMZ-24 genome for acquiring MDR against in-practice antibiotics.

Molecular epidemiology of carbapenem-resistant Acinetobacter baumannii group in Taiwan

Acinetobacter, particularly the Acinetobacter baumannii group, is a major cause of nosocomial infections, and carbapenem-resistant Acinetobacter spp. are important human pathogens. We collected 492 Acinetobacter spp. strains from two hospitals in Taiwan and classified them using MALDI-TOF MS and blaOXA-51-like PCR; 94.5% were A. baumannii, and 5.5% were non-A. baumannii (NAB). We confirmed their identity by rpoB gene sequencing of 239 randomly selected A. baumannii strains and all 27 NAB strains. Our analysis revealed that the rpoB alleles of OXA51-like-negative strains matched those of two NAB species, A. seifertii and A. nosocomialis, while all OXA51-like-positive strains matched A. baumannii, as per the Pasteur MLST scheme database. Among the 492 strains, 240 exhibited carbapenem resistance, including 237 carbapenem-resistant A. baumannii (CRAB) strains and three CR-NAB strains. All CRAB strains were positive for blaOXA-51-like; 72.6% also carried blaOXA-23-like, 22.8% carried blaOXA-24-like, 3.4% co-carried blaOXA-23-like+blaOXA-24-like, and 1.27% carried blaOXA-51-like alone. Among the three CR-NAB strains, one carried blaNDM-1, and two co-carried blaOXA-58-like+blaIMP. We also established a new multiplex PCR method for rapid screening of common capsular types (KL), which showed a difference between CRAB and carbapenem-susceptible A. baumannii (CSAB). KL2, KL10, KL22, and KL52 accounted for 76.6% of CRAB strains, whereas about half of the CSAB strains were other KL types. Of the remaining CSAB strains, KL14 was the most predominant type at 10.3%. We further conducted MLST Pasteur typing for 262 isolates and found that the carbapenemase genes were correlated with either ST or KL types. Additionally, KL types showed correlations with ST types, carbapenem resistance, and certain clinical records. Whole-genome sequencing of a blaNDM-1-carrying A. seifertii strain revealed a plasmid transferable via in vitro conjugation, suggesting A. seifertii may be a reservoir for NDM-1 plasmids.IMPORTANCECarbapenem-resistant Acinetobacter spp. have been identified by the World Health Organization as a top priority for new antibiotic development. We established a rapid KL-typing method for efficient screening of Acinetobacter baumannii strains to enable epidemiological surveillance and provide a foundation for effective infection control. Our investigation of the molecular epidemiology of the A. baumannii group isolates revealed the prevalence of carbapenemase genes and major KL types among CR and CS strains of A. baumannii and NAB. We identified an A. seifertii strain carrying a Ti-type conjugative operon on a small plasmid that harbored genes encoding the NDM-1 carbapenemase alongside genes conferring resistance to aminoglycosides and bleomycin and closely resembled sequences detected in A. soli and A. pittii in Taiwan and China, respectively, suggesting its potential for transmitting multidrug resistance and contributing to the spread of antimicrobial resistance.

Acinetobacter baumannii Clinical Isolates Resist Complement-Mediated Lysis by Inhibiting the Complement Cascade and Improperly Depositing MAC

INTRODUCTION

Acinetobacter baumannii is a gram-negative opportunistic bacterium that causes life-threatening infections in immunocompromised hosts. The complement system is a critical mechanism of innate immunity that protects the human body from bacterial infections. Complement activation leads to the deposition of the membrane attack complex (MAC), which can directly lyse gram-negative bacteria. However, A. baumannii has developed evasion mechanisms to protect itself from complement.

METHODS

Complement deposition was investigated by flow cytometry and Western blotting. Soluble MAC formation was assessed by ELISA. Bacterial serum resistance was determined by the SYTOX Green Assay. Galleria mellonella was used as an infection model. Genome sequencing revealed virulence genes carried by isolates.

RESULTS

We examined clinical isolates of A. baumannii and found 11 isolates with MAC deposition and 5 isolates without deposition. Trypsinization of MAC-positive isolates significantly reduced MAC, indicating incorrect insertion, consistent with a lack of lysis of these strains. MAC-negative isolates inhibited alternative pathway activation and were significantly more serum-resistant. These strains were also more virulent in a G. mellonella infection model. Whole genome sequencing revealed that MAC-negative isolates carried more virulence genes, and both MAC-negative and MAC-positive A. baumannii significantly differed in capsule type. Importantly, a correlation was observed between complement inhibition and capsule type (e.g., capsule locus KL171) of MAC-negative bacteria, while the capsule type (e.g., KL230) of MAC-positive A. baumannii was associated with increased sensitivity to MAC-mediated lysis.

CONCLUSION

Our findings suggest a relationship between capsule type, complement resistance, and host virulence in A. baumannii.

INTRODUCTION

Acinetobacter baumannii is a gram-negative opportunistic bacterium that causes life-threatening infections in immunocompromised hosts. The complement system is a critical mechanism of innate immunity that protects the human body from bacterial infections. Complement activation leads to the deposition of the membrane attack complex (MAC), which can directly lyse gram-negative bacteria. However, A. baumannii has developed evasion mechanisms to protect itself from complement.

METHODS

Complement deposition was investigated by flow cytometry and Western blotting. Soluble MAC formation was assessed by ELISA. Bacterial serum resistance was determined by the SYTOX Green Assay. Galleria mellonella was used as an infection model. Genome sequencing revealed virulence genes carried by isolates.

RESULTS

We examined clinical isolates of A. baumannii and found 11 isolates with MAC deposition and 5 isolates without deposition. Trypsinization of MAC-positive isolates significantly reduced MAC, indicating incorrect insertion, consistent with a lack of lysis of these strains. MAC-negative isolates inhibited alternative pathway activation and were significantly more serum-resistant. These strains were also more virulent in a G. mellonella infection model. Whole genome sequencing revealed that MAC-negative isolates carried more virulence genes, and both MAC-negative and MAC-positive A. baumannii significantly differed in capsule type. Importantly, a correlation was observed between complement inhibition and capsule type (e.g., capsule locus KL171) of MAC-negative bacteria, while the capsule type (e.g., KL230) of MAC-positive A. baumannii was associated with increased sensitivity to MAC-mediated lysis.

CONCLUSION

Our findings suggest a relationship between capsule type, complement resistance, and host virulence in A. baumannii.

Development of a novel multi-epitope subunit mRNA vaccine candidate to combat Acinetobacter baumannii

Acinetobacter baumannii, an opportunistic bacterium prevalent in various environment, is a significant cause of nosocomial infections in ICUs. As the causative agent of pneumonia, septicemia, and meningitis, A. baumannii typically exhibits multidrug resistance and is associated with poor prognosis, thus led to a challenge for researchers in developing new treatment and prevention methods. This study involved the development of a novel multi-epitope mRNA vaccine for A. baumannii and validation of in silico approaches was conducted. We screened 11 immunodominant epitopes for cytotoxic T cells, 5 for helper T cells, and 10 for Linear B-cell based on promising candidate proteins omp33-36, ompA and ompW, the selection of these three proteins is based on reverse vaccinology screening and previous work by other researchers. All predicted epitopes demonstrated strong antigenicity, immunogenicity without posing any potential harm to humans. Additionally, high conservancy is required to cover different strains. All epitopes, as well as adjuvants, were constructed into a final vaccine, which was further assessed by calculating its physicochemical properties. Next, we docked the vaccine protein with immune receptors and analyzed the complexes with dynamic simulations to evaluate its affinity to receptors. At last, the constructed sequence is translated to an mRNA sequence. The results indicated the constructed vaccine is capability of eliciting robust humoral and cellular immune responses, making it a promising candidate for protection against the targeted pathogen.

Epidemiological and Clinical Insights into Acinetobacter baumannii: A Six-Year Study on Age, Antibiotics, and Specimens

Background

This six-year retrospective study provides an in-depth analysis of the epidemiological and clinical patterns associated with Acinetobacter baumannii (A. baumannii) infections, focusing on age distribution, antibiotic resistance profiles, and specimen types.

