Baumannii ATCC Research Articles

Divergent Synthesis and Antigenicity Evaluation of Core Oligosaccharides of the Lipopolysaccharides from Acinetobacter baumannii SMAL and ATCC 19606.

Acinetobacter baumannii poses a serious threat to human health. Pathogenic bacterial lipopolysaccharides (LPSs) are potent immunogens for the development of antibacterial vaccines. To investigate the antigenic properties of A. baumannii LPS, five well-defined core oligosaccharide fragments from the LPS of A. baumannii SMAL and ATCC 19606 were synthesized. A divergent synthesis strategy based on orthogonally protected α-(2 → 5)-linked Kdo dimer 6 was developed. Selective exposure of different positions in this key precursor and then elongation of sugar chains via stereocontrolled formation of both 1,2-trans and 1,2-cis-2-aminoglycosidic linkages permitted the efficient synthesis of the targets. The synthetic route also highlights a 4-O and then 7-O glycosylation sequence for assembly of the novel 4,7-branched Kdo framework. Antigenicity assay using the glycan microarray technique disclosed that tetrasaccharide 3 featuring both 4,7-branch and α-(2 → 5)-Kdo-Kdo structural elements was a potential antigenic determinant.

Co-Occurrence of Two Plasmids Encoding Transferable blaNDM-1 and tet(Y) Genes in Carbapenem-Resistant Acinetobacter bereziniae.

Acinetobacter bereziniae has emerged as a significant human pathogen, acquiring multiple antibiotic resistance genes, including carbapenemases. This study focuses on characterizing the plasmids harboring the blaNDM-1 and tet(Y) genes in two carbapenem-resistant A. bereziniae isolates (UCO-553 and UCO-554) obtained in Chile during the COVID-19 pandemic. Methods: Antibiotic susceptibility testing was conducted on UCO-553 and UCO-554. Both isolates underwent whole-genome sequencing to ascertain their sequence type (ST), core genome multilocus sequence-typing (cgMLST) profile, antibiotic resistance genes, plasmids, and mobile genetic elements. Conjugation experiments were performed for both isolates. Results: Both isolates exhibited broad resistance, including resistance to carbapenems, third-generation cephalosporins, fluoroquinolones, tetracycline, cotrimoxazole, and aminoglycosides. Both isolates belong to sequence type STPAS1761, with a difference of 17 out of 2984 alleles. Each isolate carried a 47,274 bp plasmid with blaNDM-1 and aph(3')-VI genes and two highly similar plasmids: a 35,184 bp plasmid with tet(Y), sul2, aph(6)-Id, and aph(3″)-Ib genes, and a 6078 bp plasmid containing the ant(2″)-Ia gene. Quinolone-resistance mutations were identified in the gyrA and parC genes of both isolates. Importantly, blaNDM-1 was located within a Tn125 transposon, and tet(Y) was embedded in a Tn5393 transposon. Conjugation experiments successfully transferred blaNDM-1 and tet(Y) into the A. baumannii ATCC 19606 strain, indicating the potential for horizontal gene transfer. Conclusions: This study highlights the critical role of plasmids in disseminating resistance genes in A. bereziniae and underscores the need for the continued genomic surveillance of this emerging pathogen. The findings emphasize the importance of monitoring A. bereziniae for its potential to cause difficult-to-treat infections and its capacity to spread resistance determinants against clinically significant antibiotics.

Adherence and cytotoxicity of Acinetobacter baumannii on human cervical carcinoma epithelial cells: Exploring the role of anti-OmpA antibodies

