Therapeutic options for Acinetobacter baumannii infections

Multiple host colonization and differential expansion of multidrug-resistant ST25-Acinetobacter baumannii clades

The Acinetobacter baumannii clonal lineage ST25 has been identified in humans and animals and found associated with outbreaks globally. To highlight possible similarities among ST25 A. baumannii of animal and human origins and to gather clues on the dissemination and evolution of the ST25 lineage, we conducted a phylogenetic analysis on n = 106 human and n = 35 animal A. baumannii ST25 genomes, including 44 sequenced for this study. Resistance genes and their genetic background were analyzed, as well. ST25 genomes are clustered into four clades: two are widespread in South America, while the other two are largely distributed in Europe, Asia and America. One particular clade was found to include the most recent strains and the highest number of acquired antibiotic resistance genes. OXA-23-type carbapenemase was the most common. Other resistance genes such as blaNDM-1, blaPER-7, and armA were found embedded in complex chromosomal regions present in human isolates. Genomic similarity among multidrug resistant ST25 isolates of either animal or human origin was revealed, suggesting cross-contaminations between the two sectors. Tracking the clonal complex ST25 between humans and animals should provide new insights into the mode of dissemination of these bacteria, and should help defining strategies for preserving global health.

Healthcare Equipment and Personnel Reservoirs of Carbapenem-Resistant Acinetobacter baumannii Epidemic Clones in Intensive Care Units in a Tunisian Hospital

Carbapenem-resistant Acinetobacter baumannii (CRAB) strains can cause severe and difficult-to-treat infections in patients with compromised general health. CRAB strains disseminate rapidly in nosocomial settings by patient-to-patient contact, through medical devices and inanimate reservoirs. The occurrence of CRAB in patients residing in the intensive care units (ICUs) of the Sahloul University hospital in Sousse, Tunisia is high. The objective of the current study was to determine whether the surfaces of items present in five ICU wards and the medical personnel there operating could serve as reservoirs for CRAB strains. Furthermore, CRAB isolates from patients residing in the ICUs during the sampling campaign were analyzed for genome comparison with isolates from the ICUs environment. Overall, 206 items were screened for CRAB presence and 27 (14%) were contaminated with a CRAB isolate. The items were located in several areas of three ICUs. Eight of the 54 (15%) screened people working in the wards were colonized by CRAB on the hands. Patients residing in the ICUs were infected with CRAB strains sharing extensive genomic similarity with strains recovered in the nosocomial environment. The strains belonged to three sub-clades of the internationally disseminated clone (ST2). A clone emerging in the Mediterranean basin (ST85) was detected as well. The strains were OXA-23 or NDM-1 producers and were also pan-aminoglycoside resistant due to the presence of the armA gene. Hygiene measures are urgent to be implemented in the Sahloul hospital to avoid further spread of difficult-to-treat CRAB strains and preserve health of patients and personnel operating in the ICU wards.

A novel vaccine candidate against A. baumannii based on a new OmpW family protein (OmpW2); structural characterization, antigenicity and epitope investigation, and in-vivo analysis

A. baumannii is an MDR pathogen whose SARS-CoV-2 has recently increased its mortality rate in hospitalized patients. So, the virulence factors investigation and design of a vaccine against this bacterium seem to be critical. In this regard, the OmpW2 protein was structurally characterized by this study, and its B-T cell epitopes were mapped by bioinformatic tools. In-vivo analyses were employed to verify the immunogenicity of this protein and its selected epitopes. The results indicated that OmpW2 is a conserved virulent antigen, not toxic for the host, and not similar to the human or mouse proteome. A putative interaction between OmpW2 and a Fe-S-cluster redox enzyme was detected. Based on the results, OmpW2 belongs to the OmpW superfamily and eight beta sheets have been predicted in its tight beta-barrel structure. Several exposed epitopes were detected in the OmpW2 sequence and structure, and a sub-unit potential vaccine was generated based on the epitopes. The ELISA results indicated that after the second booster vaccination of BALB/c mice with the whole OmpW2 protein or its sub-unit fragment, the IgG titer significantly raised (p < 0.05). The mortality rate and the bacterial burden in the lung, liver, kidney, and spleen in both passive and active immunized mice were significantly decreased (p ≤ 0.001). In-vivo experiments confirmed that the OmpW2 whole protein and its sub-unit fragment induce the host immune system and can be applied to design a commercial vaccine or diagnostic kit.

Assesment of polyphenolic compounds against biofilms produced by clinical Acinetobacter baumannii strains using in silico and in vitro models

Several types of microbial infections are caused by Acinetobacter baumanii that has developed resistance to antimicrobial agents. We therefore investigated the role of plant polyphenols against A. baumannii using in silico and in vitro models. The clinical strains of A. baumannii were investigated for determination of resistance pattern and resistance mechanisms including efflux pump, extended spectrum beta lactamase, phenotype detection of AmpC production, and Metallo-β-lactamase. The polyphenolic compounds were docked against transcription regulator BfmR (PDB ID 6BR7) and antimicrobial, antibiofilm, and anti-quorum sensing activities were performed. The antibiogram studies showed that all isolated strains were resistant. Strain A77 was positive in Metallo-β-lactamase production. Similarly, none of strains were producers of AmpC, however, A77, A76, A75 had active efflux pumps. Molecular docking studies confirmed a strong binding affinity of Rutin and Catechin towards transcription regulator 6BR7. A significant antimicrobial activity was recorded in case of quercetin and syringic acid (MIC 3.1 µg/mL) followed by vanillic acid and caffeic acid (MIC 12.5 µg/mL). All tested compounds presented a strong antibiofilm activity against A. baumanii strain A77 (65 to 90%). It was concluded that all tested polyphenols samples posess antimicrobial and antibiofilm activities, and hence they may be utilized to treat multidrug resistance A. baumannii infections.

Total Synthesis of a Pentasaccharide O-Glycan from Acinetobacter baumannii

Acinetobacter baumannii is a Gram-negative bacteria associated with drug resistance and infection in healthcare settings. An understanding of both the biological roles and antigenicity of surface molecules of this organism may provide an important step in the prevention and treatment of infection through vaccination or the development of monoclonal antibodies. With this in mind, we have performed the multistep synthesis of a conjugation-ready pentasaccharide O-glycan from A. baumannii with a longest linear synthetic sequence of 19 steps. This target is particularly relevant due to its role in both fitness and virulence across an apparently broad range of clinically relevant strains. Synthetic challenges include formulating an effective protecting group scheme as well as the installation of a particularly difficult glycosidic linkage between the anomeric position of a 2,3-diacetamido-2,3-dideoxy-D-glucuronic acid and the 4-position of D-galactose.

Total Synthesis of an All-1,2-cis-Linked Repeating Unit from the Acinetobacter baumannii D78 Capsular Polysaccharide

Chemical synthetic efforts have resulted in the preparation of the assigned tetrasaccharide repeating subunit from the Acinetobacter baumannii KL4-associated capsular polysaccharide. A convergent synthetic strategy hinging on a 1,2-cis-selective [2+2] glycosylation to generate the fully protected tetrasaccharide was key to the success of this synthesis.

