Potential Antibacterial Mechanism Research Articles

Antibacterial mechanism of peptide Cec4 against Acinetobacter baumannii.

BackgroundA case of Acinetobacter baumannii (A. baumannii), known as gram-negative bacteria, causes a range of nosocomial infections. Due to the continuous detection of multi-drug resistant A. baumannii in the clinic, there is an urgent need to find alternative therapies, including broad-spectrum antibacterial peptides (AMP). Recently it has been found that the peptide Cec4 has good antibacterial activity against A. baumannii, but the antibacterial mechanism remains elusive.Materials and methodsThe basic structure of Cec4 was analyzed by circular dichroism (CD) spectroscopy, and the potential antibacterial mechanism of Cec4 was detected by flow cytometry, transmission electron microscopy, fluorescence and confocal microscopy. The minimum inhibitory concentration (MIC) of antimicrobial peptides against various A. baumannii was determinated with broth microdilution techniques. The biofilm formation and the sensitivity detection of biofilms to antimicrobial peptides were detected by crystal violet staining.ResultsIn this study, the main secondary structure of the antibacterial peptide Cec4 is α-helix (99.7%) in the hydrophobic environment. Furthermore, after the treatment with Cec4, an amount of leakage of A. baumannii and the destruction of its cell membrane were detected. Moreover, it was observed that FITC-Cec4 can enter the cell, and more cells were held in the G1 phase with peptide Cec4. However, the DNA binding assay of the peptide Cec4 indicates that the peptide does not target DNA. In addition, peptide Cec4 was superior in reducing adherent biofilms of A. baumannii compared to conventional antibiotics and has no cytotoxicity.ConclusionIt is apparent that the antibacterial peptide Cec4 may achieve rapid sterilization by multi-target interaction and presents an attractive therapeutic option for the prevention and control of A. baumannii infections.

Biomedical Potentialities of Silver Nanoparticles for Clinical Multiple Drug-Resistant Acinetobacter baumannii

Multidrug-resistant A. baumannii is increasingly recognized as a significant problem in hospitals and causes high morbidity and mortality. Here, we studied the antibacterial effects of AgNPs on clinically isolated multiple drug-resistant A. baumannii, and search for the potential antibacterial mechanism. Based on the results from the colony-forming unit (CFU) method, flow cytometry (FC), and a BrdU ELISA, we conclude that AgNPs can simultaneously induce apoptosis and inhibit new DNA synthesis in bacteria in a concentration-dependent manner. This study presents the first discussion of an antibacterial effect by AgNPs in clinically isolated, multidrug-resistant A. Baumannii and provides a new strategy for the use of silver nanoparticles in the multidrug-resistant A. Baumannii clinical problem.

Antioxidant-Rich Peptide Fractions Derived from High-Altitude Chinese Caterpillar Medicinal Mushroom Ophiocordyceps sinensis (Ascomycetes) Inhibit Bacterial Pathogens.

Ophiocordyceps sinensis (=Cordyceps sinensis), a medicinal mushroom native to the Orient, has been extensively used for the past few centuries in traditional Chinese medicine because of its immunomodulatory, antiinflammatory, and nutraceutical properties. In the present study, three antioxidant and antibacterial Ophiocordyceps peptide fractions (COPs) were separated from the Indian variety of O. sinensis on a Sephadex G-25 resin. Amide bonds in the COPs were confirmed by Fourier transform infrared spectroscopy and nuclear magnetic resonance. Cationic and hydrophobic amino acids, which are reported to be the major constituent amino acids of antimicrobial peptides, were identified in the COPs by matrix-assisted laser desorption/ionization-mass spectrometry and high-performance liquid chromatography. Putative secondary structures were predicted by circular dichroism to be β-sheets and random coils. The COPs demonstrated substantial antioxidant potential by scavenging 2,2-diphenyl-l-picryl-hydrazyl-hydrate (median inhibitory concentration [IC50] values, 4.79-18.7 mg/mL) and 2,2'-azino-bis-3-ethylbenzothiazoline-6-sul-phonic acid (IC50 values, 4.51-14.05 mg/mL) free radicals and also by chelating heavy metal ions. Additionally, the peptide fractions were capable of significantly inhibiting bacterial pathogens viz. Escherichia coli and Salmonella typhi. The potential antibacterial mechanisms of action were established to be generation of reactive oxygen species and intracellular protein leakage within the bacterial cells.

