Selective Antimicrobial Activity Research Articles

Use of juglone as antibacterial and potential efflux pump inhibitors in Staphylococcus aureus isolated from the oral cavity

In this study the minimal inhibitory concentration (MICs) of tetracycline (Tet), erythromycin (Ery) and benzalkonium chloride (BC) in absence and in presence of a sub-MIC of juglone (Jug) were determined. In addition, the Ethidium bromide (EtBr) efflux assay was performed to assess the effect of Jug on EtBr cells accumulation.Our results showed a selective antimicrobial activity of Jug against the tested strains. A synergistic effect of Jug, drugs (Tet and Ery) and disinfectant (BC) was noticed with a reduction rate varied from 2 to 16-fold. In addition, the efflux of EtBr was inhibited depending on the Jug concentration. In the presence of Jug, a decrease in loss of EtBr from bacteria was observed. The concentration inducing 50 % of EtBr efflux inhibition after 15 min was about 182 μg ml−1 for S. aureus ATCC 25923, 236 μg ml−1 for S. aureus B193 and 195 μg ml−1 for S. aureus B456.It appears from this study that Jug may be used as a natural source for resistance-modifying activity in same bacteria.

Preparation, characterization, and the selective antimicrobial activity of N-alkylammonium 8-diethyleneglycol cobalt bis-dicarbollide derivatives

A consistent series of N-alkylammonium derivatives of 8-diethyleneglycol-CoIII-bisdicarbollide has been prepared via straightforward method, and characterized using NMR, HPLC, MS and X-ray. The structure of the most stable dimethylammonium zwitterion 5 was verified by the XRD. The antibacterial, and antifungal activity of the seven studied derivatives was found based on the determination of minimum inhibitory concentrations (MIC80). The growth of the Staphylococcus aureus, the most common isolated from nosocomial infections, was inhibited with high selectivity by compound 3 in concentration 3.8 mg L−1. A significant observation was the absolute selective activity of 4 in inhibiting the growth of the filamentous fungus Trichosporon cutaneum. The high selectivity and the lowest MIC80 concentrations of the designed inhibitors allow generally to decrease the number of possible side effects usually occurred during medical treatment of the specific pathogen. Our results provide a new knowledge about the possible use of metallacarboranes as antimicrobial agents; this subject is highly topical due to the emerging antibiotic resistance of a number of pathogenic microorganisms of high concern.

Antimicrobial lipopeptide tridecaptin A1 selectively binds to Gram-negative lipid II

Tridecaptin A1 (TriA1) is a nonribosomal lipopeptide with selective antimicrobial activity against Gram-negative bacteria. Here we show that TriA1 exerts its bactericidal effect by binding to the bacterial cell-wall precursor lipid II on the inner membrane, disrupting the proton motive force. Biochemical and biophysical assays show that binding to the Gram-negative variant of lipid II is required for membrane disruption and that only the proton gradient is dispersed. The NMR solution structure of TriA1 in dodecylphosphocholine micelles with lipid II has been determined, and molecular modeling was used to provide a structural model of the TriA1-lipid II complex. These results suggest that TriA1 kills Gram-negative bacteria by a mechanism of action using a lipid-II-binding motif.

Fully Zwitterionic Nanoparticle Antimicrobial Agents through Tuning of Core Size and Ligand Structure

Zwitterionic nanoparticles are generally considered nontoxic and noninteracting. Here, we report effective and selective antimicrobial activity of zwitterionic gold nanoparticles (AuNP) through modulation NP size and surface charge orientation. Using a set of 2, 4, and 6 nm core AuNPs, increasing particle size increased antimicrobial efficiency through bacterial membrane disruption. Further improvement was observed through control of the ligand structure, generating antimicrobial particles with low hemolytic activity and demonstrating the importance of size and surface structure in dictating the bioactivity properties of nanomaterials.

