Pathogenic Gram-negative Bacteria Research Articles

Photocatalytic self-cleaning membrane with polyaniline/NH2-MIL-125 heterojunction for highly oil-water/seawater separation and bacterial inactivation

Emulsified oils and microbial contaminations in water environments have posed huge risks to human health and ecological balance. In this work, we fabricated a polyaniline/NH2-MIL-125 (PANI/MIL) heterojunction decorated hydrolyzed polyacrylonitrile (HPAN) membrane with photocatalytic self-cleaning property for oil–water separation and bacterial inactivation. In which, PAN membrane was prepared by electrospinning and then HPAN membrane was obtained by alkaline hydrolysis. The photo-responsive PANI/MIL heterojunction was immobilized on HPAN membrane by vacuum-assisted assembly using protocatechuic acid (PCA) as the binder. The resultant PANI/MIL@HPAN composite membrane has a wettability of in-air superamphilicity and underwater superoleophobicity as well as surface nano-micro heterostructure. The composite membrane showed good separation efficiency (above 99.4%) and high flux (1446–3744 L m−2h−1) in a series of oil-in-water/seawater emulsions separation. In particular, the membrane can effectively deal with viscous oil fouling under visible light to achieve a desired flux recovery ratio (FRR) after separating crude oil from water, which was ascribed to the self-cleaning capacity originating from the surface coating photocatalyst. Meanwhile, the multifunctional composite membrane showed 100% photocatalytic inactivation efficiency against pathogenic Gram-negative bacteria E. coli and Gram-positive bacteria S. aureus (6 log units) in water under visible light with low power intensity. The oil–water separation performance as well as photocatalytic inactivation efficiency of PANI/MIL@HPAN are superior to MIL@HPAN. The studies on the wettability, photothermal properties and photoelectric properties suggested that the coupling of conductive polymer PANI can simultaneously enhance the underwater superoleophobicity of the composite membrane, as well as improve the photocatalytic activity by creating a type II heterojunction to promote the separation of charge carriers and amplifying the photothermal effect, making the PANI/MIL@HPAN multifunctional membrane achieve the improved oil/water separation performance and antibacterial activity synergistically. This work provides a new strategy for developing effective self-cleaning membranes both toward oil/water separation and bacterial inactivation applications based on MIL metal–organic framework coupling with conductive polymers.

A Single DNA Point Mutation Leads to the Formation of a Cysteine-Tyrosine Crosslink in the Cysteine Dioxygenase from Bacillus subtilis.

Cysteine dioxygenase (CDO) is a non-heme iron-containing enzyme that catalyzes the oxidation of cysteine (Cys) to cysteine sulfinic acid (CSA). Crystal structures of eukaryotic CDOs revealed the presence of an unusual crosslink between the sulfur of a cysteine residue (C93 in Mus musculus CDO, MmCDO) and a carbon atom adjacent to the phenyl group of a tyrosine residue (Y157). Formation of this crosslink occurs over time as a byproduct of catalysis and increases the catalytic efficiency of CDO by at least 10-fold. Interestingly, in bacterial CDOs, the residue corresponding to C93 is replaced by a highly conserved glycine (G82 in Bacillus subtilis CDO, BsCDO), which precludes the formation of a C-Y crosslink in these enzymes; yet bacterial CDOs achieve turnover rates paralleling those of fully crosslinked eukaryotic CDOs. In the present study, we prepared the G82C variant of BsCDO to determine if a single DNA point mutation could lead to C-Y crosslink formation in this enzyme. We used gel electrophoresis, peptide mass spectrometry, electron paramagnetic resonance spectroscopy, and kinetic assays to characterize this variant alongside the natively crosslinked wild-type (WT) MmCDO and the natively non-crosslinked WT BsCDO. Collectively, our results provide compelling evidence that the G82C BsCDO variant is indeed capable of C-Y crosslink formation. Our kinetic studies indicate that G82C BsCDO has a reduced catalytic efficiency compared to WT BsCDO and that activity increases as the ratio of crosslinked to non-crosslinked enzyme increases. Finally, by carrying out a bioinformatic analysis of the CDO family, we were able to identify a large number of putatively crosslinked bacterial CDOs, the majority of which are from Gram-negative pathogenic bacteria.