Aim

The research examines the incidence and characteristics of both non-Multi-Drug Resistant (non-MDR) and Multi-Drug Resistant (MDR) A. baumannii strains by reviewing patient records from January 2016 to December 2022.

Methods

Through a statistical analysis, the study highlights the incidence rates across diverse age groups and explores the impact of antibiotic treatment regimens on infection outcomes. Additionally, it identifies the primary clinical specimen types for each strain, noting an association between non-MDR A. baumannii and midstream urine samples, while MDR A. baumannii strains were more frequently found in respiratory, wound, peripheral, and central line swaps/specimens.

Results

The results indicate that in 2016, non-MDR A. baumannii infections were notably more frequent compared to MDR A. baumannii cases. However, a significant shift occurred in 2021 and 2022, with a marked decrease in non-MDR A. baumannii cases and an increase in MDR A. baumannii infections. Antibiotic susceptibility testing revealed that non-MDR strains were commonly tested against cefazolin, ceftazidime, ciprofloxacin, gentamicin, nitrofurantoin, oxacillin, piperacillin/tazobactam, and trimethoprim/sulfamethoxazole. In contrast, MDR strains were frequently tested against amikacin, cefepime, colistin, meropenem, imipenem, and tigecycline.

Conclusion

This study enhances the understanding of A. baumannii clinical behaviour and resistance patterns, offering valuable insights to support future research and inform strategies for infectious disease management and control.

Cyclic Peptide MV6, an Aminoglycoside Efficacy Enhancer Against Acinetobacter baumannii

Background/Objectives: Acinetobacter baumannii is a globally emerging pathogen with widespread antimicrobial resistance driven by multiple mechanisms, such as altered expression of efflux pumps like AdeABC, placing it as a priority for research. Driven by the lack of new treatments, alternative approaches are being explored to combat its infections, among which efficacy-enhancing adjuvants can be found. This study presents and characterizes MV6, a synthetic cyclic peptide that boosts aminoglycoside efficacy. Methods: MV6's activity was assessed through antimicrobial susceptibility testing in combination with different antibiotic classes against A. baumannii strains characterized by PCR and RT-qPCR. PAβN served as a reference efflux pump inhibitor. Synergy was evaluated using checkerboard assays, and spontaneous mutants were generated with netilmicin with/without MV6 (100 mg/L). Whole-genome sequencing and variant calling analysis were then performed. Results: MV6 presented low antimicrobial activity in A. baumannii with MICs higher than 2048 mg/L. MV6 showed a better boosting effect for aminoglycosides, especially netilmicin, exceeding that of PAβN. Checkerboard assays confirmed a strong synergy between netilmicin and MV6, and a significant correlation was found between netilmicin MIC and adeB overexpression, which was mitigated by the presence of MV6. MV6 reduced, by 16-fold, the mutant prevention concentration of netilmicin. Mutations in a TetR-family regulator and ABC-binding proteins were found in both groups, suggesting a direct or indirect implication of these proteins in the resistance acquisition process. Conclusions: MV6 lacks intrinsic antimicrobial activity, minimizing selective pressure, yet enhances netilmicin's effectiveness except for strain 210, which lacks the AdeABC efflux pump. Resistant mutants indicate specific aminoglycoside resistance mechanisms involving efflux pump mutations, suggesting synergistic interactions. Further research, including transcriptomic analysis, is essential to elucidate MV6's role in enhancing netilmicin efficacy and its resistance mechanisms.

The role of sulbactam-durlobactam in treating carbapenem-resistant Acinetobacter infections

PURPOSE OF REVIEW

Infections caused by multidrug-resistant Acinetobacter baumannii present a significant global health challenge. Available treatment options are limited and frequently constrained by unfavourable safety and pharmacokinetic profiles. Sulbactam-durlobactam is a novel β-lactamase inhibitors combination specifically developed to target A. baumannii , including carbapenem-resistant strains. The purpose of this review is to assess the current evidence supporting the role of sulbactam-durlobactam in the management of A. baumannii infections.

RECENT FINDINGS

We summarize the available evidence regarding the pharmacokinetic and pharmacodynamic profiles of sulbactam-durlobactam from key in-vitro and in-vivo studies. Additionally, efficacy results from the Phase III randomized controlled trial and real-world data on sulbactam-durlobactam's use against severe A. baumannii infections are also discussed.

SUMMARY

Sulbactam-durlobactam is a promising addition to the treatment options for carbapenem-resistant A. baumannii infections. Ongoing research and vigilance are essential to monitor the development of in-vivo resistance, assess effectiveness across diverse patient populations, and explore potential synergistic combinations with other antimicrobials. Careful stewardship and comprehensive clinician education will be crucial to optimizing the clinical use of sulbactam-durlobactam.

Development of acute Pseudomonas aeruginosa and Acinetobacter baumannii lung mono-challenge models in mice using oropharyngeal aspiration

Antimicrobial-resistant pathogens such as Pseudomonas aeruginosa and Acinetobacter baumannii can cause potentially fatal infections in susceptible individuals, with respiratory tract infections among the most common clinical presentations. The development of novel treatments or prophylactic interventions to combat these infections is urgently needed and requires robust, reliable animal models for their preclinical evaluation. In particular, the bacterial burden needs to be accurately determined before and after administration of the potential therapy under evaluation to quantify the effectiveness of the treatment. We provide two reliable, non-invasive murine acute lung challenge models with either P. aeruginosa or A. baumannii using an oropharyngeal aspiration technique, which has been widely overlooked in studies testing vaccines or treatments for these pathogens. Here, we show that this non-surgical technique to deliver suspensions into mouse lungs does not significantly impact animal welfare (based on welfare monitoring and weight) and allows uniform bilateral distribution of the bacterial dose, resulting in even bioburden in both lungs. The optimal timepoint for humane killing and organ harvest was 24 h after challenge for both pathogens, and at least 4×106 and 107 c.f.u. per mouse were needed to obtain a reproducible P. aeruginosa or A. baumannii bioburden, respectively. These mouse challenge models offer a valuable tool to assess therapeutic interventions against P. aeruginosa or A. baumannii infections.

Comprehensive Approaches to Combatting Acinetobacter baumannii Biofilms: From Biofilm Structure to Phage-Based Therapies

Acinetobacter baumannii-a multidrug-resistant (MDR) pathogen that causes, for example, skin and soft tissue wounds; urinary tract infections; pneumonia; bacteremia; and endocarditis, particularly due to its ability to form robust biofilms-poses a significant challenge in clinical settings. This structure protects the bacteria from immune responses and antibiotic treatments, making infections difficult to eradicate. Given the rise in antibiotic resistance, alternative therapeutic approaches are urgently needed. Bacteriophage-based strategies have emerged as a promising solution for combating A. baumannii biofilms. Phages, which are viruses that specifically infect bacteria, offer a targeted and effective means of disrupting biofilm and lysing bacterial cells. This review explores the current advancements in bacteriophage therapy, focusing on its potential for treating A. baumannii biofilm-related infections. We described the mechanisms by which phages interact with biofilms, the challenges in phage therapy implementation, and the strategies being developed to enhance its efficacy (phage cocktails, engineered phages, combination therapies with antibiotics). Understanding the role of bacteriophages in both biofilm disruption and in inhibition of its forming could pave the way for innovative treatments in combating MDR A. baumannii infections as well as the prevention of their development.

