Multidrug-resistant Acinetobacter Baumannii Strains Research Articles

In vitro activity of human defensins HNP-1 and hBD-3 against multidrug-resistant ESKAPE Gram-negatives of clinical origin and selected peptidoglycan recycling-defective mutants.

In the current scenario of critical need for new antimicrobials against multidrug-resistant bacteria, all options must be considered, including classic ideas such as the use of purified immune compounds. However, information regarding the activity of certain human defensins against ESKAPE Gram-negatives was incomplete. This is the first study comparatively assessing the in vitro activity of two membrane-permeabilizing/peptidoglycan construction-blocking defensins (HNP-1 and hBD-3) against relevant clinical collections of ESKAPE Gram-negatives, alone or in combination with permeabilizers, additional peptidoglycan-targeting attacks, or the blockade of its recycling. Our data suggest that hBD-3 has a notable bactericidal activity against multidrug-resistant Acinetobacter baumannii and Enterobacter cloacae strains that should be considered as potential adjuvant option. Our results suggest for the first time an increased resistance of Pseudomonas aeruginosa strains from chronic infection compared to acute origin ones, and provide new clues about the predominant mode of action of hBD-3 against Gram-negatives (permeabilization rather than peptidoglycan-targeting).

Characterization of two bacteriophages specific to Acinetobacter baumannii and their effects on catheters biofilm.

Multidrug-resistant strains of Acinetobacter baumannii cause major nosocomial infections. Bacteriophages that are specific to the bacterial species and destroy bacteria can be effectively used for treatment. In this study, we characterized lytic bacteriophages specific to A. baumannii strains. We isolated lytic bacteriophages from environmental water samples and then investigated their morphology, host range, growth characteristics, stability, genome analysis, and biofilm destruction on the catheter surface. Our results showed that the efficacy of the phages varied between 32% and 78%, tested on 78 isolates of A. baumannii; 80 phages were isolated, and two lytic bacteriophages, vB_AbaP_HB01 (henceforth called C2 phage) and vB_AbaM_HB02 (henceforth called K3 phage), were selected for characterization. Electron microscopy scans revealed that the C2 and K3 phages were members of the Podoviridae and Myoviridae families, respectively. Whole-genome sequencing revealed that the sequence of the C2 phage is available in the NCBI database (accession number: OP917929.1), and it was found sequence identity with Acinetobacter phage AB1 18%, the K3 phage DNA sequence is closely related to Acinetobacter phage vB_AbaM_phiAbaA1 (94% similarity). The cocktail of C2 and K3 phages demonstrated a promising decrease in the bacterial cell counts of the biofilm after 4 h. Under a scanning electron microscope, the cocktail treatment destructed the biofilm on the catheter. We propose that the phage cocktail could be a strong alternative to antibiotics to control the A. baumannii biofilm in catheter infections.

Host range expansion of Acinetobacter phage vB_Ab4_Hep4 driven by a spontaneous tail tubular mutation.

Bacteriophages (phages) represent promising alternative treatments against multidrug-resistant Acinetobacter baumannii (MDRAB) infections. The application of phages as antibacterial agents is limited by their generally narrow host ranges, so changing or expanding the host ranges of phages is beneficial for phage therapy. Multiple studies have identified that phage tail fiber protein mediates the recognition and binding to the host as receptor binding protein in phage infection. However, the tail tubular-dependent host specificity of phages has not been studied well. In this study, we isolated and characterized a novel lytic phage, vB_Ab4_Hep4, specifically infecting MDRAB strains. Meanwhile, we identified a spontaneous mutant of the phage, vB_Ab4_Hep4-M, which revealed an expanded host range compared to the wild-type phage. A single mutation of G to C was detected in the gene encoding the phage tail tubular protein B and thus resulted in an aspartate to histidine change. We further demonstrated that the host range expansion of the phage mutant is driven by the spontaneous mutation of guanine to cytosine using expressed tail tubular protein B. Moreover, we established that the bacterial capsule is the receptor for phage Abp4 and Abp4-M by identifying mutant genes in phage-resistant strains. In conclusion, our study provided a detailed description of phage vB_Ab4_Hep4 and revealed the tail tubular-dependent host specificity in A. baumannii phages, which may provide new insights into extending the host ranges of phages by gene-modifying tail tubular proteins.