Synthesis, characterization, and biological evaluation of new chitosan derivative bearing diphenyl pyrazole moiety

This work reports the synthesis of a new pyrazole derivative by reacting 5-amino-1,3-diphenyl pyrazole with succinic anhydride and bearing the product chemically on the chitosan chains via amide linkage to achieve a new chitosan derivative (DPPS-CH). The prepared chitosan derivative was analyzed by IR, NMR, elemental analysis, XRD, TGA-DTG, and SEM. As compared with chitosan, DPPS-CH showed an amorphous and porous structure. Coats-Redfern results showed that the thermal activation energy for the first decomposition of DPPS-CH is 43.72 KJ mol−1 lower than that required for chitosan (88.32 KJ mol−1), indicating the accelerating effect of DPPS on the thermal decomposition of DPPS-CH. The DPPS-CH manifested a powerful wide spectrum antimicrobial potential against pathogenic gram-positive and gram-negative bacteria and Candida albicans at minute concentrations (MIC = 50 μg mL−1) compared to chitosan (MIC = 100 μg mL−1). The MTT assay proved the toxic properties of DPPS-CH against a cancer cell line (MCF-7) at a minute concentration (IC50 = 15.14 μg mL−1) while affecting normal cells (WI-38) at seven times this concentration (IC50 = 107.8 μg mL−1). According to the current findings, the chitosan derivative developed in this work appears to be a promising material for use in biological domains.

Exploring the Health Benefits of Yeast Isolated from Traditional Fermented Foods in Korea: Anti-Inflammatory and Functional Properties of Saccharomyces and Non-Saccharomyces Strains.

Traditional yeast (Saccharomyces cerevisiae) has been used for its benefits in various fermentation processes; the benefits of non-Saccharomyces yeast as a material for food, feed, and pharmaceuticals have been studied recently. This study evaluated the anti-inflammatory activity and extracellular functional characteristics of wild-type yeasts isolated from traditional fermented foods (doenjang (common name: soybean paste) and nuruk) in Korea. The viability of the yeast and lipopolysaccharide (LPS)-stimulated RAWBlue™ cells was improved, similar to unstimulated RAWBlue™ cells, and the isolates demonstrated NF-κB inhibitory activity. Yeast suppressed the nitric oxide production in LPS-stimulated RAWBlue™ cells, which was attributed to the inhibition of iNOS or COX-2 mRNA expression depending on the strain. Although there were differences depending on the strain, the production of anti-inflammatory cytokines was reduced in the yeast and LPS-stimulated RAWBlue™ cells, some of which were demonstrated at the mRNA level. In addition, the isolates exhibited high antioxidant and antihypertensive activities (similar to the positive control), which varied depending on the strain. This suggests that yeast can be used for fermentation with enhanced antioxidant and antihypertensive activities. Furthermore, the isolates inhibited the growth of pathogenic Gram-negative bacteria, indicating that yeast can inhibit food spoilage and the growth of pathogenic bacteria during fermentation. Consequently, utilizing raw materials to cultivate yeast strains could be a promising avenue for developing functional foods to prevent and treat inflammatory reactions; such foods may exhibit antioxidant, antihypertensive, and antibacterial properties.

Efficient synthesis, crystallography study, antibacterial/antifungal activities, DFT/ADMET studies and molecular docking of novel α-aminophosphonates

An efficient method for the synthesis of a new series of α-aminophosphonates has been developed in a one-pot Kabachnik-Fields reaction of 4-methylaminophenol with various aldehydes and triethylphosphite under microwave irradiation and neat conditions using ZnO nanoparticles as a reusable and heterogeneous catalyst, with 82–93% yield at 250 Hz within 2-5 min. A single crystal of the studied compound 3e was selected for X-ray diffraction analysis, it crystallizes in the monoclinic crystal system with P 21/n space group. All the compounds were evaluated for their antimicrobial against a panel of Gram-negative pathogenic bacteria such as Escherichia coli, Klebsiella pneumoniae, Acinetobacter baumannii, Serratia marcescens, Morganella morganii, Pseudomonas aeruginosa and Gram-positive :Staphylococcus aureus and against fungi : Candida albicans, Candida krusei, Candida kefyr, Candida lusitaniae, and Candida tropicalis. Further in silico target hunting reveals the antibacterial activity of the designed compounds by inhibiting Dihydropteroate synthase and all the designed compounds have shown significant drug-like characteristics.