We investigated the invasion of Acinetobacter baumannii strains to epithelial cells and elucidated the role of antibodies against outer membrane protein A (OmpA). A. baumannii ATCC 19606 and clinical isolate 58ST were utilized. OmpA was expressed, purified, and administered to BALB/c mice, inducing anti-OmpA antibodies. OmpA cytotoxicity was evaluated. Two A. baumannii strains were selected to infect human cervical HeLa cells. Serum resistance was determined at sera dilutions. Adhesion, internalization, and proliferation of live and killed A. baumannii in HeLa cells were examined with and without anti-OmpA sera. HeLa cell viability was assessed with and without exposure of live A. baumannii strains to anti-OmpA sera. Cytoskeleton inhibitor experiments were conducted on epithelial cells to probe microfilament and microtubule involvement in A. baumannii invasion. OmpA prompted antibody production without toxicity in mice. A. baumannii strains displayed varying cell invasion abilities, notably the clinical strain exhibiting the highest invasion. A. baumannii cells localized within vacuoles during internalization, migrating towards the nucleus, using a zipper-like invasion process. Bacterial proliferation within host cells led to HeLa cell death. Pre-treatment with anti-OmpA antibodies significantly curbed adhesion and invasion of A. baumannii in HeLa cells. Microscopic imaging provided proof of the intracellular presence of A. baumannii in HeLa cells. In conclusion, the OmpA plays a crucial part in A. baumannii - epithelial cell interactions. The results add to our knowledge of pathogenesis during the initial stages of infection by A. baumannii.

New N-phenylpyrrolamide inhibitors of DNA gyrase with improved antibacterial activity.

This study presents the discovery of a new series of N-phenylpyrrolamide inhibitors of bacterial DNA gyrase with improved antibacterial activity. The most potent inhibitors had low nanomolar IC50 values against Escherichia coli DNA gyrase (IC50; 2-20 nM) and E. coli topoisomerase IV (22i, IC50 = 143 nM). Importantly, none of the compounds showed activity against human DNA topoisomerase IIα, indicating selectivity for bacterial targets. Among the tested compounds, 22e emerged as the most effective against Gram-positive bacteria with minimum inhibitory concentration (MIC) values of 0.25 μg mL-1 against Staphylococcus aureus ATCC 29213 and MRSA, and 0.125 μg mL-1 against Enterococcus faecalis ATCC 29212. For Gram-negative bacteria, compounds 23b and 23c showed the greatest efficacy with MIC values ranging from 4 to 32 μg mL-1 against E. coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, Acinetobacter baumannii ATCC 17978 and A. baumannii ATCC 19606. Notably, compound 23b showed promising activity against the clinically relevant Gram-negative pathogen Klebsiella pneumoniae ATCC 10031, with an MIC of 0.0625 μg mL-1. Furthermore, compounds 23a and 23c exhibited significantly lower susceptibility to resistance development compared to novobiocin in S. aureus ATCC 29213 and K. pneumoniae ATCC 10031. Overall, the most promising compounds of this series showed excellent on-target potency, marking a significant improvement over previous N-phenylpyrrolamide inhibitors.

Synergistic Antimicrobial Effects of Phage vB_AbaSi_W9 and Antibiotics against Acinetobacter baumannii Infection.

Acinetobacter baumannii is a challenging multidrug-resistant pathogen in healthcare. Phage vB_AbaSi_W9 (GenBank: PP146379.1), identified in our previous study, shows lytic activity against 26 (89.66%) of 29 carbapenem-resistant Acinetobacter baumannii (CRAB) strains with various sequence types (STs). It is a promising candidate for CRAB treatment; however, its lytic efficiency is insufficient for complete bacterial lysis. Therefore, this study aimed to investigate the clinical utility of the phage vB_AbaSi_W9 by identifying antimicrobial agents that show synergistic effects when combined with it. The A. baumannii ATCC17978 strain was used as the host for the phage vB_AbaSi_W9. Adsorption and one-step growth assays of the phage vB_AbaSi_W9 were performed at MOIs of 0.001 and 0.01, respectively. Four clinical strains of CRAB belonging to different sequence types, KBN10P04948 (ST191), LIS2013230 (ST208), KBN10P05982 (ST369), and KBN10P05231 (ST451), were used to investigate phage-antibiotic synergy. Five antibiotics were tested at the following concentration: meropenem (0.25-512 µg/mL); colistin, tigecycline, and rifampicin (0.25-256 µg/mL); and ampicillin/sulbactam (0.25/0.125-512/256 µg/mL). The in vitro synergistic effect of the phage and rifampicin was verified through an in vivo mouse infection model. Phage vB_AbaSi_W9 demonstrated 90% adsorption to host cells in 1 min, a 20 min latent period, and a burst size of 114 PFU/cell. Experiments combining phage vB_AbaSi_W9 with antibiotics demonstrated a pronounced synergistic effect against clinical strains when used with tigecycline and rifampicin. In a mouse model infected with CRAB KBN10P04948 (ST191), the group treated with rifampicin (100 μg/mL) and phage vB_AbaSi_W9 (MOI 1) achieved a 100% survival rate-a significant improvement over the phage-only treatment (8.3% survival rate) or antibiotic-only treatment (25% survival rate) groups. The bacteriophage vB_AbaSi_W9 demonstrated excellent synergy against CRAB strains when combined with tigecycline and rifampicin, suggesting potential candidates for phage-antibiotic combination therapy in treating CRAB infections.

