Acinetobacter baumannii: a universal threat to public health?

Structural and Dynamic Features of Acinetobacter baumannii OXA-66 β-Lactamase Explain Its Stability and Evolution of Novel Variants

OXA-66 is a member of the OXA-51 subfamily of class D β-lactamases native to the Acinetobacter genus that includes Acinetobacter baumannii, one of the ESKAPE pathogens and a major cause of drug-resistant nosocomial infections. Although both wild type OXA-66 and OXA-51 have low catalytic activity, they are ubiquitous in the Acinetobacter genomes. OXA-51 is also remarkably thermostable. In addition, newly emerging, single and double amino acid variants show increased activity against carbapenems, indicating that the OXA-51 subfamily is growing and gaining clinical significance. In this study, we used molecular dynamics simulations, X-ray crystallography, and thermal denaturation data to examine and compare the dynamics of OXA-66 wt and its gain-of-function variants: I129L (OXA-83), L167V (OXA-82), P130Q (OXA-109), P130A, and W222L (OXA-234). Our data indicate that OXA-66 wt also has a high melting temperature, and its remarkable stability is due to an extensive and rigid hydrophobic bridge formed by a number of residues around the active site and harbored by the three loops, P, Ω, and β5-β6. Compared to the WT enzyme, the mutants exhibit higher flexibility only in the loop regions, and are more stable than other robust carbapenemases, such as OXA-23 and OXA-24/40. All the mutants show increased rotational flexibility of residues I129 and W222, which allows carbapenems to bind. Overall, our data support the hypothesis that structural features in OXA-51 and OXA-66 promote evolution of multiple highly stable variants with increased clinical relevance in A. baumannii.

Effective Treatment of Acinetobacter baumannii Ventriculitis With Interventricular Colistin: A Case Report

Cerebrospinal fluid shunts are the primary treatment for hydrocephalus. However, prolonged external ventricular drain (EVD) use can lead to central nervous system (CNS) infections such as ventriculitis. In the ICU setting, nosocomial infections with gram-negative, multi-drug resistant (MDR) organisms such as Acinetobacter baumannii (AB) prevail, leading to poor outcomes. AB infections are notably challenging due to their genetic drug resistance. Colistin has been reintroduced for use against gram-negative MDR pathogens but has limitations in CNS penetration when administered intravenously. Therefore, intraventricular (IVT) or intrathecal administration of colistin is recommended to enhance its therapeutic reach within the CNS. We present a case of a 22-year-old male admitted after an electric scooter accident with head trauma and hydrocephalus. A ventriculoperitoneal (VP) shunt was inserted, complicated by a nosocomial neuroinfection. Empiric IV therapy with meropenem and vancomycin was initiated. The VP shunt culture identified AB susceptible only to colistin. Intravenous (IV) colistin was added to meropenem with no significant improvement. The addition of IVT colistin significantly improved the patient's neurological condition and reduced inflammatory markers. The patient experienced one myoclonic seizure during IVT colistin treatment, managed with antiepileptics. After multiple unrelated nosocomial complications, the patient was discharged in good condition to rehabilitation. This case suggests that IVT colistin, combined with IV administration, may be preferable over IV colistin alone. Medical staff should be informed about the correct prevention and care of EVD-associated infections.

Differential development of antibiotic resistance and virulence between Acinetobacter species

The two species that account for most cases of Acinetobacter-associated bacteremia in the United Kingdom are Acinetobacter lwoffii, often a commensal but also an emerging pathogen, and Acinetobacter baumannii, a well-known antibiotic-resistant species. While these species both cause similar types of human infection and occupy the same niche, A. lwoffii (unlike A. baumannii) has thus far remained susceptible to antibiotics. Comparatively little is known about the biology of A. lwoffii, and this is the largest study on it conducted to date, providing valuable insights into its behaviour and potential threat to human health. This study aimed to explain the antibiotic susceptibility, virulence, and fundamental biological differences between these two species. The relative susceptibility of A. lwoffii was explained as it encoded fewer antibiotic resistance and efflux pump genes than A. baumannii (9 and 30, respectively). While both species had markers of horizontal gene transfer, A. lwoffii encoded more DNA defense systems and harbored a far more restricted range of plasmids. Furthermore, A. lwoffii displayed a reduced ability to select for antibiotic resistance mutations, form biofilm, and infect both in vivo and in in vitro models of infection. This study suggests that the emerging pathogen A. lwoffii has remained susceptible to antibiotics because mechanisms exist to make it highly selective about the DNA it acquires, and we hypothesize that the fact that it only harbors a single RND system restricts the ability to select for resistance mutations. This provides valuable insights into how development of resistance can be constrained in Gram-negative bacteria.

IMPORTANCE

Acinetobacter lwoffii is often a harmless commensal but is also an emerging pathogen and is the most common cause of Acinetobacter-derived bloodstream infections in England and Wales. In contrast to the well-studied and often highly drug-resistant A. baumannii, A. lwoffii has remained susceptible to antibiotics. This study explains why this organism has not evolved resistance to antibiotics. These new insights are important to understand why and how some species develop antibiotic resistance, while others do not, and could inform future novel treatment strategies.

PmrAB, the two-component system of Acinetobacter baumannii, controls the phosphoethanolamine modification of lipooligosaccharide in response to metal ions

Acinetobacter baumannii is highly resistant to antimicrobial agents, and XDR strains have become widespread. A. baumannii has developed resistance to colistin, which is considered the last resort against XDR Gram-negative bacteria, mainly caused by lipooligosaccharide (LOS) phosphoethanolamine (pEtN) and/or galactosamine (GalN) modifications induced by mutations that activate the two-component system (TCS) pmrAB. Although PmrAB of A. baumannii has been recognized as a drug resistance factor, its function as TCS, including its regulatory genes and response factors, has not been fully elucidated. In this study, to clarify the function of PmrAB as TCS, we elucidated the regulatory genes (regulon) of PmrAB via transcriptome analysis using pmrAB-activated mutant strains. We discovered that PmrAB responds to low pH, Fe2+, Zn2+, and Al3+. A. baumannii selectively recognizes Fe2+ rather than Fe3+, and a novel region ExxxE, in addition to the ExxE motif sequence, is involved in the environmental response. Furthermore, PmrAB participates in the phosphoethanolamine modification of LOS on the bacterial surface in response to metal ions such as Al3+, contributing to the attenuation of Al3+ toxicity and development of resistance to colistin and polymyxin B in A. baumannii. This study demonstrates that PmrAB in A. baumannii not only regulates genes that play an important role in drug resistance but is also involved in responses to environmental stimuli such as metal ions and pH, and this stimulation induces LOS modification. This study reveals the importance of PmrAB in the environmental adaptation and antibacterial resistance emergence mechanisms of A. baumannii.

IMPORTANCE

Antimicrobial resistance (AMR) is a pressing global issue in human health. Acinetobacter baumannii is notably high on the World Health Organization's list of bacteria for which new antimicrobial agents are urgently needed. Colistin is one of the last-resort drugs used against extensively drug-resistant (XDR) Gram-negative bacteria. However, A. baumannii has become increasingly resistant to colistin, primarily by modifying its lipooligosaccharide (LOS) via activating mutations in the two-component system (TCS) PmrAB. This study comprehensively elucidates the detailed mechanism of drug resistance of PmrAB in A. baumannii as well as its biological functions. Understanding the molecular biology of these molecules, which serve as drug resistance factors and are involved in environmental recognition mechanisms in bacteria, is crucial for developing fundamental solutions to the AMR problem.

Direct metagenomics investigation of non-surgical hard-to-heal wounds: a review

BACKGROUND

Non-surgical chronic wounds, including diabetes-related foot diseases (DRFD), pressure injuries (PIs) and venous leg ulcers (VLU), are common hard-to-heal wounds. Wound evolution partly depends on microbial colonisation or infection, which is often confused by clinicians, thereby hampering proper management. Current routine microbiology investigation of these wounds is based on in vitro culture, focusing only on a limited panel of the most frequently isolated bacteria, leaving a large part of the wound microbiome undocumented.

METHODS

A literature search was conducted on original studies published through October 2022 reporting metagenomic next generation sequencing (mNGS) of chronic wound samples. Studies were eligible for inclusion if they applied 16 S rRNA metagenomics or shotgun metagenomics for microbiome analysis or diagnosis. Case reports, prospective, or retrospective studies were included. However, review articles, animal studies, in vitro model optimisation, benchmarking, treatment optimisation studies, and non-clinical studies were excluded. Articles were identified in PubMed, Google Scholar, Web of Science, Microsoft Academic, Crossref and Semantic Scholar databases.

RESULTS

Of the 3,202 articles found in the initial search, 2,336 articles were removed after deduplication and 834 articles following title and abstract screening. A further 14 were removed after full text reading, with 18 articles finally included. Data were provided for 3,628 patients, including 1,535 DRFDs, 956 VLUs, and 791 PIs, with 164 microbial genera and 116 species identified using mNGS approaches. A high microbial diversity was observed depending on the geographical location and wound evolution. Clinically infected wounds were the most diverse, possibly due to a widespread colonisation by pathogenic bacteria from body and environmental microbiota. mNGS data identified the presence of virus (EBV) and fungi (Candida and Aspergillus species), as well as Staphylococcus and Pseudomonas bacteriophages.