Comparative evaluation of protective immunity against Francisella tularensis induced by subunit or adenovirus-vectored vaccines.

Tularemia is a highly contagious disease caused by infection with Francisella tularensis (Ft), a pathogenic intracellular gram-negative bacterium that infects a wide range of animals and causes severe disease and death in people, making it a public health concern. Vaccines are the most effective way to prevent tularemia. However, there are no Food and Drug Administration (FDA)-approved Ft vaccines thus far due to safety concerns. Herein, three membrane proteins of Ft, Tul4, OmpA, and FopA, and a molecular chaperone, DnaK, were identified as potential protective antigens using a multifactor protective antigen platform. Moreover, the recombinant DnaK, FopA, and Tul4 protein vaccines elicited a high level of IgG antibodies but did not protect against challenge. In contrast, protective immunity was elicited by a replication-defective human type 5 adenovirus (Ad5) encoding the Tul4, OmpA, FopA, and DnaK proteins (Ad5-Tul4, Ad5-OmpA, Ad5-FopA, and Ad5-DnaK) after a single immunization, and all Ad5-based vaccines stimulated a Th1-biased immune response. Moreover, intramuscular and intranasal vaccination with Ad5-Tul4 using the prime-boost strategy effectively eliminated Ft lung, spleen and liver colonization and provided nearly 80% protection against intranasal challenge with the Ft live vaccine strain (LVS). Only intramuscular, not intranasal vaccination, with Ad5-Tul4 protected mice from intraperitoneal challenge. This study provides a comprehensive comparison of protective immunity against Ft provided by subunit or adenovirus-vectored vaccines and suggests that mucosal vaccination with Ad5-Tul4 may yield desirable protective efficacy against mucosal infection, while intramuscular vaccination offers greater overall protection against intraperitoneal tularemia.

Long-chain polyphosphates inhibit type I interferon signaling and augment LPS-induced cytokine secretion in human leukocytes.

Inorganic polyphosphates are evolutionarily conserved bioactive phosphate polymers found as various chain lengths in all living organisms. In mammals, polyphosphates play a vital role in the regulation of cellular metabolism, coagulation, and inflammation. Long-chain polyphosphates are found along with endotoxins in pathogenic gram-negative bacteria and can participate in bacterial virulence. We aimed to investigate whether exogenously administered polyphosphates modulate human leukocyte function in vitro by treating the cells with 3 different chain lengths of polyphosphates (P14, P100, and P700). The long-chain polyphosphates, P700, had a remarkable capacity to downregulate type I interferon signaling dose dependently in THP1-Dual cells while only a slight elevation could be observed in the NF-κB pathway with the highest dose of P700. P700 treatment decreased lipopolysaccharide-induced IFNβ transcription and secretion, reduced STAT1 phosphorylation, and downregulated subsequent interferon-stimulated gene expression in primary human peripheral blood mononuclear cells. P700 also augmented lipopolysaccharide-induced secretion of IL-1α, IL-1β, IL-4, IL-5, IL-10, and IFNγ. Furthermore, P700 has previously been reported to increase the phosphorylation of several intracellular signaling mediators, such as AKT, mTOR, ERK, p38, GSK3α/β, HSP27, and JNK pathway components, which was supported by our findings. Taken together, these observations demonstrate the extensive modulatory effects P700 has on cytokine signaling and the inhibitory effects specifically targeted to type I interferon signaling in human leukocytes.

Scope and Limitations of Exploiting the Ability of the Chemosensitizer NV716 to Enhance the Activity of Tetracycline Derivatives against Pseudomonas aeruginosa.

The spread of antibiotic resistance is an urgent threat to global health that requires new therapeutic approaches. Treatments for pathogenic Gram-negative bacteria are particularly challenging to identify due to the robust OM permeability barrier in these organisms. One strategy is to use antibiotic adjuvants, a class of drugs that have no significant antibacterial activity on their own but can act synergistically with certain antibiotics. Previous studies described the discovery and development of polyaminoisoprenyl molecules as antibiotic adjuvants with an OM effect. In particular, the compound NV716 has been shown to sensitize Pseudomonas aeruginosa to tetracycline antibiotics such as doxycycline. Here, we sought to explore the disruption of OM to sensitize P. aeruginosa to otherwise inactive antimicrobials using a series of tetracycline derivatives in the presence of NV716. We found that OM disruption expands the hydrophobicity threshold consistent with antibacterial activity to include hydrophobic molecules, thereby altering permeation rules in Gram-negative bacteria.