TagP, a PAAR-domain containing protein, plays roles in the fitness and virulence of Acinetobacter baumannii.

Type VI secretion system (T6SS) is widely present in Gram-negative bacteria and directly mediates antagonistic prokaryote interactions. PAAR (proline-alanine-alanine-arginine repeats) proteins have been proven essential for T6SS-mediated secretion and target cell killing. Although PAAR proteins are commonly found in A. baumannii, their biological functions are not fully disclosed yet. In this study, we investigated the functions of a PAAR protein termed TagP (T6SS-associated-gene PAAR), encoded by the gene ACX60_RS09070 outside the core T6SS locus of A. baumannii strain ATCC 17978. In this study, tagP null and complement A. baumannii ATCC 17978 strains were constructed. The influence of TagP on T6SS function was investigated through Hcp detection and bacterial competition assay; the influence on environmental fitness was studied through in vitro growth, biofilm formation assay, surface motility assay, survivability in various simulated environmental conditions; the influence on pathogenicity was explored through cell adhesion and invasion assays, intramacrophage survival assay, serum survival assay, and G. melonella Killing assays. Quantitative transcriptomic and proteomic analyses were utilized to observe the global impact of TagP on bacterial status. Compared with the wildtype strain, the tagP null mutant was impaired in several tested phenotypes such as surface motility, biofilm formation, tolerance to adverse environments, adherence to eukaryotic cells, endurance to serum complement killing, and virulence to Galleria melonella. Notably, although RNA-Seq and proteomics analysis revealed that many genes were significantly down-regulated in the tagP null mutant compared to the wildtype strain, there is no significant difference in their antagonistic abilities. We also found that Histone-like nucleoid structuring protein (H-NS) was significantly upregulated in the tagP null mutant at both mRNA and protein levels. This study enriches our understanding of the biofunction of PAAR proteins in A. baumannii. The results indicates that TagP involved in a unique modulation of fitness and virulence control in A. baumannii, it is more than a classic PAAR protein involved in T6SS, while how TagP play roles in the fitness and virulence of A. baumannii needs further investigation to clarify.

Antibacterial activity and biosynthetic potential of Streptomyces sp. PBR19, isolated from forest rhizosphere soil of Assam.

An Actinomycetia isolate, designated as PBR19, was derived from the rhizosphere soil of Pobitora Wildlife Sanctuary (PWS), Assam, India. The isolate, identified as Streptomyces sp., shares a sequence similarity of 93.96% with its nearest type strain, Streptomyces atrovirens. This finding indicates the potential classification of PBR19 as a new taxon within the Actinomycetota phylum. PBR19 displayed notable antibacterial action against some ESKAPE pathogens. The ethyl acetate extract of PBR19 (EtAc-PBR19) showed the lowest minimum inhibitory concentration (MIC) of ≥ 0.195µg/mL against Acinetobacter baumannii ATCC BAA-1705. A lower MIC indicates higher potency against the tested pathogen. Scanning electron microscope (SEM) findings revealed significant changes in the cytoplasmic membrane structure of the pathogen. This suggests that the antibacterial activity may be linked to the disruption of the microbial membrane. The predominant chemical compound detected in the EtAc-PBR19 was identified as phenol, 3,5-bis(1,1-dimethylethyl), comprising 48.59% of the area percentage. Additionally, PBR19 was found to contain the type II polyketide synthases (PKS type II) gene associated with antibiotic synthesis. The predicted gene product of PKSII was identified as the macrolide antibiotic Megalomicin A. The taxonomic distinctiveness, potent antibacterial effects, and the presence of a gene associated with antibiotic synthesis suggest that PBR19 could be a valuable candidate for further exploration in drug development and synthetic biology. The study contributes to the broader understanding of microbial diversity and the potential for discovering bioactive compounds in less-explored environments.