Investigating an outbreak of extensively drug-resistant Acinetobacter baumannii in a tertiary healthcare centre in lebanon using next-generation sequencing

The frequent occurrence of Acinetobacter baumannii in hospital settings and the elevated rate of antimicrobial resistance in this pathogen represent a serious clinical and public health threat worldwide, and particularly in Lebanon where outbreak surveillance and control are still insufficient. Whole-genome sequencing (WGS) is a fast and reliable tool to study outbreaks at the molecular level and obtain actionable knowledge, leading to better control measures. A total of 59 A. baumannii isolates were collected from intensive care unit (ICU) patients (57 isolates) and from the hospital environment (2 isolates) between August 2022 and May 2023, antimicrobial susceptibility testing (AST) was performed and gDNA was subjected to WGS. Analysis was performed to reveal the sequence types (ST), the relatedness to strains that caused other outbreaks and the arsenal of resistance genes harboured by these bacteria. Of 59 isolates, 85% were categorised as extensively drug-resistant (XDR), 13.6% as multidrug-resistant (MDR) and 1.7% as pan-drug-resistant. All isolates belonged to international clone (IC)2, of which the majority were of ST2 (91.5%). The isolates clustered well with those of a previous outbreak in the same hospital. In addition, isolates from hospitals in Lebanon clustered well together and some clustered with those originating from other countries. The observed genetic relatedness between the current isolates and those from the previous outbreaks underscores the importance of strict surveillance to limit the threat of outbreaks. Moreover, the clustering of isolates from Lebanon with others from distant countries proves the necessity to further investigate the international spread of drug-resistant pathogens and the implementation of control strategies.

Bactericidal and Synergistic Effects of Lippia origanoides Essential Oil and Its Main Constituents against Multidrug-Resistant Strains of Acinetobacter baumannii

Bacterial resistance in Acinetobacter baumannii is a significant public health challenge, as these bacteria can evade multiple antibiotics, leading to difficult-to-treat infections with high mortality rates. As part of the search for alternatives, essential oils from medicinal plants have shown promising antibacterial potential due to their diverse chemical constituents. This study evaluated the antibacterial, antibiofilm, and synergistic activities of the essential oil of Lippia origanoides (EOLo) and its main constituents against multidrug-resistant clinical isolates of A. baumannii. Additionally, the antibacterial and antibiofilm potential of a nanoemulsion containing carvacrol (NE-CAR) was assessed. EOLo was extracted through hydrodistillation, and its components were identified via gas chromatography coupled with mass spectrometry. The A. baumannii isolates (n = 9) were identified and tested for antimicrobial susceptibility using standard disk diffusion methods. Antibacterial activity was determined by broth microdilution, while antibiofilm activity was measured using colorimetric methods with crystal violet and scanning electron microscopy. Synergism tests with antibiotics (meropenem, ciprofloxacin, gentamicin, and ampicillin+sulbactam) were performed using the checkerboard method. The primary constituents of EOLo included carvacrol (48.44%), p-cymene (14.58%), and thymol (10.16%). EOLo, carvacrol, and thymol demonstrated significant antibacterial activity, with carvacrol showing the strongest effect. They were also effective in reducing biofilm formation, as was NE-CAR. The combinations with antibiotics revealed significant synergistic effects, lowering the minimum inhibitory concentration of the tested antibiotics. Therefore, this study confirms the notable antibacterial activity of the essential oil of L. origanoides and its constituents, especially carvacrol, suggesting its potential as a therapeutic alternative for A. baumannii infections.

The Comparative Characterization of a Hypervirulent Acinetobacter baumannii Bacteremia Clinical Isolate Reveals a Novel Mechanism of Pathogenesis

Acinetobacter baumannii is an opportunistic Gram-negative pathogen with exquisite survival capabilities under various environmental conditions and displays widespread resistance to common antibiotics. A. baumannii is a leading cause of nosocomial infections that result in high morbidity and mortality rates. Accordingly, when multidrug resistance rates surpass threshold levels, the percentage of A. baumannii clinical isolates surges. Research into A. baumannii has increased in the past decade, and multiple mechanisms of pathogenesis have been identified, including mechanisms underlying biofilm development, quorum sensing, exotoxin production, secretion system utilization, and more. To date, the two gold-standard strains used to investigate different aspects of A. baumannii pathogenesis include ATCC 17978 and ATCC 19606. Here, we report a comparative characterization study of three additional A. baumannii clinical isolates obtained from different infection types and derived from different anatomical regions of infected patients. The comparison of three clinical isolates in addition to the ATCC strains revealed that the hypervirulent bacteremia clinical isolate, known as HUMC1, employs a completely different mechanism of pathogenesis when compared to all its counterparts. In stark contrast to the other genetic variants, the hypervirulent HUMC1 isolate does not form biofilms, is antibiotic-susceptible, and has the capacity to reach higher levels of quorum compared to the other clinically relevant strains. Our data also reveal that HUMC1 does not shed endotoxin into the extracellular milieu, rather secretes the evolutionarily conserved, host-mimicking, Zonula occludens toxin (Zot). Taken together, our hypothesis that HUMC1 cells have the ability to reach higher levels of quorum and lack biofilm production and endotoxin shedding, accompanied by the substantial elaboration of Zot, suggests a novel mechanism of pathogenesis that appears to afford the hypervirulent pathogen with stealth-like capabilities when disseminating through the circulatory system in a state of bacteremia.

ESKAPE Pathogens: Antimicrobial Resistance Patterns, Risk Factors, and Outcomes a Retrospective Cross-Sectional Study of Hospitalized Patients in Palestine

BACKGROUND

Antimicrobial resistance to ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp). remains a major challenge in hospital settings.

OBJECTIVE

This study aimed to determine the ESKAPE antimicrobial resistance patterns and associated factors with multi-drug resistance strains among hospitalized patients in a single tertiary care medical hospital in Palestine.

METHODS

A single-center retrospective cross-sectional study was conducted by reviewing patients' electronic medical records and laboratory results from November 1, 2021, to November 30, 2022, at the Palestine Medical Complex in Palestine. The study included patients aged > 18 years who had been infected with ESKAPE pathogens 48 hours after hospital admission.

RESULTS

This study included 231 patients, of whom 90.5% had MDR infections. In total, 331 clinical samples of ESKAPE pathogens were identified. A. baumannii was the most prevalent MDR pathogen (95.6%) with Carbapenem-resistant exceeding 95%, followed by K. pneumoniae (83.8%) with extended-spectrum cephalosporin resistance exceeding 90%, S. aureus (68.2) with 85% oxacillin-resistance, E. faecium (40%) with 20% vancomycin resistance, P. aeruginosa (22.6%) with 30% carbapenem resistance. Furthermore, emergent colistin resistance has been observed in A. baumannii, K. pneumoniae, and P. aerogenesis. Risk factors for MDR infection included age (p< 0.035), department (p< 0.001), and invasive procedures such as IUC (p< 0.001), CVC (p< 0.000), and MV (p< 0.008). Patients diagnosed with MDR bacteria had increased 30-day mortality (p< 0.001).

CONCLUSION

The findings of this study show alarming MDR among hospitalized patients infected with ESKAPE pathogens, with resistance to first-line antimicrobial agents and emerging resistance to colistin, minimizing treatment options. Healthcare providers and the Ministry of Health must take steps, adopt policies to prevent antimicrobial resistance, adhere to infection control guidelines, implement antimicrobial stewardship programs to prevent and limit the growing health crisis, and support research to discover new treatment options.

Tracing Acinetobacter baumannii's Journey from Hospitals to Aquatic Ecosystems

BACKGROUND

This study provides a comprehensive analysis of Acinetobacter baumannii in aquatic environments and fish microbiota by integrating culture-dependent methods, 16S metagenomics, and antibiotic resistance profiling.

METHODS

A total of 83 A. baumannii isolates were recovered using culture-dependent methods from intra-hospital infections (IHI) and wastewater (WW) and surface water (SW) samples from two southern Romanian cities in August 2022. The antibiotic susceptibility was screened using disc diffusion, microdilution, PCR, and Whole Genome Sequencing assays.