Green Synthesis and Bioactivity of Copper Nanoparticles from Asparagus aethiopicus and Asparagus densiflorus

An aqueous extract of the shade-dried parts of Asparagus aethiopicus L. and Asparagus densiflorus (Kunth) Jessop was used to synthesize copper (CuO) nanoparticles (Cu NPs). UV-visible spectroscopy was performed to assess the formation of Cu NPs. Maximum absorbance was obtained between 310–360 nm, confirming the formation of Cu NPs. CuO NPs were effective against Pseudomonas aeruginosa (ATCC 27853), a gram-negative human pathogenic bacterium. The bacterial growth curve showed that the NPs inhibited bacterial growth. This study was conducted using different parts of the plant, such as the roots, shoots, fruits, and seeds of A. aethiopicus and the roots and shoots of A. densiflorus. The fruit and seeds of A. aethiopicus showed better results than the roots and shoots. Therefore, employing green synthetic processes inhibits the release of harmful by-products. Compared to traditional techniques of NP synthesis, the transition to the extracellular production of CuO NPs utilizing dried biomass appears to be economical and environmentally beneficial.

Structural Requirements for Ga3+ Coordination in Synthetic Analogues of the Siderophore Piscibactin Deduced by Chemical Synthesis and Density Functional Theory Calculations.

Stereoselective total synthesis of several analogues of piscibactin (Pcb), the siderophore produced by different pathogenic Gram-negative bacteria, was performed. The acid-sensitive α-methylthiazoline moiety was replaced by a more stable thiazole ring, differing in the configuration of the OH group at the C-13 position. The ability of these Pcb analogues to form complexes with Ga3+ as a mimic of Fe3+ showed that the configuration of the hydroxyl group at C-13 as 13S is crucial for the chelation of Ga3+ to preserve the metal coordination, while the presence of a thiazole ring instead of the α-methylthiazoline moiety does not affect such coordination. A complete 1H and 13C NMR chemical shift assignment of the diastereoisomer mixtures around C9/C10 was done for diagnostic stereochemical disposition. Additionally, density functional theory calculations were performed not only for confirming the stereochemistry of the Ga3+ complex among the six possible diastereoisomers but also for deducing the ability of these to form octahedral coordination spheres with gallium. Finally, the lack of antimicrobial activity of Pcb and Pcb thiazole analogue Ga3+ complexes against Vibrio anguillarum agrees with one of the roles of siderophores in protecting pathogens from metal ion toxicity. The efficient metal coordination shown by this scaffold suggests its possible use as a starting point for the design of new chelating agents or vectors for the development of new antibacterials that exploit the "Trojan horse" strategy using the microbial iron uptake mechanisms. The results obtained will be of great help in the development of biotechnological applications for these types of compounds.

A Potential Adhesin/Invasin STM0306 Participates in Host Cell Inflammation Induced by Salmonella enterica Serovar Typhimurium.

Salmonella enterica serovar typhimurium (S. Typhimurium) is a common Gram-negative foodborne pathogenic bacterium that causes gastrointestinal disease in humans and animals. It is well known that adhesins and invasins play crucial roles in the infection mechanism of S. Typhimurium. S. Typhimurium STM0306 has been denoted as a putative protein and its functions have rarely been reported. In this study, we constructed the STM0306 gene mutant strain of S. Typhimurium and purified the recombinant STM0306 from Escherichia coli. Deletion of the STM0306 gene resulted in reduced adhesion and invasion of S. Typhimurium to IPEC-J2, Caco-2, and RAW264.7 cells. In addition, STM0306 could bind to intestinal epithelial cells and induced F-actin modulation in IPEC-J2 cells. Furthermore, we found that STM0306 activated the nuclear factor kappa B (NF-κB) signaling pathway and increased the mRNA expression of pro-inflammatory cytokines such as IL-1β, TNF-α, as well as chemokine CXCL2, thus resulting in cellular inflammation in host cells. In vivo, the deletion of the STM0306 gene led to reduced pathogenicity of S. Typhimurium, as evidenced by lower fecal bacterial counts and reduced body weight loss in S. Typhimurium infected mice. In conclusion, the STM0306 of S. Typhimurium is an important adhesin/invasin involved in the pathogenic process and cellular inflammation of the host.