Channel-forming activity of syringopeptin 25A in mercury-supported phospholipid monolayers and negatively charged bilayers

Interactions of the cationic lipodepsipeptide syringopeptin 25A (SP25A) with mercury-supported dioleoylphosphatidylcholine (DOPC), dioleoylphosphatidylserine (DOPS) and dioeleoylphosphatidic acid (DOPA) self-assembled monolayers (SAMs) were investigated by AC voltammetry in 0.1M KCl at pH3, 5.4 and 6.8. SP25A targets and penetrates the DOPS SAM much more effectively than the other SAMs not only at pH6.8, where the DOPS SAM is negatively charged, but also at pH3, where it is positively charged just as SP25A. Similar investigations at tethered bilayer lipid membranes (tBLMs) consisting of a thiolipid called DPTL anchored to mercury, with a DOPS, DOPA or DOPC distal monolayer on top of it, showed that, at physiological transmembrane potentials, SP25A forms ion channels spanning the tBLM only if DOPS is the distal monolayer. The distinguishing chemical feature of the DOPS SAM is the ionic interaction between the protonated amino group of a DOPS molecule and the carboxylate group of an adjacent phospholipid molecule. Under the reasonable assumption that SP25A preferentially interacts with this ion pair, the selective lipodepsipeptide antimicrobial activity against Gram-positive bacteria may be tentatively explained by its affinity for similar protonated amino-carboxylate pairs, which are expected to be present in the peptide moieties of peptidoglycan strands.

273 Establishment of an autologous microbiome transplant in atopic dermatitis targeting Staphylococcus aureus

The skin microbiome has been hypothesized to participate in host defense through direct and indirect immunological mechanisms. We recently demonstrated that some coagulase-negative Staphylococcus (CoNS) residing on the skin can directly kill Staphylococcus aureus by releasing antimicrobial peptides (AMPs). This function was specific to strain and not seen in all isolates from each CoNS species. Furthermore, patients with atopic dermatitis (AD) were shown to be deficient in these active CoNS strains. In this study, we hypothesized that the transplant of bacteria that produce AMPs could restore the deficient microbiome function observed in AD and suppress S. aureus survival. To test this, we first identified CoNS strains producing AMPs against S. aureus from normal healthy skin and validated their therapeutic potential by demonstrating that the application of such active CoNS strains at a physiologically relevant density (1×105 CFU/cm2) would decrease S. aureus survival on pig skin and on mice. Next, a similar screening protocol was applied to bacteria residing on the skin of AD subjects to isolate the rare CoNS colonies with the capacity to inhibit S. aureus. These active CoNS strains were identified to be members of several species including S. epidermidis and S. hominis. Under double-blinded conditions, isolates were autologously reapplied at 1×105 CFU/cm2 to lesional skin of one arm of the AD subject while vehicle only was applied to the contralateral arm. A single application of the active bacterial transplant reduced colonization by S. aureus by 99.1% within 24 hrs compared to vehicle treatment (n=5, p=0.022). Analysis of the AMPs produced by representative strains of S. epidermidis or S. hominis through MALDI-TOF-MS2 and genome sequencing demonstrated that many of these AMPs were previously unknown and show selective antimicrobial activity against a wide range of pathogens. These observations suggest that the rational selection of targeted bacteriotherapies will be a useful therapeutic strategy to manage S. aureus colonization in AD.

Fine‐tuning the Selectivity of Pore‐forming Peptides from Loss‐of‐function High Throughput Screening