CONCLUSION

This study highlighted the benefit of mNGS for time-effective pathogen genome detection. Despite the majority of the included studies investigating only 16 S rDNA, ignoring a part of viral, fungal and parasite colonisation, mNGS detected a large number of bacteria through the included studies. Such technology could be implemented in routine microbiology for hard-to-heal wound microbiota investigation and post-treatment wound colonisation surveillance.

An outbreak analysis of wound infection due to Acinetobacter baumannii in earthquake-trauma patients

BACKGROUND

Multidrug-resistant Acinetobacter baumannii is still a major contributor to outbreaks and infections health care-associated infections. This study aimed to investigate an outbreak of wound infection due to A baumannii in trauma patients injured in the Kahramanmaraş earthquake.

METHODS

This retrospective case-control study was conducted on an outbreak of wound infection caused by A. baumannii in trauma patients affected by the February 6 Turkey earthquake. Among the patients who underwent at least one extremity surgery due to earthquake-related crush-trauma injury, patients with wound infection due to A baumannii were included in the case group and without infection were included in the control group. Multivariate analysis and logistic regression were performed to identify risk factors. Environmental cultures were taken to identify the source of the outbreak. Molecular typing by pulsed-field gel electrophoresis was used to confirm the relationships of the wound infection agent A. baumannii strains.

RESULTS

A total of 44 patients were included in the case group and 62 patients in the control group. Time under the debris; 22.0 versus 35.7 (odds ratio [OR]:1.02, 95% confidence interval [CI]: 1.00-1.04) and hemodialysis (OR: 6.09, 95% CI: 1.64-22.66) were identified as risk factors for in the multivariate analysis. Performing the first intervention in a fully equipped tertiary hospital was seen as an infection-reducing factor compared to performing it in a field hospital (OR: 0.21, 95% CI: 0.06-0.68). Dressing trolleys and scissors were identified as the source of the outbreak.

CONCLUSIONS

After devastating earthquakes, a large number of patients are admitted and require emergency interventions due to life-threatening conditions. Organ failure often develops and requires the use of invasive catheters and procedures. Compliance with infection control measures and clean surgical interventions reduce wound site infections and allow extremities to heal, while problems in adhering to infection control measures can lead to many problems such as outbreaks of gram-negative bacteria. This highlights the importance of infection control measures.

Colony phase variation switch modulates antimicrobial tolerance and biofilm formation in Acinetobacter baumannii

Carbapenem-resistant Acinetobacter baumannii causes one of the most difficult-to-treat nosocomial infections. Polycationic drugs like polymyxin B or colistin and tetracycline drugs such as doxycycline or minocycline are commonly used to treat infections caused by carbapenem-resistant A. baumannii. Here, we show that a subpopulation of cells associated with the opaque/translucent colony phase variation by A. baumannii AB5075 displays differential tolerance to subinhibitory concentrations of colistin and tetracycline. Using a variety of microscopic techniques, we demonstrate that extracellular polysaccharide moieties mediate colistin tolerance to opaque A. baumannii at single-cell level and that mushroom-shaped biofilm structures protect opaque bacteria at the community level. The colony switch phenotype is found to alter several traits of A. baumannii, including long-term survival under desiccation, tolerance to ethanol, competition with Escherichia coli, and intracellular survival in the environmental model host Acanthamoeba castellanii. Additionally, our findings suggest that extracellular DNA associated with membrane vesicles can promote colony switching in a DNA recombinase-dependent manner.IMPORTANCEAs a WHO top-priority drug-resistant microbe, Acinetobacter baumannii significantly contributes to hospital-associated infections worldwide. One particularly intriguing aspect is its ability to reversibly switch its colony morphotype on agar plates, which has been remarkably underexplored. In this study, we employed various microscopic techniques and phenotypic assays to investigate the colony phase variation switch under different clinically and environmentally relevant conditions. Our findings reveal that the presence of a poly N-acetylglucosamine-positive extracellular matrix layer contributes to the protection of bacteria from the bactericidal effects of colistin. Furthermore, we provide intriguing insights into the multicellular lifestyle of A. baumannii, specifically in the context of colony switch variation within its predatory host, Acanthamoeba castellanii.

Anti-OmpA antibodies as potential inhibitors of Acinetobacter baumannii biofilm formation, adherence to, and proliferation in A549 human alveolar epithelial cells

Outer membrane protein A (OmpA) is a critical virulence factor in Acinetobacter baumannii, influencing adhesion, biofilm formation, host immune response, and host cell apoptosis. We investigated the invasion of A549 alveolar epithelial cells by A. baumannii and examined how anti-OmpA antibodies impact these interactions. OmpA was expressed and purified, inducing anti-OmpA antibodies in BALB/c mice. The potential toxicity of OmpA was evaluated in mice by analyzing histology from six organs. A549 cells were exposed to A. baumannii strains 19606 and a clinical isolate. Using cell culture and light microscopy, we scrutinized the effects of anti-OmpA sera on serum resistance, adherence, internalization, and proliferation of A. baumannii in A549 cells. The viability of A549 cells was assessed upon exposure to live A. baumannii and anti-OmpA sera. OmpA-induced antibody demonstrated potent bactericidal effects on both strains of A. baumannii. Both strains formed biofilms, which were reduced by anti-OmpA serum, along with decreased bacterial adherence, internalization, and proliferation in A549 cells. Anti-OmpA serum improved the survival of A549 cells post-infection. Pre-treatment with cytochalasin D hindered bacterial internalization, highlighting the role of actin polymerization in invasion. Microscopic examination revealed varied interactions encompassing adherence, apoptosis, membrane alterations, vacuolization, and damage. A549 cells treated with anti-OmpA serum exhibited improved structures and reduced damage. The findings indicate that A. baumannii can adhere to and proliferate within epithelial cells with OmpA playing a pivotal role in these interactions, and the complex nature of these interactions shapes the intricate course of A. baumannii infection in host cells.

Antibiotic therapy for nonfermenting Gram-negative bacilli infections: future perspectives

PURPOSE OF REVIEW

Serious infections caused by nonfermenting Gram-negative bacteria (NF-GNB) pose a significant challenge for clinicians due to the limited treatment options available, which are frequently associated with issues of toxicity and unfavourable pharmacokinetic profiles. The aim of this review is to provide a brief overview of the existing data concerning the ongoing development of antiinfective agents targeting NF-GNB.

RECENT FINDINGS

Several agents exhibiting efficacy against NF-GNB are under clinical investigation. Durlobactam-sulbactam and cefepime-taniborbactam emerge as promising therapeutic avenues against carbapenem-resistant Acinetobacter baumanii . Cefepime-zidebactam may serve as a suitable treatment option for urinary tract infections caused by a wide range of NF-GNB. Cefepime-enmetazobactam demonstrates potent in vitro activity against various NF-GNB strains; however, its role as an anti- Pseudomonal agent is inadequately substantiated by available data. Xeruborbactam is a wide β-lactamase inhibitor that can be associated with a range of agents, enhancing in-vitro activity of these against many NF-GNB, including those resistant to newer, broader spectrum options. Lastly, murepavadin appears to be a potential pathogen-specific solution for severe Pseudomonas infections; however, additional investigation is necessary to establish the safety profile of this compound.

SUMMARY

Each of the novel molecules reviewed possesses an interesting range of in-vitro activity against NF-GNB. In addition, some of them have already been proved effective in vivo, underscoring their potential as future treatment options.

Insights into the epidemiology, risk factors, and clinical outcomes of carbapenem-resistant Acinetobacter baumannii infections in critically ill children

Background and aims

Carbapenem-resistant Acinetobacter baumannii (CRAB) has become a leading cause of nosocomial infections with an increasing impact on critically ill patients, yet there is limited data on contributing factors. This study was aim to evaluate the prevalence and risk factors, and clinical outcomes of CRAB infections among critically ill children in a tertiary university teaching hospital in China.

Methods

From January 2016 to December 2021, all children diagnosed with nosocomial Acinetobacter baumannii (A. baumannii) infections in the pediatric intensive care unit (PICU) were identified through the computerized microbiology laboratory databases. Among them, children suffering from CRAB infection were designated as a case group, while children with carbapenem susceptible A. baumannii (CSAB) infection were assigned to a control group. This retrospective case-control study was based on two groups of patients to determine potential clinical factors contributing to CRAB infection and death among critically ill children via univariate and multivariate analyses.

Results

During the 6-year study period, a total of 372 episodes of nosocomial A. baumannii infection in the PICU were eligible and included in the study. These isolates displayed moderate or high rates of resistance to all tested antimicrobials except colistin. The overall prevalence of CRAB and MDRAB (multidrug-resistant A. baumannii) was 78.0% and 80.9%, respectively. Several risk factors found to significantly increase CRAB infection included receiving invasive operation (OR = 9.412, p = 0.001), gastric intubation (OR = 2.478, p = 0.026), prior carbapenems exposure (OR = 2.543, p = 0.003), severe pneumonia (OR = 3.235, p = 0.001), and hemoglobin <110g/L (OR = 3.049, p = 0.005). Of 372 patients with CRAB infection, the mortality rate was 30.9% (115/372) and mortality did not differ between children with CRAB and CSAB infections. Septic shock (OR = 2.992, p = 0.001), AST > 46U/L (OR = 2.015, p = 0.005), bone marrow aspiration (OR = 2.704, p = 0.008), lymphocyte <20 % (OR = 1.992, p = 0.006) and age (OR = 1.094, p = 0.002) were independent risk factors for the death of A. baumanni infection.