Silver nanoparticles: A novel antibacterial agent for control of Cronobacter sakazakii

Silver nanoparticles (AgNP) have been widely applied because of their broad spectrum of antimicrobial activities against bacteria, fungi, and viruses. However, little research has been done to evaluate their effects on Cronobacter sakazakii, an opportunistic pathogen usually infecting infants and having a high fatality rate. The aims of this work were to investigate the antibacterial property of novel, synthesized, positively charged silver nanoparticles against C. sakazakii and to discuss the potential antibacterial mechanisms involved. In this study, the spherical and face-centered cubic silver nanoparticles had a mean particle size of 31.2 nm and were synthesized by reducing Ag+ using citrate and dispersed by glycerol and polyvinylpyrrolidone (PVP) under alkaline conditions. Minimum inhibitory concentrations (MIC) and inhibition zone tests showed that the AgNP exhibited strong antibacterial activity against 4 tested C. sakazakii strains with mean MIC of 62.5 to 125 mg/L and average inhibition zone diameters of 13.8 to 16.3 mm. Silver nanoparticles caused cell membrane injury accompanied by adsorption of AgNP onto the cell surface, as shown by changes in cell morphology, cell membrane hyperpolarization, and accelerated leakage of intracellular reducing sugars and proteins outward from the cytoplasm. In addition, dysfunction of the respiratory chain was induced after treatment with AgNP, which was supported by a decrease in intracellular ATP and inhibition of related dehydrogenases. This research indicates that AgNP could be a novel and efficient antibacterial agent to control C. sakazakii contamination in environments producing powdered infant formulas from milk.

Potential antibacterial mechanism of silver nanoparticles and the optimization of orthopedic implants by advanced modification technologies.

Infection, as a common postoperative complication of orthopedic surgery, is the main reason leading to implant failure. Silver nanoparticles (AgNPs) are considered as a promising antibacterial agent and always used to modify orthopedic implants to prevent infection. To optimize the implants in a reasonable manner, it is critical for us to know the specific antibacterial mechanism, which is still unclear. In this review, we analyzed the potential antibacterial mechanisms of AgNPs, and the influences of AgNPs on osteogenic-related cells, including cellular adhesion, proliferation, and differentiation, were also discussed. In addition, methods to enhance biocompatibility of AgNPs as well as advanced implants modifications technologies were also summarized.

Seeds of the Wild Progenitor of Maize Possess Bacteria That Antagonize Foodborne Pathogens.

Endophytes are microorganisms that inhabit plant tissues without causing disease. Some endophytes help their hosts to combat pathogens. Here we explored the hypothesis that the plant-derived foods consumed by humans and other animals host endophytes that also antagonize foodborne pathogens or food-rotting agents. Our laboratory previously cultured a library of bacterial endophytes from different members of the maize/corn family (Zea) including wild relatives. Here, 190 of these endophytes were screened for their ability to antagonize four foodborne pathogens (Escherichia coli O157:H7, Listeria monocytogenes, Clostridium perfringens, and Salmonella enterica Newport) and a food spoiling agent (Pseudomonas fluorescens) using dual culture assays. Two Paenibacillus polymyxa endophytes (strains 3C6 and 3G11) were found to inhibit the growth of all five deleterious strains on agar. Using conserved polymerase chain reaction primers and sequencing, both beneficial endophytes were found to encode polymyxin genes, suggesting a potential antibacterial mechanism of action. Polymyxin production by both strains was confirmed using enzyme-linked immunosorbent assay. Strains 3C6 and 3G11 originated, respectively, from the seeds of the wild Central American maize species Zea diploperennis, and the wild ancestor of modern maize, Zea mays ssp parviglumis (Parviglumis). As the latter is the direct ancestor of modern maize, we discuss the role its endophyte(s) may have played in promoting crop domestication by suppressing foodborne pathogens and/or food-spoilage agents.