Comparative genomics and characterization of a multidrug-resistant Acinetobacter baumannii VRL-M19 isolated from a crowded setting in India

A crowded vegetable market serves as a mass gathering, posing a potential risk for infection transmission. In this study, we isolated a multidrug-resistant Acinetobacter baumannii strain, VRL-M19, from the air of such a market and conducted comparative genomics and phenotypic characterization. Antimicrobial susceptibility testing, genome sequencing using Illumina HiSeq X10, and pan-genome analysis with 788 clinical isolates identified core, accessory, and unique drug-resistant determinants. Mutational analysis of drug-resistance genes, virulence factor annotation, in vitro pathogenicity assessment, subsystem analysis, Multilocus sequence typing, and whole genome phylogenetic analysis were performed. VRL-M19 exhibited multidrug resistance with 69 determinants, and analysis across 788 clinical isolates and 350 Indian isolates revealed more accessory genes (52 out of 69) in the Indian isolates. Multiple mutations were observed in drug target modification genes, and the strain was identified as a moderate biofilm-former with 55 virulence factors. Whole genome phylogenetics indicated a close relationship between VRL-M19 and clinical A. baumannii strains. In conclusion, our comprehensive study suggests that VRL-M19 is a multidrug-resistant, potential pathogen with biofilm-forming capabilities, closely associated with clinical A. baumannii strains.

Safety and pharmacokinetics of SPR206 in subjects with varying degrees of renal impairment.

SPR206 is a novel polymyxin derivative with potent in vitro activity against susceptible and multidrug-resistant strains of Acinetobacter baumannii, Pseudomonas aeruginosa, Klebsiella pneumoniae, Escherichia coli, and Enterobacter species. SPR206 is eliminated renally. The safety, tolerability, and pharmacokinetics (PK) of SPR206 were evaluated in healthy subjects with normal renal function (Cohort 1) and subjects with varying degrees of renal impairment (RI) (Cohorts 2-4) or end-stage renal disease (ESRD) on hemodialysis (HD) (Cohort 5). Subjects in Cohorts 1-4 received a 100-mg intravenous (IV) dose of SPR206. Subjects in Cohort 5 received a 100-mg IV dose within 2 h after HD on day 1 and 1 h before HD on day 5. Safety and PK analyses included 37 subjects. Mostly mild but no serious treatment-related adverse events were reported. Systemic exposure to SPR206 increased as renal function decreased, with mean area under the concentration-time curve from time 0 to the last quantifiable concentration (AUC0-last) values 39% to 239% greater in subjects with RI vs healthy subjects. Mean plasma clearance (CL) of SPR206 decreased with decreasing renal function (29% to 76% lower vs healthy subjects). In subjects with ESRD, AUC0-last decreased by 51%, and CL increased by 92% for dialyzed vs nondialyzed conditions. SPR206 was excreted in urine within 12 h in healthy subjects and subjects with mild RI (Cohort 2) but was prolonged in those with moderate and severe RI (Cohorts 3 and 4, respectively). In summary, SPR206 was generally safe and well tolerated, and the PK of SPR206 was well characterized in subjects with RI.

Synergistic Antibiofilm Action of Cinnamomum verum and Brazilian Green Propolis Hydroethanolic Extracts against Multidrug-Resistant Strains of Acinetobacter baumannii and Pseudomonas aeruginosa and Their Biocompatibility on Human Keratinocytes.