Conclusions

This study highlights considerable incidence rate and remarkable mortality of children with A. baumanni (especially CRAB) infections, and identifies age-specific risk factors for CRAB infection and mortality in critically ill children. These risk factors should be taken into account in pediatric hospitals in order to establish early intervention and rational treatment to improve clinical outcomes.

Excess mortality and long-term disability from healthcare-associated carbapenem-resistant Acinetobacter baumannii infections: A nationwide population-based matched cohort study

BACKGROUND

Carbapenem resistance is perceived as a clinical challenge in the management of debilitated and immunocompromised patients who eventually will die from underlying diseases. We aimed to examine whether carbapenem resistance per se, rather than the underlying diseases, negatively affect outcomes, by comparing the excess mortality and morbidity from healthcare-associated infections (HAIs) caused by carbapenem-resistant Acinetobacter baumannii (CRAB) and carbapenem-susceptible A. baumannii (CSAB).

METHODS

This was a nationwide retrospective matched cohort study of hospitalized patients in 96 hospitals which participated in Taiwan Nosocomial Infection Surveillance (TNIS). A total of 2,213 patients with A. baumannii HAIs were individually matched to 4,426 patients without HAIs. Main outcomes were excess risks for one-year all-cause mortality and one-year new-onset chronic ventilator dependence or dialysis-dependent end-stage renal disease.

RESULTS

Excess one-year mortality was 27.2% in CRAB patients, compared with their matched uninfected inpatients, as well as 15.4% in CSAB patients (also compared with their matched uninfected inpatients), resulting in an attributable mortality of 11.8% (P <0.001) associated with carbapenem resistance. The excess risk associated with carbapenem resistance for new-onset chronic ventilator dependence was 5.2% (P <0.001). Carbapenem resistance was also associated with an extra cost of $2,511 per case of A. baumannii HAIs (P <0.001).

CONCLUSION

Carbapenem resistance is associated with a significant disease burden in terms of excess mortality, long-term ventilator dependence, and medical cost. Further studies on effects of antimicrobial stewardship programs in decreasing this burden are warranted.

Acinetobacter baumannii outer membrane protein A induces autophagy in bone marrow-derived dendritic cells involving the PI3K/mTOR pathway

BACKGROUND

Outer membrane protein A (OmpA) is the major virulence factor of Acinetobacter baumannii and plays a wide role in the pathogenesis and antimicrobial resistance of A. baumannii. Dendritic cells (DCs) are the most effective antigen-presenting cells and play a crucial role in regulating the immune response to multiple antigens and immune sentries. We aimed to study the role and molecular mechanisms of OmpA-induced mouse bone marrow-derived dendritic cells (BMDCs) autophagy in the immune response of A. baumannii.

METHODS

First, purified A. baumannii OmpA was assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and western blot. OmpA effect on BMDCs viability was evaluated by MTT assay. BMDCs were pretreated with autophagy inhibitor chloroquine or transfected with overexpression plasmids (oe-NC or oe-PI3K). Then BMDCs apoptosis, inflammatory cytokines, protein kinase B (PI3K)/mammalian target of rapamycin (mTOR) pathway, and autophagy-related factors levels were evaluated.

RESULTS

SDS-PAGE and western blot verified the successful purification of OmpA. BMDCs viability repressed gradually with the increase of OmpA concentration. OmpA treatment of BMDCs led to apoptosis and inflammation in BMDCs. OmpA caused incomplete autophagy in BMDCs, and light chain 3 (LC3), Beclin1, P62, and LC3II/I levels were significantly elevated with the increase of the time and concentration of OmpA treatment. Chloroquine reversed OmpA effects on autophagy in BMDCs, that was, LC3, Beclin1, and LC3II/I levels were reduced, while P62 level was elevated. Furthermore, chloroquine reversed OmpA effects on apoptosis and inflammation in BMDCs. PI3K/mTOR pathway-related factor expression was affected by OmpA treatment of BMDCs. After overexpression of PI3K, these effects were reversed.

CONCLUSIONS

A. baumannii OmpA induced autophagy in BMDCs involving the PI3K/mTOR pathway. Our study may provide a novel therapeutic target and theoretical basis for treating infections caused by A. baumannii.

Using an Aluminum Hydroxide–Chitosan Matrix Increased the Vaccine Potential and Immune Response of Mice against Multi-Drug-Resistant Acinetobacter baumannii

Acinetobacter baumannii is a Gram-negative, immobile, aerobic nosocomial opportunistic coccobacillus that causes pneumonia, septicemia, and urinary tract infections in immunosuppressed patients. There are no commercially available alternative antimicrobials, and multi-drug resistance is an urgent concern that requires emergency measures and new therapeutic strategies. This study evaluated a multi-drug-resistant A. baumannii whole-cell vaccine, inactivated and adsorbed on an aluminum hydroxide–chitosan (mAhC) matrix, in an A. baumannii sepsis model in immunosuppressed mice by cyclophosphamide (CY). CY-treated mice were divided into immunized, non-immunized, and adjuvant-inoculated groups. Three vaccine doses were given at 0D, 14D, and 28D, followed by a lethal dose of 4.0 × 108 CFU/mL of A. baumannii. Immunized CY-treated mice underwent a significant humoral response, with the highest IgG levels and a higher survival rate (85%); this differed from the non-immunized CY-treated mice, none of whom survived (p < 0.001), and from the adjuvant group, with 45% survival (p < 0.05). Histological data revealed the evident expansion of white spleen pulp from immunized CY-treated mice, whereas, in non-immunized and adjuvanted CY-treated mice, there was more significant organ tissue damage. Our results confirmed the proof-of-concept of the immune response and vaccine protection in a sepsis model in CY-treated mice, contributing to the advancement of new alternatives for protection against A. baumannii infections.

Uncovering the Secretion Systems of Acinetobacter baumannii: Structures and Functions in Pathogenicity and Antibiotic Resistance

Infections led by Acinetobacter baumannii strains are of great concern in healthcare environments due to the strong ability of the bacteria to spread through different apparatuses and develop drug resistance. Severe diseases can be caused by A. baumannii in critically ill patients, but its biological process and mechanism are not well understood. Secretion systems have recently been demonstrated to be involved in the pathogenic process, and five types of secretion systems out of the currently known six from Gram-negative bacteria have been found in A. baumannii. They can promote the fitness and pathogenesis of the bacteria by releasing a variety of effectors. Additionally, antibiotic resistance is found to be related to some types of secretion systems. In this review, we describe the genetic and structural compositions of the five secretion systems that exist in Acinetobacter. In addition, the function and molecular mechanism of each secretion system are summarized to explain how they enable these critical pathogens to overcome eukaryotic hosts and prokaryotic competitors to cause diseases.

Epidemiology, Mechanisms of Resistance and Treatment Algorithm for Infections Due to Carbapenem-Resistant Gram-Negative Bacteria: An Expert Panel Opinion

Antimicrobial resistance represents a serious threat for global health, causing an unacceptable burden in terms of morbidity, mortality and healthcare costs. In particular, in 2017, carbapenem-resistant organisms were listed by the WHO among the group of pathogens for which novel treatment strategies are urgently needed. Fortunately, several drugs and combinations have been introduced in recent years to treat multi-drug-resistant (MDR) bacteria. However, a correct use of these molecules is needed to preserve their efficacy. In the present paper, we will provide an overview on the epidemiology and mechanisms of resistance of the most common MDR Gram-negative bacteria, proposing a treatment algorithm for the management of infections due to carbapenem-resistant bacteria based on the most recent clinical evidence.

Intrathecal/Intraventricular Colistin for Antibiotic-Resistant Bacterial CNS Infections in Pediatric Population: A Systematic Review

Central nervous system (CNS) infections constitute a life-threatening condition, especially in children. Treatment limitations exist for drug-resistant CNS bacterial infections. Inadequate CNS penetration and intravenous (IV) antibiotic treatment failure represent a major clinical challenge. However, patients with antibiotic-resistant bacterial CNS infections may benefit from intrathecal (IT) or intraventricular (IVT) colistin. The authors aimed to assess the safety and effectiveness of IT/IVT colistin therapy in the pediatric population, with or without other antibiotics, for the treatment of antibiotic-resistant CNS infections. A comprehensive literature search was conducted using the electronic databases of PubMed, Ovid, and Embase for relevant articles using the following terms: “Colistin”, “CNS infection”, and “Outcome”, as well as their combinations. The retrieved articles were filtered by age (Child), language (English), route of administration (IT/IVT), and species (Humans). The present systematic review comprised 20 articles that included 31 children (19; 61.2% were boys) with multidrug-resistant CNS infection. Their ages ranged from less than one month to 18 years (median: 9 months). Acinetobacter baumannii was the main causative organism in 22 patients (70.9%), and infection occurred mainly after neurosurgical interventions (83.8%). An external ventricular drain was inserted to administer colistin into the ventricular system in 29 cases (93.5%). The median duration for colistin therapy was 18 days. Twenty-three patients (74%) recovered, while five patients (16%) had residual disability, and three patients (10%) died. The authors concluded that IT/IVT colistin therapy is safe and effective as either the primary or adjunct treatment for antibiotic-resistant cases with CNS infection.