Dynamic Gene Clusters Mediating Carbapenem-Resistant Acinetobacter baumannii Clinical Isolates

Acinetobacter baumanni (A. baumannii), a nonfermenting Gram-negative bacterium, has recently been associated with a broad range of nosocomial infections. To gain more meaningful insight into the problem of nosocomial illnesses caused by the multidrug-resistant (MDR) A. baumannii, as well as the factors that increase the risk of catching these infections, this investigation included a total of 86 clinical A. baumannii infections. Repetitive extragenic palindromic (REP)-PCR was used to investigate imipenem-resistant A. baumannii isolates for dynamic gene clusters causing carbapenem resistance. Four distinct A. baumannii lineages were found in the REP-PCR-DNA fingerprints of all isolates, with 95% of the samples coming from two dominant lineages. Imipenem, amikacin, and ciprofloxacin were less effective against genotype (A) isolates because of enhanced antibiotic tolerance. Lastly, to gain more insight into the mode of action of imipenem, we explored the binding affinity of imipenem toward different Acinetobacter baumannii OXA beta-lactamase class enzymes.

DcaP porin and its epitope-based subunit promise effective vaccines against Acinetobacter baumannii; in-silico and in-vivo approaches

A. baumannii is a multi-drug resistant pathogen with a relatively high mortality rate. To date, no vaccine has been approved against this bacterium. DcaP is a high abundance porin during infection that its structure has been recently determined, but no information about its immunogenic properties has been reported yet. So, in this study DcaP properties were analyzed and its vaccine potential was evaluated. The results showed this porin is an extremely conserved antigen with no allergenicity and toxicity that bears no resemblance to human proteins. Six potential immunogen areas in the DcaP sequence were detected based on in-silico B and T-cell epitope mapping and other approaches. A multiple-epitope potential vaccine was designed based on the predicted linear epitopes and amplified by overlap extension PCR technique. In-vivo results indicated that active and passive immunization of mice with the DcaP protein or its designed subunit vaccine raises the antibody titers and decreases the mortality rate of the immunized mice infected with A. baumannii. Based on the results, DcaP and its indicated immunogen regions can be considered as a peptide or subunit vaccine. The immunogen regions could also be applied in multivalent subunit vaccine candidates against A. baumannii and other bacteria.

Physicochemical and structural characterization, epitope mapping and vaccine potential investigation of a new protein containing Tetratrico Peptide Repeats of Acinetobacter baumannii: An in-silico and in-vivo approach

Acinetobacter baumannii is an opportunistic multidrug-resistant pathogen that causes a significant mortality rate. The proteins containing Tetratrico Peptide Repeats (TPRs) are involved in the pathogenicity and virulence of bacteria and have different roles such as transfer of bacterial virulence factors to host cells, binding to the host cells and inhibition of phagolysosomal maturation. So, in this study, physicochemical properties of a new protein containing TPRs in A. baumannii which was named PcTPRs1 by this study were characterized and its 3D structure was predicted by in-silico tools. The protein B and T cell epitopes were mapped and its vaccine potential was in-silico and in-vivo investigated. Domain analysis indicated that the protein contains the Flp pilus assembly protein TadD domain which has three TPRs. The helix is dominant in the protein structure, and this protein is an outer membrane antigen which, is extremely conserved among A. baumannii strains; thus, has good properties to be applied as a recombinant vaccine. The best-predicted and refined model was applied in ligand-binding sites and conformational epitopes prediction. Based on epitope mapping results, several epitopes were characterized which could stimulate both immune systems. BLAST results showed the introduced epitopes are completely conserved among A. baumannii strains. The in-vivo analysis indicates that a 101 amino acid fragment of the protein which contains the best selected epitope, can produce a good protectivity against A. baumannii as well as the whole TPR protein and thus could be investigated as an effective subunit and potential vaccines.

Anti-Omp34 antibodies protect against Acinetobacter baumannii in a murine sepsis model

Acinetobacter baumannii, an opportunistic extracellular pathogen is one of the major causes of nosocomial infections. Omp34, also known as Omp33-36, is a bacterial porin protein involved in the virulence and fitness of this pathogen by adhesion to the host cell. This antigen nominated as an appropriate candidate for immunization against A. baumannii. In this study, the expression of the recombinant Omp34 (rOmp34) was carried out in E. coli BL21 (DE3). The immunogenicity of the rOmp34 in A. baumannii was studied in a murine sepsis model. Antibody response in mice injected with the recombinant protein was assessed using indirect ELISA. Bactericidal activity of rOmp34-immunized mice sera (1:10 dilution) against A. baumannii ATCC 19606 after 0, 1, 2, 4, and 8 h of incubation at 37 °C was assessed. In addition to survival rate, load of bacteria in liver and spleen of the infected mice were evaluated. A high titer of specific antibody equivalent to optical density of 1.54 ± 0.06 against rOmp34 was elicited in the immunized mice sera. Viability of the A. baumannii incubated 8 h with immunized mice sera was 64%. Homogenized liver and spleen samples of the control mice challenged with A. baumannii were loaded with 8 × 10³ and 9 × 10³ CFU per gram tissue respectively 48 h post-challenge as against complete clearance of A. baumannii in the immunized group. The protective immunity was achieved by challenging the mice groups with 5 × LD₅₀ of live A. baumannii. Omp34 can be nominated as an immunogen that can bring about protection against Acinetobacter baumannii.

CRISPR-Cas, a Revolution in the Treatment and Study of ESKAPE Infections: Pre-Clinical Studies

One of the biggest threats we face globally is the emergence of antimicrobial-resistant (AMR) bacteria, which runs in parallel with the lack in the development of new antimicrobials. Among these AMR bacteria pathogens belonging to the ESKAPE group can be highlighted (Enterococcus spp., Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter spp.) due to their profile of drug resistance and virulence. Therefore, innovative lines of treatment must be developed for these bacteria. In this review, we summarize the different strategies for the treatment and study of molecular mechanisms of AMR in the ESKAPE pathogens based on the clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated (Cas) proteins’ technologies: loss of plasmid or cellular viability, random mutation or gene deletion as well directed mutations that lead to a gene’s loss of function.

Advances in Bacteriophage Therapy against Relevant MultiDrug-Resistant Pathogens

The increase of multiresistance in bacteria and the shortage of new antibiotics in the market is becoming a major public health concern. The World Health Organization (WHO) has declared critical priority to develop new antimicrobials against three types of bacteria: carbapenem-resistant A. baumannii, carbapenem-resistant P. aeruginosa and carbapenem-resistant and ESBL-producing Enterobacteriaceae. Phage therapy is a promising alternative therapy with renewed research in Western countries. This field includes studies in vitro, in vivo, clinical trials and clinical cases of patients receiving phages as the last resource after failure of standard treatments due to multidrug resistance. Importantly, this alternative treatment has been shown to be more effective when administered in combination with antibiotics, including infections with biofilm formation. This review summarizes the most recent studies of this strategy in animal models, case reports and clinical trials to deal with infections caused by resistant A. baumannii, K. pneumoniae, E. coli, and P. aeruginosa strains, as well as discusses the main limitations of phage therapy.

Correlation between Acinetobacter baumannii Resistance and Hospital Use of Meropenem, Cefepime, and Ciprofloxacin: Time Series Analysis and Dynamic Regression Models

Acinetobacter baumannii is one of the most difficult-to-treat pathogens worldwide, due to developed resistance. The aim of this study was to evaluate the use of widely prescribed antimicrobials and the respective resistance rates of A. baumannii, and to explore the relationship between antimicrobial use and the emergence of A. baumannii resistance in a tertiary care hospital. Monthly data on A. baumannii susceptibility rates and antimicrobial use, between January 2014 and December 2017, were analyzed using time series analysis (Autoregressive Integrated Moving Average (ARIMA) models) and dynamic regression models. Temporal correlations between meropenem, cefepime, and ciprofloxacin use and the corresponding rates of A. baumannii resistance were documented. The results of ARIMA models showed statistically significant correlation between meropenem use and the detection rate of meropenem-resistant A. baumannii with a lag of two months (p = 0.024). A positive association, with one month lag, was identified between cefepime use and cefepime-resistant A. baumannii (p = 0.028), as well as between ciprofloxacin use and its resistance (p < 0.001). The dynamic regression models offered explanation of variance for the resistance rates (R² > 0.60). The magnitude of the effect on resistance for each antimicrobial agent differed significantly.

