AN OUTBREAK OF EXTENSIVELY DRUG-RESISTANT ACINETOBACTER BAUMANNII IN A BELGIAN TERTIARY BURN WOUND CENTER.

The burn intensive care unit (ICU) of the Queen Astrid Military Hospital experienced an outbreak with an extensively drug-resistant Acinetobacter baumannii (XDR-Ab) strain, which began when all burn wound patients from all over Belgium were sent there as part of the national COVID-19 action plan. The purpose of this study is to report on the investigation and strategies that were implemented to contain the outbreak. Between October 2020 and May 2021, five of the 72 patients admitted to the ICU met the acute outbreak case definition (attack rate 7%). Their median age was 46 years and their median total body surface area burned was 39%. All patients developed at least one XDR-Ab infection, with in total three pulmonary, three bloodstream and five burn wound infections. One patient died. All XDR-Ab isolates were only susceptible to colistin. Whole genome sequencing of the isolates from the first two patients revealed an identical A. baumannii ST2 genotype, suggesting an outbreak. XDR-Ab-positive patients were cohorted with dedicated staff. The infection control team intensified its training on hand hygiene, excreta management and bio-cleaning procedures. Concurrently, 30 environmental samples were collected, which proved negative for XDR-Ab. Spatio-temporal associations were found for all XDR-Ab-positive patients, suggesting cross-transmission via staff's hands. We describe an XDR-Ab outbreak in a burn ICU over a seven-month period, in a context of increased workload. This series underlines the importance of a correct staff-to-patient ratio, especially in outbreak situations.

L'unité de soins intensifs (USI) pour brûlés de l'Hôpital Militaire Reine Astrid a connu une épidémie avec une souche d'Acinetobacter baumannii extrêmement résistante aux antibiotiques (XDR-Ab), qui a commencé pendant la période où tous les patients brûlés de Belgique y étaient référés à la suite du plan national COVID-19. Le but de cette étude est de décrire l'enquête épidémiologique et les stratégies utilisées pour contenir l'épidémie. Entre octobre 2020 et mai 2021, cinq des 72 patients admis à l'USI ont répondu à la définition de cas (taux d'attaque 7%). L'âge médian était de 46 ans, la surface corporelle brûlée médiane de 39%. Tous les patients ont développé au moins une infection par XDR-Ab : trois pneumonies, trois bactériémies et cinq infections de brûlures. Un patient est décédé. Tous les isolats XDR-Ab n'étaient sensibles qu'à la colistine. Le séquençage du génome entier des isolats des deux premiers patients a révélé un génotype identique d'A. baumannii ST2, suggérant une épidémie. Les patients XDR-Ab positifs ont été cohortés avec du personnel dédié. L'équipe d'hygiène hospitalière a intensifié sa formation sur l'hygiène des mains, la gestion des excréta et les procédures de bio-nettoyage. Simultanément, 30 échantillons environnementaux ont été collectés, qui étaient négatifs pour XDR-Ab. Des liens spatio-temporels ont été trouvés pour tous les patients XDR-Ab positifs, suggérant une transmission croisée manuportée. Nous décrivons une épidémie de XDR-Ab dans une USI pour brûlés sur une période de sept mois, dans un contexte de charge de travail accrue. Cette série souligne l'importance d'un ratio personnel-patients approprié, en particulier dans les situations d'épidémie.

Acinetobacter baumannii Endogenous Endophthalmitis Presenting with Iris Nodules.

AIM: We report a unique finding of iris nodules in a woman with endogenous endophthalmitis due to Acinetobacter baumannii with no history of ocular surgery or trauma and good visual outcome. MATERIALS & METHODS: Retrospective case report. RESULTS: A 39-year-old woman with a history of type 2 diabetes mellitus presented with a decrease in vision in the right eye of 1-month duration. On examination, her BCVA was CF2m (OD) and 6/6 (OS). Right eye examination showed medium-to-large-sized keratic precipitates, iris nodules, and vitritis. PCR on the aqueous showed faint positivity for Propionibacterium acne and was negative to panfungal genome. Despite two intravitreal injections of vancomycin (1 mg/0.1 ml) and intravenous cefazolin 1 g bd for 5 days, there was progression to hypopyon. Vitrectomy with lensectomy was done. The vitreous culture grew Acinetobacter baumannii. She was given multiple intravitreal ceftazidime (2.25 mg/0.1 ml) with dexamethasone (0.4 mg/0.1 ml) injections. She was also put on tab bactrim DS twice a day for 3 months along with tab doxycycline 100 mg twice a day for 3 months by the infectious disease specialist. As the inflammation improved, the iris nodules were the last to resolve completely in 6 weeks. At 15-month follow-up, her eye was quiet, and vision was 6/9 (OD) with aphakic correction. CONCLUSION: We report a rare finding of iris nodules in a patient with culture proven Acinetobacter baumannii endogenous endophthalmitis.