Mass spectrometric analysis of bioactive conditioned media of bacteria isolated from reptilian gut.

To determine whether selected gut bacteria of crocodile exhibit antibacterial properties. Two bacteria isolated from Crocodylus porosus gut were used, namely: Pseudomonas aeruginosa and Aeromonas dhakensis. Conditioned media were tested against pathogenic bacteria and metabolites were analyzed using liquid chromatography-mass spectrometry. Antibacterial assays revealed that conditioned media showed potent effects against pathogenic Gram-positive and Gram-negative bacteria. LC-MS revealed identity of 210 metabolites. The abundant metabolites were, N-Acetyl-L-tyrosine, Acetaminophen, Trans-Ferulic acid, N, N-Dimethylformamide, Pyrocatechol, Cyclohexanone, Diphenhydramine, Melatonin, Gamma-terpinene, Cysteamine, 3-phenoxypropionic acid, Indole-3-carbinol, Benzaldehyde, Benzocaine, 2-Aminobenzoic acid, 3-Methylindole. These findings suggest that crocodile gut bacteria are potential source of novel bioactive molecules that can be utilized as pre/post/antibiotics for the benefit of human health.

A magnetic levitation-based system to study the mechanisms of bacterial flocculation and autoaggregation

Objective. To evaluate the potential of magnetic levitation systems when studying the autoaggregation of gram-negative and gram-positive pathogenic bacteria and elucidating mechanisms controlling autoaggregation.Materials and methods. Escherichia coli O157:H7, Pseudomonas aeruginosa, Staphylococcus aureus, and Listeria monocytogenes were used. The number of alive bacteria was determined using a Live/Dead® dye. E. coli curli were stained with Congo red.Results. All four tested bacterial species formed autoaggregates that levitated within the liquid volume for up to 72 hours (observation time). After 72 hours, the number of alive bacteria in the autoaggregates ranged from 82% (E. coli) to 99% (L. monocytogenes). The formation of E. coli autoaggregates was shown to depend on the production of curli, which represent surface structures playing an important role in biofilm formation.Conclusion. The proposed system of magnetic levitation can be used to study molecular mechanisms of bacterial autoaggregation and flocculation.

Green Synthesis of Zinc Oxide Nanoparticles Using an Aqueous Extract of Punica granatum for Antimicrobial and Catalytic Activity.

The peel aqueous extract of Punica granatum was utilized to fabricate zinc oxide nanoparticles (ZnO-NPs) as a green approach. The synthesized NPs were characterized by UV-Vis spectroscopy, Fourier transform infrared (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy, which was attached to an energy dispersive X-ray (SEM-EDX). Spherical, well arranged, and crystallographic structures of ZnO-NPs were formed with sizes of 10-45 nm. The biological activities of ZnO-NPs, including antimicrobial and catalytic activity for methylene blue dye, were assessed. Data analysis showed that the antimicrobial activity against pathogenic Gram-positive and Gram-negative bacteria, as well as unicellular fungi, was observed to occur in a dose-dependent manner, displaying varied inhibition zones and low minimum inhibitory concentration (MIC) values in the ranges of 6.25-12.5 µg mL-1. The degradation efficacy of methylene blue (MB) using ZnO-NPs is dependent on nano-catalyst concentration, contact time, and incubation condition (UV-light emission). The maximum MB degradation percentages of 93.4 ± 0.2% was attained at 20 µg mL-1 after 210 min in presence of UV-light. Data analysis showed that there is no significant difference between the degradation percentages after 210, 1440, and 1800 min. Moreover, the nano-catalyst showed high stability and efficacy to degrade MB for five cycles with decreasing values of 4%. Overall, P. granatum-based ZnO-NPs are promising tools to inhibit the growth of pathogenic microbes and degradation of MB in the presence of UV-light emission.