Molecular docking, dynamics and free energy analyses of Acinetobacter baumannii OXA class enzymes with carbapenems investigating their hydrolytic mechanisms

Introduction. Acinetobacter baumannii is a critical priority pathogen listed by the World Health Organization due to increasing levels of resistance to carbapenem classes of antibiotics. It causes wound and other nosocomial infections, which can be life-threatening. Hence, there is an urgent need for the development of new classes of antibiotics.Aim. To study the interaction of carabapenems with class D beta-lactamases (oxacillinases) and analyse drug resistance by studying enzyme-substrate complexes using modelling approaches as a means of establishing correlations with the phenotypic data.Methodology. The three-dimensional structures of carbapenems (doripenem, ertapenem, imipenem and meropenem) were obtained from DrugBank and screened against class D beta-lactamases. Further, the study was extended with their variants. The variants' structure was homology-modelled using the Schrödinger Prime module (Schrödinger LLC, NY, USA).Results. The first discovered intrinsic beta-lactamase of Acinetobacter baumannii, OXA-51, had a binding energy value of -40.984 kcal mol^-1, whereas other OXA-51 variants, such as OXA-64, OXA-110 and OXA-111, have values of -60.638, -66.756 and -67.751 kcal mol^-1, respectively. The free energy values of OXA-51 variants produced better results than those of other groups.Conclusions. Imipenem and meropenem showed MIC values of 2 and 8 µg ml^-1, respectively against OXA-51 in earlier studies, indicating that these are the most effective drugs for treatment of A. baumannii infection. According to our results, OXA-51 is an active enzyme that shows better interactions and is capable of hydrolyzing carbapenems. When correlating the hydrogen-bonding interaction with MIC values, the predicted results are in good agreement and might provide initial insights into performing similar studies related to OXA variants or other antibiotic-enzyme-based studies.

In vitro activity of sulbactam/durlobactam against clinical isolates of Acinetobacter baumannii collected in China

Background

Durlobactam is a broad-spectrum inhibitor of class A, C and D β-lactamases. Sulbactam is a generic β-lactam most commonly used as a β-lactamase inhibitor in combination with ampicillin; however, it has a unique property in that it has selective intrinsic activity against Acinetobacter baumannii. Currently, there is widespread resistance caused by multiple β-lactamases including class A carbapenemases and class C and class D enzymes. The addition of durlobactam to sulbactam restores in vitro activity against MDR A. baumannii that possess multiple β-lactamases.

Objectives

Previously, susceptibility data for sulbactam/durlobactam were limited to isolates from patients in Western countries. This study was undertaken to determine the activity of sulbactam/durlobactam against A. baumannii isolated from patients in mainland China.

Methods

Nine hundred and eighty-two recent A. baumannii clinical isolates were collected from 22 sites across mainland China during 2016–18. The isolates were collected from lower respiratory tract, intra-abdominal, urinary tract and skin and skin structure infections. The in vitro activities of sulbactam/durlobactam and comparators were determined by broth microdilution.

Results

The addition of durlobactam restored the activity of sulbactam against the majority of the strains tested. The MIC90 of sulbactam/durlobactam was 2 mg/L for all A. baumannii, compared with 64 mg/L for sulbactam alone. The MIC90 of sulbactam/durlobactam of 2 mg/L remained unchanged for 831 carbapenem-resistant isolates. Colistin was the only comparator with comparable activity (MIC90 = 1 mg/L).

Conclusions

This study demonstrated the potential utility of sulbactam/durlobactam for the treatment of infections caused by A. baumannii in China.

Pandrug-resistant Acinetobacter Baumannii Infection Identified in a Non-intensive Care Unit Patient: A Case Study

Acinetobacter baumannii is a major cause of hospital-acquired infections, particularly in patients treated in intensive care units (ICUs). It can be a causal agent of conditions like pneumonia, bacteremia, meningitis, soft-tissue, and urinary tract infections, and is associated with high mortality rates. We present a case of a 72-year-old male patient treated for fractured neck of femur who went on to develop an infection from a pandrug-resistant Acinetobacter baumannii isolated in blood and urine cultures during his hospitalization in trauma and orthopedic ward. The patient was operated on the second day following his injury with a cephalomedullary nail device and became febrile with rigors on day six. His clinical condition deteriorated over the next days and his inflammatory markers reached a peak value on day 10 post-injury. Acinetobacter baumannii was isolated from blood and urine cultures and a regimen combining rifampicin, tigecycline, and vancomycin in their maximum doses was initiated. The patient was discharged on day 26 post-injury. Before discharge, he had received the above-mentioned intravenous antibiotic regimen for 14 days. He had also been afebrile for six days and undergone three consecutive negative blood culture samples.

Thioredoxin-A is a virulence factor and mediator of the type IV pilus system in Acinetobacter baumannii

The Gram-negative pathogen, Acinetobacter baumannii has emerged as a global nosocomial health threat affecting the majority of hospitals in the U.S. and abroad. The redox protein thioredoxin has been shown to play several roles in modulation of cellular functions affecting various virulence factors in Gram-negative pathogens. This study aims to explore the role of thioredoxin-A protein (TrxA) in A. baumannii virulence. We determined that deletion of the TrxA gene did not significantly affect resistance to environmental stressors such as temperature, salt, and pH. However, TrxA was critical for survival in the presence of elevated levels of hydrogen peroxide. Lack of TrxA was associated with decreased expression of type IV pili related genes and an inability to undergo normal twitching motility. Interestingly, the TrxA-null mutant was able to form biofilms better than the wildtype (WT) and was observed to be significantly less virulent than the WT in a pulmonary infection model. These results are supportive of thioredoxin playing a key role in A. baumannii virulence.

Phenotypic and Genotypic Characterization of Acinetobacter spp. Panel Strains: A Cornerstone to Facilitate Antimicrobial Development

Acinetobacter spp. have emerged as significant pathogens causing nosocomial infections. Treatment of these pathogens has become a major challenge to clinicians worldwide, due to their increasing tendency to antibiotic resistance. To address this, much revenue and technology are currently being dedicated toward developing novel drugs and antibiotic combinations to combat antimicrobial resistance. To address this issue, we have constructed a panel of Acinetobacter spp. strains expressing different antimicrobial resistance determinants such as narrow spectrum β-lactamases, extended-spectrum β-lactamases, OXA-type-carbapenemase, metallo-beta-lactamase, and over-expressed AmpC β-lactamase. Bacterial strains exhibiting different resistance phenotypes were collected between 2008 and 2013 from Severance Hospital, Seoul. Antimicrobial susceptibility was determined according to the CLSI guidelines using agar dilution method. Selected strains were sequenced using Ion Torrent PGM system, annotated using RAST server and analyzed using Geneious pro 8.0. Genotypic determinants, such as acquired resistance genes, changes in the expression of efflux pumps, mutations, and porin alternations, contributing to the relevant expressed phenotype were characterized. Isolates expressing ESBL phenotype consisted of bla _PER-1 gene, the overproduction of intrinsic AmpC beta-lactamase associated with ISAba1 insertion, and carbapenem resistance associated with production of carbapenem-hydrolyzing Ambler class D β-lactamases, such as OXA-23, OXA-66, OXA-120, OXA-500, and metallo-β-lactamase, SIM-1. We have analyzed the relative expression of Ade efflux systems, and determined the sequences of their regulators to correlate with phenotypic resistance. Quinolone resistance-determining regions were analyzed to understand fluoroquinolone-resistance. Virulence factors responsible for pathogenesis were also identified. Due to several mutations, acquisition of multiple resistance genes and transposon insertion, phenotypic resistance decision scheme for for evaluating the resistance proved inaccurate, which highlights the urgent need for modification to this scheme. This complete illustration of mechanism contributing to specific resistance phenotypes can be used as a target for novel drug development. It can also be used as a reference strain in the clinical laboratory and for the evaluation of antibiotic efficacy for specific resistance mechanisms.