Genotypic and Phenotypic Characterization of Novel Sequence Types of Carbapenem-Resistant Acinetobacter baumannii, With Heterogeneous Resistance Determinants and Targeted Variations in Efflux Operons

Acinetobacter baumannii has emerged as one of the dominant nosocomial human pathogens associated with high morbidity and mortality globally. Increased incidences of carbapenem-resistant A. baumannii (CRAB) have resulted in an enormous socioeconomic burden on health-care systems. Here, we report the genotypic and phenotypic characterization of novel ST1816 and ST128 variants in A. baumannii strains belonging to International clone II (GC2) with capsule types KL1:OCL8 and KL3:OCL1d from India. Sequence analysis revealed the presence of diverse virulome and resistome in these clinical strains, in addition to islands, prophages, and resistance genes. The oxacillinase bla _OXA-23 detected in the genomic island also highlighted the coexistence of bla _OXA-66 /bla _OXA-98 , bla _ADC73 /bla _ADC-3 , and bla _TEM-1D in their mobile scaffolds, which is alarming. Together with these resistance-determining enzymes, multidrug efflux transporters also harbored substitutions, with increased expression in CRAB strains. The hotspot mutations in colistin resistance-conferring operons, PmrAB, LpxACD, and AdeRS, were additionally confirmed. Phenotype microarray analysis indicated that multidrug-resistant strains A. baumannii DR2 and A. baumannii AB067 preferred a range of antimicrobial compounds as their substrates relative to the other. To our knowledge, this is the first comprehensive report on the characterization of A. baumannii variants ST1816 and ST128, with different genetic makeup and genome organization. The occurrence of CRAB infections worldwide is a severe threat to available limited therapeutic options; hence, continued surveillance to monitor the emergence and dissemination of such novel ST variants in A. baumannii is imperative.

Carbapenem resistance in Acinetobacter baumannii, and their importance in hospital-acquired infections: a scientific review

Carbapenem is an important therapy for serious hospital-acquired infections and for the care of patients affected by multidrug-resistant organisms, specifically Acinetobacter baumannii; however, with the global increase of carbapenem-resistant A. baumannii, this pathogen has significantly threatened public health. Thus, there is a pressing need to better understand this pathogen in order to develop novel treatments and control strategies for dealing with A. baumannii. In this review, we discuss an overview of carbapenem, including its discovery, development, classification and biological characteristics, and its importance in hospital medicine especially in critical care units. We also describe the peculiarity of bacterial pathogen, A. baumannii, including its commonly reported virulence factors, environmental persistence and carbapenem resistance mechanisms. In closing, we discuss various control strategies for overcoming carbapenem resistance in hospitals and for limiting outbreaks. With the appearance of strains that resist carbapenem, the aim of this review is to highlight the importance of understanding this increasingly problematic healthcare-associated pathogen that creates significant concern in the field of nosocomial infections and overall public health.

A plethora of carbapenem resistance in Acinetobacter baumannii: no end to a long insidious genetic journey

Acinetobacter baumannii, notorious for causing nosocomial infections especially in patients admitted to intensive care unit (ICU) and burn units, is best at displaying resistance to all existing antibiotic classes. Consequences of high potential for antibiotic resistance has resulted in extensive drug or even pan drug resistant A. baumannii. Carbapenems, mainly imipenem and meropenem, the last resort for the treatment of A. baumannii infections have fallen short due to the emergence of carbapenem resistant A. baumannii (CRAB). Though enzymatic degradation by production of class D β-lactamases (Oxacillinases) and class B β-lactamases (Metallo β-lactamases) is the core mechanism of carbapenem resistance in A. baumannii; however over-expression of efflux pumps such as resistance-nodulation cell division (RND) family and variant form of porin proteins such as CarO have been implicated for CRAB inception. Transduction and outer membrane vesicles-mediated transfer play a role in carbapenemase determinants spread. Colistin, considered as the most promising antibacterial agent, nevertheless faces adverse effects flaws. Cefiderocol, eravacycline, new β-lactam antibiotics, non-β-lactam-β-lactamase inhibitors, polymyxin B-derived molecules and bacteriophages are some other new treatment options streamlined.

Molecular Epidemiology and Mechanisms of Carbapenem-Resistant Acinetobacter baumannii Isolates from ICU and Respiratory Department Patients of a Chinese University Hospital

Background

The objective of our study is to estimate the differences in molecular epidemiology and resistance mechanisms in carbapenem-resistant Acinetobacter baumannii (CRAB) isolates from the ICU and respiratory department(RD) in Fourth Affiliated Hospital of Harbin Medical University.

Methods

Carbapenemase genes associated with carbapenem resistance were studied by polymerase chain reaction(PCR). Genotyping was analyzed using multi-locus sequence typing (MLST) and pulsed field gel electrophoresis (PFGE).

Results

Sixty non-duplicate CRAB isolates from the ICU and RD (n=30, respectively) were collected. All of CRAB strains were not resistant to colistin (0%). The CRAB strains from the ICU were significantly more resistant to tigecycline and cefoperazone/sulbactam compared with the RD (23.3% vs 0%, P=0.03; 53.3% % vs 23.3%, P=0.01, respectively). PCR detection of genes associated with CRAB revealed that the ratio in both the ICU and the RD of blaVIM-2, blaIMP-4, blaNDM-1, blaOXA-23, ampC, and mutation of CarO were present in 23.3% vs 0% (P=0.01), 40% vs 10% (P=0.02), 20% vs 0% (P=0.02), 80% vs 56.7%, 16.7% vs 13.3% and 86.7% vs 60% (P=0.04), respectively. Seven genotypes were detected by the PFGE in the RD and the ICU, respectively. Genotype I was significantly more frequent in the ICU compared with the RD (63.3% vs 36.6%, P=0.03). MLST showed that there were 10 ST genotypes in the RD and four in the ICU, but ST92 in both groups was 33.3% vs 63.3% (P=0.03), respectively.

Conclusion

There are differences in molecular epidemiology and resistance mechanisms in the CRAB isolates between the ICU and RD.

Infective endocarditis by Acinetobacter species: a systematic review

A. baumannii - A. calcoaceticus complex infections are increasingly frequent, especially in intensive care units. Such infections are associated with a mortality that can be as high as 62%. On the other hand, infective endocarditis (IE) is an uncommon disease with notable morbidity and mortality. Even though IE is rarely caused by Acinetobacter species, these infections can be particularly problematic due to increasing antimicrobial resistance. The purpose of this study was to systemically review all published cases of IE by Acinetobacter species in the literature. A systematic review of PubMed, Scopus and Cochrane library (through 25 April 2020) for studies providing epidemiological, clinical, microbiological as well as treatment data and outcomes of IE by Acinetobacter species was performed. A total of 35 studies, containing data of 37 patients, were included. A prosthetic valve was present in 40.5%, while the most common causative pathogen was A. baumannii - A. calcoaceticus complex, followed by A. lwoffii. Aortic valve was the commonest infected site, followed by mitral valve. Diagnosis was set with transthoracic echocardiography in 48.6%, while the diagnosis was set at autopsy in 20%. Fever and sepsis were the commonest clinical presentations, followed by heart failure and embolic phenomena. Aminoglycosides, cephalosporins and carbapenems were the commonest antimicrobials used. Clinical cure was noted in 70.3%, while overall mortality was 32.4%. Development of heart failure was independently associated with mortality by IE. This systematic review thoroughly describes IE by Acinetobacter and provides information on epidemiology, clinical presentation, treatment and outcomes.

A Clinical Study on the Use of Intraventricular Polymyxin B Supplemented by Continuous External Ventricular Drainage in the Treatment of Drug-Resistant Gram-Negative Bacilli Intracranial Infection

Purpose

To investigate the clinical effect of ventricular polymyxin B supplemented by continuous external ventricular drainage in the treatment of intracranial infection with multidrug-resistant (MDR) or extensively drug-resistant (XDR) Gram-negative (G-) bacilli following neurosurgery.

Patients and Methods

A retrospective analysis was performed on 28 patients who had G-bacilli intracranial infection following neurosurgery in our department between January 2017 and December 2019. The patients were treated with intraventricular polymyxin B supplemented by continuous external ventricular drainage. The clinical characteristics, treatment process, cerebrospinal-fluid-related indicators, results and prognosis were analysed.