RESULTS

The highest microbial load in the analyzed samples was found in Glina, Bucharest, for both WW and SW samples across all investigated phenotypes. For Bucharest isolates, the resistance levels corresponded to fluoroquinolones > aminoglycosides > β-lactam antibiotics. In contrast, A. baumannii from upstream SW samples in Târgoviște showed the highest resistance to aminoglycosides. The blaOXA-23 gene was frequently detected in IHI, WW, and SW isolates in Bucharest, but was absent in Târgoviște. Molecular phylogeny revealed the presence of ST10 in Târgoviște isolates and ST2 in Bucharest isolates, while other minor STs were not specifically correlated with a sampling point. Using 16S rRNA sequencing, significant differences in microbial populations between the two locations was identified. The low abundance of Alphaproteobacteria and Actinobacteria in both locations suggests environmental pressures or contamination events.

CONCLUSIONS

These findings indicate significant fecal contamination and potential public health risks, emphasizing the need for improved water quality monitoring and management.

Loop-mediated isothermal amplification assay detects multiple alleles of bla OXA-51-like genes in Acinetobacter baumannii and other Gram-negative bacteria despite primer-template mismatches

The known intrinsic and polymorphic bla OXA-51-like genes of Acinetobacter baumannii were recently reported in other non-A. baumannii Gram-negative pathogens. Accurate detection of this potentially transferrable carbapenemase gene in the clinical setting is critical. This study developed a loop-mediated isothermal amplification (LAMP) assay targetting multiple alleles of bla OXA-51-like genes. Specifically, an alignment-based primer design, in silico primer screening, and in vitro assay confirmation were conducted. Both in silico and in vitro results revealed the tolerance of the LAMP assay to up to five primer-template mismatches outside the 3'-end primer regions. Within 90 min, the LAMP assay also detected the gene targets in other Gram-negative bacteria with known and novel bla OXA-51-like genes. Finally, it showed a superior limit of detection (as low as 101 CFU/mL) compared with polymerase chain reaction, and high specificity against non-targets. This study developed a highly adaptable LAMP assay to monitor bla OXA-51-like genes in the clinical setting and provided important insights into LAMP primer design and screening.

Zinc(ii)-mediated stereoselective construction of 1,2-cis 2-azido-2-deoxy glycosidic linkage: assembly of Acinetobacter baumannii K48 capsular pentasaccharide derivative

The capsular polysaccharide (CPS) is a major virulence factor of the pathogenic Acinetobacter baumannii and a promising target for vaccine development. However, the synthesis of the 1,2-cis-2-amino-2-deoxyglycoside core of CPS remains challenging to date. Here we develop a highly α-selective ZnI2-mediated 1,2-cis 2-azido-2-deoxy chemical glycosylation strategy using 2-azido-2-deoxy glucosyl donors equipped with various 4,6-O-tethered groups. Among them the tetraisopropyldisiloxane (TIPDS)-protected 2-azido-2-deoxy-d-glucosyl donor afforded predominantly α-glycoside (α : β = >20 : 1) in maximum yield. This novel approach applies to a wide acceptor substrate scope, including various aliphatic alcohols, sugar alcohols, and natural products. We demonstrated the versatility and effectiveness of this strategy by the synthesis of A. baumannii K48 capsular pentasaccharide repeating fragments, employing the developed reaction as the key step for constructing the 1,2-cis 2-azido-2-deoxy glycosidic linkage. The reaction mechanism was explored with combined experimental variable-temperature NMR (VT-NMR) studies and mass spectroscopy (MS) analysis, and theoretical density functional theory calculations, which suggested the formation of covalent α-C1GlcN-iodide intermediate in equilibrium with separated oxocarbenium-counter ion pair, followed by an SN1-like α-nucleophilic attack most likely from separated ion pairs by the ZnI2-activated acceptor complex under the influence of the 2-azido gauche effect.

Hypothetical adhesin CAM87009.1 formulated in alum or biogenic silver nanoparticles protects mice from lethal infection by multidrug-resistant Acinetobacter baumannii

Due to its antimicrobial resistance characteristics, the World Health Organization (WHO) classifies A. baumannii as one of the critical priority pathogens for the development of new therapeutic strategies. Vaccination has been approached as an interesting strategy to overcome the lack of effective antimicrobials and the long time required to develop and approve new drugs. In this study, we aimed to evaluate as a vaccine the hypothetical adhesin protein CAM87009.1 in its recombinant format (rCAM87009.1) associated with aluminum hydroxide (Alhydrogel®) or biogenic silver nanoparticles (bio-AgNP) as adjuvant components against lethal infection by A. baumannii MDR strain. Both vaccine formulations were administered in three doses intramuscularly in BALB/c murine models and the vaccinated animals were tested in a challenge assay with A. baumannii MDR strain (DL100). rCAM87009.1 protein associated with both adjuvants was able to protect 100 % of animals challenged with the lethal strain during the challenge period. After the euthanasia of the animals, no A. baumannii colonies were detected in the lungs of animals vaccinated with the rCAM87009.1 protein in both formulations. Since the first immunization, high IgG antibody titers were observed (1:819,200), with results being statistically similar in both vaccine formulations evaluated. rCAM87009.1 associated with both adjuvants was capable of inducing at least one class of isotypes associated with the processes of neutralization (IgG2b and IgA for bio-AgNP and Alhydrogel®, respectively), opsonization (IgG1 in both vaccines) and complement activation (IgM and IgG3 for bio-AgNP and Alhydrogel®, respectively). Furthermore, reduced tissue damage was observed in animals vaccinated with rCAM87009.1 + bio-AgNP when compared to animals vaccinated with Alhydrogel®. Our results indicate that the rCAM87009.1 protein associated with both bio-AgNP and Alhydrogel® are combinations capable of promoting immunity against infections caused by A. baumannii MDR. Additionally, we demonstrate the potential of silver nanoparticles as alternative adjuvant molecules to the use of aluminum salts.

Current treatment strategies for targeting virulence factors and biofilm formation in Acinetobacter baumannii

A higher prevalence of Acinetobacter baumannii infections and mortality rate has been reported recently in hospital-acquired infections (HAI). The biofilm-forming capability of A. baumannii makes it an extremely dangerous pathogen, especially in device-associated hospital-acquired infections (DA-HAI), thereby it resists the penetration of antibiotics. Further, the transmission of the SARS-CoV-2 virus was exacerbated in DA-HAI during the epidemic. This review specifically examines the complex interconnections between several components and genes that play a role in the biofilm formation and the development of infections. The current review provides insights into innovative treatments and therapeutic approaches to combat A. baumannii biofilm-related infections, thereby ultimately improving patient outcomes and reducing the burden of HAI.

Expanding antibiotic, vaccine, and diagnostics development and access to tackle antimicrobial resistance

The increasing number of bacterial infections globally that do not respond to any available antibiotics indicates a need to invest in-and ensure access to-new antibiotics, vaccines, and diagnostics. The traditional model of drug development, which depends on substantial revenues to motivate investment, is no longer economically viable without push and pull incentives. Moreover, drugs developed through these mechanisms are unlikely to be affordable for all patients in need, particularly in low-income and middle-income countries. New, publicly funded models based on public-private partnerships could support investment in antibiotics and novel alternatives, and lower patients' out-of-pocket costs, making drugs more accessible. Cost reductions can be achieved with public goods, such as clinical trial networks and platform-based quality assurance, manufacturing, and product development support. Preserving antibiotic effectiveness relies on accurate and timely diagnosis; however scaling up diagnostics faces technological, economic, and behavioural challenges. New technologies appeared during the COVID-19 pandemic, but there is a need for a deeper understanding of market, physician, and consumer behaviour to improve the use of diagnostics in patient management. Ensuring sustainable access to antibiotics also requires infection prevention. Vaccines offer the potential to prevent infections from drug-resistant pathogens, but funding for vaccine development has been scarce in this context. The High-Level Meeting of the UN General Assembly in 2024 offers an opportunity to rethink how research and development can be reoriented to serve disease management, prevention, patient access, and antibiotic stewardship.