While screening a combinatorial peptide library of pore‐forming peptides for gain‐of‐function, we also screened for loss‐of‐function in parallel. We used melittin, a 26 amino acid long lytic peptide from honey bee venom, as a template. For the loss‐of‐function screen we assayed library members for failure to cause leakage of entrapped contents from lipid vesicles at a peptide to lipid ratio (P:L) of 1:20, ten‐fold higher than the concentration at which melittin efficiently permeabilizes. Surprisingly, about one third of the library members are inactive under these conditions. In the selected loss‐of‐function peptides, two changes of hydrophobic residues to glycine were especially abundant. We show that a single residue change from a leucine to a glycine at position 16 completely prevents lytic activity. Unlike the potently lytic melittin, the loss‐of‐function peptides, including the single site variant, are essentially inactive against phosphatidylcholine vesicles and multiple types of eukaryotic cells. Circular dichroism spectra reveal the loss‐of‐function peptides to shift in the binding‐folding equilibrium away from the bound, a‐helical state towards the unbound, random coil state. Accordingly, the addition of anionic lipids to synthetic lipid vesicles restored binding, a‐helical secondary structure and potent activity of the “negative” peptides. The single site variant had potent, melittin‐like antimicrobial activity against Gram‐positive Staph aureus and Gram‐negative E. Coli, with minimum sterilization concentration (MIC) of 10 μM and 7.5 μM, respectively. These results show that conformational fine‐tuning of pore‐forming peptides is a powerful way to modulate potent cytotoxic peptides toward selective antimicrobial activity.

Photocatalytic properties and selective antimicrobial activity of TiO2(Eu)/CuO nanocomposite

TiO2(Eu)/CuO nanocomposites were prepared by precipitation method. The anatase nanocrystallites with a size of 26nm exhibited well crystallized and characteristical dipyramidal morphology and {101} and {001} faceting. Transmission electron microscopy photographs with atomic resolution showed that the Eu(III) dopants were bounded on surface of titania. In the composites, the CuO nanocrystals exhibiting a monoclinic tenorite structure with a size in the range from 2 to 5nm were grafted to the surface of titania. The influence of copper(II) oxide led to distinct selectivity in the photocatalytic and antimicrobial properties of the investigated TiO2(Eu)/CuO nanocomposites. While the presence of CuO nanocrystals strongly increased the photocatalytic production of hydrogen by ethanol reforming, it decreased the activity in photoinduced total mineralization of phenol comparing with non-modified TiO2(Eu). In investigated TiO2(Eu)/CuO powders, the photoinduced antimicrobial activity against membranes of Enterococcus species was influenced by the selective binding of CuO to the surface of the microorganism leading to distinct selectivity in their action. The activity against Enterococcus faecalis was higher than against Enterococcus faecium.

Selective Antimicrobial Activities and Action Mechanism of Micelles Self-Assembled by Cationic Oligomeric Surfactants.

This work reports that cationic micelles formed by cationic trimeric, tetrameric, and hexameric surfactants bearing amide moieties in spacers can efficiently kill Gram-negative E. coli with a very low minimum inhibitory concentration (1.70-0.93 μM), and do not cause obvious toxicity to mammalian cells at the concentrations used. With the increase of the oligomerization degree, the antibacterial activity of the oligomeric surfactants increases, i.e., hexameric surfactant > tetrameric surfactant > trimeric surfactant. Isothermal titration microcalorimetry, scanning electron microscopy, and zeta potential results reveal that the cationic micelles interact with the cell membrane of E. coli through two processes. First, the integrity of outer membrane of E. coli is disrupted by the electrostatic interaction of the cationic ammonium groups of the surfactants with anionic groups of E. coli, resulting in loss of the barrier function of the outer membrane. The inner membrane then is disintegrated by the hydrophobic interaction of the surfactant hydrocarbon chains with the hydrophobic domains of the inner membrane, leading to the cytoplast leakage. The formation of micelles of these cationic oligomeric surfactants at very low concentration enables more efficient interaction with bacterial cell membrane, which endows the oligomeric surfactants with high antibacterial activity.

Evidence to indicate that maillard reaction products can provide selective antimicrobial activity

Evidence to indicate that maillard reaction products can provide selective antimicrobial activity

Antimicrobial activity of Anonna mucosa (Jacq.) grown in vivo and obtained by in vitroculture.

