Synthetic Channel Specifically Inserts into the Lipid Bilayer of Gram‐Positive Bacteria but not that of Mammalian Erythrocytes

A series of tubular molecules with different lengths have been synthesized by attaching Trp‐incorporated peptides to the pillar[5]arene backbone. The tubular molecules are able to insert into the lipid bilayer to form unimolecular transmembrane channels. One of the channels has been revealed to specifically insert into the bilayer of the Gram‐positive bacteria. In contrast, this channel cannot insert into the membranes of the mammalian rat erythrocytes even at the high concentration of 100 μm . It was further demonstrated that, as a result of this high membrane selectivity, the channel exhibits efficient antimicrobial activity for the Gram‐positive bacteria and very low hemolytic toxicity for mammalian erythrocytes.     

Defect‐Rich Adhesive Nanozymes as Efficient Antibiotics for Enhanced Bacterial Inhibition

Nanozymes have emerged as a new generation of antibiotics with exciting broad‐spectrum antimicrobial properties and negligible biotoxicities. However, their antibacterial efficacies are unsatisfactory due to their inability to trap bacteria and their low catalytic activity. Herein, we report nanozymes with rough surfaces and defect‐rich active edges. The rough surface increases bacterial adhesion and the defect‐rich edges exhibit higher intrinsic peroxidase‐like activity compared to pristine nanozymes due to their lower adsorption energies of H₂O₂ and desorption energy of OH*, as well as the larger exothermic process for the whole reaction. This was demonstrated using drug‐resistant Gram‐negative Escherichia coli and Gram‐positive Staphylococcus aureus in vitro and in vivo. This strategy can be used to engineer nanozymes with enhanced antibacterial function and will pave a new way for the development of alternative antibiotics.     

Structure,Biosynthesis, and Occurrence of Bacterial Pyrrolizidine Alkaloids

Pyrrolizidine alkaloids (PAs) are widespread plant natural products with potent toxicity and bioactivity. Herein, the identification of bacterial PAs from entomopathogenic bacteria using differential analysis by 2D NMR spectroscopy (DANS) and mass spectrometry is described. Their biosynthesis was elucidated to involve a non‐ribosomal peptide synthetase. The occurrence of these biosynthesis gene clusters in Gram‐negative and Gram‐positive bacteria indicates an important biological function in bacteria.     

Living and Conducting: Coating Individual Bacterial Cells with In Situ Formed Polypyrrole

Coating individual bacterial cells with conjugated polymers to endow them with more functionalities is highly desirable. Here, we developed an in situ polymerization method to coat polypyrrole on the surface of individual Shewanella oneidensis MR‐1, Escherichia coli, Ochrobacterium anthropic or Streptococcus thermophilus. All of these as‐coated cells from different bacterial species displayed enhanced conductivities without affecting viability, suggesting the generality of our coating method. Because of their excellent conductivity, we employed polypyrrole‐coated Shewanella oneidensis MR‐1 as an anode in microbial fuel cells (MFCs) and found that not only direct contact‐based extracellular electron transfer is dramatically enhanced, but also the viability of bacterial cells in MFCs is improved. Our results indicate that coating individual bacteria with conjugated polymers could be a promising strategy to enhance their performance or enrich them with more functionalities.     

Structure,Biosynthesis, and Occurrence of Bacterial Pyrrolizidine Alkaloids

Pyrrolizidine alkaloids (PAs) are widespread plant natural products with potent toxicity and bioactivity. Herein, the identification of bacterial PAs from entomopathogenic bacteria using differential analysis by 2D NMR spectroscopy (DANS) and mass spectrometry is described. Their biosynthesis was elucidated to involve a non‐ribosomal peptide synthetase. The occurrence of these biosynthesis gene clusters in Gram‐negative and Gram‐positive bacteria indicates an important biological function in bacteria.     

Membrane Disruption and Enhanced Inhibition of Cell‐Wall Biosynthesis: A Synergistic Approach to Tackle Vancomycin‐Resistant Bacteria

Resistance to glycopeptide antibiotics, the drugs of choice for life‐threatening bacterial infections, is on the rise. In order to counter the threat of glycopeptide‐resistant bacteria, we report development of a new class of semi‐synthetic glycopeptide antibiotics, which not only target the bacterial membrane but also display enhanced inhibition of cell‐wall biosynthesis through increased binding affinity to their target peptides. The combined effect of these two mechanisms resulted in improved in vitro activity of two to three orders of magnitude over vancomycin and no propensity to trigger drug resistance in bacteria. In murine model of kidney infection, the optimized compound was able to bring bacterial burden down by about 6 logs at 12 mg kg^?1 with no observed toxicity. The results furnished in this report emphasize the potential of this class of compounds as future antibiotics for drug‐resistant Gram‐positive infections.     