Co-production of AmpC and extended spectrum beta-lactamases in cephalosporin-resistant Acinetobacter baumannii in Egypt

Acinetobacter baumannii is an opportunistic pathogen that has been held responsible for a lot of infections worldwide. Infections caused by this pathogen are difficult to control because of the widespread of antimicrobial resistance mechanisms. The aim of the present study is to assess the prevalence of extended spectrum β-lactamases (ESBLs) and AmpC β-lactamases among isolates of A. baumannii collected from different clinical sources in Mansoura University Hospitals, Egypt. Antimicrobial susceptibility testing has demonstrated elevated resistance level to β-lactams, quinolones and aminoglycosides. All isolates were sensitive to colistin and polymyxin B. ESBL activity was detected in 86% of the isolates. Among the tested ESBL encoding genes, bla_TEM gene was the most prevalent gene as it was detected in 52% of the isolates. While bla_PER, bla_SHV and bla_VEB were detected in 12%, 4%, and 2%, respectively. AmpC activity and bla_ADC gene were detected in 90% of the tested isolates. Insertion sequence ISAba1 was located 9 bp upstream of bla_ADC gene in 88.9% of the ADC-expressing isolates providing a potent promoter activity for its expression. To our knowledge this is the first report of loss of intrinsic ADC activity, in 10% of the tested isolates, as a result of insertional inactivation by an element belonging to IS5 family transposase. Co-expression of both ESBLs and AmpC β-lactamases was detected in 78% of the isolates. The study demonstrates high prevalence of resistance to β-lactam antibiotics through ESBLs and AmpC β-lactamases production among A. baumannii clinical isolates. Prevalence of β-lactamases should be detected routinely and reported in hospitals to avoid inappropriate use of antibiotics and therapeutic failure.

Acinetobacter etiology respiratory tract infections associated with mechanical ventilation: what impacts on the prognosis? A retrospective cohort study

INTRODUCTION

Acinetobacter species treatment often represents a challenge. The main objective of this study is identify predictors of ICU mortality in patients submitted to mechanical ventilation (MV).

MATERIALS AND METHODS

Retrospective cohort study. Patients with MV > 48 h who developed a respiratory tract positive culture for Acinetobacter were included, and distinguished among colonized, ventilator-associated pneumonia (VAP) or ventilator-associated tracheobronchitis (VAT) patients. Primary outcome was ICU mortality.

RESULTS

153 patients were in MV and presented positive culture for Acinetobacter calcoaceticus-baumanii complex, 70 of them with VAP, 59 with VAT and 24 patients were colonized. The factors related to ICU mortality were VAP (OR 2.2, 95% CI 1.1-4.5) and shock at the time of diagnosis (OR 4.8, 95% CI 1.8-2.3). In multivariate analysis, only SOFA score at the time of diagnosis (OR 1.06, 95% CI 1.03-1.09) was related with ICU mortality. A paired-matched analysis was performed to assess effect of dual therapy on outcomes, and no effect was found in terms of clinical cure, ICU or hospital mortality or duration of antimicrobial therapy.

CONCLUSIONS

Previous comorbidities and degree of associated organic injury seem to be more important factors in the prognosis than double antibiotic therapy in patients with Acinetobacter-related respiratory infection.

Antimicrobial Survey of Local Herbal Drugs against Acinetobacter baumannii Isolated from Patients Admitted to a Level-I Trauma Center

Objective:

To determine the antimicrobial activity and entity of several local herbal plants against Acintobacters isolated from trauma patients admitted to a Level-I trauma center.

Methods:

The antibacterial activities of the Satureja bachtiarica oil and someselected Iranian medicinal plants (Artemisia sieberi and Tanacetum dumosum belonging to the Asteraceae/Compositae; Salvia mirzayanii and Mentha mozaffarianii belonging to the Lamiaceae/Labiatae) were assayed on A. baumannii by microdilution and agar disc diffusion methods. Having obtained the acceptable antibacterial data, the shade-dried aerial parts of the plants were extracted by hydrodistillation method using Clevenger apparatus according to European pharmacopeia for 3 h. The analysis of S. bachtiarica essential oil accompanied by other herbal drug oils were performed by using GC/FID and GC/MS methods.

Results:

Outcomes revealed that the S. bachtiarica essential oil exhibited the potent antibacterial capability against Acinetobacter strains in comparison with Colistin, as a positive control. For S. bachtiarica,the growth inhibition zone and minimum inhibitory concentration (MIC) values were 21 mm and 0.5 mg/ml, while, for Colistin, the data were in order: 8 mm and 0.016 mg/ml. Consequently, GC/MS outcomes demonstrated that the major components of the essence were carvacrol (48.6%), followed by p-Cymene (16.6%), γ-terpinene (6.9%) and linalool (5.3%).

Conclusion:

Based on the considerable inhibitory activity against nosocomial infections by essential oil of S. bachtiarica, it could be considered as the suitable candidate in the food industry and pharmaceutical uses.

The role of TonB-dependent copper receptor in virulence of Acinetobacter baumannii

Acinetobacter baumannii is an opportunistic gram negative pathogen that can adhere to different surfaces and cause different nosocomial infections. To investigate the role of TonB-dependent copper receptor, an outer membrane protein, in virulence of A. baumannii, we deleted this receptor from A. baumannii chromosome. There was a significant decrease in biofilm formation by copper receptor deficient mutant strain. Similarly, the adherence to human epithelial cell and the hydrophobicity were declined. The survival rate of the mutant strain in human sera was reduced while no change was observed in motility of strains. In murine pneumonia model, the bacterial lethal dose 0 (LD₀), LD₅₀ and LD₁₀₀ were increased for mutant strain. Moreover, in vivo and in vitro experiments revealed changes in growth rate and dissemination of mutant strain; so that the bacterial load of the mutant was significantly reduced in the spleen and lung. The findings suggest a critical role for TonB-dependent copper receptor in virulence of A. baumannii.

Molecular Epidemiology and Mechanism of Sulbactam Resistance in Acinetobacter baumannii Isolates with Diverse Genetic Backgrounds in China

Sulbactam is a plausible option for treating Acinetobacter infections because of its intrinsic antibacterial activity against the members of the Acinetobacter genus, but the mechanisms of sulbactam resistance have not been fully studied in Acinetobacter baumannii In this study, a total of 2,197 clinical A. baumannii isolates were collected from 27 provinces in China. Eighty-eight isolates with various MICs for sulbactam were selected on the basis of their diverse clonality and underwent multilocus sequence typing (MLST), antimicrobial susceptibility testing, and resistance gene screening. The copy number and relative expression of bla_TEM-1D and ampC were measured via quantitative PCR and quantitative reverse transcription-PCR, respectively. The genetic structure of multicopy bla_TEM-1D was determined using the whole-genome sequencing technology. The cefoperazone-sulbactam resistance rate of the 2,197 isolates was 39.7%. The rate of positivity for bla_TEM-1D or ISAba1-ampC in the sulbactam-nonsusceptible group (64.91% and 78.95%, respectively) was significantly higher than that in the sulbactam-susceptible group (0% and 0%, respectively; P < 0.001). The MIC of sulbactam (P < 0.001) varied considerably between the groups expressing ampC with or without upstream ISAba1 Notably, the genetic structure of the multicopy bla_TEM-1D gene in strain ZS3 revealed that bla_TEM-1D was embedded within four tandem copies of the cassette IS26-bla_TEM-1D-Tn3-IS26 Therefore, bla_TEM-1D and ISAba1-ampC represent the prevalent mechanism underlying sulbactam resistance in clinical A. baumannii isolates in China. The structure of the four tandem copies of bla_TEM-1D first identified may increase sulbactam resistance.