The accumulated dental biofilm can be a source of oral bacteria that are aspirated into the lower respiratory tract causing ventilator-associated pneumonia in hospitalized patients. The aim of this study was to evaluate the synergistic antibiofilm action of the produced and phytochemically characterized extracts of Cinnamomum verum and Brazilian green propolis (BGP) hydroethanolic extracts against multidrug-resistant clinical strains of Acinetobacter baumannii and Pseudomonas aeruginosa, in addition to their biocompatibility on human keratinocyte cell lines (HaCaT). For this, High-performance liquid chromatography analysis of the plant extracts was performed; then the minimum inhibitory and minimum bactericidal concentrations of the extracts were determined; and antibiofilm activity was evaluated with MTT assay to prevent biofilm formation and to reduce the mature biofilms. The cytotoxicity of the extracts was verified using the MTT colorimetric test, evaluating the cellular enzymatic activity. The data were analyzed with one-way ANOVA and Tukey's tests as well as Kruskal-Wallis and Dunn's tests, considering a significance level of 5%. It was possible to identify the cinnamic aldehyde in C. verum and p-coumaric, caffeic, and caffeoylquinic acids as well as flavonoids such as kaempferol and kaempferide and Artepillin-C in BGP. The combined extracts were effective in preventing biofilm formation and reducing the mature biofilms of A. baumannii and P. aeruginosa. Moreover, both extracts were biocompatible in different concentrations. Therefore, C. verum and BGP hydroethanolic extracts have bactericidal and antibiofilm action against multidrug resistant strains of A. baumannii and P. aeruginosa. In addition, the combined extracts were capable of expressively inhibiting the formation of A. baumannii and P. aeruginosa biofilms (prophylactic effect) acting similarly to 0.12% chlorhexidine gluconate.

Phenotypic and Genotypic Characterization of Recently Isolated Multidrug-Resistant Acinetobacter baumannii Clinical and Aquatic Strains and Demonstration of Silver Nanoparticle Potency.

This study aims to demonstrate the effectiveness of silver nanoparticles (Ag NPs) on multidrug-resistant (MDR) Acinetobacter baumannii (AB) strains isolated from the clinical and aquatic environment. Three types of Ag NPs were investigated for their antimicrobial, antibiofilm, and antivirulence properties on a total number of 132 AB strains isolated in the same temporal sequence from intra-hospital infections (IHIs), wastewater (WW), and surface water (SW) samples between 2019 and 2022 from different Romanian locations and characterized at the phenotypic and genotypic levels. The comparative analysis of the antimicrobial resistance (AR) profiles according to the isolation source and the geographical location demonstrated a decrease in MDR level in AB recovered from WW samples in 2022 from north-eastern/central/southern regions (N-E/C-W/analyzed strains S): 87.5/60/32.5%. The AB strains were lecithinase, caseinase, amylase, and lipase producers, had variable biofilm formation ability, and belonged to six genotypes associated with the presence of different virulence genes (ompA, csuE, bap, and bfmS). The Ag NPs synthesized with the solvothermal method exhibited an inhibitory effect on microbial growth, the adherence capacity to the inert substratum, and on the production of soluble virulence factors. We report here the first description of a powerful antibacterial agent against MDR AB strains circulating between hospitals and anthropically polluted water in Romania.

Amphiphilic peptide Mastoparan-B induces conformational changes within the AdeB efflux pump, down-regulates adeB gene expression, and restores antibiotic susceptibility in an MDR strain of Acinetobacter baumannii.

Mastoparan B (MP-B) is an amphiphilic peptide with a potent antimicrobial activity against most Gram-negative bacteria. However, there is little information available on the inhibition of the Acinetobacter baumannii resistance-nodulation-cell-division (RND) efflux pump using this antimicrobial peptide. Here, we carried out a series of in-silico experiments to find the mechanisms underlying the anti-efflux activity of MP-B using a multi-drug resistant (MDR) strain of A. baumannii (AB). According to our findings, MP-B demonstrated a potent antibacterial activity against an MDR-AB (minimum inhibitory concentration [MIC] = 1 μg/mL) followed by a 20-fold reduction in the adeB gene expression in the presence of sub-MIC of this peptide. Using Groningen Machine for Chemicals Simulation (GROMACS)via PyMOL Graphical User Interface (GUI), (we observed that, the AdeB transporter had conserved helix-turn-helix regions and a tight pore rich in Phe and Ala residues. To understand how inhibition of the AdeB is achieved, we generated 20 apo-MP-B poses using the InterPep and SiteMap tools. The high-quality model was created by homology modeling and used for docking via AutoDock/Vina to identify the MP-B binding sites. We established that the most apo-MP-B formed H-bonds to the backbone of five amino acids in the Helix-5. As a result, the dihedral angles of the involved amino acids shift by 9.0-9.6 Ǻ, causing a change in the conformation of the AdeB protein. This led to helix conformation stereoisomerization and block the AdeB activity. MP-B presumably has dual mechanisms. (1) It blocks the AdeB transporter by changing its conformation. (2) MP-B influences the adeB gene expression by binding to G-protein which laterally controls efflux regulators like MarA, RamA, SoxS, and Rob proteins.