From Genome to Proteome to Elucidation of Reactions for All Eleven Known Lytic Transglycosylases from Pseudomonas aeruginosa

An enzyme superfamily, the lytic transglycosylases (LTs), occupies the space between the two membranes of Gram‐negative bacteria. LTs catalyze the non‐hydrolytic cleavage of the bacterial peptidoglycan cell‐wall polymer. This reaction is central to the growth of the cell wall, for excavating the cell wall for protein insertion, and for monitoring the cell wall so as to initiate resistance responses to cell‐wall‐acting antibiotics. The nefarious Gram‐negative pathogen Pseudomonas aeruginosa encodes eleven LTs. With few exceptions, their substrates and functions are unknown. Each P. aeruginosa LT was expressed as a soluble protein and evaluated with a panel of substrates (both simple and complex mimetics of their natural substrates). Thirty‐one distinct products distinguish these LTs with respect to substrate recognition, catalytic activity, and relative exolytic or endolytic ability. These properties are foundational to an understanding of the LTs as catalysts and as antibiotic targets.     

Capillary electrophoresis for fast detection of heterogeneous population in colistin‐resistant Gram‐negative bacteria

It has been shown that diverse strains of bacteria can be separated according to their characteristic surface properties by means of CE. We employed here this analytical technique to the study of colistin‐resistance in Gram‐negative bacteria, which involves the selection of mutants with modified outer membrane composition resulting in changes of surface cell properties. In the same way as with molecular entities, we performed firstly the validation of an ITP‐based CE method for three common pathogenic Gram‐negative bacteria namely Escherichia coli, Pseudomonas aeruginosa, and Klebsiella pneumoniae. Secondly, we compared the electrophoretic profiles of bacterial samples from a colistin‐susceptible clinical isolate of K. pneumoniae and from the corresponding colistin‐resistant derivative. By a simple CE run taking a few minutes, the coexistence of several bacterial subpopulations in the colistin‐resistant derivative was clearly evidenced. This work encourages further research that would allow applications of CE in clinical laboratory for a daily monitoring of bacterial population in cared patients when “last‐chance” colistin treatment is initiated against multidrug‐resistant bacteria.     

Dual Fluorescent‐ and Isotopic‐Labelled Self‐Assembling Vancomycin for in vivo Imaging of Bacterial Infections

The increase of bacterial resistance demands rapid and accurate diagnosis of bacterial infections. Biosurface‐induced supramolecular assembly for diagnosis and therapy has received little attention in detecting bacterial infections. Herein we present a dual fluorescent‐nuclear probe based on self‐assembly of vancomycin (Van) on Gram‐positive bacteria for imaging bacterial infection. A Van‐ and rhodamine‐modified peptide derivative (Rho‐FF‐Van), as the imaging agent, binds to the terminal peptide of the methicillin‐resistant staphylococcus aureus (MRSA) and self‐assembles to form nanoaggregates on the surface of MRSA . In an in vivo myositis model, Rho‐FF‐Van results in a significant increased fluorescence signal at the MRSA infected site. Radiolabeled with iodine‐125, Rho‐FF‐Van shows strong radioactive signal in the MRSA ‐infected lungs in a murine model. This novel dual fluorescent and nuclear probe promises a new way for in vivo imaging of bacterial infections.     

Facile Heterocyclic Synthesis and Antibacterial Activity of Substituted Isoxazol‐5(4H)‐ones

An efficient, simple, and green procedure for the synthesis of isoxazol‐5(4H)‐one derivatives are described here through a convenient one‐pot, three‐component reaction at room temperature. The title compounds are isolated in high to excellent yields and after short reaction times, and are characterized by various spectroscopic methods such as IR, ¹H NMR, and ¹³C NMR. The synthesized compounds 4a–c and 4e–i were tested for their in vitro activity against a panel of Gram‐positive and Gram‐negative bacteria, demonstrating their ability to inhibit microorganisms with a zone of inhibition ranging from 15 to 30 mm, minimum inhibitory concentration between 250 and 900 μg/mL, and minimum bacterial concentration between 700 and 1000 μg/mL.     