Results

All of 28 patients developed an infection subsequent to neurosurgery, and cerebrospinal fluid (CSF) cultures demonstrated MDR/XDR G- bacilli, including Acinetobacter baumannii in 14 cases, Klebsiella pneumoniae in 9 cases, Pseudomonas aeruginosa in 3 cases, and Enterobacter cloacae in 2 cases. The ventricular drainage tube remained unobstructed in all patients during treatment, and intraventricular polymyxin B combined with intravenous antibiotics were administered each day. The duration of treatment with intraventricular polymyxin B was 14.96±4.28 days, and the time required to obtain a negative CSF culture was 8.23±4.02 days. The bacterial clearance rate from cerebrospinal fluid was 92.9% (26/28), and the clinical cure rate was 82.1% (23/28). Among them, 18 patients underwent ventriculoperitoneal shunt insertion for hydrocephalus 82.5 (59.5,114.75) days after the infection was cured, and the mortality rate was 17.6% (5/28). There was no significant change in patient blood creatinine levels before and after treatment. Cured patients were followed up for 4 months to 3 years, and no recurrences were observed.

Conclusion

Treatment of intracranial infection with MDR/XDR G- bacilli using early intraventricular polymyxin B supplemented by continuous external ventricular drainage treatment may be a safe and effective treatment strategy.

Dissemination of Plasmid-Mediated Aminoglycoside-Modifying Enzymes Among MDR Acinetobacter baumannii Isolates from a Tertiary Care Egyptian Hospital

Background:

Acinetobacter baumannii is one of the most challenging multidrug-resistant (MDR) nosocomial pathogens worldwide. Aminoglycosides are used for the treatment of A. baumannii infections, however, resistance to aminoglycosides is currently emerging, limiting therapeutic choices.

Objective:

In this study, the prevalence of aminoglycoside resistance and plasmid-mediated mechanisms of aminoglycoside resistance were investigated in A. baumannii clinical isolates collected from ICU patients at a tertiary care hospital in Egypt.

Methods:

The automated Vitek 2 system was used to identify A. baumannii species and determination of the antimicrobial susceptibility pattern. The identification of A. baumannii was confirmed by the detection of the blaOXA-51-like gene intrinsic to this species. Minimum Inhibitory Concentration (MIC) of gentamicin was determined using E-test following the CLSI breakpoints. Isolates were screened for the prevalence and diversity of the plasmid-carried aminoglycoside-modifying enzymes encoding genes aacC1, aadA1, aadB and aphA6. For genetic diversity analysis, the ERIC-PCR method was performed.

Results:

All A. baumannii isolates were MDR with high resistance rates to tested antimicrobials. The resistance rate to gentamicin was 92.9% with elevated MICs (≥ 32 μg/mL). The gentamicin-resistant isolates harboured one or more of the studied genes with the prevalence of aphA6 (81%). ERIC-based genotyping revealed that there was no evidence of A. baumannii clonal dissemination among isolates.

Conclusion:

The study concluded that MDR A. baumannii isolates were highly resistant to gentamicin. The plasmid-carried aminoglycoside-modifying enzymes encoding genes were disseminated among isolates with the AphA6 gene, which was the most prevalent one. The acquisition of more than one aminoglycoside resistance gene was associated with an elevated MIC of gentamicin. Thus, regular surveillance studies of the emerging resistance to antimicrobials and strict measures to control the dissemination of resistance determinants genes are warranted.

Carbapenemases: Transforming Acinetobacter baumannii into a Yet More Dangerous Menace

Acinetobacter baumannii is a common cause of serious nosocomial infections. Although community-acquired infections are observed, the vast majority occur in people with preexisting comorbidities. A. baumannii emerged as a problematic pathogen in the 1980s when an increase in virulence, difficulty in treatment due to drug resistance, and opportunities for infection turned it into one of the most important threats to human health. Some of the clinical manifestations of A. baumannii nosocomial infection are pneumonia; bloodstream infections; lower respiratory tract, urinary tract, and wound infections; burn infections; skin and soft tissue infections (including necrotizing fasciitis); meningitis; osteomyelitis; and endocarditis. A. baumannii has an extraordinary genetic plasticity that results in a high capacity to acquire antimicrobial resistance traits. In particular, acquisition of resistance to carbapenems, which are among the antimicrobials of last resort for treatment of multidrug infections, is increasing among A. baumannii strains compounding the problem of nosocomial infections caused by this pathogen. It is not uncommon to find multidrug-resistant (MDR, resistance to at least three classes of antimicrobials), extensively drug-resistant (XDR, MDR plus resistance to carbapenems), and pan-drug-resistant (PDR, XDR plus resistance to polymyxins) nosocomial isolates that are hard to treat with the currently available drugs. In this article we review the acquired resistance to carbapenems by A. baumannii. We describe the enzymes within the OXA, NDM, VIM, IMP, and KPC groups of carbapenemases and the coding genes found in A. baumannii clinical isolates.

Mechanism of eravacycline resistance in Acinetobacter baumannii mediated by a deletion mutation in the sensor kinase adeS, leading to elevated expression of the efflux pump AdeABC

Acinetobacter baumannii is an important pathogen and presents a major burden in healthcare as strains frequently cause hospital associated opportunistic infections with high mortality rates. Due to increasing numbers of drug resistant A. baumannii strains, newly developed antibiotics are being used to treat infections caused by such strains. One novel synthetic antibiotic of the tetracycline class with activity against A. baumannii is eravacycline. To investigate possible mechanisms of eravacycline resistance, we performed an in vitro evolution experiment to select for an eravacycline resistant strain, with the clinical isolate MDR-ZJ06 as parental strain. We obtained a strain designated MDR-ZJ06-E6 that was able to grow in 64-fold MIC. Genomic mutations were identified by whole genome sequencing, where we found a deletion mutation in the gene adeS. Using complementation experiments, including growth rate determination and antibiotics susceptibility testing, we could confirm that this mutation was responsible for eravacycline resistance of strain MDR-ZJ06-E6. As a mechanism of resistance, we identified a significant overexpression of the efflux pump AdeABC which seems to be regulated by the mutation in adeS in A. baumannii.

Lung Disease Diagnostic Model Through IgG Sensitization to Microbial Extracellular Vesicles

Purpose

Recently, there has been a rise in the interest to understand the composition of indoor dust due to its association with lung diseases such as asthma, chronic obstructive pulmonary disease (COPD) and lung cancer. Furthermore, it has been found that bacterial extracellular vesicles (EVs) within indoor dust particles can induce pulmonary inflammation, suggesting that these might play a role in lung disease.

Methods

We performed microbiome analysis of indoor dust EVs isolated from mattresses in apartments and hospitals. We developed diagnostic models based on the bacterial EVs antibodies detected in serum samples via enzyme-linked immunosorbent assay (ELISA) in this analysis.

Results

Proteobacteria was the most abundant bacterial EV taxa observed at the phylum level while Pseudomonas, Enterobacteriaceae (f) and Acinetobacter were the most prominent organisms at the genus level, followed by Staphylococcus. Based on the microbiome analysis, serum anti-bacterial EV immunoglobulin G (IgG), IgG1 and IgG4 were analyzed using ELISA with EV antibodies that targeted Staphylococcus aureus, Acinetobacter baumannii, Enterobacter cloacae and Pseudomonas aeruginosa. The levels of anti-bacterial EV antibodies were found to be significantly higher in patients with asthma, COPD and lung cancer compared to the healthy control group. We then developed a diagnostic model through logistic regression of antibodies that showed significant differences between groups with smoking history as a covariate. Four different variable selection methods were compared to construct an optimal diagnostic model with area under the curves ranging from 0.72 to 0.81.

Conclusions

The results of this study suggest that ELISA-based analysis of anti-bacterial EV antibodies titers can be used as a diagnostic tool for lung disease. The present findings provide insights into the pathogenesis of lung disease as well as a foundation for developing a novel diagnostic methodology that synergizes microbial EV metagenomics and immune assays.

Postoperative multidrug-resistant Acinetobacter baumannii meningitis successfully treated with intravenous doxycycline and intraventricular gentamicin: A case report

BACKGROUND

Multidrug-resistant Acinetobacter baumannii (MDRAB) has emerged as an increasingly important pathogen that causes nosocomial meningitis. However, MDRAB-associated nosocomial meningitis is rarely reported in children.

CASE SUMMARY

We report the case of a 1-year-old girl with a choroid plexus papilloma, who developed postoperative nosocomial meningitis due to MDRAB. The bacterial strain was sensitive only to tigecycline and colistin, and showed varying degrees of resistance to penicillin, amikacin, ceftriaxone, cefixime, cefotaxime, ciprofloxacin, levofloxacin, gentamicin, meropenem, imipenem, and tobramycin. She was cured with intravenous doxycycline and intraventricular gentamicin treatment.

CONCLUSION

Doxycycline and gentamicin were shown to be effective and safe in the treatment of a pediatric case of MDRAB meningitis.