Replicative Acinetobacter baumannii strains interfere with phagosomal maturation by modulating the vacuolar pH.

Bacterial pneumonia is a common infection of the lower respiratory tract that can afflict patients of all ages. Multidrug-resistant strains of Acinetobacter baumannii are increasingly responsible for causing nosocomial pneumonias, thus posing an urgent threat. Alveolar macrophages play a critical role in overcoming respiratory infections caused by this pathogen. Recently, we and others have shown that new clinical isolates of A. baumannii, but not the common lab strain ATCC 19606 (19606), can persist and replicate in macrophages within spacious vacuoles that we called Acinetobacter Containing Vacuoles (ACV). In this work, we demonstrate that the modern A. baumannii clinical isolate 398, but not the lab strain 19606, can infect alveolar macrophages and produce ACVs in vivo in a murine pneumonia model. Both strains initially interact with the macrophage endocytic pathway, as indicated by EEA1 and LAMP1 markers; however, the fate of these strains diverges at a later stage. While 19606 is eliminated in an autophagy pathway, 398 replicates in ACVs and are not degraded. We show that 398 reverts the natural acidification of the phagosome by secreting large amounts of ammonia, a by-product of amino acid catabolism. We propose that this ability to survive within macrophages may be critical for the persistence of clinical A. baumannii isolates in the lung during a respiratory infection.

Heterocyclic Diaryliodonium-Based Inhibitors of Carbapenem-Resistant Acinetobacter baumannii.

Finding new therapeutic strategies against Gram-negative pathogens such as Acinetobacter baumannii is challenging. Starting from diphenyleneiodonium (dPI) salts, which are moderate Gram-positive antibacterials, we synthesized a focused heterocyclic library and found a potent inhibitor of patient-derived multidrug-resistant Acinetobacter baumannii strains that significantly reduced bacterial burden in an animal model of infection caused by carbapenem-resistant Acinetobacter baumannii (CRAB), listed as a priority 1 critical pathogen by the World Health Organization. Next, using advanced chemoproteomics platforms and activity-based protein profiling (ABPP), we identified and biochemically validated betaine aldehyde dehydrogenase (BetB), an enzyme that is involved in the metabolism and maintenance of osmolarity, as a potential target for this compound. Together, using a new class of heterocyclic iodonium salts, a potent CRAB inhibitor was identified, and our study lays the foundation for the identification of new druggable targets against this critical pathogen. IMPORTANCE Discovery of novel antibiotics targeting multidrug-resistant (MDR) pathogens such as A. baumannii is an urgent, unmet medical need. Our work has highlighted the potential of this unique scaffold to annihilate MDR A. baumannii alone and in combination with amikacin both in vitro and in animals, that too without inducing resistance. Further in depth analysis identified central metabolism to be a putative target. Taken together, these experiments lay down the foundation for effective management of infections caused due to highly MDR pathogens.

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

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

Horizontal Gene Transfer, Fitness Costs and Mobility Shape the Spread of Antibiotic Resistance Genes into Experimental Populations of Acinetobacter Baylyi.

Horizontal gene transfer (HGT) is important for microbial evolution, but how evolutionary forces shape the frequencies of horizontally transferred genetic variants in the absence of strong selection remains an open question. In this study, we evolve laboratory populations of Acinetobacter baylyi (ADP1) with HGT from two clinically relevant strains of multidrug-resistant Acinetobacter baumannii (AB5075 and A9844). We find that DNA can cross the species barrier, even without strong selection, and despite substantial DNA sequence divergence between the two species. Our results confirm previous findings that HGT can drive the spread of antibiotic resistance genes (ARGs) without selection for that antibiotic, but not for all of the resistance genes present in the donor genome. We quantify the costs and benefits of horizontally transferred variants and use whole population sequencing to track the spread of ARGs from HGT donors into antibiotic-sensitive recipients. We find that even though most ARGs are taken up by populations of A. baylyi, the long-term fate of an individual gene depends both on its fitness cost and on the type of genetic element that carries the gene. Interestingly, we also found that an integron, but not its host plasmid, is able to spread in A. baylyi populations despite its strong deleterious effect. Altogether, our results show how HGT provides an evolutionary advantage to evolving populations by facilitating the spread of non-selected genetic variation including costly ARGs.