A review of the fighting Acinetobacter baumannii on three fronts: antibiotics, phages, and nanoparticles.

In the current era of antibiotic resistance, researchers are exploring alternative ways to treat bacterial infections that are resistant to multiple drugs. Acinetobacter baumannii (A. baumannii) is a bacterium that is commonly encountered in clinical settings and is known to be resistant to several drugs. Due to the increase in drug-resistant infections caused by this bacteria, there is an urgent need to investigate alternative treatment options such as phage therapy and combination therapy. Despite the success of phages in some cases, there are some limitations in their clinical application that can be overcome by combining phages with other substrates such as nanoparticles to improve their function. The integration of nanotechnology with phage therapy against A. baumannii promises to overcome antibiotic resistance. By exploiting the targeted delivery and controlled release capabilities of nanoparticles, we can enhance the therapeutic potential of phages while minimizing their limitations. Continued research in this field will undoubtedly pave the way for more effective and precise treatments against A. baumannii infections and provide hope in the fight against antibiotic-resistant bacteria.

Molecular Detection of Carbapenemases in Acinetobacter baumannii Strains of Portugal and Association With Sequence Types, Capsular Types, and Virulence.

PURPOSE: Carbapenem-resistant Acinetobacter baumannii (CRAB) is an important nosocomial pathogen. The capsular type (K-type) is considered a major virulence factor, contributing to the evasion of host defenses. The global spread and dissemination dynamics between K-types, sequence types (ST), antibiotic resistance genes, and virulence factors remain largely unknown in Portugal. METHODS: A collection of 96 CRAB clinical samples collected between 2005 and 2019 in the northern region of Portugal were tested for antimicrobial susceptibility profile and screened by polymerase chain reaction for resistance genetic determinants. A subset of 26 representative isolates was subjected to whole-genome sequencing to assess K types, ST types, and genomic relatedness. The pathogenicity of distinct K-types was also tested using Galleria mellonella model. FINDINGS: For the 96 CRAB isolates analyzed, high antimicrobial resistance (>90%) was observed to the carbapenems, fluoroquinolones, and miscellaneous agents. Greater antimicrobial susceptibility (∼30%-57%) was observed for aminoglycosides, particularly tobramycin, and amikacin. Genotypically, 75 strains (78.5%) carried blaOXA-23-like, 18 strains (18.8%) carried blaIMP-like, and 11 strains (14.9%) carried blaOXA-40-like carbapenem resistance genes, respectively. Associations between OXA and ST/capsular locus (KL) types were observed over the years (eg, OXA-40-like/ST46Past/KL120 and OXA-23-like/ST2Past/KL2). ST2Past of clonal complex II was present in most strains, a dominant drug-resistant lineage in the United States and Europe. KL7 was also the most prevalent KL-type (38.5%), followed by KL2 (34.6%), KL120 (23.1%), and KL9 (3.8%). Virulence assessment for different K-types in a Galleria mellonella model revealed a significantly increased virulence for KL120 when compared with KL7, KL9, and KL2. IMPLICATIONS: There are specific CRAB serotypes circulating in Portugal, accounting by the low diversity of acquired carbapenemase genes (OXA-23-like and OXA-40-like), ST types (ST2 and ST46) and KL types (KL2, KL7, KL9, and KL120) identified. The high prevalent of ST2, especially when associated with KL2 and blaOXA-23-like, suggest that antibiotic resistance has been driven by clonal expansion of clonal complex II. Such findings provide useful information on the diversity of multidrug-resistant bacterium that might be relevant for antibacterial interventions.

Comparison of antimicrobial activities and resistance mechanisms of eravacycline and tigecycline against clinical Acinetobacter baumannii isolates in China.