Brazilian flora includes numerous species of medicinal importance that can be used to develop new drugs. Plant tissue culture offers strategies for conservation and use of these species allowing continuous production of plants and bioactive substances. Annona mucosa has produced substances such as acetogenins and alkaloids that exhibit antimicrobial activities. The widespread use of antibiotics has led to an increase in multidrug-resistant bacteria, which represents a serious risk of infection. In view of this problem, the aim of this work was to evaluate the antibacterial potential of extracts of A. mucosa obtained by in vitro techniques and also cultured under in vivo conditions. Segments from seedlings were inoculated onto different culture media containing the auxin picloram and the cytokinin kinetin at different concentrations. The calluses obtained were used to produce cell suspension cultures. The materials were subjected to methanol extraction and subsequent fractionation in hexane and dichloromethane. The antimicrobial activity against 20 strains of clinical relevance was evaluated by the macrodilution method at minimum inhibitory and minimum bactericidal concentrations. The extracts showed selective antimicrobial activity, inhibiting the growth of Streptococcus pyogenes and Bacillus thuringiensis at different concentrations. The plant tissue culture methods produced plant materials with antibacterial properties, as well as in vivo grown plants. The antibacterial activity of material obtained through biotechnological procedures of A. mucosa is reported here for the first time.

The Anticancer, Antioxidant and Antimicrobial Properties of the Sesquiterpene β-Caryophyllene from the Essential Oil of Aquilaria crassna.

The present study reports a bioassay-guided isolation of β-caryophyllene from the essential oil of Aquilaria crassna. The structure of β-caryophyllene was confirmed using FT-IR, NMR and MS. The antimicrobial effect of β-caryophyllene was examined using human pathogenic bacterial and fungal strains. Its anti-oxidant properties were evaluated by DPPH and FRAP scavenging assays. The cytotoxicity of β-caryophyllene was tested against seven human cancer cell lines. The corresponding selectivity index was determined by testing its cytotoxicity on normal cells. The effects of β-caryophyllene were studied on a series of in vitro antitumor-promoting assays using colon cancer cells. Results showed that β-caryophyllene demonstrated selective antibacterial activity against S. aureus (MIC 3 ± 1.0 µM) and more pronounced anti-fungal activity than kanamycin. β-Caryophyllene also displayed strong antioxidant effects. Additionally, β-caryophyllene exhibited selective anti-proliferative effects against colorectal cancer cells (IC50 19 µM). The results also showed that β-caryophyllene induces apoptosis via nuclear condensation and fragmentation pathways including disruption of mitochondrial membrane potential. Further, β-caryophyllene demonstrated potent inhibition against clonogenicity, migration, invasion and spheroid formation in colon cancer cells. These results prompt us to state that β-caryophyllene is the active principle responsible for the selective anticancer and antimicrobial activities of A. crassnia. β-Caryophyllene has great potential to be further developed as a promising chemotherapeutic agent against colorectal malignancies.

HPLC–NMR and HPLC–MS investigation of antimicrobial constituents in Cystophora monilifera and Cystophora subfarcinata

The crude dichloromethane extracts of the marine brown algae Cystophora monilifera and Cystophora subfarcinata were subjected to phytochemical profiling. This enabled the structures of both new and known phloroglucinols to be dereplicated and proposed using HPLC–NMR and HPLC–MS. Subsequent isolation confirmed the presence of four new and eight previously reported compounds. Five of the isolated phloroglucinols displayed selective antimicrobial activity.

A novel cathelicidin from Bufo bufo gargarizans Cantor showed specific activity to its habitat bacteria