Targeting BAM for Novel Therapeutics against Pathogenic Gram-Negative Bacteria.

The growing emergence of multidrug resistance in bacterial pathogens is an immediate threat to human health worldwide. Unfortunately, there has not been a matching increase in the discovery of new antibiotics to combat this alarming trend. Novel contemporary approaches aimed at antibiotic discovery against Gram-negative bacterial pathogens have expanded focus to also include essential surface-exposed receptors and protein complexes, which have classically been targeted for vaccine development. One surface-exposed protein complex that has gained recent attention is the β-barrel assembly machinery (BAM), which is conserved and essential across all Gram-negative bacteria. BAM is responsible for the biogenesis of β-barrel outer membrane proteins (β-OMPs) into the outer membrane. These β-OMPs serve essential roles for the cell including nutrient uptake, signaling, and adhesion, but can also serve as virulence factors mediating pathogenesis. The mechanism for how BAM mediates β-OMP biogenesis is known to be dynamic and complex, offering multiple modes for inhibition by small molecules and targeting by larger biologics. In this review, we introduce BAM and establish why it is a promising and exciting new therapeutic target and present recent studies reporting novel compounds and vaccines targeting BAM across various bacteria. These reports have fueled ongoing and future research on BAM and have boosted interest in BAM for its therapeutic promise in combatting multidrug resistance in Gram-negative bacterial pathogens.

Synthesis and characterization of Zn0.8Cu0.2Fe2O4 nanoparticles

The present work aims to synthesize Zinc copper Ferrite (ZCF) Nanoparticles (NP’s) by using low cost hydrothermal technique. Afterwards, the prepared ZCF NP’s characterized by various techniques. In this connection, the presence of metal oxide bonds were confirmed by Fourier transform infrared spectroscopy (FTIR), Further, X-ray diffraction (XRD) analysis revealed the presence of cubic spinel structured NP’s with single phase. The average particle and surface morphology is studied by using field emission scanning electron microscope (FESEM). In addition, the antimicrobial studies carried out against Proteus vulgaris. confirmed that the prepared NP’s exhibit excellent antimicrobial performance against different pathogenic gram-positive and gram-negative bacteria.

Green synthesis of zinc oxide nanoparticles using lychee peel and its application in anti-bacterial properties and CR dye removal from wastewater

In nanoscience and nanobiotechnology, using plant extracts in synthesizing metal nanoparticles (NPs) has recently come to light as an exciting opportunity with several benefits over traditional physicochemical methods. In the present work, zinc oxide (ZnO) based nanoparticles (NPs) were synthesized by green chemistry route using lychee peel extract to capture hazardous congo red dye from wastewater and illustrate their antimicrobial behavior. The X-Ray Diffraction (XRD) spectra confirm the wurtzite crystal structure, and Fourier Transform Infrared (FTIR) spectra confirm the functional group in ZnO, which is suitable for dye adsorption. It was found that the NPs were spherical and had a size of <10 nm. The synthesized ZnO NPs could effectively remove >98% of CR dye from wastewater within 120 min of contact time at a wide pH range from 2 to 10. The primary mechanism involved in removing dye was the electrostatic interaction between ZnO adsorbent and CR dye. The antimicrobial performance of synthesized ZnO NPs was found to show 34% inhibition against Bacillus subtilis (ATCC 6538), 52% against Escherichia coli (ATCC 11103), 58% against Pseudomonas aeruginosa (ATCC 25668) and 32% against Staphylococcus aureus (ATCC 25923) using well diffusion assay. ZnO demonstrates a suitable anti-bacterial property over both gram-positive and gram-negative pathogenic bacteria. Overall, the green synthesized method for developing ZnO NPs shows promising and significant anti-bacterial performance and is a highly potential adsorbent for removing CR dye from wastewater.

Integrative structural analysis of the type III secretion system needle complex from Shigella flexneri.