Facile fabrication of rice husk based silicon dioxide nanospheres loaded with silver nanoparticles as a rice antibacterial agent.

Bacterial leaf blight of rice caused by Xanthomonas oryzae pv. oryzae (Xoo) is a major disease of rice, leading to reduction in production by 10–50%. In order to control this disease, various chemical bactericides have been used. Wide and prolonged application of chemical bactericides resulted in the resistant strain of Xoo that was isolated from rice. To address this problem, we were searching for an environmentally friendly alternative to the commonly used chemical bactericides. In this work, we demonstrate that silicon dioxide nanospheres loaded with silver nanoparticles (SiO2-Ag) can be prepared by using rice husk as base material precursor. The results of the antibacterial tests showed that SiO2-Ag composites displayed antibacterial activity against Xoo. At cellular level, the cell wall/membrane was damaged and intercellular contents were leaked out by slow-releasing of silver ions from SiO2-Ag composites. At molecular level, this composite induced reactive oxygen species production and inhibited DNA replication. Based on the results above, we proposed the potential antibacterial mechanism of SiO2-Ag composites. Moreover, the cytotoxicity assay indicated that the composites showed mild toxicity with rice cells. Thus, this work provided a new strategy to develop biocide derived from residual biomass.

Graphene film doped with silver nanoparticles: self-assembly formation, structural characterizations, antibacterial ability, and biocompatibility.

Graphene and silver nanoparticles (AgNPs) are important building blocks for the synthesis of functional nanomaterials for bio-related applications. Here, we report a facile strategy to decorate AgNPs onto reduced graphene oxide (RGO) by the simultaneous reduction of silver ions and graphene oxide nanosheets within one system, and further to fabricate a dimension-adjustable RGO/AgNP multi-layered film by a thermal-driven self-assembly process. The structures of the fabricated RGO/AgNP hybrid films were identified by UV-visible spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and transmission electron microscopy. The thickness of the fabricated RGO/AgNP film was further measured by scanning electron microscopy. The hydrophilicity of the RGO/AgNP films was tested by contact angle measurement. Antibacterial and cell culture experiments based on the fabricated RGO/AgNP films indicate that this kind of hybrid film exhibits excellent antibacterial activity and high biocompatibility. A potential antibacterial mechanism of the fabricated RGO/AgNP hybrid film was proposed.

The Potential Anti Helicobacter pylori and antioxidant effects of Artemisia Judaica

Artemisia judaica (AJ) is one of the common species of the genus Artemisia that grows in Saudi Arabia desert and Sinai, Egypt where animals graze on it. It is widely used in traditional medicine and by Bedouins there. (AJ) has anthelmintic, antibacterial, antiinflammatory, analgesic and antipyretic effects. The present study aimed to (1) elucidates the antibacterial action of AJ against H. pylori and different other bacterial species (2) delineate the potential antibacterial mechanism of action of AJ in comparison with tetracycline and cefotaxime (3) measure the trolox equivalent antioxidant capacity (TEAC) of the AJ water extract. Preparation of the (AJ) extracts was done by three different methods two of them are usually performed by population in Middle East by boiling of the shade-dried herb in water as tea (decoction), or soaked in tap water for over night (infusion), other method was done by concentrating the aqueous extract of Artemisia judaica under vacuum. The results of this study revealed that (AJ) has neither antibacterial effects either against H. pylorinor any other bacterial species. On the other hand the extract of AJ prepared by any of the above mentioned methods shows significant (p<0.005) antioxidant action as compared with blank and related to trolox antioxidant capacity.