Tigecycline (TGC) is currently used to treat carbapenem-resistant Acinetobacter baumannii (CRAB) infections, while eravacycline (ERV), a new-generation tetracycline, holds promise as a novel therapeutic option for these infections. However, differences in resistance mechanism between ERV and TGC against A. baumannii remain unclear. This study sought to compare the characteristics and mechanisms of ERV and TGC resistance among clinical A. baumannii isolates. A total of 492 isolates, including 253 CRAB and 239 carbapenem-sensitive A. baumannii (CSAB) isolates, were collected from hospitalized patients in China. The MICs of ERV and TGC against A. baumannii were determined by broth microdilution. Genetic mutations and expressions of adeB, adeG, adeJ, adeS, adeL, and adeN in resistant strains were examined by PCR and qPCR, respectively. The in vitro recombination experiments were used to verify the resistance mechanism of ERV and TGC in A. baumannii. The MIC90 of ERV in CRAB and CSAB isolates were lower than those of TGC. A total of 24 strains resistant to ERV and/or TGC were categorized into three groups: only ERV-resistant (n = 2), both ERV- and TGC-resistant (n = 7), and only TGC-resistant (n = 15). ST208 (75%, n = 18) was a major clone that has disseminated in all three groups. The ISAba1 insertion in adeS was identified in 66.7% (6/9) of strains in the only ERV-resistant and both ERV- and TGC-resistant groups, while the ISAba1 insertion in adeN was found in 53.3% (8/15) of strains in the only TGC-resistant group. The adeABC and adeRS expressions were significantly increased in the only ERV-resistant and both ERV- and TGC-resistant groups, while the adeABC and adeIJK expressions were significantly increased and adeN was significantly decreased in the only TGC-resistant group. Expression of adeS with the ISAba1 insertion in ERV- and TGC-sensitive strains significantly increased the ERV and TGC MICs and upregulated adeABC and adeRS expressions. Complementation of the wildtype adeN in TGC-resistant strains with the ISAba1 insertion in adeN restored TGC sensitivity and significantly downregulated adeIJK expression. In conclusion, our data illustrates that ERV is more effective against A. baumannii clinical isolates than TGC. ERV resistance is correlated with the ISAba1 insertion in adeS, while TGC resistance is associated with the ISAba1 insertion in adeN or adeS in A. baumannii.

Impact of acidic and alkaline conditions on Staphylococcus aureus and Acinetobacter baumannii interactions and their biofilms.

Bacterial biofilms pose significant challenges due to their association with antibiotic resistance, metabolic adaptation, and survival under harsh conditions. Among notable pathogens forming biofilms, Staphylococcus aureus and Acinetobacter baumannii are concerning pathogens in nosocomial settings. However, their behaviour under acidic (pH 4.5) and alkaline (pH10.5) conditions, especially in co-culture setups, remains insufficiently understood. This study investigates these aspects, by examining growth rates, biofilm formation, pH shifts, phenotypic analysis, and gene expression profiles. The results showed A. baumannii exhibited reduced  growth and biofilm formation at pH 4.5, while S. aureus showed slow growth and low biofilm formation at pH10.5 in mono-cultures. S. aureus leaned towards an acidic pH (6-6.5), whereas A. baumannii shifted towards an alkaline pH (8-9). In co-culture environments, growth rates and biofilm formation increased across all pH conditions, converging towards a neutral pH over time. Phenotypic motility assays indicated that A. baumannii exhibited greater motility in alkaline conditions, while S. aureus showed increased staphyloxanthin production under acidic conditions. Gene expression analyses revealed that the fibronectin-binding protein A (FnbA) and N-acetylglucosaminyl-transferase (icaA) genes, responsible for initial attachment during biofilm formation, were highly expressed in acidic co-culture condition but poorly expressed in alkaline condition. In A. baumannii, the outer membrane protein A (OmpA) gene associated with adhesion and virulence, was upregulated in co-culture. The LuxR gene involved in quorum sensing was upregulated in acidic conditions and poorly expressed at pH 10.5. This study elucidates the metabolic adaptability and biofilm formation tendencies of S. aureus towards acidic conditions and A. baumannii towards alkaline conditions, providing insights for better management of biofilm-related infections.

Environmental contamination with carbapenem resistant Acinetobacter baumannii in healthcare settings in Fiji: a potential source of infection.