Antimicrobial activity of D-amino acid in combination with photo-sonoactivated hypericin nanoparticles against Acinetobacter baumannii

BackgroundThe emergence of multidrug-resistant Acinetobacter baumannii strains is increasing worldwide. To overcome these life-threatening infections, the development of new treatment approaches is critical. For this purpose, this study was conducted to determine the antimicrobial photo-sonodynamic therapy (aPSDT) using hypericin nanoparticles (HypNP) in combination with D-Tryptophan (D-Trp) against A. baumannii.Materials and methodsHypNP was synthesized and characterized, followed by the determination of the fractional inhibitory concentration (FIC) index of HypNP and D-Trp by checkerboard assay. Next, the antimicrobial and anti-biofilm potential of HypNP@D-Trp-mediated aPSDT against A. baumannii was evaluated. Finally, the anti-virulence activity of aPSDT using HypNP@D-Trp was accessed following the characterization of HypNP@D-Trp interaction with AbaI using in silico virtual screening and molecular docking.ResultsA synergistic activity in the combination of HypNP and D-Trp against A. baumannii was observed with a FIC index value of 0.5. There was a 5.10 log10 CFU/mL reduction in the cell viability of A. baumannii when the bacterial cells were treated with 1/2 × MIC of HypNP@D-Trp and subsequently exposed to ultrasound waves and blue light (P < 0.05). Moreover, a significant biofilm degradation effect on biofilm-associated cells of A. baumannii was observed after treatment with aPSDT using 2 × MIC of HypNP@D-Trp in comparison with the control groups (P < 0.05). According to the molecular docking analysis of the protein-ligand complex, Hyp with a high affinity for AbaI showed a binding affinity of − 9.41 kcal/mol. Also, the expression level of abaI gene was significantly downregulated by 10.32-fold in A. baumannii treated with aPSDT as comprised with the control group (P < 0.05).ConclusionsIt can be concluded that HypNP@D-Trp-mediated aPSDT can be considered a promising strategy to overcome the infections caused by A. baumannii by reducing the growth of bacterial biofilm and decreasing the expression of abaI as a gene involved in A. baumannii biofilm formation.

Arc discharge rapid synthesis of engineered copper oxides nano shapes with potent antibacterial activity against multi-drug resistant bacteria

Nowadays Nano metals have received an eminent compromise of attention. Even though different nanostructure of same metal maybe gives different results in wide range applications. Copper oxide (CuO-NPs) and Copper Nano wires (CuO-NWs) were prepared in controlled size via the alternating current Arc discharge process. Deionized water and argon gas were the chosen dielectric medium during the process to obtain 2 different forms of copper oxides. By changing the dielectric material from deionized water to argon gas the shape of CuO nanoparticles changed from spherical (CuO-NPs) to wires (CuO-NWS). The yield prepared depicted the purity of the prepared CuO, and their diameters were about 10 ± 5 nm and 30 ± 3 nm for CuO-NWs and CuO-NPs respectively. In vitro cytotoxic effect of the prepared CuO-NWs & CuO-NPs using human normal lung fibroblast cell line (WI-38 cells) revealed that CuO-NWs & CuO-NPs CC50 values were 458.8 and 155.6 µg/mL respectively. Both yields showed potent antibacterial activity against different multi-drug resistant Acinetobacter baumannii strains. A complete eradication of the bacterial growth was noticed after 4 Hrs incubation with CuO-NWs. Moreover, CuO-NWs showed superior antibacterial activity (with minimum inhibitory concentration reached 1.8 µg/mL) over CuO-NPs. The detailed antibacterial activity mechanism of CuO-NWs was further investigated; data proved the precipitation and adsorption of the nanoparticles on the bacterial cell surface leading to cell deformation with reactive oxygen species increment. The results explicated that the nanoparticles shape plays an essential role in the antibacterial activity. Rotational Arc discharge machine might be a promising tool to obtain various metal nanostructures with low cost and environmentally friendly with potent activity.