Homo and Hetero-Branched Lipopeptide Dendrimers: Synthesis and Antimicrobial Activity

Di-branched and tetra-branched versions of a previously reported analogue of the lipopeptide battacin were successfully synthesised using thiol-maleimide click and 1, 2, 3-triazole click chemistry. Antimicrobial studies against drug resistant clinical isolates of Escherichia coli (ESBL E. coli Ctx-M14), Pseudomonas aeruginosa (P. aeruginosa Q502), and Methicillin resistant Staphylococcus aureus (MRSA ATCC 33593), as well as clinically isolated Acinetobacter baumannii (A. baumannii ATCC 19606), and P. aeruginosa (ATCC 27853), revealed that the dendrimeric peptides have antimicrobial activity in the low micromolar range (0.5 –– 4 μM) which was 10 times more potent than the monomer peptides. Under high salt concentrations (150 mM NaCl, 2 mM MgCl2, and 2.5 mM CaCl2) the di-branched lipopeptides retained their antimicrobial activity while the monomer peptides were not active (>100 μM). The di-branched triazole click lipopeptide, Peptide 12, was membrane lytic, showed faster killing kinetics, and exhibited antibiofilm activity against A. baumannii and MRSA and eradicated > 85 % preformed biofilms at low micromolar concentrations. The di-branched analogues were > 30-fold potent than the monomers against Candida albicans. Peptide 12 was not haemolytic (HC10 = 932.12 μM) and showed up to 40-fold higher selectivity against bacteria and fungi than the monomer peptide. Peptide 12 exhibited strong proteolytic stability (>80 % not degraded) in rat serum over 24 h whereas > 95 % of the thiol-maleimide analogue (Peptide 10) was degraded. The tetra-branched peptides showed comparable antibacterial potency to the di-branched analogues. These findings indicate that dual branching using triazole click chemistry is a promising strategy to improve the antimicrobial activity and proteolytic stability of battacin based lipopeptides. The information gathered can be used to build effective antimicrobial dendrimeric peptides as new peptide antibiotics.

AdeIJK Pump-Specific Inhibitors Effective against Multidrug Resistant Acinetobacter baumannii.

Multidrug-resistant Acinetobacter baumannii is a serious threat pathogen rapidly spreading in clinics and causing a range of complicated human infections. The major contributor to A. baumannii antibiotic resistance is the overproduction of AdeIJK and AdeABC multidrug efflux pumps of the resistance-nodulation-division (RND) superfamily of proteins. The dominant role of efflux in antibiotic resistance and the relatively high permeability of the A. baumannii outer membrane to amphiphilic compounds make this pathogen a promising target for the discovery of clinically relevant efflux pump inhibitors. In this study, we identified 4,6-diaminoquoniline analogs with inhibitory activities against A. baumannii AdeIJK efflux pump and followed up on these compounds with a focused synthetic program to improve the target specificity and to reduce cytotoxicity. We identified several candidates that potentiate antibacterial activities of antibiotics erythromycin, tetracycline, and novobiocin not only in the laboratory antibiotic susceptible strain A. baumannii ATCC17978 but also in multidrug-resistant clinical isolates AB5075 and AYE. The best analogs potentiated the activities of antibiotics in low micromolar concentrations, did not have antibacterial activities on their own, inhibited AdeIJK-mediated efflux of its fluorescent substrate ethidium ion, and had low cytotoxicity in A549 human lung epithelial cells.