Introduction: There are multiple ongoing outbreaks of carbapenem resistant Acinetobacter baumannii (CRAb) infection in Fiji's hospitals. CRAb is able to colonize and persist on various hospital surfaces for extended periods. We conducted a study to understand the extent of hospital environmental contamination and phylogenetic links with clinical isolates. Methods: Swabs were collected from high-touch surfaces at Colonial War Memorial Hospital (CWMH) September 2021 and December 2022; Lautoka Hospital (LTKH) August 2022; and Labasa Hospital (LBSH) November 2022. All bacterial isolates were identified, and antimicrobial susceptibility testing (AST) performed; isolates resistant to carbapenems and producing a carbapenemase underwent whole genome sequencing. Comparison was made to clinical isolates obtained from CWMH in 2016-2017 and 2019-2021 and from LTKH and LBSH from 2020-2021. Results: From the 180 environmental samples collected, ten (5.6%) CRAb were isolated; no other carbapenem-resistant gram-negative organisms were isolated. Seven (70%) of the CRAb were isolated from CWMH and three (30%) from LTKH; no CRAb were isolated from LBSH. Of the seven CWMH CRAb, two were sequence type 2 (ST2), three ST25, and two ST499. All LTKH isolates were ST499. The two environmental CRAb ST2 isolates were closely genetically linked to isolates obtained from patients in CWMH, LTKH, and LBSH 2020-2021. Similarly, the three environmental CRAb ST25 isolates were closely genetically linked to isolates obtained from patients admitted to CWMH in 2019-2021 and LBSH in 2020. The environmental CRAb ST499 isolates represented two distinct clones, with clone 1 comprising two genetically identical isolates from CWMH and clone 2 the three isolates from LTKH. Although no genetic linkages were observed when comparing environmental ST499 isolates to those from CWMH patients in 2020-2021, both clone 1 isolates were genetically identical to an isolate obtained from a patient admitted during the sampling period. Conclusion: Our study highlights the contamination of high-touch surfaces within Fiji hospitals with CRAb, suggesting that these may serve as important sources for CRAb. Phylogenetic linkages to CRAb isolated from patients since 2019 underscores the persistence of this resistant pathogen in hospital settings and the ongoing risk for hospital-acquired infections.

Potentially effective antimicrobial treatment for pneumonia caused by isolates of carbapenem-resistant and extensively drug-resistant Acinetobacter baumannii complex species: what can we expect in the future?

INTRODUCTION: Acinetobacter baumannii complex (Abc) is currently a significant cause of difficult-to-treat pneumonia. Due to the high prevalence rates of carbapenem- and extensively drug-resistant (CR, XDR) phenotypes, limited antibiotic options are available for the effective treatment of pneumonia caused by CR/XDR-Abc. AREAS COVERED: In vitro susceptibility data, relevant pharmacokinetic profiles (especially the penetration ratios from plasma into epithelial-lining fluid), and pharmacodynamic indices of key antibiotics against CR/XDR-Abc are reviewed. EXPERT OPINION: Doubling the routine intravenous maintenance dosages of conventional tigecycline (100 mg every 12 h) and minocycline (200 mg every 12 h) might be recommended for the effective treatment of pneumonia caused by CR/XDR-Abc. Nebulized polymyxin E, novel parenteral rifabutin BV100, and new polymyxin derivatives (SPR206, MRX-8, and QPX9003) could be considered supplementary combination options with other antibiotic classes. Regarding other novel antibiotics, the potency of sulbactam-durlobactam (1 g/1 g infused over 3 h every 6 h intravenously) combined with imipenem-cilastatin, and the ß-lactamase inhibitor xeruborbactam, is promising. Continuous infusion of full-dose cefiderocol is likely an effective treatment regimen for CR/XDR-Abc pneumonia. Zosurabalpin exhibits potent anti-CR/XDR-Abc activity in vitro, but its practical use in clinical therapy remains to be evaluated. The clinical application of antimicrobial peptides and bacteriophages requires validation.

A unique cell division protein critical for the assembly of the bacterial divisome.

Identification of unique essential bacterial genes is important for not only the understanding of their cell biology but also the development of new antimicrobials. Here, we report a previously unrecognized core component of the Acinetobacter baumannii divisome. Our results reveal that the protein, termed Aeg1 interacts with multiple cell division proteins, including FtsN, which is required for components of the divisome to localize to the midcell. We demonstrate that the FtsAE202K and FtsBE65A mutants effectively bypassed the need of Aeg1 by A. baumannii, as did the activation variants FtsWM254I and FtsWS274G. Our results suggest that Aeg1 is a cell division protein that arrives at the division site to initiate cell division by recruiting FtsN, which activates FtsQLB and FtsA to induce the septal peptidoglycan synthase FtsWI. The discovery of the new essential cell division protein has provided a new target for the development of antibacterial agents.