Extended spectrum and metalo beta-lactamase producing airborne Pseudomonas aeruginosa and Acinetobacter baumanii in restricted settings of a referral hospital: a neglected condition

BACKGROUND

Frequently encountered multidrug-resistant bacterial isolates of P. aeruginosa and A. baumannii are common and prevalent in a hospital environment. The aim of this study was to determine the prevalence and pattern of antibiotic resistance, extended spectrum and metallo beta-lactamase producing P. aeruginosa and A. baumannii isolates from restricted settings of indoor air hospital environment.

METHODS

A hospital-based cross-sectional study was conducted in Wolaita Sodo University Teaching and referral Hospital, Ethiopia from December 1/2015 to April 30/2015. The Air samples were collected from delivery room, intensive care unit and operation theatre of the hospital by active, Anderson six slate sampler technique during the first week of the months, twice a week during Monday's and Friday's. Standard microbiological procedures were followed to isolate P. aeruginosa and A. baumannii. Susceptibility testing was performed on isolates using the Kirby-Bauer disk diffusion technique. Extended spectrum beta lactamase production was detected by double disc synergy test and Imipenem-resistant isolates were screened for producing Metallo-beta lactamase.

RESULTS

A total number of 216 indoor air samples were collected from the delivery room, intensive care unit, and operation room. Correspondingly, 43 A. baumannii isolates were identified (13 from delivery room, 21 from intensive care unit and 9 from operation room). Likewise 24 P. aeruginosa isolates were obtained (4 from delivery room, 13 from intensive care unit and 7 from operation room). Extended spectrum beta lactamase and metalo-beta lactamase production were observed in 24 (55.8%) and 13 (30.2%) isolates of A. baumannii respectively, whereas P. aeruginosa showed 15 (62.5%) extended spectrum beta lactamase and 9 (37.5%) metallo-beta lactamase production.

CONCLUSIONS

Extended spectrum beta lactamase and metallo-beta lactamase producing bacteria in hospital air is a new dimension for specific setting of the study area where antimicrobial resistance is increasing and surgical site infection is prevalent. So, identification of these microorganisms has a great role in reducing the burden of antibiotic resistance and could also provide a significant input for framing hospital infection control policies.

Magnetic Extraction of Acinetobacter baumannii Using Colistin-Functionalized γ-Fe2O3/Au Core/Shell Composite Nanoclusters

Acinetobacter baumannii is a Gram-negative bacterium of increasing concern due to its virulence and persistence in combat and healthcare environments. The incidence of both community-acquired and nosocomial A. baumannii infections is on the rise in foreign and domestic healthcare facilities. Treatment options are limited due to the acquisition of multidrug resistance to the few effective antibiotics. Currently, the most effective pharmaceutically based treatment for multidrug-resistant A. baumannii infections is the antibiotic colistin (polymyxin E). To minimize side effects associated with administration of colistin or other toxic antimicrobial agents, we propose the development of a nanotechnology-mediated treatment strategy. In this design-based effort, colistin-functionalized multilayered, inorganic, magnetoplasmonic nanoconstructs were fabricated to bind to the surface of A. baumannii. This result, for the first time, demonstrates a robust, pharmaceutical-based motif for high affinity, composite nanoparticulates targeting the A. baumannii surface. The antibiotic-activated nanomaterials demonstrated cytocompatibility with human cells and no acute bacterial toxicity at nanoparticle to bacterial concentrations <10 000:1. The magnetomotive characteristics of the nanomaterial enabled magnetic extraction of the bacteria. In a macroscale environment, maximal separation efficiencies exceeding 38% were achieved. This result demonstrates the potential for implementation of this technology into micro- or mesofluidic-based separation environments to enhance extraction efficiencies. The future development of such a mesofluidic-based, nanotechnology-mediated platform is potentially suitable for adjuvant therapies to assist in the treatment of sepsis.

Vaccination with a live attenuated Acinetobacter baumannii deficient in thioredoxin provides protection against systemic Acinetobacter infection

Multi-drug resistant Acinetobacter baumannii (MDR-Ab), an opportunistic pathogen associated with nosocomial and combat related infections, has a high mortality due to its virulence and limited treatment options. Deletion of the thioredoxin gene (TrxA) from a clinical isolate of MDR-Ab resulted in a 100-fold increase in 50% lethal dose (LD₅₀) in a systemic challenge murine model. Thus, we investigated the potential use of this attenuated strain as a live vaccine against MDR-Ab. Mice were vaccinated by subcutaneous (s.c.) injection of 2×10⁵ CFU of the ΔtrxA mutant, boosted 14days later with an equivalent inoculum, and then challenged 30days post-vaccination by i.p. injection with 10 LD₅₀ of the wild type (WT) Ci79 strain. Efficacy of vaccination was evaluated by monitoring MDR-Ab specific antibody titers and cytokine production, observing pathology and organ burdens after WT challenge, and measuring levels of serum pentraxin-3, a molecular correlate of A. baumannii infection severity, before and after challenge. Mice vaccinated with ΔtrxA were fully protected against the lethal challenge of WT. However, minimal immunoglobulin class switching was observed with IgM predominating. Spleens harvested from vaccinated mice exhibited negligible levels of IL-4, IFN-γ and IL-17 production when stimulated with UV-inactivated WT Ci79. Importantly, tissues obtained from vaccinated mice displayed reduced pathology and organ burden compared to challenged non-vaccinated mice. Additionally, serum pentraxin-3 concentrations were not increased 24h after challenge in vaccinated mice, correlating with reduction of WT MDR-Ab infection in ΔtrxA immunized mice. Furthermore, passive immunization with ΔtrxA-immune sera provided protection against lethal systemic Ci79 challenge. Collectively, the defined live attenuated ΔtrxA strain is a vaccine candidate against emerging MDR Acinetobacter infection.

Activity of Gallium Meso- and Protoporphyrin IX against Biofilms of Multidrug-Resistant Acinetobacter baumannii Isolates

Acinetobacter baumannii is a challenging pathogen due to antimicrobial resistance and biofilm development. The role of iron in bacterial physiology has prompted the evaluation of iron-modulation as an antimicrobial strategy. The non-reducible iron analog gallium(III) nitrate, Ga(NO₃)₃, has been shown to inhibit A. baumannii planktonic growth; however, utilization of heme-iron by clinical isolates has been associated with development of tolerance. These observations prompted the evaluation of iron-heme sources on planktonic and biofilm growth, as well as antimicrobial activities of gallium meso- and protoporphyrin IX (Ga-MPIX and Ga-PPIX), metal heme derivatives against planktonic and biofilm bacteria of multidrug-resistant (MDR) clinical isolates of A. baumannii in vitro. Ga(NO₃)₃ was moderately effective at reducing planktonic bacteria (64 to 128 µM) with little activity against biofilms (≥512 µM). In contrast, Ga-MPIX and Ga-PPIX were highly active against planktonic bacteria (0.25 to 8 µM). Cytotoxic effects in human fibroblasts were observed following exposure to concentrations exceeding 128 µM of Ga-MPIX and Ga-PPIX. We observed that the gallium metal heme conjugates were more active against planktonic and biofilm bacteria, possibly due to utilization of heme-iron as demonstrated by the enhanced effects on bacterial growth and biofilm formation.

