Identification of Antibacterial Components in the Methanol-Phase Extract from Edible Herbaceous Plant Rumex madaio Makino and Their Antibacterial Action Modes.

Outbreaks and prevalence of infectious diseases worldwide are some of the major contributors to morbidity and morbidity in humans. Pharmacophageous plants are the best source for searching antibacterial compounds with low toxicity to humans. In this study, we identified, for the first time, antibacterial components and action modes of methanol-phase extract from such one edible herbaceous plant Rumex madaio Makino. The bacteriostatic rate of the extract was 75% against 23 species of common pathogenic bacteria. The extract was further purified using the preparative high-performance liquid chromatography (Prep-HPLC) technique, and five separated componential complexes (CC) were obtained. Among these, the CC 1 significantly increased cell surface hydrophobicity and membrane permeability and decreased membrane fluidity, which damaged cell structure integrity of Gram-positive and -negative pathogens tested. A total of 58 different compounds in the extract were identified using ultra-HPLC and mass spectrometry (UHPLC-MS) techniques. Comparative transcriptomic analyses revealed a number of differentially expressed genes and various changed metabolic pathways mediated by the CC1 action, such as down-regulated carbohydrate transport and/or utilization and energy metabolism in four pathogenic strains tested. Overall, the results in this study demonstrated that the CC1 from R. madaio Makino are promising candidates for antibacterial medicine and human health care products.

The determination of antibacterial mode for cationic lipopeptides brevibacillins against Salmonella typhimurium by quantum chemistry calculation.

Brevibacillins are broad-spectrum cationic antimicrobial lipopeptides produced by Brevibacillus laterosporus fmb70 CGMCC 18426. The antibacterial mode of brevibacillins against Salmonella typhimurium CICC 21493 was investigated by quantum chemistry calculation in this study. The addition of LPS, Mg2+, and Ca2+ partially reduced the antimicrobial activity of brevibacillin and brevibacillin V against S. typhimurium, which indicated that the two cationic lipopeptides could bind to LPS and displaced the divalent cations on the LPS network. Release of LPS from S. typhimurium by brevibacillin and brevibacillin V resulted in destroying the dense LPS network and increasing the permeability of the outer membrane. Quantum chemistry calculation analysis revealed that Lys7 is the most critical amino acid residue to destroy the outer membrane. The total average N-H charge difference of the three protonated amino groups (Orn3-NH3, Lys7-NH3, and Lys10-NH3) determined the ability of brevibacillin V to bind LPS stronger than brevibacillin. Calcein complete leakage from liposomes and release of DiSC3-5 from the cytoplasmic membrane (CM) indicated that brevibacillin and brevibacillin V may destroy the CM. Brevibacillin and brevibacillin V exhibited their antimicrobial activities through membrane damages, where the OM permeability with high concentration of 64-256 µg/mL and membrane damage of CM with a low concentration of 4 µg/mL. Our finding might be helpful to understand the broad-spectrum antimicrobial mechanism of cationic lipopeptide and to design the novel antimicrobial peptide. KEY POINTS: • Brevibacillin V had stronger affinity for LPS than brevibacillin. • The N-H charge difference was the key of the difference in the affinity to LPS. • Brevibacillins inhibited Salmonella by displacing the divalent cations on the LPS.

Antibacterial mode of action of trans-cinnamaldehyde derived from cinnamon bark (Cinnamomum verum) essential oil against Agrobacterium tumefaciens.

The fumigant antibacterial activities of 50 plant essential oils belonging to 10 families were investigated against Agrobacterium tumefaciens. Among the test plant essential oils, Cinnamomum verum (cinnamon bark) essential oil showed the most potent fumigant antibacterial activity. When we investigated the antibacterial activities of compounds identified from cinnamon bark essential oil and 9 congeners of trans-cinnamaldehyde, lengths of inhibition zone of trans-cinnamaldehyde, salicylaldehyde and hydrocinnamaldehyde were 1.28, 1.73, and 1.24 cm at 0.625 mg/paper disc concentration, respectively. To determine the mode of action of trans-cinnamaldehyde and salicylaldehyde, intercellular reactive oxygen species (ROS) generation and cell membrane integrity were determined using a confocal laser scanning microscopy. Furthermore, we compared the up- and down-regulated gene expression of A. tumefaciens treated with trans-cinnamaldehyde and salicylaldehyde with that of untreated A. tumefaciens. With cutoffs of |log2FC| > 1 and FDR < 0.05, 29 and 43 down-regulated genes and 27 and 117 up-regulated genes were found in the treatment of trans-cinnamaldehyde and salicylaldehyde, respectively. Based on the ROS generation results, cell membrane integrity assay, and gene expression, we conclude that the antibacterial mode of action of trans-cinnamaldehyde and salicylaldehyde is ROS generation by the Fenton reaction caused by the down-regulation of an ATP synthesis-related gene cluster, corrupted iron ion homeostasis, and a corrupted ROS defense mechanism. The high concentration of ROS damaged the A. tumefaciens cell membrane, which caused cell death.