Investigating an Outbreak of Extensively Drug-Resistant Acinetobacter baumannii in a Tertiary Healthcare Center 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 currently a fast and reliable tool to study outbreaks at the molecular level and obtain actionable knowledge leading to better control measures. We collected 59 A. baumannii isolates from intensive care unit (ICU) patients and from the hospital environment between August 2022 and May 2023, performed AST and subjected their gDNA 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 harbored by these bacteria. Out of 59 isolates, 81.4% were categorized as extensively drug-resistant (XDR), 13.6% as multi-drug-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%). Our isolates clustered well with those of a previous outbreak in the same hospital. In addition, isolates from Lebanese hospitals clustered well together and some clustered with those originating from different countries. The observed genetic relatedness between our current isolates with those from the previous outbreaks underscores the importance of strict surveillance to limit the threat of outbreaks. Moreover, the clustering of Lebanese isolates with others from distant countries proves the necessity of further investigations addressing the international spread of drug-resistant pathogens and resulting in the implementation of control strategies.

Nosocomial carbapenem-drug resistant Acinetobacter baumannii, related factors and clinical outcomes in Northeast Iran.

BACKGROUND AND OBJECTIVES: Nosocomial infections, including drug-resistant Acinetobacter baumannii infections, continue to impact the health of hospitalized patients. This study sought to determine the prevalence of these infections and assess the associated risk factors and clinical outcomes in Gorgan, Iran. METHODS: A retrospective cross-sectional study was conducted on 143 infected patients with Acinetobacter baumannii in two educational hospitals in Gorgan city, Iran between 2016 and 2018. Patient information including age, gender, reason and duration of hospitalization, background of diseases, type of sample culture, symptoms, laboratory findings, prescribed antibiotics, and antibiogram were collected and analyzed. The Logistic regression and survival statistical methods were used by software of SPSS 26. RESULTS: A total of 37 patients (25.87%) died during hospitalization. The less than one year and 45-65 years age groups demonstrated more deaths (29.7%; p-value < 0.001). Being single (not being married) was found to be a risk factor in increasing the chance of death among patients (OR = 2.154, 95% CI: 1.02-4.53; p = 0.048). Hospitalization in intensive care units (ICUs) was a risk factor for the death of patients (OR = 4.655, 95% CI: 7.6-83.2). The resistance to carbapenems was reported to be an important risk factor for the death of patients. CONCLUSIONS: Acinetobacter baumannii infections, particularly those resistant to carbapenems, are a significant risk for patients in ICUs and can lead to higher mortality rates.

In vitro and in vivo activities of scutellarein, a novel polyphosphate kinase 1 inhibitor against Acinetobacter baumannii infection.

BACKGROUND: Inorganic polyphosphate (polyP)-targeted polyphosphate kinase 1 (PPK1) has attracted much attention by virtue of its importance in bacterial pathogenicity and persistence, as well as its exclusive presence in microorganisms. However, only very few drugs have been found to be efficacious in inhibiting the Acinetobacter baumannii (A. baumannii) PPK1 protein. RESULTS: In this study, we identified Scutellarein (Scu), a potent PPK1 inhibitor that could significantly influence PPK1-regulated motility, biofilm formation, and bacterial persistence, which was further validated by the results of transcriptome analysis. Mechanistic explorations revealed that Scu achieved its enzyme inhibitory activity predominantly through direct engagement with the active center of PPK1. Moreover, the survival rate of Galleria mellonella larvae was increased by about 35% with 20 mg/kg of Scu treatment. The remarkable therapeutic benefits of Scu were also observed in the mouse pneumonia model, shown mainly by reduced bacterial colonization, pathological lesions, and inflammatory factors. CONCLUSION: Our results revealed that Scu could attenuate the pathogenicity and persistence of A. baumannii by interfering with its important kinase PPK1.

The context of blaOXA-23 gene in Iraqi carbapenem-resistant Acinetobacter baumannii isolates belonging to global clone 1 and global clone 2.