The outer membrane porin OmpW of Acinetobacter baumannii is involved in iron uptake and colistin binding

This study was undertaken to characterize functions of the outer membrane protein OmpW, which potentially contributes to the development of colistin- and imipenem-resistance in Acinetobacter baumannii. Reconstitution of OmpW in artificial lipid bilayers showed that it forms small channels (23 pS in 1 m KCl) and markedly interacts with iron and colistin, but not with imipenem. In vivo, (55) Fe uptake assays comparing the behaviours of ΔompW mutant and wild-type strains confirmed a role for OmpW in A. baumannii iron homeostasis. However, the loss of OmpW expression did not have an impact on A. baumannii susceptibilities to colistin or imipenem.

Comparison of colistin monotherapy and non-colistin combinations in the treatment of multi-drug resistant Acinetobacter spp. bloodstream infections: a multicenter retrospective analysis

Objectives:

To compare the efficacy of colistin (COL) monotherapy versus non-COL based combinations in the treatment of bloodstream infections (BSIs) due to multidrug resistant Acinetobacter spp.(MDR-A).

Materials and Methods:

Retrospective data of 107 MDR-A BSI cases from 27 tertiary centers in Turkey were included.

Primary End-Point:

14-day mortality.

Secondary End-Points:

Microbial eradication and clinical improvement.

Results:

Thirty-six patients in the COL monotherapy (CM) group and 71 in the non-COL based combinations (NCC) group were included in the study. Mean age was 59.98 ± 20 years (range: 18–89) and 50.5% were male. Median duration of follow-up was 40 days (range: 9–297). The 14-day survival rates were 52.8% in CM and 47.23% in NCC group (P = 0.36). Microbiological eradication was achieved in 69% of CM and 83% of NCC group (P = 0.13). Treatment failure was detected in 22.9% of cases in both CM and NCC groups. Univariate analysis revealed that mean age (P = 0.001), Charlson comorbidity index (P = 0.03), duration of hospital stay before MDR-A BSI (P = 0.04), Pitt bacteremia score (P = 0.043) and Acute Physiology and Chronic Health Evaluation II score (P = 0.05) were significant in terms of 14-day mortality. Advanced age (P = 0.01) and duration of hospital stay before MDR-A BSI (P = 0.04) were independently associated with 14-day mortality in multivariate analysis.

Conclusion:

No significant difference was detected between CM and non-COL based combinations in the treatment of MDR-A BSIs in terms of efficacy and 14-day mortality.

Crystal Structure of Hcp from Acinetobacter baumannii: A Component of the Type VI Secretion System

The type VI secretion system (T6SS) is a bacterial macromolecular machine widely distributed in Gram-negative bacteria, which transports effector proteins into eukaryotic host cells or other bacteria. Membrane complexes and a central tubular structure, which resembles the tail of contractile bacteriophages, compose the T6SS. One of the proteins forming this tube is the hemolysin co-regulated protein (Hcp), which acts as virulence factor, as transporter of effectors and as a chaperone. In this study, we present the structure of Hcp from Acinetobacter baumannii, together with functional and oligomerization studies. The structure of this protein exhibits a tight β barrel formed by two β sheets and flanked at one side by a short α-helix. Six Hcp molecules associate to form a donut-shaped hexamer, as observed in both the crystal structure and solution. These results emphasize the importance of this oligomerization state in this family of proteins, despite the low similarity of sequence among them. The structure presented in this study is the first one for a protein forming part of a functional T6SS from A. baumannii. These results will help us to understand the mechanism and function of this secretion system in this opportunistic nosocomial pathogen.

Sequence-activity relationship, and mechanism of action of mastoparan analogues against extended-drug resistant Acinetobacter baumannii

The treatment of some infectious diseases can currently be very challenging since the spread of multi-, extended- or pan-resistant bacteria has considerably increased over time. On the other hand, the number of new antibiotics approved by the FDA has decreased drastically over the last 30 years. The main objective of this study was to investigate the activity of wasp peptides, specifically mastoparan and some of its derivatives against extended-resistant Acinetobacter baumannii. We optimized the stability of mastoparan in human serum since the specie obtained after the action of the enzymes present in human serum is not active. Thus, 10 derivatives of mastoparan were synthetized. Mastoparan analogues (guanidilated at the N-terminal, enantiomeric version and mastoparan with an extra positive charge at the C-terminal) showed the same activity against Acinetobacter baumannii as the original peptide (2.7 μM) and maintained their stability to more than 24 h in the presence of human serum compared to the original compound. The mechanism of action of all the peptides was carried out using a leakage assay. It was shown that mastoparan and the abovementioned analogues were those that released more carboxyfluorescein. In addition, the effect of mastoparan and its enantiomer against A. baumannii was studied using transmission electron microscopy (TEM). These results suggested that several analogues of mastoparan could be good candidates in the battle against highly resistant A. baumannii infections since they showed good activity and high stability.

Immunization with lipopolysaccharide-deficient whole cells provides protective immunity in an experimental mouse model of Acinetobacter baumannii infection

The increasing clinical importance of infections caused by multidrug resistant Acinetobacter baumannii warrants the development of novel approaches for prevention and treatment. In this context, vaccination of certain patient populations may contribute to reducing the morbidity and mortality caused by this pathogen. Vaccines against Gram-negative bacteria based on inactivated bacterial cells are highly immunogenic and have been shown to produce protective immunity against a number of bacterial species. However, the high endotoxin levels present in these vaccines due to the presence of lipopolysaccharide complicates their use in human vaccination. In the present study, we used a laboratory-derived strain of A. baumannii that completely lacks lipopolysaccharide due to a mutation in the lpxD gene (IB010), one of the genes involved in the first steps of lipopolysaccharide biosynthesis, for vaccination. We demonstrate that IB010 has greatly reduced endotoxin content (<1.0 endotoxin unit/106 cells) compared to wild type cells. Immunization with formalin inactivated IB010 produced a robust antibody response consisting of both IgG1 and IgG2c subtypes. Mice immunized with IB010 had significantly lower post-infection tissue bacterial loads and significantly lower serum levels of the pro-inflammatory cytokines IL-1β, TNF-α and IL-6 compared to control mice in a mouse model of disseminated A. baumannii infection. Importantly, immunized mice were protected from infection with the ATCC 19606 strain and an A. baumannii clinical isolate. These data suggest that immunization with inactivated A. baumannii whole cells deficient in lipopolysaccharide could serve as the basis for a vaccine for the prevention of infection caused by A. baumannii.

Ability of bacteriophage in resolving wound infection caused by multidrug-resistant Acinetobacter baumannii in uncontrolled diabetic rats

Acinetobacter baumannii, a substantial nosocomial pathogen, has developed resistance to almost all available antimicrobial drugs. Bacteriophage therapy is a possible alternative treatment for multidrug-resistant (MDR) bacterial infections. In this study, we have successfully isolated bacteriophage active against clinical strains of A. baumannii by enrichment from hospital sewage sludge using representatives of those strains. The bacteriophage isolated against A. baumannii formed plaques against beta-lactamases producing strains of A. baumannii. The utility of bacteriophage specific for A. baumannii to resolve wound infection in uncontrolled diabetic rats was evaluated. Five groups of uncontrolled diabetic rats were used. Group I was noninfected (Control), Group II was infected with MDR A. baumannii and challenged with bacteriophage, Group III was infected with MDR A. baumannii, Group IV was infected with MDR A. baumannii and challenged with antibiotic colistin, and Group V consisted of noninfected rats and sprayed with phage (Phage control). A significant decrease in infection, period of epithelization, and wound contraction was observed in the phage-challenged group when compared with antibiotic-treated uncontrolled diabetic rats and the control group. To conclude the study, new insights are provided into the biology of the broad host range of A. baumannii phage, demonstrating that A. baumannii phage has prospects for the treatment of infections caused by the MDR A. baumannii.