Caprylic acid reduces Salmonella Enteritidis populations in various segments of digestive tract and internal organs of 3- and 6-week-old broiler chickens, therapeutically ,

We investigated the efficacy of feed supplemented with caprylic acid (CA), a natural, 8-carbon fatty acid for reducing Salmonella enterica serovar Enteritidis colonization in commercial broiler chickens. In separate 3- and 6-wk trials, 1-d-old straight-run broiler chicks (n = 70 birds/trial) were assigned to a control group (challenged with Salmonella Enteritidis, no CA) and 2 replicates of 0.7 and 1% CA (n = 14 birds/group). Water and feed were provided ad libitum. On d 1, birds were tested for any inherent Salmonella (n = 2 birds/group). For the 3-wk trial, on d 5, birds were challenged with 8 log(10) cfu of Salmonella Enteritidis of a 4-strain mixture by crop gavage, and after 5 d postchallenge, birds (n = 2 birds/group) were euthanized to ensure Salmonella Enteritidis colonization. Caprylic acid was supplemented the last 5 d before tissue collection (n = 10 birds/group). For the 6-wk trial, on d 25, birds were challenged and confirmed for Salmonella Enteritidis colonization. The birds (n = 10 birds/group) were euthanized for tissue samples after CA supplementation for the last 5 d. Caprylic acid at 0.7 or 1% decreased Salmonella Enteritidis populations in cecum, small intestine, cloaca, liver, and spleen in both 3- and 6-wk trials. Body weight of birds did not differ between the groups (P ≥ 0.05). Further, to elucidate a potential antibacterial mechanism of action of CA, we investigated if CA could reduce Salmonella Enteritidis invasion of an avian epithelial cell line and expression of invasion genes hilA and hilD. The cell invasion study revealed that CA reduced invasive abilities of all Salmonella Enteritidis strains by ~80% (P < 0.05). Gene expression studies indicated that CA downregulated (P < 0.001) Salmonella invasion genes hilA and hilD. These results suggest that supplementation of CA through feed could reduce Salmonella Enteritidis colonization in broiler chicken and potentially reduces the pathogen's ability to invade intestinal epithelial cells by downregulating key invasion genes, hilA and hilD.

Three flavonoids targeting the β‐hydroxyacyl‐acyl carrier protein dehydratase from Helicobacter pylori: Crystal structure characterization with enzymatic inhibition assay

Flavonoids are the major functional components of many herbal and insect preparations and demonstrate varied pharmacological functions including antibacterial activity. Here by enzymatic assay and crystal structure analysis, we studied the inhibition of three flavonoids (quercetin, apigenin, and (S)-sakuranetin) against the beta-hydroxyacyl-acyl carrier protein dehydratase from Helicobacter pylori (HpFabZ). These three flavonoids are all competitive inhibitors against HpFabZ by either binding to the entrance of substrate tunnel B (binding model A) or plugging into the tunnel C near the catalytic residues (binding model B) mainly by hydrophobic interaction and hydrogen-bond pattern. Surrounded by hydrophobic residues of HpFabZ at both positions of models A and B, the methoxy group at C-7 of (S)-sakuranetin seems to play an important role for the inhibitor's binding to HpFabZ, partly responsible for the higher inhibitory activity of (S)-sakuranetin than those of quercetin and apigenin against HpFabZ (IC(50) in microM: (S)-sakuranetin, 2.0 +/- 0.1; quercetin: 39.3 +/- 2.7; apigenin, 11.0 +/- 2.5). Our work is expected to supply useful information for understanding the potential antibacterial mechanism of flavonoids.

D-Alanine: d-alanine ligase as a new target for the flavonoids quercetin and apigenin

Flavonoids are polyphenolic compounds that are ubiquitous in nature. They possess varied promising properties for medical use. Quercetin (3,3′,4′,5,7-pentahydroxyflavone) and apigenin (4′,5,7-trihydroxyflavone) are two representative flavonoids, both of which have been reported to possess antibacterial activity by acting on multiple targets. Here, we determined that d-alanine: d-alanine ligase (Ddl) is another new target for quercetin and apigenin. Kinetic analysis indicated that these two flavonoids function as reversible inhibitors that are competitive with the substrate ATP of Ddl, whereas they are non-competitive with the other substrate d-Ala. The fact that quercetin showed lower 50% inhibitory concentration (IC 50) and inhibitor binding constant ( K i) values than apigenin against both the Helicobacter pylori Ddl and the Escherichia coli DdlB implies that the two additional hydroxyls on the flavone skeleton of quercetin in structure might facilitate its inhibitory activity and binding affinity to Ddl. This work is expected to help shed more light on the potential antibacterial mechanism of flavonoids.