BACKGROUND AND OBJECTIVES: Of the genes conferring resistance to carbapenems in Acinetobacter baumannii, the blaOXA-23 gene is the most widely found across the world. The gene carrying blaOXA-23 transposons in A. baumannii isolates of global clones GC1 and GC2 is found worldwide. Here, we examined whether transposons play a role in the dissemination of the blaOXA-23 in globally distributed clones, GC1 and GC2 A. baumannii isolates from Iraq. MATERIALS AND METHODS: The 119 non-repetitive A. baumannii isolates including 94 recovered from clinical specimens and 25 isolates from hospital environment between September 2021 and April 2022 from different medical centers located at various regions in Baghdad, Iraq. The global clones (GC) and the genes encoding carbapenem resistance, including blaOXA-23, blaOXA-24, and blaOXA-58 were identified using multiplex PCR assays. Antibiotic susceptibility testing was performed by the Kirby-Bauer disk diffusion susceptibility method. The transposons carrying blaOXA-23 were examined using PCR mapping. In cases when carbapenem susceptible A. baumannii isolates were found, they were subjected to E test, full length sequencing of blaOXA-Ab (blaOXA-51-like) and Institut Pasteur multi-locus sequence typing scheme. RESULTS: All but two isolates (92 clinical and 25 environmental) were identified carbapenem-resistant A. baumannii (CRAB). Of 117 CRAB isolates, 20 belong to GC1, 19 contained blaOXA-23; of them, 17 isolates harbored the blaOXA-23 located on Tn2006. Among the 46 CRAB belonging to GC2, 39 contained blaOXA-23; of them, 34 carried the blaOXA-23 located on Tn2006. The remaining GC1 and GC2 isolates, one GC1 as well as one GC2 isolate, were susceptible to imipenem, doripenem, and meropenem and considered carbapenem-susceptible A. baumannii (CSAB). Full-length sequencing of the blaOXA-Ab and MLST for the two CSAB isolates belonging to GC1 and GC2 confirmed that the GC1 isolate belongs to ST 623 and contained an allele that encodes an blaOXA-69 variant of the blaOXA-Ab while the GC2 belong to ST2 and carried an blaOXA-66 variant. CONCLUSION: This study provides evidence for the dissemination of blaOXA-23 on the Tn2006 in CRAB isolates in Baghdad, Iraq. It appears that this transposon is widespread in GC1 and 2 isolates as in the other parts of the world. Interestingly, one GC1 and one GC2 isolate from Iraq were found to be susceptible to carbapenem while the isolates belonging to GC1 and GC2 have so far rarely been found to be susceptible to carbapenem globally.

Molecular genotyping reveals multiple carbapenemase genes and unique blaOXA-51-like (oxaAb) alleles among clinically isolated Acinetobacter baumannii from a Philippine tertiary hospital.

BACKGROUND: Acinetobacter baumannii continued to be an important Gram-negative pathogen of concern in the clinical context. The resistance of this pathogen to carbapenems due to the production of carbapenemases is considered a global threat. Despite the efforts to track carbapenemase synthesis among A. baumannii in the Philippines, local data on its molecular features are very scarce. This study aims to characterize A. baumannii clinical isolates from a Philippine tertiary hospital through genotyping of the pathogen's carbapenemase genes. METHODS: Antibiotic susceptibility profiling, phenotypic testing of carbapenemase production, and polymerase chain reaction assays to detect the different classes of carbapenemase genes (class A blaKPC, class B blaNDM, blaIMP, blaVIM, and class D blaOXA-23-like, blaOXA-24/40-like, blaOXA-48-like, blaOXA-51-like, ISAba1-blaOXA-51-like, blaOXA-58-like) were performed in all collected A. baumannii, both carbapenem resistant and susceptible (n = 52). RESULTS: Results showed that the majority of the carbapenem-resistant strains phenotypically produced carbapenemases (up to 84% in carbapenem inactivation methods) and possessed the ISAba1-blaOXA-51-like gene complex (80%). Meanwhile, both carbapenem-resistant and carbapenem-susceptible isolates possessed multi-class carbapenemase genes including blaNDM (1.9%), blaVIM (3.9%), blaOXA-24/40-like (5.8%), blaOXA-58-like (5.8%), blaKPC (11.5%), and blaOXA-23-like (94.2%), which coexist with each other in some strains (17.3%). In terms of the intrinsic blaOXA-51-like (oxaAb) genes, 23 unique alleles were reported (blaOXA-1058 to blaOXA-1080), the majority of which are closely related to blaOXA-66. Isolates possessing these alleles showed varying carbapenem resistance profiles. CONCLUSIONS: In summary, this study highlighted the importance of molecular genotyping in the characterization of A. baumannii by revealing the carbapenemase profiles of the pathogen (which may not be captured accurately in phenotypic tests), in identifying potent carriers of transferrable carbapenemase genes (which may not be expressed straightforwardly in antimicrobial susceptibility testing), and in monitoring unique pathogen epidemiology in the local clinical setting.