Cerastecins inhibit membrane lipooligosaccharide transport in drug-resistant Acinetobacter baumannii

Carbapenem-resistant Acinetobacter baumannii infections have limited treatment options. Synthesis, transport and placement of lipopolysaccharide or lipooligosaccharide (LOS) in the outer membrane of Gram-negative bacteria are important for bacterial virulence and survival. Here we describe the cerastecins, inhibitors of the A. baumannii transporter MsbA, an LOS flippase. These molecules are potent and bactericidal against A. baumannii, including clinical carbapenem-resistant Acinetobacter baumannii isolates. Using cryo-electron microscopy and biochemical analysis, we show that the cerastecins adopt a serpentine configuration in the central vault of the MsbA dimer, stalling the enzyme and uncoupling ATP hydrolysis from substrate flipping. A derivative with optimized potency and pharmacokinetic properties showed efficacy in murine models of bloodstream or pulmonary A. baumannii infection. While resistance development is inevitable, targeting a clinically unexploited mechanism avoids existing antibiotic resistance mechanisms. Although clinical validation of LOS transport remains undetermined, the cerastecins may open a path to narrow-spectrum treatment modalities for important nosocomial infections.

In vitro and in silico assessment of anti-biofilm and anti-quorum sensing properties of 2,4-Di-tert butylphenol against Acinetobacter baumannii

Introduction. Acinetobacter baumannii is a nosocomial pathogen with a high potential to cause food-borne infections. It is designated as a critical pathogen by the World Health Organization due to its multi-drug resistance and mortalities reported. Biofilm governs major virulence factors, which promotes drug resistance in A. baumannii. Thus, a compound with minimum selection pressure on the pathogen can be helpful to breach biofilm-related virulence.Hypothesis/Gap Statement. To identify anti-biofilm and anti-virulent metabolites from extracts of wild Mangifera indica (mango) brine pickle bacteria that diminishes pathogenesis and resistance of A. baumannii.Aim. This study reports anti-biofilm and anti-quorum sensing (QS) efficacy of secondary metabolites from bacterial isolates of fermented food origin.Method. Cell-free supernatants (CFS) of 13 bacterial isolates from fermented mango brine pickles were screened for their efficiency in inhibiting biofilm formation and GC-MS was used to identify its metabolites. Anti-biofilm metabolite was tested on early and mature biofilms, pellicle formation, extra polymeric substances (EPS), cellular adherence, motility and resistance of A. baumannii. Gene expression and in silico studies were also carried out to validate the compounds efficacy.Results. CFS of TMP6b identified as Bacillus vallismortis, inhibited biofilm production (83.02 %). Of these, major compound was identified as 2,4-Di-tert-butyl phenol (2,4-DBP). At sub-lethal concentrations, 2,4-DBP disrupted both early and mature biofilm formation. Treatment with 2,4-DBP destructed in situ biofilm formed on glass and plastic. In addition, key virulence traits like pellicle (77.5 %), surfactant (95.3 %), EPS production (3-fold) and cell adherence (65.55 %) reduced significantly. A. baumannii cells treated with 2,4-DBP showed enhanced sensitivity towards antibiotics, oxide radicals and blood cells. Expression of biofilm-concomitant virulence genes like csuA/B, pgaC, pgaA, bap, bfmR, katE and ompA along with QS genes abaI, abaR significantly decreased. The in silico studies further validated the higher binding affinity of 2,4-DBP to the AbaR protein than the cognate ligand molecule.Conclusion. To our knowledge, this is the first report to demonstrate 2,4- DBP has anti-pathogenic potential alone and with antibiotics by in vitro, and in silico studies against A. baumannii. It also indicates its potential use in therapeutics and bio-preservatives.

Deciphering the structure of a multi-drug resistant Acinetobacter baumannii short-chain dehydrogenase reductase

The rapidly increasing threat of multi-drug-resistant Acinetobacter baumannii infections globally, encompassing a range of clinical manifestations from skin and soft tissue infections to life-threatening conditions like meningitis and pneumonia, underscores an urgent need for novel therapeutic strategies. These infections, prevalent in both hospital and community settings, present a formidable challenge to the healthcare system due to the bacterium's widespread nature and dwindling effective treatment options. Against this backdrop, the exploration of bacterial short-chain dehydrogenase reductases (SDRs) emerges as a promising avenue. These enzymes play pivotal roles in various critical bacterial processes, including fatty acid synthesis, homeostasis, metabolism, and contributing to drug resistance mechanisms. In this study, we present the first examination of the X-ray crystallographic structure of an uncharacterized SDR enzyme from A. baumannii. The tertiary structure of this SDR is distinguished by a central parallel β-sheet, consisting of seven strands, which is flanked by eight α-helices. This configuration exhibits structural parallels with other enzymes in the SDR family, underscoring a conserved architectural theme within this enzyme class. Despite the current ambiguity regarding the enzyme's natural substrate, the importance of many SDR enzymes as targets in anti-bacterial agent design is well-established. Therefore, the detailed structural insights provided in this study open new pathways for the in-silico design of therapeutic agents. By offering a structural blueprint, our findings may provide a platform for future research aimed at developing targeted treatments against this and other multi-drug-resistant infections.

Treatment and Management of Acinetobacter Pneumonia: Lessons Learned from Recent World Event

Acinetobacter pneumonia is a significant healthcare-associated infection that poses a considerable challenge to clinicians due to its multidrug-resistant nature. Recent world events, such as the COVID-19 pandemic, have highlighted the need for effective treatment and management strategies for Acinetobacter pneumonia. In this review, we discuss lessons learned from recent world events, particularly the COVID-19 pandemic, in the context of the treatment and management of Acinetobacter pneumonia. We performed an extensive literature review to uncover studies and information pertinent to the topic. The COVID-19 pandemic underscored the importance of infection control measures in healthcare settings, including proper hand hygiene, isolation protocols, and personal protective equipment use, to prevent the spread of multidrug-resistant pathogens like Acinetobacter. Additionally, the pandemic highlighted the crucial role of antimicrobial stewardship programs in optimizing antibiotic use and curbing the emergence of resistance. Advances in diagnostic techniques, such as rapid molecular testing, have also proven valuable in identifying Acinetobacter infections promptly. Furthermore, due to the limited availability of antibiotics for treating infections caused A. baumannii, alternative strategies are needed like the use of antimicrobial peptides, bacteriophages and their enzymes, nanoparticles, photodynamic and chelate therapy. Recent world events, particularly the COVID-19 pandemic, have provided valuable insights into the treatment and management of Acinetobacter pneumonia. These lessons emphasize the significance of infection control, antimicrobial stewardship, and early diagnostics in combating this challenging infection.

Metabolomics Method in Understanding and Sensitizing Carbapenem-Resistant Acinetobacter baumannii to Meropenem

Carbapenem-resistant Acinetobacter baumannii (CRAB) strains are prevalent worldwide and represent a major threat to public health. However, treatment options for infections caused by CRAB are very limited as they are resistant to most of the commonly used antibiotics. Consequently, understanding the mechanisms underlying carbapenem resistance and restoring bacterial susceptibility to carbapenems hold immense importance. The present study used gas chromatography-mass spectrometry (GC-MS)-based metabolomics to investigate the metabolic mechanisms of antibiotic resistance in clinically isolated CRAB. Inactivation of the pyruvate cycle and purine metabolism is the most typical characteristic of CRAB. The CRAB exhibited a reduction in the activity of enzymes involved in the pyruvate cycle, proton motive force, and ATP levels. This decline in central carbon metabolism resulted in a decrease in the metabolic flux of the α-ketoglutarate-glutamate-glutamine pathway toward purine metabolism, ultimately leading to a decline in adenine nucleotide interconversion. Exogenous adenosine monophosphate (AMP) and adenosine triphosphate (ATP) enhance the killing efficacy of Meropenem against CRAB. The combination of ATP and Meropenem also has a synergistic effect on eliminating CRAB persisters and the biofilm, as well as protecting mice against peritonitis-sepsis. This study presents a novel therapeutic modality to treat infections caused by CRAB based on the metabolism reprogramming strategy.