Toad Bufo bufo gargarizans Cantor is still used in China as traditional Chinese medicine. However, present investigations on its skin secretions were mainly focused on the bufadienolides, the proteins/peptides contained in the secretions are largely unknown. A cDNA encoding a novel cathelicidin termed BG-CATH was identified by analysis of the toad skin transcriptome. The BG-CATH precursor was predicted to have 2 possible cleavage sites following dibasic cleavage signals at its C-terminal, which will generate two mature peptides, BG-CATH37 and BG-CATH(5-37). Phylogenetic analysis suggests that amphibian cathelicidins might evolve from common ancestors. The two predicted mature cathelicidins from B. bufo gargarizans were synthesized and both of them showed weak antimicrobial activities against human pathogenic bacteria Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus (MIC≥200μg/mL). However, BG-CATH37 and BG-CATH(5-37) had strong antimicrobial activities against aquatic bacteria of Vibrio splendidus, Streptococcus iniae and Aeromorus hydrophila, which were common microorganisms in the habitat of B. bufo gargarizans (MIC 3.125–40μg/mL). BG-CATH37 and BG-CATH(5-37) showed no hemolytic activity even at high concentrations (400μg/mL). CD spectra analysis suggested that structure rigidity of BG-CATH37 and BG-CATH(5-37) might play an important role to regulate their biological activities. Selective antimicrobial activity against habitat microorganisms might reflect the adaptation of amphibians to their living environments.

The specific antibacterial activity of liposome-encapsulated Clove oil and its application in tofu

In this study, the antibacterial activities of Clove oil and liposome-encapsulated Clove oil were investigated. First, the antibacterial activity of Clove oil demonstrated that the essential oil exhibited favorable antimicrobial activity for both Escherichia coli and Staphylococcus aureus. However, a setback of using Clove oil as a disinfectant is its low chemical stability. Then Clove oil was incorporated into a liposome formulation to increase its stability. The optimal polydispersity index (PDI) (0.196), Zeta potential (−24.5 mV) and entrapment efficiency (20.41%) of liposome were obtained at the concentration of Clove oil to 5.0 mg/mL. In addition, selective antimicrobial activity for S. aureus by utilizing pore-forming toxins (PFTs) to activate Clove oil release from liposome was observed. By contrast, liposome-encapsulated Clove oil has no effect on E. coli that doesn't secrete PFTs because antimicrobial component can't reach bacteria. Gas chromatography (GC) assay found that when liposome met S. aureus that secrete PFTs, PFTs would insert into the liposome membranes and form pores, through which the encapsulated Clove oil was released. Besides, liposome-encapsulated Clove oil exhibited efficient antimicrobial activity for S. aureus in tofu.

A Cactus‐Derived Toxin‐Like Cystine Knot Peptide with Selective Antimicrobial Activity

Naturally occurring cystine knot peptides show a wide range of biological activity, and as they have inherent stability they represent potential scaffolds for peptide-based drug design and biomolecular engineering. Here we report the discovery, sequencing, chemical synthesis, three-dimensional solution structure determination and bioactivity of the first cystine knot peptide from Cactaceae (cactus) family: Ep-AMP1 from Echinopsis pachanoi. The structure of Ep-AMP1 (35 amino acids) conforms to that of the inhibitor cystine knot (or knottin) family but represents a novel diverse sequence; its activity was more than 500 times higher against bacterial than against eukaryotic cells. Rapid bactericidal action and liposome leakage implicate membrane permeabilisation as the mechanism of action. Sequence homology places Ec-AMP1 in the plant C6-type of antimicrobial peptides, but the three dimensional structure is highly similar to that of a spider neurotoxin.

Molecular characterization of the liver-expressed antimicrobial peptide 2 (LEAP-2) in a teleost fish, Plecoglossus altivelis: Antimicrobial activity and molecular mechanism

Liver-expressed antimicrobial peptide 2 (LEAP-2) is widespread in fish and plays an important role in the host's innate immune system. In this study, full-length cDNA for LEAP-2 (PaLEAP-2) gene was cloned and sequenced from ayu, Plecoglossus altivelis. PaLEAP-2 mRNA was detected in a wide range of tissues, with the highest level of transcripts found in the liver. Upon induction by Vibrio anguillarum, its expression significantly increased in the liver, kidney, spleen, gill, and heart, but decreased in the intestine. The PaLEAP-2 mature peptide was chemically synthesized; it exhibited selective antimicrobial activity against various bacteria in vitro. PaLEAP-2 at high concentration reduced the bacterial load and improved the survival rate of V. anguillarum-infected ayu. Moreover, it inhibited the expression of mRNAs for TNF-α and IL-1β in V. anguillarum-infected ayu, both at high and low concentrations. PaLEAP-2 induced hydrolysis of the pET-22b plasmid DNA and bacterium genomic DNA. These results suggest that PaLEAP-2 plays a role in ayu immune responses against bacterial infection.