Pharmacophore generation of 2-substituted benzothiazoles as AdeABC efflux pump inhibitors in A. baumannii

RND family efflux pumps are important for multidrug resistance in Gram-negative bacteria. To date no efflux pump inhibitors for clinical use have been found, so developing the specific inhibitors of this pump system will be beneficial for the treatment of infections caused by these multidrug-resistant pathogens. A set of BSN-coded 2-substituted benzothiazoles were tested alone and in combination with ciprofloxacin (CIP) against the RND family efflux pump AdeABC overexpressor Acinetobacter baumannii SbMox-2 strain. The results indicated that the BSN compounds did not have antimicrobial activity when tested alone. However, if they were applied in combination with CIP, it was observed that the antibiotic had antimicrobial activity against the tested pathogen, possessing a minimum inhibitory concentration value that could be utilized in clinical treatment. A 3D-common features pharmacophore model was applied by using the HipHop method and the generated pharmacophore hypothesis revealed that the hydrogen bond acceptor property of nitrogen in the thiazole ring and the oxygen of the amide substituted at the second position of the benzothiazole ring system were significant for binding to the target protein. Moreover, three hydrophobic aromatic features were found to be essential for inhibitory activity.

Co-production of ESBL and AmpC β-Lactamases in Clinical Isolates of A. baumannii and A. lwoffii in a Tertiary Care Hospital From Northern India

BACKGROUND

Acinetobacter baumannii is an important cause of health care associated infections which are difficult to control and treat, because of widespread antimicrobial resistance which is possessed by this organism.

AIMS

The aim of the present study was to know the prevalence of ESBLs and AmpC β-lactamases in clinical isolates of Acinetobacter spp. which were cultured from various clinical specimens by using different phenotypic methods.

SETTINGS AND DESIGN

Study was conducted over a period of one year at the Microbiology Department of a tertiary care teaching hospital. A total of 100 consecutive, non-duplicate strains of Acinetobacter species which were isolated from various clinical samples were included.

MATERIALS AND METHODS

All the isolates were identified by standard microbiological procedures and antimicrobial susceptibility testing was done by Kirby-Bauer disc diffusion technique. Isolates which showed reduced susceptibilities to third generation cephalosporins were tested for ESBL production by CLSI double disc synergy method and also by using sulbactam as an inhibitory agent. Isolates which showed reduced susceptibilities to cefoxitin were tested for AmpC detection by doing AmpC disc test.

STATISTICAL ANALYSIS

SPSS, version 17 was used to calculate p-value. If the p-value was <0.05, it was considered to be significant.

RESULTS

Out of 100 isolates, 82 were Acinetobacter baumannii and 18 were Acinetobacter lwoffii. ESBL were mentioned in 4% of the Acinetobacter isolates and in 77% of the isolates by using clavulanic acid and sulbactam as inhibitory agents respectively. AmpC β-lactamase production was detected in 60% isolates of Acinetobacter spp. Co-production of both ESBL and AmpC enzymes were seen in 29% of the Acinetobacter strains.

CONCLUSION

Failure in detecting β-lactamases contributes to their uncontrolled spread and therapeutic failures. Hence, these β-lactamases should be detected routinely and they should be reported to clinicians in time, so that inappropriate use of antibiotics can be stopped in time.

Intranasal immunization protects against Acinetobacter baumannii-associated pneumonia in mice

Multidrug-resistant Acinetobacter baumannii has become an important causative agent of healthcare associated infections. Hospital- and community-acquired pneumonia is the most common clinical manifestation of A. baumannii infection worldwide and is often associated with high mortality. Most experimental vaccine studies to date have evaluated vaccines against systemic A. baumannii infections following systemic immunization. We recently demonstrated that a mouse model of respiratory A. baumannii infection using the strain LAC-4 results in disease progression that is similar to that observed in humans. Here we used this model in conjunction with an inactivated whole cell vaccine to evaluate the feasibility of developing protective mucosal vaccines against respiratory A. baumannii infection and to investigate the potential mechanism of protection of such vaccines. Our results showed that intranasal immunization with formalin-killed whole cells of the LAC-4 strain elicited mucosal and systemic antigen-specific immune responses, and protected mice against lethal intranasal or intraperitoneal challenges. Compared to naïve mice, immunized mice had significantly fewer bacteria in their lungs, and the pathogen was barely detectable in blood and spleens at 24h post challenge, indicating the ability of immunized mice to control extrapulmonary dissemination of the pathogen. Mechanistic studies using gene-deficient mice, neutropenic mice, or passive immunization showed that B cells and neutrophils, but not FcRγ, played crucial roles in the protection against respiratory A. baumannii challenge of intranasally immunized mice whereas passive transfer of hyperimmune sera only prolonged the survival time of challenged mice by 48 h. These results provide immunological insights for the rational design of novel mucosal vaccines to protect against respiratory A. baumannii infection and demonstrate the feasibility to develop such vaccines.

Comparison of colistin-carbapenem, colistin-sulbactam, and colistin plus other antibacterial agents for the treatment of extremely drug-resistant Acinetobacter baumannii bloodstream infections

The purpose of this investigation was to compare the efficacy of colistin-based therapies in extremely drug-resistant Acinetobacter spp. bloodstream infections (XDR-ABSI). A retrospective study was conducted in 27 tertiary-care centers from January 2009 to August 2012. The primary end-point was 14-day survival, and the secondary end-points were clinical and microbiological outcomes. Thirty-six and 214 patients [102 (47.7%): colistin-carbapenem (CC), 69 (32.2%): colistin-sulbactam (CS), and 43 (20.1%: tigecycline): colistin with other agent (CO)] received colistin monotherapy and colistin-based combinations, respectively. Rates of complete response/cure and 14-day survival were relatively higher, and microbiological eradication was significantly higher in the combination group. Also, the in-hospital mortality rate was significantly lower in the combination group. No significant difference was found in the clinical (p = 0.97) and microbiological (p = 0.92) outcomes and 14-day survival rates (p = 0.79) between the three combination groups. Neither the timing of initial effective treatment nor the presence of any concomitant infection was significant between the three groups (p > 0.05) and also for 14-day survival (p > 0.05). Higher Pitt bacteremia score (PBS), Acute Physiology and Chronic Health Evaluation II (APACHE II) score, Charlson comorbidity index (CCI), and prolonged hospital and intensive care unit (ICU) stay before XDR-ABSI were significant risk factors for 14-day mortality (p = 0.02, p = 0.0001, p = 0.0001, p = 0.02, and p = 0.01, respectively). In the multivariable analysis, PBS, age, and duration of ICU stay were independent risk factors for 14-day mortality (p < 0.0001, p < 0.0001, and p = 0.001, respectively). Colistin-based combination therapy resulted in significantly higher microbiological eradication rates, relatively higher cure and 14-day survival rates, and lower in-hospital mortality compared to colistin monotherapy. CC, CS, and CO combinations for XDR-ABSI did not reveal significant differences with respect to 14-day survival and clinical or microbiological outcome before and after propensity score matching (PSM). PBS, age, and length of ICU stay were independent risk factors for 14-day mortality.