Deformylated Gramicidin A and Its Derivatives Showing High Antimicrobial Activity and Low Hemolytic Toxicity

Gramicidin A is a natural peptide, which shows high antimicrobial activity to Gram‐positive bacteria. However, the hemolytic toxicity prevents its therapeutic usage. We demonstrated that by simply removing the formyl group at the N terminus, the hemolytic toxicity of the peptide could be obviously decreased. The deformylated gramicidin A ( 1 ) could efficiently insert into the lipid bilayer to form transmembrane channels. The peptide can also selectively insert into the membrane of Gram‐positive bacteria but not that of erythrocytes, leading to its high antimicrobial activity and very low hemolytic toxicity. The derivation of 1 could be achieved by decoration at the terminal NH₂ group, which also produced peptides showing high activity and low hemolytic toxicity. This derivation method provided us with an efficient strategy to build a library for future activity and cytotoxicity screening in vitro and in vivo.     

Hybrid 4‐Aminoquinoline‐1,3,5‐triazine Derivatives: Design,Synthesis, Characterization,and Antibacterial Evaluation

A series of novel 4‐aminoquinoline 1,3,5‐triazine derivatives were synthesized and characterized by FTIR, ¹H‐NMR, ¹³C‐NMR, MS, and elemental analysis. The antibacterial activities of synthesized compounds were tested against three Gram‐positive bacteria, namely Bacillus subtilis (NCIM‐2063), Bacillus cereus (NCIM‐2156), and Staphylococcus aureus (NCIM‐2079), and four Gram‐negative bacteria, namely Proteus vulgaris (NCIM‐2027), Proteus mirabilis (NCIM‐2241), Escherichia coli (NCIM‐2065), and Pseudomonas aeruginosa (NCIM‐2036), using ciprofloxacin as reference standard drug. Results showed compound 9a and 9e as potent antibacterial agents against all bacterial strains except Bacillus cereus (NCIM‐2156). Copyright © 2014 HeteroCorporation     

Sulfonium,an Underestimated Moiety for Structural Modification,Alters the Antibacterial Profile of Vancomycin Against Multidrug‐Resistant Bacteria

In the antibiotics arsenal, vancomycin is a last resort for the treatment of intractable infections. However, this situation is under threat because of the increasing appearance of vancomycin‐resistant bacteria (VRB). Herein, we report a series of novel vancomycin derivatives carrying a sulfonium moiety. The sulfonium–vancomycin derivatives exhibited enhanced antibacterial activity against VRB both in vitro and in vivo. These derivatives also exhibited activity against some Gram‐negative bacteria. The sulfonium modification enhanced the interaction of vancomycin with the bacterial cell membrane and disrupts membrane integrity. Furthermore, the in vivo pharmacokinetic profile, stability, and toxicity of these derivatives demonstrated good druggability of the sulfonium–vancomycin analogues. This work provides a promising strategy for combating drug‐resistant bacterial infection, and advances the knowledge on sulfonium derivatives for structural optimization and drug development.     

Sulfonium,an Underestimated Moiety for Structural Modification,Alters the Antibacterial Profile of Vancomycin Against Multidrug‐Resistant Bacteria

In the antibiotics arsenal, vancomycin is a last resort for the treatment of intractable infections. However, this situation is under threat because of the increasing appearance of vancomycin‐resistant bacteria (VRB). Herein, we report a series of novel vancomycin derivatives carrying a sulfonium moiety. The sulfonium–vancomycin derivatives exhibited enhanced antibacterial activity against VRB both in vitro and in vivo. These derivatives also exhibited activity against some Gram‐negative bacteria. The sulfonium modification enhanced the interaction of vancomycin with the bacterial cell membrane and disrupts membrane integrity. Furthermore, the in vivo pharmacokinetic profile, stability, and toxicity of these derivatives demonstrated good druggability of the sulfonium–vancomycin analogues. This work provides a promising strategy for combating drug‐resistant bacterial infection, and advances the knowledge on sulfonium derivatives for structural optimization and drug development.     

Antimicrobial Photodynamic Efficiency of Novel Cationic Porphyrins towards Periodontal Gram‐positive and Gram‐negative Pathogenic Bacteria

The Gram‐negative Aggregatibacter actinomycetemcomitans and Fusobacterium nucleatum are major causative agents of aggressive periodontal disease. Due to increase in the number of antibiotic‐resistant bacteria, antimicrobial Photodynamic therapy (aPDT) seems to be a plausible alternative. In this work, photosensitization was performed on Gram‐positive and Gram‐negative bacteria in pure culture using new‐age cationic porphyrins, namely mesoimidazolium‐substituted porphyrin derivative ( ImP ) and pyridinium‐substituted porphyrin derivative ( PyP ). The photophysical properties of both the sensitizers including absorption, fluorescence emission, quantum yields of the triplet excited states and singlet oxygen generation efficiencies were evaluated in the context of aPDT application. The studied porphyrins exhibited high ability to accumulate into bacterial cells with complete penetration into early stage biofilms. As compared with ImP, PyP was found to be more effective for photoinactivation of bacterial strains associated with periodontitis, without any signs of dark toxicity, owing to its high photocytotoxicity.     