Multidrug-Resistant Strains of Acinetobacter baumannii from Intensive Care Unit Patients Show Genetic Diversity and Distribution of Genes Associated with Aminoglycoside Resistance

Multidrug-Resistant Strains of Acinetobacter baumannii from Intensive Care Unit Patients Show Genetic Diversity and Distribution of Genes Associated with Aminoglycoside Resistance

A rare occurrence of multidrug-resistant environmental Acinetobacter baumannii strains from the soil of Mangaluru, India.

Over the last decade, Acinetobacter baumannii has emerged as one of the main causes of infections acquired in the hospital setting. Outbreaks associated with this pathogen are caused mainly due to contamination and transmission in hospital territories. However, the natural habitats of A. baumannii of clinical significance still remain unclear. In this study, we highlight the isolation and identification of multidrug-resistant environmental strains of A. baumannii from the soil of Mangaluru city. All the recovered isolates were biofilm formers, and two isolates were multidrug-resistant and showed resistance to fluoroquinolone, aminoglycosides, sulfonamide, tetracycline, and carbapenems. In addition, they exhibited protease activity, and produced phospholipase C and siderophore. To the best of our knowledge, this is the first study to isolate and identify drug-resistant strains of A. baumannii from the soil.

Characterization of Novel Lytic Myoviridae Phage Infecting Multidrug-Resistant Acinetobacter baumannii and Synergistic Antimicrobial Efficacy between Phage and Sacha Inchi Oil.

Multidrug-resistant (MDR) strains of Acinetobacter baumannii have become a major cause of hospital-acquired infections, resulting in an increase in morbidity and mortality worldwide. Many alternative treatments, including phage therapy, are attractive approaches for overcoming problems posed by antibiotic resistance. A newly isolated phage, vWUPSU-specific MDR A. baumannii, showed a narrow host range against MDR A. baumannii. This research was conducted to isolate, characterize, and apply the phage with sacha inchi oil as an alternative antimicrobial agent. Genome analysis suggested that phage vWUPSU is a novel phage belonging to the family Myoviridae, order Caudoviridae. This phage prevented biofilm formation and eradicated preformed biofilms in a dose-dependent manner. In addition, a synergistic antimicrobial effect of the interaction between phage vWUPSU and sacha inchi oil on planktonic cells was observed. The combination of phage and sacha inchi oil significantly inhibited and removed biofilms, compared with the effects of either single treatment. The results of this work indicate that phage vWUPSU could potentially be applied to control MDR A. baumannii. The antibacterial and antibiofilm activities of the combination of phage vWUPSU and sacha inchi oil have attracted significant interests in the development of antibacterial phage products as beneficial treatment options.

The Antimicrobial Peptide Esc(1-21) Synergizes with Colistin in Inhibiting the Growth and in Killing Multidrug Resistant Acinetobacter baumannii Strains.

Multidrug-resistant microbial infections and the scarce availability of new antibiotics capable of eradicating them are posing a serious problem to global health security. Among the microorganisms that easily acquire resistance to antibiotics and that are the etiological cause of severe infections, there is Acinetobacter baumannii. Carbapenems are the principal agents used to treat A. baumannii infections. However, when strains develop resistance to this class of antibiotics, colistin is considered one of the last-resort drugs. However, the appearance of resistance to colistin also makes treatment of the Acinetobacter infections very difficult. Antimicrobial peptides (AMP) from the innate immunity hold promise as new alternative antibiotics due to their multiple biological properties. In this study, we characterized the activity and the membrane-perturbing mechanism of bactericidal action of a derivative of a frog-skin AMP, namely Esc(1-21), when used alone or in combination with colistin against multidrug-resistant A. baumannii clinical isolates. We found that the mixture of the two compounds had a synergistic effect in inhibiting the growth and killing of all of the tested strains. When combined at dosages below the minimal inhibitory concentration, the two drugs were also able to slow down the microbial growth and to potentiate the membrane-perturbing effect. To the best of our knowledge, this is the first report showing a synergistic effect between AMPs, i.e., Esc(1-21), and colistin against colistin-resistant A. baumannii clinical isolates, highlighting the potential clinical application of such combinational therapy.