Genomic surveillance as a scalable framework for precision phage therapy against antibiotic-resistant pathogens.

Phage therapy is gaining increasing interest in the fight against critically antibiotic-resistant nosocomial pathogens. However, the narrow host range of bacteriophages hampers the development of broadly effective phage therapeutics and demands precision approaches. Here, we combine large-scale phylogeographic analysis with high-throughput phage typing to guide the development of precision phage cocktails targeting carbapenem-resistant Acinetobacter baumannii, a top-priority pathogen. Our analysis reveals that a few strain types dominate infections in each world region, with their geographical distribution remaining stable within 6 years. As we demonstrate in Eastern Europe, this spatiotemporal distribution enables preemptive preparation of region-specific phage collections that target most local infections. Finally, we showcase the efficacy of phage cocktails against prevalent strain types using in vitro and animal infection models. Ultimately, genomic surveillance identifies patients benefiting from the same phages across geographical scales, thus providing a scalable framework for precision phage therapy.

The physiological role of Acinetobacter baumannii DacC is exerted through influencing cell shape, biofilm formation, the fitness of survival and manifesting DD-carboxypeptidase and beta-lactamase dual-enzyme activities.

With the growing threat of drug-resistant Acinetobacter baumannii, there is an urgent need to comprehensively understand the physiology of this nosocomial pathogen. As penicillin-binding proteins are attractive targets for antibacterial therapy, we have tried to explore the physiological roles of two putative DD-carboxypeptidases, viz., DacC and DacD, in A. baumannii. Surprisingly, the deletion of dacC resulted in a reduced growth rate, loss of rod-shaped morphology, reduction in biofilm-forming ability, and enhanced susceptibility towards beta-lactams. In contrast, the deletion of dacD had no such effect. Interestingly, ectopic expression of dacC restored the lost phenotypes. The ∆dacCD mutant showed properties similar to the ∆dacC mutant. Conversely, in vitro enzyme kinetics assessments reveal that DacD is a stronger DD-CPase than DacC. Finally, we conclude that DacC might have DD-CPase and beta-lactamase activities, whereas DacD is a strong DD-CPase.

The K129 capsular polysaccharide produced by Acinetobacter baumannii MAR 15-4076 has the same composition as K84 but differs in the linkage between units altering the overall branching topology.

Capsular polysaccharide (CPS) is a heteroglycan that coats the cell surface of most isolates of the important Gram-negative bacterial pathogen, Acinetobacter baumannii. Strain MAR 15-4076, a clinical isolate recovered in Russia in 2015, was found to carry the KL129 sequence at the CPS biosynthesis K locus. The CPS was isolated from the strain and studied by sugar analysis, Smith degradation, one- and two-dimensional 1H and 13C NMR spectroscopy. It was composed of branched pentasaccharide units that include a →3)-α-l-Rhap-(1 â†’ 3)-α-l-Rhap-(1 â†’ 3)-ß-d-GlcpNAc-(1→ mainchain and α-d-ManpNAc-(1 â†’ 3)-l-Rhap side branch. Though the pentasaccharide units are identical to those that make up the K84 CPS produced by A. baumannii LUH5540, the units are linked differently via the substitution of an alternate l-Rhap residue, resulting in a difference in the overall topology of the CPS. This was due to the replacement of the Wzy polymerase gene encoded at the K locus.

Repurposing FDA-approved drugs for combating tigecycline resistance in Acinetobacter baumannii: in silico screening against BaeR protein.