First isolation of carbapenem-resistant Acinetobacter beijerinckii from an environmental sample

The emergence of opportunistic Acinetobacter spp. in healthcare settings poses a significant threat to public health. The major reasons for nosocomial spread of these species are their abilities to develop and transfer drug resistance against various classes of antibiotics. Considering that Acinetobacter spp. are ubiquitous in nature, can utilize several carbon sources, and reach humans via various pathways, our aim was to obtain information about the environmental strains of this genus. Our first step was to develop and test a multistep isolation procedure based on traditional scientific methods. Antibiotic resistance patterns of the isolated strains were determined, as susceptibility to 12 antibiotics of 7 classes was tested by MIC Test Strip method. Altogether 366 samples (groundwater, surface water, and soil) of 24 sites were investigated and a collection of 37 Acinetobacter isolates was obtained. Among others, clinically important human pathogen Acinetobacter spp., such as A. baumannii, A. johnsonii, and A. gyllenbergii were identified. Three environmental strains were determined as multidrug-resistant including a carbapenem-resistant, hemolytic Acinetobacter beijerinckii strain isolated from a hydrocarbon-contaminated groundwater sample. In summary, it has been found that the applied multistep isolation procedure is applicable to isolate various species of Acinetobacter genus. Based on the antibiotic resistance assay, we can conclude that environmental representatives of Acinetobacter spp. are able to develop multidrug resistance, but at a lower rate than their clinical counterparts.

Outcome Following the Treatment of Ventriculitis Caused by Multi/Extensive Drug Resistance Gram Negative Bacilli; Acinetobacter baumannii and Klebsiella pneumonia

Introduction: CNS ventriculitis is a serious complication following an intracranial insult that demands immediate treatment with broad-spectrum antibiotics in a critical care setting. Infections due to multi/extensive drug resistance (MDR/XDR) microorganisms are very challenging, which may demand an additional approach to the ongoing practice; intravenous and intraventricular administration of antibiotics.

Aim: To study the efficacy and safety of thorough ventricular irrigation followed by daily intraventricular antibiotic administration in patients with MDR/XDR ventriculitis.

Materials and Methods: A retrospective analysis was done on 19 inpatients with ventriculitis caused by Acinetobacter baumannii (AB) or Klebsiella pneumonia (KP), at Shanghai Tenth People's Hospital from January 2016 to October 2017. We reviewed our experience; the role of thorough ventricular irrigation with Colistin mixed normal saline, followed by intraventricular Colistin therapy. Treatment outcomes were evaluated based on the clinical symptoms, Cerebro-Spinal Fluid (CSF) culture, laboratory findings and complications.

Results: A total of 19 patients were included (15 males and 4 females), with a mean age in years of 51, which ranged from 18–67. Fourteen patients had Acinetobacter baumannii (AB) and 5 had Klebsiella pneumoniae (KP). The average CSF sterilization period following ventricular irrigation and intraventricular Colistin was 6 days. Sixteen patients (84%) were cured, and 3 patients (15%) died during the course of the treatment.

Conclusion: In addition to Intraventricular Colistin, thorough ventricular irrigation could increase the cure rate up to 84% in patients suffering from MDR/XDR CNS ventriculitis.

Treatment of severe ventriculitis caused by extensively drug-resistant Acinetobacter baumannii by intraventricular lavage and administration of colistin

Background

Severe ventriculitis (SV) caused by multidrug-resistant bacteria is associated with high morbidity and mortality in neurosurgical patients. This study assessed the outcomes of patients with SV caused by Acinetobacter baumannii who were treated by intraventricular (IVT) lavage and colistin administration.

Methods

This retrospective study included consecutive patients with SV caused by A. baumannii who were admitted at the Neurosurgical Department of Shanghai Tenth People’s Hospital from January 2014 to September 2017. Patients’ medical records, radiographic images, and surgical notes were reviewed. The patients were followed up for at least 6 months after discharge.

Results

A total of 25 patients, including 20 male and five female, were enrolled in this study; the average age was 45.6 years. All patients underwent neurosurgery before infection, and all A. baumannii cultures from cerebrospinal fluid (CSF) showed extensive resistance to the tested antibiotics except for tigecycline and colistin. All the patients underwent IVT lavage followed by daily administration of colistin after surgery; 24 patients received a daily colistin dose of 100,000 IU, while one received 50,000 IU. The patients also received tigecycline-based systemic antibiotic treatment. The mean duration of IVT colistin was 13.4±2.8 days. The time required to obtain a negative CSF culture was 8.9±4.0 days. Of the 20 patients who were cured, eight underwent shunt surgery due to hydrocephalus before they were discharged to a rehabilitation center. Five patients died, including one who was re-admitted due to recurrence 1 month after discharge.

Conclusions

IVT lavage and colistin treatment may be an effective treatment for SV caused by extensively drug-resistant A. baumannii. Future studies with a larger sample size may be needed to verify the findings in this study.

Multidrug-Resistant Acinetobacter baumannii Ventriculostomy-Related Infection, Treated by a Colistin, Tigecycline, and Intraventricular Fibrinolysis

BACKGROUND

Acinetobacter baumannii meningitis and ventriculitis are difficult issues, because of the low diffusion of antibiotics in the cerebrospinal fluid and bacterial multidrug resistance. The presence of an infected intraventricular hematoma, constituting an equivalent of undrained abscess, may promote biofilm formation and failure of medical treatment.

CASE DESCRIPTION

In this case of ventriculostomy-related infection after ventricular hemorrhage, Acinetobacter baumannii was sensitive only to colistin and tigecycline. Despite a combination therapy involving intraventricular injections of colistin, we observed clinical and bacteriologic failure. Therefore, at day 4 of antibiotic therapy, we performed intraventricular fibrinolysis, which dissolved the clot, enabling sterilization of the cerebrospinal fluid after 48 hours.

CONCLUSION

This clinical case suggests the usefulness of intraventricular fibrinolysis to lyse the clot and optimize the action of antibiotics.

Urinary tract infection by Acinetobacter baumannii and Pseudomonas aeruginosa: evolution of antimicrobial resistance and therapeutic alternatives

Purpose. Acinetobacter baumannii and Pseudomonas aeruginosa are responsible for numerous nosocomial infections. The objective of this study was to determine the development of their susceptibility to ten antibiotics and the antibiotic consumption of patients with suspicion of urinary tract infection (UTI).Methodology. A retrospective study was conducted on the susceptibility profiles of A. baumannii and P. aeruginosa isolates from 749 urine samples gathered between January 2013 and December 2016, and on the consumption of imipenem, meropenem and piperacillin-tazobactam between 2014 and 2016.Results. Hospital patients were the source of 82 (91.1 %) of the 90 A. baumannii isolates detected and 555 (84.2 %) of the 659 P. aeruginosa isolates. Globally, the lowest percentage susceptibility values were found for fosfomycin, aztreonam and ciprofloxacin, while colistin continued to be the most active antibiotic in vitro. In 2016, the susceptibility of A. baumannii to carbapenem and piperacillin-tazobactam decreased to very low values, while the susceptibility of P. aeruginosa to carbapenem remained stable but its susceptibility to piperacillin-tazobactam decreased. There was a marked increase in the consumption of piperacillin-tazobactam.Conclusion. In our setting, it is no longer possible to use carbapenems and piperacillin-tazobactam for empirical treatment of UTI due to A. baumannii or to use piperacillin-tazobactam for empirical treatment of UTI due to P. aeruginosa. Colistin was found to be the most active antibiotic in vitro. There was a marked increase in the consumption of piperacillin-tazobactam.

Trans-Cinnamaldehyde and Eugenol Increase Acinetobacter baumannii Sensitivity to Beta-Lactam Antibiotics

Multi-drug resistant (MDR) Acinetobacter baumannii is a major nosocomial pathogen causing a wide range of clinical conditions with significant mortality rates. A. baumannii strains are equipped with a multitude of antibiotic resistance mechanisms, rendering them resistant to most of the currently available antibiotics. Thus, there is a critical need to explore novel strategies for controlling antibiotic resistance in A. baumannii. This study investigated the efficacy of two food-grade, plant-derived antimicrobials (PDAs), namely trans-cinnamaldehyde (TC) and eugenol (EG) in decreasing A. baumannii’s resistance to seven β-lactam antibiotics, including ampicillin, methicillin, meropenem, penicillin, aztreonam, amoxicillin, and piperacillin. Two MDR A. baumannii isolates (ATCC 17978 and AB 251847) were separately cultured in tryptic soy broth (∼6 log CFU/ml) containing the minimum inhibitory concentration (MIC) of TC or EG with or without the MIC of each antibiotic at 37°C for 18 h. A. baumannii strains not exposed to the PDAs or antibiotics served as controls. Following incubation, A. baumannii counts were determined by broth dilution assay. In addition, the effect of PDAs on the permeability of outer membrane and efflux pumps in A. baumannii was measured. Further, the effect of TC and EG on the expression of A. baumannii genes encoding resistance to β-lactam antibiotics (blaP), efflux pumps (adeABC), and multi-drug resistant protein (mdrp) was studied using real-time quantitative PCR (RT-qPCR). The experiment was replicated three times with duplicate samples of each treatment and control. The results from broth dilution assay indicated that both TC and EG in combination with antibiotics increased the sensitivity of A. baumannii to all the tested antibiotics (P < 0.05). The two PDAs inhibited the function of A. baumannii efflux pump, (AdeABC), but did not increase the permeability of its outer membrane. Moreover, RT-qPCR data revealed that TC and EG down-regulated the expression of majority of the genes associated with β-lactam antibiotic resistance, especially blaP and adeABC (P < 0.05). The results suggest that TC and EG could potentially be used along with β-lactam antibiotics for controlling MDR A. baumannii infections; however, their clinical significance needs to be determined using in vivo studies.