Genetic characterization of plasmid-borne blaOXA-58 and blaOXA-72 in Acinetobacter pittii in Shaanxi, China

ObjectivesAcinetobacter pittii has emerged as an opportunistic nosocomial pathogen associated with hospital-acquired infections. The purpose of this study was to investigate the genetic structures of plasmids carrying carbapenemase genes blaOXA-58 and blaOXA-72 in A. pittii strains AR3676 and AR3651 isolated from patients. MethodsAntimicrobial susceptibility testing was performed using broth microdilution. Whole-genome sequencing and bioinformatics analysis were performed to characterize the genome of A. pittii AR3676 and AR3651. Conjugation experiments were conducted to evaluate plasmid transferability. Phylogenetic and comparative genomic analysis were performed to explore the characteristics of carbapenem-resistant A. pittii isolates worldwide. ResultsThe AR3676 strain showed resistance to imipenem. The 19 700-bp plasmid pAR3676-OXA-58 harboured blaOXA-58 with genetic contexts consisting of a truncated ISAba3-like-blaOXA58-ISAba3. Additionally, the AR3651 strain showed resistance to imipenem and meropenem. The AR3651 genome comprised one 9,837-bp RepA_AB plasmid pAR3651-OXA-72 harbouring blaOXA-72. This blaOXA-72 was flanked by XerC/XerD recombination sites. The conjugation of plasmids pAR3676-OXA-58 and pAR3651-OXA-72 from A. pittii to Acinetobacter baumannii ATCC 17978RIFR failed three independent times. Phylogenetic analysis of A. pittii strains AR3676, AR3651, and a further 504 A. pittii strains collected between 1966 and 2022 from various geographic localities revealed genetic diversity with a heterogeneous distribution of carbapenemase genes. ConclusionsA. pittii strains with a plasmid carrying blaOXA-58 or blaOXA-72 may serve as an important reservoir of carbapenemase genes. Carbapenemase genes on a single plasmid may facilitate their dissemination and persistence. Additionally, pdif sites and mobile elements play an important role in the mobilization of resistance genes and plasmid evolution.

Antimicrobial Properties of Newly Developed Silver-Enriched Red Onion-Polymer Composites.

Simple low-cost, nontoxic, environmentally friendly plant-extract-based polymer films play an important role in their application in medicine, the food industry, and agriculture. The addition of silver nanoparticles to the composition of these films enhances their antimicrobial capabilities and makes them suitable for the treatment and prevention of infections. In this study, polymer-based gels and films (AgRonPVA) containing silver nanoparticles (AgNPs) were produced at room temperature from fresh red onion peel extract ("Ron"), silver nitrate, and polyvinyl alcohol (PVA). Silver nanoparticles were synthesized directly in a polymer matrix, which was irradiated by UV light. The presence of nanoparticles was approved by analyzing characteristic local surface plasmon resonance peaks occurring in UV-Vis absorbance spectra of irradiated experimental samples. The proof of evidence was supported by the results of XRD and EDX measurements. The diffusion-based method was applied to investigate the antimicrobial activity of several types of microbes located in the environment of the produced samples. Bacteria Staphylococcus aureus ATCC 29213, Acinetobacter baumannii ATCC BAA 747, and Pseudomonas aeruginosa ATCC 15442; yeasts Candida parapsilosis CBS 8836 and Candida albicans ATCC 90028; and microscopic fungi assays Aspergillus flavus BTL G-33 and Aspergillus fumigatus BTL G-38 were used in this investigation. The greatest effect was observed on Staphylococcus aureus, Acinetobacter baumannii, and Pseudomonas aeruginosa bacteria, defining these films as potential candidates for antimicrobial applications. The antimicrobial features of the films were less effective against fungi and the weakest against yeasts.

Production and characterization of polyvinyl alcohol films containing essential oil

Packaging plays an important role in protecting foodstuffs against physicochemical damage and microbial activity, as well as extending shelf life. In recent years, petrochemical compounds that cause environmental pollution and contamination due to their non-biodegradability have been replaced by biocompatible polymer-based films in the food packaging industry. Due to aromatic essential oils (EO), various biological activities, and their potential to replace chemical preservatives in the field of food preservation, Star Anise essential oil, which has properties, such as free radical scavenger, antibacterial, antifungal and antiviral, was used as an additive in this study. Biodegradable and biocompatible polyvinyl alcohol (PVA) polymer was used as the matrix and polymer-based films were produced in 3 different concentrations. Spectral analysis, structural, chemical, and thermal characterizations, and surface morphologies of the produced films by the direct incorporation method were examined. In addition, the antibacterial activities of the films on Staphylococcus epidermidis ATCC 12228, Escherichia coli ATCC 25922, and Acinetobacter baumannii ATCC BAA 747 bacteria were investigated. As a result of the examinations, it was determined that an interfacial interaction occurred between the matrix and the filler, and the produced films were thermally resistant and showed antibacterial activity against Gram (+)/Gram (−) bacteria. Consequently, it can be concluded that PVA films containing Star Anise essential oil present a prospective substitute in a variety of industrial packaging systems, including those for food, medicine, and cosmetics.