An Analysis of the Novel Fluorocycline TP-6076 Bound to Both the Ribosome and Multidrug Efflux Pump AdeJ from Acinetobacter baumannii.

ABSTRACTAntibiotic resistance among bacterial pathogens continues to pose a serious global health threat. Multidrug-resistant (MDR) strains of the Gram-negative organism Acinetobacter baumannii utilize a number of resistance determinants to evade current antibiotics. One of the major resistance mechanisms employed by these pathogens is the use of multidrug efflux pumps. These pumps extrude xenobiotics directly out of bacterial cells, resulting in treatment failures when common antibiotics are administered. Here, the structure of the novel tetracycline antibiotic TP-6076, bound to both the Acinetobacter drug efflux pump AdeJ and the ribosome from Acinetobacter baumannii, using single-particle cryo-electron microscopy (cryo-EM), is elucidated. In this work, the structure of the AdeJ–TP-6076 complex is solved, and we show that AdeJ utilizes a network of hydrophobic interactions to recognize this fluorocycline. Concomitant with this, we elucidate three structures of TP-6076 bound to the A. baumannii ribosome and determine that its binding is stabilized largely by electrostatic interactions. We then compare the differences in binding modes between TP-6076 and the related tetracycline antibiotic eravacycline in both targets. These differences suggest that modifications to the tetracycline core may be able to alter AdeJ binding while maintaining interactions with the ribosome. Together, this work highlights how different mechanisms are used to stabilize the binding of tetracycline-based compounds to unique bacterial targets and provides guidance for the future clinical development of tetracycline antibiotics.

Molecular Analysis of Oxacillinase Genes and Identification of Drug Resistance Pattern in MDR Strains of Acinetobacter baumannii Isolated from Burn Wound Samples in Kermanshah, Iran

Introduction: Carbapenem Resistant Acinetobacter Baumannii (CRAB) is a dangerous nosocomial pathogen that can cause high mortality in patients. This bacterium has a remarkable ability to acquire various resistance mechanisms due to this it is considered as one of the health priorities. Aim: To investigate the prevalence of the OXA-23, OXA-24, and OXA-58 genes in Acinetobacter baumannii isolates collected from burn wound samples in Kermanshah, Iran. Materials and Methods: A cross-sectional study was done during 11 months period from December 2018 to October 2019, 74 A. baumannii isolates were collected from those admitted to the Burns Unit of Imam Khomeini Hospital in Kermanshah, Iran. The 74 A. baumannii isolates were detected using particular bacteriological methods. Following determination of the antibiotic sensitivity of the specimens using the disk diffusion technique, polymerase chain reaction was performed to determine the frequency of the OXA-23, OXA-24, and OXA-58 genes using their specific primers. Data were analysed using Fisher’s-exact test and Chi-squared test in Statistical Package for the Social Sciences (SPSS) version 20.0. A p-value &lt;0.05 was considered statistically significant. Results: All the 74 A. baumannii isolates were MultidrugResistant (MDR) (41 from males and 33 from females). The highest drug resistance was against cefotaxime (100%) and piperacillin (98.6%), while all the isolates were sensitive to polymyxin B and colistin. Oxacillinase genes with the highest and lowest frequencies were OXA-23 (64.7%) and OXA-58 (3.5%), respectively. The highest frequency of isolates with two genes were related to OXA-23 and OXA-24. A significant relationship was observed among the existence of oxacillinase genes and resistance to some antibiotics. Conclusion: The results of this study indicated the significance of OXA carbapenemase genes in burn patients. Due to the high drug resistance of A. baumannii isolates collected from wound samples, the identification of carbapenemase-producing A. baumannii isolates is paramount in developing prevention and control programs for these drug-resistant isolates.