In vitro and in vivo antimicrobial potential of lithium complex against multi-drug resistant Acinetobacter baumannii

IMPORTANCE

Multi-drug resistance (MDR) by virtue of evolving resistance and virulence mechanisms among A. baumannii is a global concern which is responsible for lethal hospital-acquired infections. Therefore, it is crucial to develop new therapeutics against it. Metal complexes are compact structures with diverse mechanisms that the pathogens cannot evade easily which make them a strong drug candidate. In this study, we assessed the in vitro and in vivo efficacy of lithium complex {[Li(phen)2 sal]} against biofilm-forming MDR A. baumannii. The lithium complex displayed strong antimicrobial activity and reduced the pre-formed mature biofilm which is key barrier for antimicrobial action. Moreover, it employs oxidative stress as one of its mode of actions and causes cellular rupturing. Lithium complex was non-toxic and was significantly effective to overcome pneumonia in mice model. These results highlight the untapped potential of metal complexes that can be explored and utilized for combating notorious A. baumannii infections.

Current viewpoint on the epidemiology of nonfermenting Gram-negative bacterial strains

PURPOSE OF REVIEW

This article aims to review the epidemiology of nonfermenting Gram-negative bacilli (NFGNB) based on recent literature reports, particularly, of the less common, but with emerging clinical significance species.

RECENT FINDINGS

The reported frequency of multidrug-resistant Acinetobacter baumannii and Pseudomonas aeruginosa is increasing, with very significant variability, however, between different countries. Apart from the major NFGNB, that is, A. baumannii and P. aeruginosa, already recognized as of critical importance healthcare risks, several other NFGNB genera have been increasingly associated with diverse severe infections, such as Stenotrophomonas maltophilia, Burkholderia spp., Elizabethkingia spp., Chryseobacterium spp., Achromobacter spp., Alcaligenes spp., Sphingomonas spp., Shewanella spp. and Ralstonia spp., among others.

SUMMARY

The exploration of the epidemiology, as well as the pathogenic potential of the of the less frequent, but emerging and increasingly reported NFGNB, is crucial, not only for immunocompromised patients, but also for critically ill patients without overt immunosuppression. As we are heading fast towards a postantibiotic era, such information would contribute to the optimal antimicrobial management, that is, providing prompt, appropriate antimicrobial coverage when needed and, at the same time, avoiding overuse and/or inappropriate use of antimicrobial therapy. Also, it would help to better understand their transmission dynamics and to develop effective prevention strategies.

Acinetobacter baumannii: assessing susceptibility patterns, management practices, and mortality predictors in a tertiary teaching hospital in Lebanon

BACKGROUND

Acinetobacter baumannii is a major nosocomial pathogen capable of causing life-threatening infections. This bacterium is highly resistant to antibiotics and associated with high mortality rates. Therefore, this study aimed to evaluate A. baumannii's susceptibility patterns to antimicrobials, assess the appropriateness of the initiated antimicrobial therapy, determine the mortality rate, and identify predictors associated with mortality.

METHODS

A retrospective observational study was conducted among patients infected with A. baumannii at a university hospital in Lebanon through the revision of medical records. Kaplan-Meier survival analysis and log-rank tests were used to analyze time-to-mortality. Binary logistic regression was performed to identify predictors of mortality.

RESULTS

The records of 188 patients were screened, and 111 patients with A. baumannii infection were enrolled. Almost all isolates were resistant to carbapenem, and 43% of the isolates were extensively-drug resistant. Almost half of the patients received initial inappropriate antimicrobial therapy (n = 50, 45.1%). The 30-day mortality rate associated with A. baumannii infection was 71.2% (79/111). The time to mortality in patients who received inappropriate antimicrobial therapy (5.70 ± 1.07 days) was significantly shorter than in those who received appropriate antimicrobial therapy (12.43 ± 1.01 days, P < 0.01). Binary logistic regression revealed that inappropriate antimicrobial therapy (adjusted odds ratio [AOR] = 16.22, 95% CI 2.68-9.97, P = 0.002), mechanical ventilation (AOR = 14.72, 95% CI 3.27-6.61, P < 0.001), and thrombocytopenia (AOR = 8.82, 95% CI 1.12-9.75, P = 0.003) were more likely associated with mortality.

CONCLUSIONS

A. baumannii exhibits an alarming mortality rate among infected patients. Thrombocytopenia, mechanical ventilation, and inappropriate antibiotic administration are associated with mortality in patients infected with A. baumannii. The prompt initiation of appropriate antimicrobial therapy, infection control measures, and effective stewardship program are crucial to reduce the incidence of A. baumannii and improve the treatment outcomes.

Identification of novel compounds against Acinetobacter baumannii 3-oxoacyl-[acyl-carrier-protein] synthase I (FabB) via comprehensive structure-based computational approaches

Acinetobacter baumannii is one of the most serious opportunistic pathogens according to WHO. The difference between bacterial and mammalian fatty acid biosynthesis pathways makes FASII enzymes attractive targets in drug discovery. 3-oxoacyl-[acyl-carrier-protein] synthase I (FabB) from the FAS II pathway catalyze the condensation of malonyl ACP with acyl-ACP, and elongates the fatty acid chain by two carbons. To investigate potential inhibitors of the A. baumannii FabB, we used computational approaches including homology modeling, high-throughput virtual screening, molecular docking, molecular dynamics simulations, and MM-GBSA free energy calculations. After the high-throughput virtual screening, the resulting ligands were further screened using the QM-polarized ligand docking (QPLD) and induced fit docking (IFD) approaches. Molecular dynamics simulations were performed for 100 ns. And according to binding free energy calculations, we have identified nine compounds with the best binding affinities. Three of these compounds were selected for an additional 1 μs MD simulation to assess ligand stability. Two of them named L6 and L7 showed promised stability and affinity to the target. Here, we present novel compounds against A. baumannii FabB via structure-based computational approaches. These compounds might pave the way for the design of new lead structures and inhibitors for multidrug-resistant A. baumannii.

Early detection of a possible multidrug-resistant Acinetobacter baumannii outbreak in the local hospital setting by using random amplified polymorphism DNA-polymerase chain reaction (RAPD-PCR), oxacillinase gene profiles, and antibiograms

Background and Objectives

Detecting the source of a potential outbreak of multidrug resistant (MDR) Acinetobacter baumannii is necessary to be investigated. This study aimed to detect the possibility of A. baumannii outbreak in a hospital setting using a combination of random amplified polymorphism DNA-polymerase chain reaction (RAPD-PCR), antibiograms, and the presence of oxacillinase genes.

Materials and Methods

The antibiogram of 31 clinical isolates and six environmental isolates of A. baumannii were determined by Vitek® 2 Compact. Oxacillinase genes (OXA-23, -24, -51, and -58) were detected by PCR, and RAPD-PCR was conducted using DAF-4 and ERIC-2 primers. The Similarity Index and dendrogram were generated using GelJ v2.3 software.

Results

The antibiograms showed that all MDR A. baumannii isolates has very limited susceptibility to cephalosporins, but mostly susceptible to tigecycline. All isolates were positive for bla OXA-51-like gene, thirty-two of 37 total isolates (86.5%) were positive for bla OXA-23-like gene, and none were positive for bla OXA-24-like and bla OXA-58-like genes. RAPD-PCR showed that the DAF-4 primer on average had more band visualization and lower Similarity Index's variation compared to the ERIC-2. The discriminatory power of DAF-4 was 0.906. There was a significant correlation between the DAF-4 dendrogram pattern with the antibiogram (r=0.494, p<0.001) and the presence of bla OXA-23-like gene (r=0.634, p<0.001) from all ICU A isolates. Six out of fourteen ICU A isolates belonged to the same cluster with >95% Similarity Index, while one clinical isolate having an identical dendrogram and antibiogram pattern with an environmental isolate within this cluster.

Conclusion

There is a high probability of MDR A. baumannii outbreak within ICU A detected by multiple analysis of RAPD-PCR, antibiogram and the bla OXA-23-like gene profiles. This combinatorial approach is conceivable to mitigate possible outbreak situations of A. baumannii in the local hospital without sophisticated microbiology laboratory.