Roles of DJ41_1407 and DJ41_1408 in Acinetobacter baumannii ATCC19606 Virulence and Antibiotic Response.

Acinetobacter baumannii is a major cause of nosocomial infections, and its highly adaptive nature and broad range of antibiotic resistance enable it to persist in hospital environments. A. baumannii often employs two-component systems (TCSs) to regulate adaptive responses and virulence-related traits. This study describes a previously uncharacterized TCS in the A. baumannii ATCC19606 strain, consisting of a transcriptional sensor, DJ41_1407, and its regulator, DJ41_1408, located adjacent to GacA of the GacSA TCS. Markerless mutagenesis was performed to construct DJ41_1407 and DJ41_1408 single and double mutants. DJ41_1408 was found to upregulate 49 genes and downregulate 43 genes, most of which were associated with carbon metabolism and other metabolic pathways, such as benzoate degradation. MEME analysis revealed a putative binding box for DJ41_1408, 5'TGTAAATRATTAYCAWTWAT3'. Colony size, motility, biofilm-forming ability, virulence, and antibiotic resistance of DJ41_1407 and DJ41_1408 single and double mutant strains were assessed against wild type. DJ41_1407 was found to enhance motility, while DJ41_1408 was found to upregulate biofilm-forming ability, and may also modulate antibiotic response. Both DJ41_1407 and DJ41_1408 suppressed virulence, based on results from a G. mellonella infection assay. These results showcase a novel A. baumannii TCS involved in metabolism, with effects on motility, biofilm-forming ability, virulence, and antibiotic response.

Simultaneous effect of medicinal plants as natural photosensitizers and low-level laser on photodynamic inactivation.

Photodynamic inactivation (PDI) technology is a promising alternative to antibiotics. This technology is defined as the inhibition of bacterial growth with photosensitizers while irradiated with low-level laser light in the wavelength of 532 ± 2.08nm. A challenging area in this field is selecting photosensitizers with antibacterial potential. In this paper, to enhance the antibacterial efficiency, the photosensitizers (the selected plant extracts) with a high absorption peak at the selected laser frequency, 532nm, were prepared. Low-concentration ethanolic plant extracts of Hibiscus sabdariffa and Opuntia ficus-indica were found to exhibit significant antibacterial activity against, Acinetobacter baumannii ATCC 19606 and, Staphylococcus aureus ATCC 33591 as two important human pathogenic bacteria. The effectiveness of these natural photosensitizers was measured by determining their Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) values and by performing a time-killing assay in the absence and the presence of laser irradiation. Our results showed that the combination of low-level laser irradiation and the selected photosensitizers had excellent potential for treating in vitro bacterial infections. Therefore, PDI technology has great potential as a viable alternative to traditional antibiotics for combating bacterial infections. This study presents a promising avenue for further exploration of PDI and the use of laser technology in medical science.

The synergic and addictive activity of biogenic silver nanoparticle associated with meropenem against carbapenem-resistant Acinetobacter baumannii.