Recent Advances in the Application of Antibacterial Complexes Using Essential Oils.

Although antibacterial spectrum of essential oils (EOs) has been analyzed along with consumers' needs on natural biocides, singular treatments generally require high concentration of EOs and long-term exposures to eliminate target bacteria. To overcome these limitations, antibacterial complex has been developed and this review analyzed previous reports regarding the combined antibacterial effects of EOs. Since unexpectable combined effects (synergism or antagonism) can be derived from the treatment of antibacterial complex, synergistic and antagonistic combinations have been identified to improve the treatment efficiency and to avoid the overestimation of bactericidal efficacy, respectively. Although antibacterial mechanism of EOs is not yet clearly revealed, mode of action regarding synergistic effects especially for the elimination of pathogens by using low quantity of EOs with short-term exposure was reported. Whereas comprehensive analysis on previous literatures for EO-based disinfectant products implies that the composition of constituents in antibacterial complexes is variable and thus analyzing the impact of constituting substances (e.g., surfactant, emulsifier) on antibacterial effects is further needed. This review provides practical information regarding advances in the EO-based combined treatment technologies and highlights the importance of following researches on the interaction of constituents in antibacterial complex to clarify the mechanisms of antibacterial synergism and/or antagonism.

Antimicrobial activity of GN peptides and their mode of action.

Increasing prevalence of bacteria that carries resistance towards conventional antibiotics has prompted the investigation into new compounds for bacterial intervention to ensure efficient infection control in the future. One group of potential lead structures for antibiotics is antimicrobial peptides due to their characteristics as naturally derived compounds with antimicrobial activity. In this study, we aimed at characterizing the mechanism of action of a small set of in silico optimized peptides. Following determination of peptide activity against E. coli, S. aureus, and P. aeruginosa, toxicity was assessed revealing meaningful selectivity indexes for the majority of the peptides. Investigation of the peptides effect on bacteria demonstrated a rapid growth inhibition with signs of bacterial lysis together with increased bacterial size. Both visual and quantitative assays clearly demonstrated bacterial membrane disruption after 10 min for the most active peptides. The membrane disrupting effect was verified by measuring the release of calcein from bacterial mimicking liposomes. This revealed the most active peptides as inducers of immediate release, indicating the kinetics of membrane permeabilization as an important determinant of bacterial activity. No well-defined secondary structure of the peptides could be determined using CD-spectroscopy in the presence of different liposomes mixtures, implying that there is no correlation between peptide secondary structure and the observed anti-bacterial and cytotoxic activity for this set of peptides. In conjunction, these findings provide strong indications of membrane disruption as the primary mechanism of bacterial growth inhibition for the tested peptides. © 2015 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 106: 172-183, 2016.

Antibacterial mode of action of garviecin LG34 against Gram-negative bacterium Salmonella typhimurium.

Garviecin LG34 produced by Lactococcus garvieae LG34 exhibits wide-spectrum antibacterial activity against both Gram-positive and Gram-negative bacteria. This work aimed at clarifying the antibacterial mode of action of garviecin LG34 against Gram-negative bacterium Salmonella typhimurium. To determine the concentration for the bacteriocin antimicrobial mode experiments, the minimum inhibitory concentration of garviecin LG34 against S. typhimurium CICC21484 was determined as 0.25 mg/ml. Garviecin LG34 decreased the viable count of S. typhimurium CICC21484 and its antibacterial activity was the dose and time dependant. Garviecin LG34 led to the dissipation of transmembrane potential, the rise in the extracellular conductivity, UV-absorbing material at 260 nm, and LDH level of S. typhimurium CICC21484. Scanning electron micrographs results shown that garviecin LG34 cause dramatic deformation and fragmentation including the flagellum shedding, pores formation in surface, and even completely breakage of S. typhimurium cell. Moreover, garviecin LG34 decreased the intracellular ATP level. The results of this study demonstrated that garviecin LG34 can destroy cell structure, increase membrane permeability of S. typhimurium, thereby might be used as biopreservative for treating food borne and salmonellosis resulting from Gram-negative bacterium S. typhimurium.