Hit 'em Where It Hurts: Gram-Negative Bacterial Lipopolysaccharide as a Vaccine Target

Infections with antimicrobial-resistant (AMR) bacteria pose an increasing threat to the ability to perform surgical procedures, organ transplantation, and treat cancer among many other medical conditions. There are few new antimicrobials in the development pipeline. Vaccines against AMR Gram-negative bacteria may reduce the use of antimicrobials and prevent bacterial transmission. This review traces the origins of lipopolysaccharide (LPS)-based vaccines against Gram-negative bacteria, the role of O polysaccharides and LPS core regions as potential vaccine targets, the development of new vaccine technologies, and their application to vaccines in current development.

Global Risk Maps of Climate Change Impacts on the Distribution of Acinetobacter baumannii Using GIS

Impacts of climate change rank among the century's most significant ecological and medical concerns. As a result of climatic changes, the distribution of some bacterial species will alter across time and space. Numerous bacterial infections will reorganize as a result worldwide. Acinetobacter baumannii Bouvet and Grimont is one of the most significant and frequently occurring bacteria identified in soil and air. The COVID-19 pandemic has changed how bacteriologists perceive this species as a new threat to human health. In order to estimate the existing and future worldwide distribution of A. baumannii under various climate change scenarios, about 1000 A. baumannii occurrence records were employed. Given its superior accuracy and dependability versus alternative modeling techniques, maximum entropy implemented in MaxEnt was selected as the modeling tool. The bioclimatic variable that contributes the most to the distribution of A. baumannii is the mean temperature of the coldest quarter (bio_11). The created current distribution model agreed with the species' actual globally dispersed distribution. It is projected that A. baumannii will experience a severe range expansion due to the increase in temperature brought on by global warming in different regions of its range. According to the risk maps created for 2050 and 2070 using two alternative RCPs, there are various regions that will be under risk of this bacterium as a result of rising temperature. Future data science and GIS evaluation of the current results are necessary, especially on a local level.

Epitope mapping of Acinetobacter baumannii outer membrane protein W (OmpW) and laboratory study of an OmpW-derivative peptide

Outer membrane protein W (OmpW) is a less-known A. baumannii antigen with potential immunogenic properties. The epitopes of this protein are not well-identified yet. Therefore, in the present study, B- and T-cell epitopes of A. baumannii OmpW were found using comprehensive in silico and partially in vitro studies. The T-cell (both class-I and class-II) and B-cell (both linear and conformational) epitopes were predicted and screened through many bioinformatics approaches including the prediction of IFN-γ production, immunogenicity, toxicity, allergenicity, human similarity, and clustering. A single 15-mer epitopic peptide containing a linear B-cell and both classes of T-cell epitopes were found and used for further assays. For in vitro assays, patient- and healthy control-derived peripheral blood mononuclear cells were stimulated with the 15-mer peptide, Phytohemagglutinin, or medium alone, and cell proliferation and IFN-γ production assays were performed. The bioinformatics studies led to mapping OmpW epitopes and introducing a 15-mer peptide. In vitro assays to some extent showed its potency in cell proliferation but not in IFN-γ induction, although the responses were not very expressive and faced some questions/limitations. In general, in the current study, we mapped the most immunogenic epitopes of OmpW that may be used for future studies and also assayed one of these epitopes in vitro, which was shown to have an immunogenicity potential. However, the induced immune responses were not strong which suggests that the present peptide needs a series of biotechnological manipulations to be used as a potential vaccine candidate. More studies in this field are recommended.

The Challenge of Overcoming Antibiotic Resistance in Carbapenem-Resistant Gram-Negative Bacteria: "Attack on Titan"

The global burden of bacterial resistance remains one of the most serious public health concerns. Infections caused by multidrug-resistant (MDR) bacteria in critically ill patients require immediate empirical treatment, which may not only be ineffective due to the resistance of MDR bacteria to multiple classes of antibiotics, but may also contribute to the selection and spread of antimicrobial resistance. Both the WHO and the ECDC consider carbapenem-resistant Enterobacteriaceae (CRE), carbapenem-resistant Pseudomonas aeruginosa (CRPA), and carbapenem-resistant Acinetobacter baumannii (CRAB) to be the highest priority. The ability to form biofilm and the acquisition of multiple drug resistance genes, in particular to carbapenems, have made these pathogens particularly difficult to treat. They are a growing cause of healthcare-associated infections and a significant threat to public health, associated with a high mortality rate. Moreover, co-colonization with these pathogens in critically ill patients was found to be a significant predictor for in-hospital mortality. Importantly, they have the potential to spread resistance using mobile genetic elements. Given the current situation, it is clear that finding new ways to combat antimicrobial resistance can no longer be delayed. The aim of this review was to evaluate the literature on how these pathogens contribute to the global burden of AMR. The review also highlights the importance of the rational use of antibiotics and the need to implement antimicrobial stewardship principles to prevent the transmission of drug-resistant organisms in healthcare settings. Finally, the review discusses the advantages and limitations of alternative therapies for the treatment of infections caused by these "titans" of antibiotic resistance.

Moving toward Extensively Drug-Resistant: Four-Year Antimicrobial Resistance Trends of Acinetobacter baumannii from the Largest Department of Internal Medicine in Slovakia

A. baumannii imposes a great burden on medical systems worldwide. Surveillance of trends of antibiotic resistance provides a great deal of information needed for antimicrobial stewardship programmes nationwide. Clinical data from long-term, continuous surveillance on trends of antibiotic resistance of A. baumannii in Slovakia is missing. One hundred and forty-nine samples of A. baumannii were isolated over a period of four years. A panel of 19 antibiotics from seven antibiotic categories were tested for the bacterium's susceptibility. Resistance results were evaluated, and the significance of patterns was estimated using simple linear regression analysis. All isolates were more than 85% resistant to at least 13 out of the 19 tested antibiotics. A significant rise in resistance was recorded for aminoglycosides and imipenem from 2019 to 2022. Colistin and ampicillin-sulbactam have been the only antibiotics maintaining more than 80% efficacy on the bacterium to date. A significant rise in extensively drug-resistant (XDR) strains among carbapenem-resistant (CR) isolates has been recorded. Multidrug-resistance (MDR) among all A. baumannii isolates and XDR among CR strains of the bacterium have risen significantly in the last four years.

Prevalence of Carbapenemases in Carbapenem-Resistant Acinetobacter baumannii Isolates from the Kingdom of Bahrain

BACKGROUND

Acinetobacter baumannii is regarded as a significant cause of death in hospitals. The WHO recently added carbapenem-resistant Acinetobacter baumannii (CRAB) to its global pathogen priority list. There is a dearth of information on CRAB from our region.

METHODS

Fifty CRAB isolates were collected from four main hospitals in Bahrain for this study. Bacterial identification and antibiotic susceptibility tests were carried out using the BD Phoenix^TM and VITEK-2 compact, respectively. Using conventional PCR, these isolates were further screened for carbapenem resistance markers (bla_OXA-51, bla_OXA-23, blaO_XA-24, bla_OXA-40, bla_IMP, bla_NDM, bla_VIM, and bla_KPC).

RESULTS

All of the isolates were resistant to imipenem (100%), meropenem (98%), and cephalosporins (96-98%), followed by other commonly used antibiotics. All these isolates were least resistant to gentamicin (64%). The detection of resistance determinants showed that the majority harbored bla_OXA-51 (100%) and bla_IMP (94%), followed by bla_OXA-23 (82%), bla_OXA-24 (46%), bla_OXA-40 (14%), bla_NDM (6%), bla_VIM (2%), and bla_KPC (2%).

CONCLUSION

The study isolates showed a high level of antibiotic resistance. Class D carbapenemases were more prevalent in our CRAB isolate collection. The resistance genes were found in various combinations. This study emphasizes the importance of strengthening surveillance and stringent infection control measures in clinical settings to prevent the emergence and further spread of such isolates.