Antibiotic management of infections caused by Acinetobacter baumannii often fails due to antibiotic resistance (especially to carbapenems) and biofilm-forming strains. Thus, the objective here was to evaluate in vitro the antibacterial and antibiofilm activity of biogenic silver nanoparticle (Bio-AgNP) combined with meropenem, against multidrug-resistant isolates of A. baumannii. In this study, A. baumannii ATCC® 19606™ and four carbapenem-resistant A. baumannii (Ab) strains were used. The antibacterial activity of Bio-AgNP and meropenem was evaluated through broth microdilution. The effect of the Bio-AgNP association with meropenem was determined by the checkboard method. Also, the time-kill assay and the integrity of the bacterial cell membrane were evaluated. Furthermore, the antibiofilm activity of Bio-AgNP and meropenem alone and in combination was determined. Bio-AgNP has antibacterial activity with minimum inhibitory concentration (MIC) and minimum bactericidal concentration ranging from 0.46 to 1.87 μg ml-1. The combination of Bio-AgNP and meropenem showed a synergistic and additive effect against Ab strains, and Bio-AgNP was able to reduce the MIC of meropenem from 4- to 8-fold. Considering the time-kill of the cell, meropenem and Bio-AgNP when used in combination reduced bacterial load to undetectable levels within 10 min to 24 h after treatment. Protein leakage was observed in all treatments evaluated. When combined, meropenem/Bio-AgNP presents biofilm inhibition for Ab2 isolate and ATCC® 19606™, with 21% and 19%, and disrupts the biofilm from 22% to 50%, respectively. The increase in nonviable cells in the biofilm can be observed after treatment with Bio-AgNP and meropenem in carbapenem-resistant A. baumannii strains. The combination of Bio-AgNP with meropenem can be a therapeutic option in the treatment of infections caused by carbapenem-resistant A. baumannii.

Fragment synthesis of A. baumannii ATCC 17961 O-antigen

Acinetobacter baumannii can cause many diseases including septiceamia, pneumonia, meningitis, soft tissue and urinary tract infections. Herein, we described the synthesis of one trisaccharide and two tetrasaccharide fragments derived from A. baumannii ATCC 17961 O-antigen, which can be used for screening novel glyco-epitope and developing synthetic carbohydrate-based vaccine against A. baumannii infection. The overall yields for the synthesis of trisaccharide 1, tetrasaccharide 2 and tetrasaccharide 3 are 26.8% (8 steps), 21.6% (9 steps) and 24.5% (6 steps), respectively.

Gene Expression of Ethanol and Acetate Metabolic Pathways in the Acinetobacter baumannii EmaSR Regulon.

Previous studies have confirmed the involvement of EmaSR (ethanol metabolism a sensor/regulator) in the regulation of Acinetobacter baumannii ATCC 19606 ethanol and acetate metabolism. RNA-seq analysis further revealed that DJ41_568-571, DJ41_2796, DJ41_3218, and DJ41_3568 regulatory gene clusters potentially participate in ethanol and acetate metabolism under the control of EmaSR. This study fused the EmaSR regulon promoter segments with reporter genes and used fluorescence expression levels to determine whether EmaSR influences regulon expression in ethanol or acetate salt environments. The enzymatic function and kinetics of significantly regulated regulons were also studied. The EmaSR regulons P2796 and P3218 exhibited > 2-fold increase in fluorescence expression in wild type compared to mutant strains in both ethanol and acetate environments, and PemaR demonstrated a comparable trend. Moreover, increases in DJ41_2796 concentration enhanced the conversion of acetate and succinyl-CoA into acetyl-CoA and succinate, suggesting that DJ41_2796 possesses acetate: succinyl-CoA transferase (ASCT) activity. The kcat/KM values for DJ41_2796 with potassium acetate, sodium acetate, and succinyl-CoA were 0.2131, 0.4547, and 20.4623 mM-1s-1, respectively. In A. baumannii, EmaSR controls genes involved in ethanol and acetate metabolism, and the EmaSR regulon DJ41_2796 was found to possess ASCT activity.

Size-Controlled Synthesis of Gold Nanoparticles Tethering Antimicrobial Peptides with Potent Broad-Spectrum Antimicrobial and Antibiofilm Activities.