Acinetobacter baumannii is becoming a gravely threatening nosocomial infection with a higher mortality rate. The present study targets the BaeR protein that mediates resistance to tigecycline antibiotics. The BaeR protein, along with the aid of BaeS, senses the incoming antibiotics and stimulates the expression of resistance proteins. These resistance proteins efflux the antibiotics and protect the cells from its effect. The main goal of the current study is to determine potential inhibitors from already existing FDA-approved drugs that could mitigate the BaeR protein. A range of in silico approaches, including molecular dynamics, virtual screening, SIFT analysis, ADMET, DFT, MM/GBSA, MMPBSA and per residue interaction analysis, were performed to identify inhibitors against this protein. The screening of FDA-approved compounds against the BaeR protein yielded 620 compounds. These compounds were clustered by SIFT to distinguish related compounds, it resulted in 20 different clusters. The top five clusters that can accommodate the binding site with better interaction and score by fulfilling all criteria were selected. The DFT analysis showed a smaller energy gap among all the compounds, indicating the ability of the compound to form firm interactions. All the compounds showed less binding free energy in both MM/GBSA and MM/PBSA analyses. The compounds were observed to be stable throughout the simulation. The per-residue interaction analysis confirmed that interactions with binding site residues were stable throughout the simulation. As a result of the study, four compounds, namely ZINC000003801919, DB01203, DB11217 and ZINC0000000056652, were identified as efficient candidates to deal with antimicrobial resistance in A. baumannii.

High mortality of Acinetobacter baumannii infection is attributed to macrophage-mediated induction of cytokine storm but preventable by naproxen.

BACKGROUND: The continuous emergence of multidrug-resistant (MDR) Acinetobacter baumannii (Ab) strains poses further challenges in its control and clinical management. It is necessary to decipher the mechanisms underlying the high mortality of Ab infections to explore unconventional strategies for controlling outbreaks of drug-resistant infections. METHODS: The immune responses of Ab sepsis infection were investigated using flow cytometry, RNA-seq, qRT-PCR, and ELISA and scRNA-seq. The detailed pathways mediating Ab immune responses were also depicted and a specific therapy was developed based on the understanding of the mechanisms underlying Ab-induced cytokine storms. FINDINGS: The results highlighted the critical role of alveolar and interstitial macrophages as targets of Ab during the infection process. These cells were found to undergo polarization towards the M1 phenotype, triggering a cytokine storm that eventually caused the death of the host. The polarization and excessive inflammatory response mediated by macrophages were mainly regulated by the TLR2/Myd88/NF-κB signaling pathway. Suppression of Ab-triggered inflammatory responses and M1 polarization by the drug naproxen (NPXS) was shown to confer full protection of mice from lethal infections. INTERPRETATION: The findings in this work depict the major mechanisms underlying the high mortality rate of Ab infections and highlight the clinical potential application of anti-inflammatory drugs or immunosuppressants in reducing the mortality of such infections, including those caused by MDR strains. FUNDING: Funding sources are described in the acknowledgments section.

Comparison of Hypervirulent and Non-Hypervirulent Carbapenem-Resistant Acinetobacter baumannii Isolated from Bloodstream Infections: Mortality, Potential Virulence Factors, and Combination Therapy In Vitro.

Hypervirulent carbapenem-resistant Acinetobacter baumannii (hv-CRAB) has emerged in bloodstream infections (BSI). Cases of BSI caused by hv-CRAB (hv-CRAB-BSI) had posed a significant threat to hospitalized patients. In this study, 31 CRAB strains isolated from Chinese BSI patients were analyzed, of which 24 were identified as hv-CRAB-BSI and 7 as non-hv-CRAB-BSI, using the Galleria mellonella infection model. Patients with hv-CRAB-BSI had higher rates of septic shock (79.2% vs. 14.3%, p = 0.004) and mortality (66.7% vs. 14.3%, p = 0.028). All strains were resistant to most antibiotics but sensitive to colistin. Hv-CRAB-BSI showed lower resistance to minocycline than non-hv-CRAB-BSI (54.2% vs. 100%, p = 0.03). Whole-genome sequencing revealed that the detection rates of immune modulation genes ptk and epsA in hv-CRAB-BSI were significantly higher than in non-hv-CRAB-BSI (91.7% vs. 28.6%, p = 0.002). Additionally, all ST457 hv-CRAB-BSI lacked abaR, and all ST1486 non-hv-CRAB-BSI lacked adeG. The checkerboard dilution method assessed the efficacies of various antibiotic combinations, revealing that although synergism was rarely observed, the combination of colistin and minocycline showed the best efficacy for treating CRAB-BSI, regardless of whether the infections were hv-CRAB-BSI or non-hv-CRAB-BSI. These findings highlight the importance of analyzing molecular characteristics and exploring effective treatment strategies for hv-CRAB-BSI.