Positively Charged Nanoaggregates Based on Zwitterionic Pillar[5]arene that Combat Planktonic Bacteria and Disrupt Biofilms

Bacterial biofilms are difficult to eradicate because they are less susceptible to antibiotics and more easily develop resistance. Therefore, there is an urgent need for new materials that can combat planktonic bacteria and disrupt established biofilms. To tackle this challenge, we design a multifunctional zwitterionic pillar[5]arene, which can self‐assemble into weakly positively charged nanoaggregates that exhibit antibacterial activity against Gram‐negative Escherichia coli (DH5α) and Gram‐positive Staphylococcus aureus (SH1000) bacterial strains in solution. In addition, the zwitterionic pillar[5]arene can efficiently disrupt pre‐existing Escherichia coli (DH5α) biofilms and kill the biofilm‐enclosed bacteria without rapid generation of resistance.     

Synthesis and antibacterial activity of ethyl 2-amino-6-methyl-5-oxo- 4-aryl-5,6-dihydro-4H-pyrano[3,2-c]quinoline-3-carboxylate

The three-component reaction of 4-hydroxy-1-methyl-2(1H)-quinolinone, aromatic aldehydes and ethyl cyanoacetate was carried out in the presence of a catalytic amount of 4-dimethyl aminopyridine(DMAP) in aqueous ethanol. The reactions result in the formation of pyranoquinoline derivatives in excellent yields. Antibacterial activity has been evaluated against Gram positive and Gram negative bacteria for some of the synthesized compounds. The results indicated that these compounds are moderately effective against bacterial growth and their effectiveness is highest against Pseudomonas aeruginosa.     

Capillary electrophoresis in the diagnosis of surgical site infections

A surgical site infection (SSI) is an infection that occurs after surgery in the part of the body where the surgery took place. An SSI may range from a spontaneously limited wound discharge within 7–10 days of an operation to a life‐threatening postoperative complication, such as a sternal infection after open heart surgery. Most SSIs are caused by contamination of an incision with microorganisms from the patient's own body during surgery. From the analytical point of view, the complex nature of these samples as well as the low concentrations of analytes require a system with high sensitivity and efficiency. Such situation requires a technique such as CE, which is a powerful and versatile separation technique that promises to rival HPLC when applied to the separation of both charged and neutral species. During the study, it has been demonstrated that CZE identifies characteristics of such groups of pathogens such as bacteria Gram (+) and different species of bacteria Gram (?), and also develops weekly individual profiles for patients after application of antibiotics. This was done in order to show the impact of antibiotic therapy in change “numbers” of bacteria present in the wound after surgery. The method proved to be the ideal straight specificity in the case of Escherichia coli (100%). Finally, analysis of the spectra and the second derivatives of the UV‐Vis spectra confirmed the similarity in the profiles and showed that the CZE is a great method for fast screening test in bacterial infection.     

Convenient One Pot Synthesis and Antibacterial Evaluation of Some New Mannich Bases Carrying 1,2,4‐Triazolyl Moiety

A series of Mannich bases were synthesized by a three‐component Mannich reaction. The newly synthesized compounds were well characterized by elemental analyses, IR, NMR and mass spectroscopic studies. The potential antibacterial effects of the synthesized compounds were investigated using standard bacterial strains: Gram‐positive and Gram‐negative bacteria. Interestingly, all the synthesized compounds were observed to be promising leads, possessing moderate to significant inhibitory activity as compared to standard.     

Capillary electrophoresis of microbial aggregates

Uncontrolled aggregation of bacterial cells is a significant disadvantage of electrophoretic separations. Various aspects of the electrophoretic behavior of different strains of Gram‐positive Bacillus cereus, Bacillus subtilis, Sarcina lutea, Staphylococcus aureus(1), and Micrococcus luteus bacteria and Gram‐negative Escherichia coli bacteria were investigated in this study. Our findings indicate that bacteria can be rapidly analyzed by CZE with surface charge modification by calcium ions (Ca²⁺). Bound Ca²⁺ ions increase zeta potential to more than 2.0 mV and significantly reduce repulsive forces. Under the above conditions, bacterial cells create compact aggregates, and fewer high‐intensity signals are observed in electropherograms. The above can be attributed to the bridging effect of Ca²⁺ between bacterial cells. CE was performed to analyze bacterial aggregates in an isotachophoretic mode. A single peak was observed in the electropherogram.