The Prevalence of Multidrug-Resistant Acinetobacter baumannii and Its Vaccination Status among Healthcare Providers

There is growing concern among healthcare providers worldwide regarding the prevalence of multidrug-resistant Acinetobacter baumannii (A. baumannii). Some of the worst hospital-acquired infections, often in intensive care units (ICUs), are caused by this bacterial pathogen. In recent years, the rise in multidrug-resistant A. baumannii has been linked to the overuse of antimicrobial drugs and the lack of adequate infection control measures. Infections caused by this bacterial pathogen are the result of prolonged hospitalization and ICU stays, and they are associated with increased morbidity and mortality. This review outlines the epidemiology, risk factors, and antimicrobial resistance associated with A. baumannii in various countries, with a special focus on the Kingdom of Saudi Arabia. In response to the growing concern regarding this drug-resistant bacteria, fundamental information about its pathology has been incorporated into the development of vaccines. Although these vaccines have been successful in animal models, their effectiveness in humans remains unproven. The review will discuss the development of A. baumannii vaccines, potential related obstacles, and efforts to find an effective strategy against this pathogen.

Acinetobacter baumannii in the critically ill: complex infections get complicated

Acinetobacter baumannii is increasingly associated with various epidemics, representing a serious concern due to the broad level of antimicrobial resistance and clinical manifestations. During the last decades, A. baumannii has emerged as a major pathogen in vulnerable and critically ill patients. Bacteremia, pneumonia, urinary tract, and skin and soft tissue infections are the most common presentations of A. baumannii, with attributable mortality rates approaching 35%. Carbapenems have been considered the first choice to treat A. baumannii infections. However, due to the widespread prevalence of carbapenem-resistant A. baumannii (CRAB), colistin represents the main therapeutic option, while the role of the new siderophore cephalosporin cefiderocol still needs to be ascertained. Furthermore, high clinical failure rates have been reported for colistin monotherapy when used to treat CRAB infections. Thus, the most effective antibiotic combination remains disputed. In addition to its ability to develop antibiotic resistance, A. baumannii is also known to form biofilm on medical devices, including central venous catheters or endotracheal tubes. Thus, the worrisome spread of biofilm-producing strains in multidrug-resistant populations of A. baumannii poses a significant treatment challenge. This review provides an updated account of antimicrobial resistance patterns and biofilm-mediated tolerance in A. baumannii infections with a special focus on fragile and critically ill patients.

Investigation of Peptidoglycan-Associated Lipoprotein of Acinetobacter baumannii and Its Interaction with Fibronectin To Find Its Therapeutic Potential

Acinetobacter baumannii causes hospital-acquired infections and is responsible for high mortality and morbidity. The interaction of this bacterium with the host is critical in bacterial pathogenesis and infection. Here, we report the interaction of peptidoglycan-associated lipoprotein (PAL) of A. baumannii with host fibronectin (FN) to find its therapeutic potential. The proteome of A. baumannii was explored in the host-pathogen interaction database to filter out the PAL of the bacterial outer membrane that interacts with the host's FN protein. This interaction was confirmed experimentally using purified recombinant PAL and pure FN protein. To investigate the pleiotropic role of PAL protein, different biochemical assays using wild-type PAL and PAL mutants were performed. The result showed that PAL mediates bacterial pathogenesis, adherence, and invasion in host pulmonary epithelial cells and has a role in the biofilm formation, bacterial motility, and membrane integrity of bacteria. All of the results suggest that PAL's interaction with FN plays a vital role in host-cell interaction. In addition, the PAL protein also interacts with Toll-like receptor 2 and MARCO receptor, which suggests the role of PAL protein in innate immune responses. We have also investigated the therapeutic potential of this protein for vaccine and therapeutic design. Using reverse vaccinology, PAL's potential epitopes were filtered out that exhibit binding potential with host major histocompatibility complex class I (MHC-I), MHC-II, and B cells, suggesting that PAL protein is a potential vaccine target. The immune simulation showed that PAL protein could elevate innate and adaptive immune response with the generation of memory cells and would have subsequent potential to eliminate bacterial infection. Therefore, the present study highlights the interaction ability of a novel host-pathogen interacting partner (PAL-FN) and uncovers its therapeutic potential to combat infection caused by A. baumannii.

Drug‑resistant Acinetobacter baumannii: From molecular mechanisms to potential therapeutics (Review)

Bacterial drug resistance is increasingly becoming an important problem that needs to be solved urgently in modern clinical practices. Infection caused by Acinetobacter baumannii is a serious threat to the life and health of patients. The drug resistance rate of Acinetobacter baumannii strains is increasing, thus research on the drug resistance of Acinetobacter baumannii has also seen an increase. When patients are infected with drug-resistant Acinetobacter baumannii, the availability of suitable antibiotics commonly used in clinical practices is becoming increasingly limited and the prognosis of patients is worsening. Studying the molecular mechanism of the drug resistance of Acinetobacter baumannii is fundamental to solving the problem of drug-resistant Acinetobacter baumannii and potentially other 'super bacteria'. Drug resistance mechanisms primarily include enzymes, membrane proteins, efflux pumps and beneficial mutations. Research on the underlying mechanisms provides a theoretical basis for the use and development of antibiotics and the development of novel treatment methods.

The Prevalence of Virulence Factor Genes among Carbapenem-Non-Susceptible Acinetobacter baumannii Clinical Strains and Their Usefulness as Potential Molecular Biomarkers of Infection

Healthcare-associated infections caused by multidrug-resistant Acinetobacter baumannii strains are a serious global threat. Therefore, it is important to expand the knowledge on the mechanisms of pathogenicity of these particular bacteria. The aim of this study was to assess the distribution of selected virulence factor genes (bap, surA1, omp33-36, bauA, bauS, and pld) among carbapenem-non-susceptible clinical A. baumannii isolates and to evaluate their potential usefulness as genetic markers for rapid diagnostics of A. baumannii infections. Moreover, we aimed to compare the virulence genes prevalence with the occurrence of carbapenemases genes. A total of 100 carbapenem-non-susceptible A. baumannii clinical isolates were included in the study. The presence of virulence factors and blaOXA genes was evaluated by real-time PCR. The occurrence of virulence factors genes was as follows: 100.0% for the bap and surA1 genes, 99.0% for the basD and pld genes. The bauA and omp33-36 genes were absent among the studied strains. The predominant genes (bap and surA1) are involved in biofilm formation and their presence among all clinical strains can be applied as a genetic marker to recognize A. baumannii infection. High frequencies of the basD gene—involved in siderophore biosynthesis and the gene encoding phospholipase D (pld)—were also noted among blaOXA-positive strains, showing their potential role in a pathogenicity of blaOXA-positive A. baumannii clinical strains.

Outer Membrane Vesicle-Coated Nanoparticle Vaccine Protects Against Acinetobacter baumannii Pneumonia and Sepsis

The highly multidrug-resistant (MDR) Gram-negative bacterial pathogen Acinetobacter baumannii is a top global health priority where an effective vaccine could protect susceptible populations and limit resistance acquisition. Outer membrane vesicles (OMVs) shed from Gram-negative bacteria are enriched with virulence factors and membrane lipids but heterogeneous in size and cargo. We report a vaccine platform combining precise and replicable nanoparticle technology with immunogenic A. baumannii OMVs (Ab-OMVs). Gold nanoparticle cores coated with Ab-OMVs (Ab-NPs) induced robust IgG titers in rabbits that enhanced human neutrophil opsonophagocytic killing and passively protected against lethal A. baumannii sepsis in mice. Active Ab-NP immunization in mice protected against sepsis and pneumonia, accompanied by B cell recruitment to draining lymph nodes, activation of dendritic cell markers, improved splenic neutrophil responses, and mitigation of proinflammatory cytokine storm. Nanoparticles are an efficient and efficacious platform for OMV vaccine delivery against A. baumannii and perhaps other high-priority MDR pathogens.