New antimicrobials are urgently needed to combat the rising global health concern of antibiotic resistance. Antimicrobial peptides (AMPs) are one of the leading candidates as new antimicrobials since they target bacterial membranes and are therefore less prone to bacterial resistance. However, poor enzymatic stability, high production costs, and toxicity are drawbacks that limit their clinical use. Conjugation of AMPs to gold nanoparticles (NPs) may help to improve enzymatic stability and, thus, their overall antimicrobial efficiency. We did a one-pot synthesis of size-controlled (10 nm) gold NPs selectively conjugated to lipopeptides and determined their antibacterial activity. The conjugates exhibited potent (0.13-1.25 μM) antimicrobial activity against clinical isolates, including Gram-positive methicillin-resistant Staphylococcus aureus (S. aureus) ATCC33593, Gram-negative Escherichia coli (E. coli) CTX-M-14, multidrug-resistant Pseudomonas aeruginosa LESB58 and Acinetobacter baumannii ATCC19606, and showed promising activity (90% inhibition of initial biofilms and 80% reduction of preformed biofilms) against S. aureus and E. coli DH5α biofilms at low micromolar concentrations. The conjugates were stable in rat serum and not toxic to representative mammalian cell lines in vitro (≤64 μM) and in vivo (≤100 μM).

Selective inhibitory activity of multidrug-resistant bacteria by zinc oxide nanoparticles

The emergence of multidrug-resistant bacteria has attracted much attention from the global community due to their potential to cause harm to health. In this context, ZnO nanoparticles (NPs) produced under different synthesis conditions were successfully applied to inhibit several species of multiresistant bacteria from clinical isolates. Five gram-positive (Staphylococcus epidermidis ATCC 35984, Staphylococcus aureus ATCC 25923, S. aureus ATCC 8095, Enterococcus faecalis ATCC 29212, and Enterococcus faecium ATCC 700221) and four gram-negative bacterial isolates (Klebsiella pneumoniae ATCC 700603, Escherichia coli ATCC 25922, Acinetobacter baumannii ATCC 19606, and Pseudomonas aeruginosa ATCC 27853), known to be involved in healthcare-associated infections and multidrug resistance, were selected for this study. Due to their physicochemical properties, we found that ZnO NPs can exhibit selective inhibition. The minimum inhibitory concentration (MIC) for multidrug-resistant bacteria sensitive to ZnO NPS was determined from varying contact time and catalyst concentration from exhaustive tests. Different characterization techniques were studied to determine the crystalline, optical, morphological, and photocatalytic characteristics of ZnO NPs. The bacterial inhibition mechanisms were discussed in detail with support of photocatalytic assays and cytotoxicity of plant species. In addition, ZnO NPs have also shown great potential for application in the environmental remediation of ecosystems contaminated by organic pollutants due to their efficiency in degrading the dye methylene blue (MB) under UV light with a photocatalytic efficiency of 75% in 60 min. The ZnO NPs showed great potential for multidrug-resistant bacteria, with MICs ranging from 256 to 512 mg/L. This demonstrates that the ZnO NPs produced here have the potential to be used as a technology with great application potential in materials used in hospital environments to mitigate the growth and development of these classes of multi-resistant bacteria.

Characterization of a novel bacteriophage endolysin (LysAB1245) with extended lytic activity against distinct capsular types associated with Acinetobacter baumannii resistance.

Capsular polysaccharides are considered as major virulence factors associated with the ability of multidrug-resistant (MDR) Acinetobacter baumannii to cause severe infections. In this study, LysAB1245, a novel bacteriophage-encoded endolysin consisting of a lysozyme-like domain from phage T1245 was successfully expressed, purified, and evaluated for its antibacterial activity against distinct capsular types associated with A. baumannii resistance. The results revealed a broad spectrum activity of LysAB1245 against all clinical MDR A. baumannii isolates belonging to capsular type (KL) 2, 3, 6, 10, 47, 49, and 52 and A. baumannii ATCC 19606. At 2 h following the treatment with 1.7 unit/reaction of LysAB1245, more than 3 log reduction in the numbers of bacterial survival was observed. In addition, LysAB1245 displayed rapid bactericidal activity within 30 min (nearly 3 log CFU/mL of bacterial reduction). Thermostability assay indicated that LysAB1245 was stable over a broad range of temperature from 4 to 70°C, while pH sensitivity assay demonstrated a wide range of pH from 4.5 to 10.5. Furthermore, both minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of LysAB1245 against all MDR A. baumannii isolates and A. baumannii ATCC 19606 were 4.21 μg/mL (0.1 unit/reaction). Conclusively, these results suggest that LysAB1245 possesses potential application for the treatment of nosocomial MDR A. baumannii infections.