The Broad-Spectrum Antimicrobial Potential of [Mn(CO)4(S2CNMe(CH2CO2H))], a Water-Soluble CO-Releasing Molecule (CORM-401): Intracellular Accumulation, Transcriptomic and Statistical Analyses, and Membrane Polarization

AIMS

Carbon monoxide (CO)-releasing molecules (CORMs) are candidates for animal and antimicrobial therapeutics. We aimed to probe the antimicrobial potential of a novel manganese CORM.

RESULTS

[Mn(CO)₄S₂CNMe(CH₂CO₂H)], CORM-401, inhibits growth of Escherichia coli and several antibiotic-resistant clinical pathogens. CORM-401 releases CO that binds oxidases in vivo, but is an ineffective respiratory inhibitor. Extensive CORM accumulation (assayed as intracellular manganese) accompanies antimicrobial activity. CORM-401 stimulates respiration, polarizes the cytoplasmic membrane in an uncoupler-like manner, and elicits loss of intracellular potassium and zinc. Transcriptomics and mathematical modeling of transcription factor activities reveal a multifaceted response characterized by elevated expression of genes encoding potassium uptake, efflux pumps, and envelope stress responses. Regulators implicated in stress responses (CpxR), respiration (Arc, Fnr), methionine biosynthesis (MetJ), and iron homeostasis (Fur) are significantly disturbed. Although CORM-401 reduces bacterial growth in combination with cefotaxime and trimethoprim, fractional inhibition studies reveal no interaction.

INNOVATION

We present the most detailed microbiological analysis yet of a CORM that is not a ruthenium carbonyl. We demonstrate CO-independent striking effects on the bacterial membrane and global transcriptomic responses.

CONCLUSIONS

CORM-401, contrary to our expectations of a CO delivery vehicle, does not inhibit respiration. It accumulates in the cytoplasm, acts like an uncoupler in disrupting cytoplasmic ion balance, and triggers multiple effects, including osmotic stress and futile respiration. Rebound Track: This work was rejected during standard peer review and rescued by rebound peer review (Antioxid Redox Signal 16: 293-296, 2012) with the following serving as open reviewers: Miguel Aon, Giancarlo Biagini, James Imlay, and Nigel Robinson. Antioxid. Redox Signal. 28, 1286-1308.

Antibiofilm activity of an EDTA-containing nanoemulsion on multidrug-resistant Acinetobacter baumannii

Acinetobacter baumannii have evolved as an exceedingly troublesome pathogenic microorganisms and prevention and controlling this pathogen is considered to be a public health problem. Nanoemulsions (NE) are a distinctive type of decontaminator produced by integration of immiscible oil phase with aqueous phase under extreme shear forces. The effectiveness of NEs and their components was determined against four stains of A. baumannii by MBC, adherence assay, biofilm assay and SEM studies. NE dilutions ranging from 125 to 225 reduced adhesion by from 61.8 to 99.9% in NE-treated groups (p<.05) as determined by MBC. Four-day-old A. baumannii biofilms were treated with NE; LIVE/DEAD staining showed dead cell intensity of 56.2-92.0% in NE-treated groups. After NE treatment and observation by SEM, cell surfaces appeared to be remarkably disintegrated. Irregular boundaries were observed and margins of cell walls were unclear. The anti-adherence, anti-biofilm and morphological disruption effects of NE suggest that this material could be useful for the development of promising antimicrobial agents.

Clinical Characteristics of Acinetobacter baumannii Infection in Solid-Organ Transplant Recipients

OBJECTIVES

Acinetobacter baumannii, depending on the immune status of the host, may result in one of the most serious hospital infections. Infections involving A. baumannii infection have been recently rising. However, little is known about the clinical features of A. baumannii infection in solid-organ transplant recipients. We aimed to share our clinical experiences with A. baumannii infection in our transplant recipients.

MATERIALS AND METHODS

Between 2011 and 2017, 41 solid-organ transplant patients developed A. baumannii infection at Baskent University Hospital. Medical records were reviewed, and patient demographics, microbiology results, and overall outcome data were noted.

RESULTS

Of 41 solid-organ transplant patients with A. baumannii infection, 29 were male and 12 were female patients with mean age of 47.15 ± 13.24 years. Our infection rate with A. baumannii infection was 6.1%. The most common sites of infection were deep tracheal aspirate (48.8%)and bloodstream (36.6%). Onset of infection 1 year posttransplant was identified in 58.5% of recipients. Risk factors included presence of invasive procedures (56.1%) and administration of high-dose corticosteroids for rejection 1 year before infection (68.3%). Thirty-day mortality rate was 41.5% (17/41 patients) and was not associated with the infection site, microbiological cure, clinical cure, and drug resistance in our study group.

CONCLUSIONS

Acinetobacter baumannii is an important cause of hospital-acquired infection and mortality worldwide. A major problem with A. baumannii infection is delayed initiation of appropriate antibiotic treatment and the rising numbers of extensively drug-resistant organisms. Predicting the potential risk factors, especially in the already at-risk solid-organ transplant population, has an important role in patient outcomes.

Characterization of multidrug-resistant strains isolated from medical intensive care units in Cali - Colombia

Introduction

The extensive use of antibiotics has led to the emergence of multi-resistant strains in some species of the genus Acinetobacter.

Objective

To investigate the molecular characteristics of multidrug-resistant of Acinetobacter ssp. strains isolated from 52 patients collected between March 2009 and July 2010 in medical intensive care units in Cali - Colombia.

Methods

The susceptibility to various classes of antibiotics was determined by disc diffusion method, and the determination of the genomic species was carried out using amplified ribosomal DNA restriction analysis (ARDRA) and by sequencing of the 16s rDNA gene. Also, the genes of beta-lactamases as well as, integrases IntI1 and IntI2 were analyzed by PCR method.

Results

The phenotypic identification showed that the isolates belong mainly to A. calcoaceticus- A. baumannii complex. All of them were multi-resistant to almost the whole antibiotics except to tigecycline and sulperazon, and they were grouped into five (I to V) different antibiotypes, being the antibiotype I the most common (50.0%). The percent of beta-lactamases detected was: blaTEM (17.3%), blaCTX-M (9.6%), blaVIM (21.2%), blaIMP (7.7%), blaOXA-58 (21.2%), and blaOXA-51 (21.2%). The phylogenetic tree analysis showed that the isolates were clustering to A. baumannii (74.1%), A. nosocomialis (11.1%) and A. calcoaceticus (7.4 %). Besides, the integron class 1 and class 2 were detected in 23.1% and 17.3% respectively.

Conclusion

The isolates were identified to species A. baumanii mainly, and they were multiresistant. The resistance to beta-lactams may be by for presence of beta-lactamases in the majority of the isolates.

Functional Characterization of Acinetobacter baumannii Lacking the RNA Chaperone Hfq

The RNA chaperone Hfq is involved in the riboregulation of diverse genes via small RNAs. Recent studies have demonstrated that Hfq contributes to the stress response and the virulence of several pathogens, and the roles of Hfq vary among bacterial species. Here, we attempted to elucidate the role of Hfq in Acinetobacter baumannii ATCC 17978. In the absence of hfq, A. baumannii exhibited retarded cell growth and was highly sensitive to environmental stress, including osmotic and oxidative pressure, pH, and temperature. Compared to the wild-type, the Hfq mutant had reduced outer membrane vesicles secretion and fimbriae production as visualized by atomic force microscopy. The absence of hfq reduced biofilm formation, airway epithelial cell adhesion and invasion, and survival in macrophage. Further, the hfq mutant induced significantly higher IL-8 levels in airway epithelial cells, which would promote bacterial clearance by the host. In addition to results similar to those reported for other bacteria, our findings demonstrate that Hfq is required in the regulation of the iron-acquisition system via downregulating the bauA and basD genes, the stress-related outer membrane proteins carO, A1S_0820, ompA, and nlpE, and the stress-related cytosolic proteins uspA and groEL. Our data indicate that Hfq plays a critical role in environmental adaptation and virulence in A. baumannii by modulating stress responses, surface architectures, and virulence factors. This study is the first to illustrate the functional role of Hfq in A. baumannii.