Rapid Dereplication and Identification of the Bioactive Constituents from the Fungus, Leucocoprinus birnbaumii

A series of fatty acids were rapidly dereplicated and partially identified from the flowerpot fungus, Leucocoprinus birnbaumii using HPLC-NMR and HPLC-MS. Subsequent off-line isolation unequivocally established the structures, and anti-microbial testing concluded that the fatty acids displayed moderate but selective anti-microbial activity. This represents the first report of these compounds occurring in this particular terrestrial fungus.

Antimicrobial Activity of Chemokine CXCL10 for Dermal and Oral Microorganisms.

CXCL10 (IP-10) is a small 10 kDa chemokine with antimicrobial activity. It is induced by IFN-γ, chemoattracts mononuclear cells, and promotes adhesion of T cells. Recently, we detected CXCL10 on the surface of the skin and in the oral cavity. In the current study, we used broth microdilution and radial diffusion assays to show that CXCL10 inhibits the growth of Escherichia coli, Staphylococcus aureus, Corynebacterium jeikeium, Corynebacterium striatum, and Candida albicans HMV4C, but not Corynebacterium bovis, Streptococcus mutans, Streptococcus mitis, Streptococcus sanguinis, Fusobacterium nucleatum, Aggregatibacter actinomycetemcomitans, Poryphromonas gingivalis, or C. albicans ATCC 64124. The reason for the selective antimicrobial activity is not yet known. However, antimicrobial activity of CXCL10 may be related to its composition and structure, as a cationic 98 amino acid residue molecule with 10 lysine residues, 7 arginine residues, a total net charge of +11, and a theoretical pI of 9.93. Modeling studies revealed that CXCL10 contains an α-helix at the N-terminal, three anti-parallel β-strands in the middle, and an α-helix at the C-terminal. Thus, CXCL10, when produced on the surface of the skin or in the oral cavity, likely has antimicrobial activity and may enhance innate antimicrobial and cellular responses to the presence of select commensal or opportunistic microorganisms.

Selective growth-inhibitory effect of 8-hydroxyquinoline towards Clostridium difficile and Bifidobacterium longum subsp. longum in co-culture analysed by flow cytometry.

The major risk factor for Clostridium difficile infection (CDI) is the use of antibiotics owing to the disruption of the equilibrium of the host gut microbiota. To preserve the beneficial resident probiotic bacteria during infection treatment, the use of molecules with selective antibacterial activity enhances the efficacy by selectively removing C. difficile. One of them is the plant alkaloid 8-hydroxyquinoline (8HQ), which has been shown to selectively inhibit clostridia without repressing bifidobacteria. Selective antimicrobial activity is generally tested by culture techniques of individual bacterial strains. However, the main limitation of these techniques is the inability to describe differential growth dynamics of more bacterial strains in co-culture within the same experiment. In the present study, we combined fluorescent in situ hybridization and flow cytometry to describe the changes in active and non-active cells of a mixed culture formed by the opportunistic pathogen C. difficile CECT 531 and the beneficial Bifidobacterium longum subsp. longum CCMDMND BL1 after exposure to 8HQ. It was observed that without 8HQ, the proportion of both strains was almost equal, oscillating between 22.7 and 77.9 % during a time lapse of 12 h, whereas with 8HQ the proportion of active C. difficile decreased after 4 h, and persisted only between 8.8 and 17.5 %. In contrast, bifidobacterial growth was not disturbed by 8HQ. The results of this study showed the selective inhibitory effect of 8HQ on clostridial and bifidobacterial growth dynamics, and the potential of this compound for the development of selective agents to control CDIs.