The type III secretion system (T3SS) is a large, transmembrane protein machinery used by various pathogenic gram-negative bacteria to transport virulence factors into the host cell during infection. Understanding the structure of T3SSs is crucial for future developments of therapeutics that could target this system. However, much of the knowledge about the structure of T3SS is available only for Salmonella, and it is unclear how this large assembly is conserved across species. Here, we combined cryo-electron microscopy, cross-linking mass spectrometry, and integrative modeling to determine the structure of the T3SS needle complex from Shigella flexneri. We show that the Shigella T3SS exhibits unique features distinguishing it from other structurally characterized T3SSs. The secretin pore complex adopts a new fold of its C-terminal S domain and the pilotin MxiM[SctG] locates around the outer surface of the pore. The export apparatus structure exhibits a conserved pseudohelical arrangement but includes the N-terminal domain of the SpaS[SctU] subunit, which was not present in any of the previously published virulence-related T3SS structures. Similar to other T3SSs, however, the apparatus is anchored within the needle complex by a network of flexible linkers that either adjust conformation to connect to equivalent patches on the secretin oligomer or bind distinct surface patches at the same height of the export apparatus. The conserved and unique features delineated by our analysis highlight the necessity to analyze T3SS in a species-specific manner, in order to fully understand the underlying molecular mechanisms of these systems. The structure of the type III secretion system from Shigella flexneri delineates conserved and unique features, which could be used for the development of broad-range therapeutics.

Discovery and Biosynthesis of Imidazolium Antibiotics from the Probiotic Bacillus licheniformis.

Antibiotic resistance is one of the world's most urgent public health problems, and novel antibiotics to kill drug-resistant bacteria are needed. Natural product-derived small molecules have been the major source of new antibiotics. Here we describe a family of antibacterial metabolites isolated from a probiotic bacterium, Bacillus licheniformis. A cross-streaking assay followed by activity-guided isolation yielded a novel antibacterial metabolite, bacillimidazole G, which possesses a rare imidazolium ring in the structure, showing MIC values of 0.7-2.6 μg/mL against human pathogenic Gram-positive and Gram-negative bacteria including methicillin-resistant Staphylococcus aureus (MRSA) and a lipopolysaccharide (LPS)-lacking Acinetobacter baumannii ΔlpxC. Bacillimidazole G also lowered MICs of colistin, a Gram-negative antibiotic, up to 8-fold against wild-type Escherichia coli MG1655 and A. baumannii. We propose a biosynthetic pathway to the characterized metabolites based on precursor-feeding studies, a chemical biological approach, biomimetic total synthesis, and a biosynthetic gene knockout method.

Chemical Composition and Antibacterial Activity of Wild Rose (Rosa canina L.) Gall Extracts against Gram-Negative Pathogenic Bacteria

Background &amp; Objectives: Treating infections due to antibiotic-resistant bacteria is a challenge and researchers are looking for new antimicrobial compounds. Galls are abnormal plant growths caused by biological agents and have active compounds. The present study was designed to examine the antibacterial effects of different extracts of wild rose gall (Rosa canina L.) against some pathogenic Gram-negative bacilli.&#x0D; Materials &amp; Methods: Methanol, acetone, and aqueous extracts from galls were prepared using Soxhlet apparatus. The antibacterial activity of the extracts was determined by agar well diffusion method, and the minimum inhibitory concentration and the minimum bactericidal concentration were assessed by the microdilution method. The phytochemical composition of galls was investigated by Gas Chromatography-Mass Spectrometry (GC-MS) method.&#x0D; Results: The inhibition zones of 500 mg/mL methanol extract of wild rose gall against Escherichia coli, Pseudomonas aeruginosa, Enterobacter aerogenes, Klebsiella pneumoniae, Acinetobacter bummani, Shigella sonei, and Salmonella typhi were 26.7, 25.0, 25.7, 25.7, 26.7, 23.7 and 18.3, respectively. The antimicrobial activity of the extracts was directly related to their concentration. The extracts were active against all the pathogenic bacteria with average MICs ranging from 15.6 to 31.3 mg/mL. The methanol extract of wild rose gall showed the highest bactericidal effect on P. aeruginosa and A. bummani at 62.5 mg/mL, respectively. Moreover, oleic acid, palmitic acid, and octadecenoic acid were composed 36.66%, 14.40%, and 13.21% of total active compounds in wild rose gall.&#x0D; Conclusion: All of the wild rose gall extracts showed significant antibacterial activities against Gram-negative bacilli. The antibacterial effects may be related to the high amounts of organic acids in wild rose gall extracts.&#x0D;