Clinical efficacy and safety of the combination of colistin plus vancomycin for the treatment of severe infections caused by carbapenem-resistant Acinetobacter baumannii

A potent synergy of a glycopeptide-colistin combination against Acinetobacter baumannii has recently been described. We set out to assess the efficacy and safety of this combination in a retrospective study including episodes of ventilator-associated pneumonia or bacteremia caused by carbapenem-resistant A. baumannii. We compared 29 patients (group I) treated with colistin plus vancomycin with 28 patients treated with colistin alone (group II). Group I received vancomycin (for empirical or targeted therapy) at the onset of colistin administration and both antimicrobials coincided for at least 5 days. Baseline characteristics, clinical cure, microbiological eradication, and mortality were similar in both groups but the rate of acute kidney injury was higher in group I (55.2 vs. 28%; p = 0.04). In critically ill patients with carbapenem-resistant A. baumannii infections, clinical outcomes do not differ in patients treated with colistin plus vancomycin from those receiving colistin without vancomycin. This combination significantly increases the risk of renal failure.

Xuebijing Protects Rats from Sepsis Challenged with Acinetobacter baumannii by Promoting Annexin A1 Expression and Inhibiting Proinflammatory Cytokines Secretion

Xuebijing (XBJ) injection is a herbal medicine that has been widely used in the treatment of sepsis in China; however, its role in the development and progression of Acinetobacter baumannii sepsis and the underlying mechanisms remain uninvestigated. In the present study, fifty-four male Wistar rats were randomly assigned to normal-control group, sepsis-control group, and sepsis + XBJ group, each containing three subgroups of different treatment time periods (6, 12, and 24 hrs following injection, resp.). The sepsis model was established by intraperitoneal injection of A. baumannii ATCC 19606. For XBJ treatment, 4 mL/kg XBJ was administrated simultaneously by intravenous injection through caudal vein every 12 hrs. All animals demonstrated ill state, obvious intestinal dysfunction, histopathological lung damages, and overactive inflammatory responses after A. baumannii infection, and these events could be partially reversed by XBJ treatment from the beginning of infection. XBJ induced an increase in the expression of anti-inflammatory mediator annexin A1; however, two proinflammatory cytokines, interleukin-8 (IL-8) and tumor necrosis factor- α (TNF- α ), were decreased at the each monitored time point. These findings suggested that XBJ via its cytokine-mediated anti-inflammatory effects might have a potential role in preventing the progression of A. baumannii infection to sepsis by early administration.

Rapid detection of antibiotic resistance in Acinetobacter baumannii using quantitative real-time PCR

OBJECTIVES

The rapid detection of antibiotic resistance in clinical isolates of Acinetobacter baumannii would shorten the period during which patients receive empirical therapy and facilitate the early initiation of directed antibiotic therapy. The objective of this study was to evaluate the ability of a real-time PCR assay to detect antibiotic resistance to four clinically relevant antibiotics from different antibiotic classes in clinical isolates of A. baumannii.

METHODS

The growth of 48 clinical isolates of A. baumannii with a broad range of MICs of imipenem, ciprofloxacin, colistin and amikacin was evaluated using a real-time PCR assay targeting a highly conserved region of the ompA gene. Fold changes in the number of copies of genomic DNA after 6 h of growth were used to determine resistance and the results were compared with those obtained using broth microdilution.

RESULTS

The results obtained using the real-time PCR assay were concordant with broth microdilution for 184 of 192 determinations (95.8%). The global values for specificity (97.5%), sensitivity (92.9%), positive predictive value (95.6%) and negative predictive value (96.0%) indicated that the real-time PCR assay was able to reliably differentiate between resistant and non-resistant strains.

CONCLUSIONS

The use of real-time PCR to monitor bacterial growth in the presence of antibiotics is effective for rapidly identifying antibiotic resistance in A. baumannii.

Emerging therapies for multidrug resistant Acinetobacter baumannii

The global emergence of multidrug resistant Acinetobacter baumannii has reduced the number of clinically available antibiotics that retain activity against this pathogen. For this reason, the development of novel prevention and treatment strategies for infections caused by A. baumannii is necessary. Several studies have begun to characterize nonantibiotic approaches that utilize novel mechanisms of action to achieve antibacterial activity. Recent advances in phage therapy, iron chelation therapy, antimicrobial peptides, prophylactic vaccination, photodynamic therapy, and nitric oxide (NO)-based therapies have all been shown to have activity against A. baumannii. However, before these approaches can be used clinically there are still limitations and remaining questions that must be addressed.

Esculentin-2CHa: a host-defense peptide with differential cytotoxicity against bacteria, erythrocytes and tumor cells

The host-defense peptide, esculentin-2CHa (GFSSIFRGVA(10)KFASKGLGK D(20)LAKLGVDLVA(30) CKISKQC) shows potent (MIC≤6 μM) growth inhibitory activity against clinical isolates of multidrug-resistant strains of Staphylococcus aureus, Acinetobacter baumannii, and Stenotrophomonas maltophilia and differential cytotoxic activity against human erythrocytes (LC(50)=150 μM) and human non-small cell lung adenocarcinoma A549 cells (LC(50)=10 μM). Esculentin-2CHa significantly (P<0.01) stimulates the release of the anti-inflammatory cytokine IL-10 by mouse lymphoid cells and elevates its production after stimulation with concanavalin A and significantly (P<0.05) stimulates TNF-α production by peritoneal macrophages. Effects on IL-6 and IL-1β production were not significant. Removal of the hydrophobic N-terminal hexapeptide (GFSSIF) from esculentin-2CHa results in abolition of growth inhibitory activity against S. aureus and cytotoxic activity against erythrocytes and A549 cells as well as a marked (≥16-fold) reduction in potency against A. baumannii and S. maltophilia. The primary structure of esculentin-2 has been poorly conserved between frog species but evolutionary pressure has acted to maintain the hydrophobic character of this N-terminal hexapeptide sequence. Removal of the cyclic C-terminal domain (CKISKQC) and replacement of the Cys(31) and Cys(37) residues by serine resulted in appreciable decreases in cytotoxicity against all microorganisms and against mammalian cells. The more cationic [D20K, D27K] analog showed a modest increase in potency against all microorganisms (up to 4-fold) but a marked increase in cytotoxicity against erythrocytes (LC(50)=11 μM) and A549 cells (LC(50)=3 μM).

Tigecycline in carbapenem-resistant Acinetobacter baumannii bacteraemia: susceptibility and clinical outcome

Although tigecycline is considered one of the few therapeutic options for carbapenem-resistant Acinetobacter baumannii (CRAB) bacteraemia, its role in the treatment of CRAB bacteraemia remains unclear. We describe the clinical outcomes of 9 patients who received tigecycline for CRAB bacteraemia. Although all CRAB blood isolates were susceptible to tigecycline, 5 (56%) deaths were related to CRAB bacteraemia and 1 case of breakthrough CRAB bacteraemia was observed during tigecycline therapy. Clinical outcomes of tigecycline therapy may be poor in patients with tigecycline-susceptible CRAB bacteraemia, although multiple factors including delayed treatment could contribute to the poor outcomes.

Acinetobacter baumannii Septicemia in a Recipient of an Allogeneic Hematopoietic Stem Cell Transplantation

Acinetobacter baumannii is a gram-negative, nonfermentative coccobacillus that causes infections in immunocompromised and chronically ill patients and is associated with multidrug resistance. Two days before receiving her nonmyeloablative stem cell allograft, a patient with acute myeloid leukemia developed Acinetobacter baumannii bacteremia that caused septic shock which was successfully treated with imipenem and removal of the central venous catheter. To our knowledge, this is the first report of Acinetobacter baumannii septicemia in a hematopietic stem cell transplantation recipient.