Antibacterial activity of exogenous glutathione and its synergism on antibiotics sensitize carbapenem-associated multidrug resistant clinical isolates of Acinetobacter baumannii

A major clinical impact of A. baumannii is hospital-acquired infections including ventilator-associated pneumonia. The treatment of this pathogen is often difficult due to its innate and acquired resistance to almost all commercially available antibiotics. Infections with carbapenem-associated multidrug resistant A. baumannii is the most problematic. Glutathione is a tripeptide thiol-antioxidant and antibacterial activity of exogenous glutathione was reported in some bacteria. However, clinical relevance and molecular details of the antibacterial activity of glutathione are currently unclear. Seventy clinical isolates of A. baumannii including 63 carbapenem-associated multidrug resistant isolates and a type strain A. baumannii ATCC 19606 were used to determine minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). Fractional inhibitory concentration (FIC) and time-killing activity with meropenem and/or glutathione were also determined in the carbapenem-associated multidrug resistant isolates. In addition, the roles of exogenous glutathione in multidrug efflux pumps and β-lactamase production were examined. Levels of MIC and MBC were ranged from 10 to 15mM of exogenous glutathione. All tested carbapenem-associated multidrug resistant isolates were sensitized by all tested antibiotics in combination with subinhibitory concentrations of glutathione. FIC levels of glutathione with carbapenem (meropenem) were all<0.5 and the carbapenem-associated multidrug resistant isolates were killed by subinhibitory concentrations of both glutathione and meropenem at>2log10 within 12h, suggesting glutathione synergistically interacts with meropenem. The roles of multidrug efflux pumps and β-lactamase production were excluded for the glutathione-mediated antibiotic susceptibility. Overall results demonstrate that the antibacterial activity of glutathione is clinically relevant and its synergism on antibiotics sensitizes clinical isolates of A. baumannii regardless of their resistance or susceptibility to antibiotics. This finding suggests that exogenous glutathione alone and/or in combination with existing antibiotics may be applicable to treat infections with carbapenem-associated multidrug resistant A. baumannii.

Successful treatment of multidrug-resistant Acinetobacter baumannii meningitis with ampicillin sulbactam in primary hospital

Introduction: Acinetobacter baumannii nosocomial infections, especially those due to multi-drug resistant strains, are increasingly detected. We want to find the effective treatment measures about multi-resistant Acinetobacter baumannii infections through this research.Methodology: The clinical features and the outcomes of twelve cases of nosocomial Acinetobacter baumannii meningitis treated with ampicillin sulbactam and intrathecal use of amikacin are reported in primary hospital. All the patients had fever, neck stiffness or meningeal signs, and a low consciousness level, and in their cerebrospinal fluid (CSF), pleocytosis, a low glucose level, and an elevated protein level were noted. For all CSF isolates were resistant to at least two antibiotics used in empirical therapy (third and fourth generation cephalosporins, carbapenems or piperacillin/tazobactam). Four cases sputum culture prompted the growth of Acinetobacter baumannii. Two CSF isolates were intermediate resistant to ampicillin sulbactam, only sensitive to amikacin. The two patients were treated with ampicillin sulbactam and intrathecal use of amikacin.Results: The dosages and the duration of treatment with ampicillin sulbactam were 2 g/1 g every 6 hours and 9-21days. Eleven patients were cured and one patient died of meningitis (8.3%). This patient died of severe respiratory Acinetobacter baumannii infection and severe sepsis. One patient had mild nausea and discomfort, given metoclopramide therapy. There were no serious side effects with the ampicillin sulbactam treatment.Conclusions: In conclusion, ampicillin sulbactam may be effective as therapy for meningitis caused by Acinetobacter baumannii resistant to imipenem and other β-lactam drugs. Meanwhile, continuous lumbar external drainage and intermittent intrathecal use of amikacin were necessary methods.

RAGE-Mediated Suppression of Interleukin-10 Results in Enhanced Mortality in a Murine Model of Acinetobacter baumannii Sepsis

The receptor for advanced glycation end products (RAGE) is a pattern recognition receptor capable of recognizing multiple pathogen-associated and danger-associated molecular patterns that contributes to the initiation and potentiation of inflammation in many disease processes. During infection, RAGE functions to either exacerbate disease severity or enhance pathogen clearance depending on the pathogen studied. Acinetobacter baumannii is an opportunistic human pathogen capable of causing severe infections, including pneumonia and sepsis, in impaired hosts. The role of RAGE signaling in response to opportunistic bacterial infections is largely unknown. In murine models of A. baumannii pneumonia, RAGE signaling alters neither inflammation nor bacterial clearance. In contrast, RAGE^-/- mice systemically infected with A. baumannii exhibit increased survival and reduced bacterial burdens in the liver and spleen. The increased survival of RAGE^-/- mice is associated with increased circulating levels of the anti-inflammatory cytokine interleukin-10 (IL-10). Neutralization of IL-10 in RAGE^-/- mice results in decreased survival during systemic A. baumannii infection that mirrors that of wild-type (WT) mice, and exogenous IL-10 administration to WT mice enhances survival in this model. These findings demonstrate the role for RAGE-dependent IL-10 suppression as a key modulator of mortality from Gram-negative sepsis.

The Impact of Antibiotic Consumption on Development of Acinetobacter Baumannii Resistance

Aim:

The aim of this study was to examine the impact of antibiotic consumption on development of antimicrobial resistance in Acinetobacter baumannii.

Material and Methods:

The study was conducted in University Clinical Center of Sarajevo. In our retrospective study Acinetobacter baumannii isolated in period from July 1^st 2009 to December 31^st 2012. Isolates were detected from different clinical samples including urine, wound swab, blood, bronchial aspirate and other samples which were collected from patients situated on various hospital wards. Clinical isolates belonged to one per patient in a given period of time.

Results:

Antimicrobial resistance was interpreted according to CLSI breakpoints. Consumption of antibiotics was analyzed according to recommendations of the ESAC-Net and current Acinetobacter baumannii classification. Pearson’s correlation showed a positive correlation between gentamicin consumption and emerging of resistance (p = 0.023).

Conclusion:

Increase in the antimicrobial use was followed with an increase in resistance of Acinetobacter baumannii isolates. Monitoring of antibiotic resistance and consumption is of a great importance in order to reduce the emergence and spread of antimicrobial resistant organisms in the health care settings.

Variables determining mortality in patients with Acinetobacter baumannii meningitis/ventriculitis treated with intrathecal colistin

AIM

To examine the variables associated with mortality in patients with Acinetobacter baumannii-related central nervous system infections treated with intrathecal colistin.

MATERIALS AND METHODS

This multi-centre retrospective case control study included patients from 11 centres in Turkey, as well as cases found during a literature review. Only patients with CNS infections caused by multidrug-resistant or extensively drug-resistant Acinetobacter baumannii treated with intrathecal colistin were included in this study. The variables associated with mortality were determined by dividing the patients into groups who died or survived during hospitalisation, and who died or survived from Acinetobacter meningitis.

RESULTS

Among the 77 cases enrolled in the study, 35 were found through a literature review and 42 were cases from our centres. Forty-four cases (57.1%) were male and the median age was 48 years (range: 20-78 years). Thirty-seven patients (48%) died during hospitalisation. The variables associated with increased all-cause mortality during hospitalisation included old age (odds ratio, 1.035; 95% confidence interval (CI), 1.004-1.067; p=0.026) and failure to provide cerebrospinal fluid sterilisation (odds ratio, 0.264; 95% confidence interval, 0.097-0.724; p=0.01). There is a trend (P=0.062) towards higher mortality with using of meropenem during meningitis treatment. Fifteen cases (19%) died from meningitis. There were no significant predictors of meningitis-related mortality.

CONCLUSIONS

The mortality rate for central nervous system infections caused by multidrug-resistant or extensively drug-resistant Acinetobacter baumannii is high. Old age and failure to provide CSF sterilisation are associated with increased mortality during hospitalisation.

Bibliometric analysis of global scientific research on carbapenem resistance (1986-2015)

BACKGROUND

Antimicrobial resistance is a global public health challenge and carbapenem resistance, in particular, is considered an urgent global health threat. This study was carried out to give a bibliometric overview of literature on carbapenem resistance. In specific, number of publications, top productive countries and institutes, highly cited articles, citation analysis, co-authorships, international collaboration, top active authors, and journals publishing articles on carbapenem resistance were analyzed and discussed.

METHODS

Specific keywords pertaining to carbapenem resistance were used in Scopus database. Quantitative and qualitative analysis of retrieved data were presented using appropriate bibliometric indicators and visualization maps.

RESULTS

A total of 2617 journal articles were retrieved. The average number of citations per article was of 21.47. The growth of publications showed a dramatic increase from 2008 to 2015. Approximately 9 % of retrieved articles on carbapenem resistance were published in Antimicrobial Agents and Chemotherapy journal. Retrieved articles were published by 102 different countries. The United States of America (USA) contributed most with 437 (16.70 %) articles followed by China with 257 (9.82 %) articles. When productivity was stratified by population size, Greece ranked first followed by France. Greece also ranked first when data were stratified by gross domestic product (GDP). Asian countries have lesser international collaboration compared with other countries in the top ten list. Five of top ten productive institutes were Europeans (France, the UK, Greece, Italy, and Switzerland) and two were Asians (China and South Korea). Other active institutes included an Israeli and a Brazilian institute. Four of the top ten cited articles were published in Antimicrobial Agents and Chemotherapy journal and two were published in The Lancet Infectious Diseases.

CONCLUSION

There was a dramatic increase in number of publications on carbapenem resistance in the past few years. These publications were produced from different world regions including Asia, Europe, Middle East, and Latin America. International collaboration needs to be encouraged particularly for researchers in Asia. Molecular biology and epidemiology dominated the theme of the top ten cited articles on carbapenem resistance. This bibliometric study will hopefully help health policy makers in planning future research and allocating funds pertaining to carbapenem resistance.