Identification of Antibacterial Components and Modes in the Methanol-Phase Extract from a Herbal Plant Potentilla kleiniana Wight et Arn.

The increase in bacterial resistance and the decline in the effectiveness of antimicrobial agents are challenging issues for the control of infectious diseases. Traditional Chinese herbal plants are potential sources of new or alternative medicine. Here, we identified antimicrobial components and action modes of the methanol-phase extract from an edible herb Potentilla kleiniana Wight et Arn, which had a 68.18% inhibition rate against 22 species of common pathogenic bacteria. The extract was purified using preparative high-performance liquid chromatography (Prep-HPLC), and three separated fragments (Fragments 1-3) were obtained. Fragment 1 significantly elevated cell surface hydrophobicity and membrane permeability but reduced membrane fluidity, disrupting the cell integrity of the Gram-negative and Gram-positive pathogens tested (p < 0.05). Sixty-six compounds in Fragment 1 were identified using Ultra-HPLC and mass spectrometry (UHPLC-MS). The identified oxymorphone (6.29%) and rutin (6.29%) were predominant in Fragment 1. Multiple cellular metabolic pathways were altered by Fragment 1, such as the repressed ABC transporters, protein translation, and energy supply in two representative Gram-negative and Gram-positive strains (p < 0.05). Overall, this study demonstrates that Fragment 1 from P. kleiniana Wight et Arn is a promising candidate for antibacterial medicine and food preservatives.

Progress in Antibacterial Hydrogel Dressing.

Antibacterial hydrogel has excellent antibacterial property and good biocompatibility, water absorption and water retention, swelling, high oxygen permeability, etc.; therefore, it widely applied in biomedicine, intelligent textiles, cosmetics, and other fields, especially for medical dressing. As a wound dressing, the antibacterial hydrogel has the characteristics of absorbing wound liquid, controlling drug release, being non-toxic, being without side effects, and not causing secondary injury to the wound. Its preparation method is simple, and can crosslink via covalent or non-covalent bond, such as γ-radiation croFsslinking, free radical polymerization, graft copolymerization, etc. The raw materials are easy to obtain; usually these include chondroitin sulfate, sodium alginate, polyvinyl alcohol, etc., with different raw materials being used for different antibacterial modes. According to the hydrogel matrix and antibacterial mode, the preparation method, performance, antibacterial mechanism, and classification of antibacterial hydrogels are summarized in this paper, and the future development direction of the antibacterial hydrogel as wound dressing is proposed.

Antibacterial Mode of Eucommia ulmoides Male Flower Extract Against Staphylococcus aureus and Its Application as a Natural Preservative in Cooked Beef.

The research was conducted to elucidate the antibacterial performance and mode of action of Eucommia ulmoides male flower extract (EUMFE) against Staphylococcus aureus and its application as a natural preservative in cooked beef. The antibacterial activity was evaluated by determining the diameter of inhibition zone (DIZ), minimum inhibitory concentration (MIC), and minimum bactericide concentration (MBC). The changes in membrane potential, contents of bacterial DNA and protein, integrity and permeability of the cell membrane, and cell morphology were analyzed to reveal the possible mode of action. The effect of EUMFE on the counts of S. aureus, pH, color, total volatile basic nitrogen (TVB-N), and thiobarbituric acid reactive substances (TBARS) of the cooked beef stored at 4°C for 9 days were studied. The results showed that the DIZ, MIC, and MBC of EUMFE against S. aureus were 12.58 ± 0.23 mm, 40 mg/mL, and 80 mg/mL, respectively. The mode of action of EUMFE against S. aureus included hyperpolarization of cell membrane, decrease in bacterial DNA and protein contents, destruction of cell membrane integrity, increase in cell membrane permeability, and damage of cell morphology. After treatments with EUMFE, the growth of S. aureus and lipid oxidation in cooked beef were significantly inhibited (P < 0.05). The pH and TVB-N values of cooked beef treated with EUMFE were significantly reduced as compared to control group (P < 0.05). The color of cooked beef samples containing EUMFE showed decreased L* and b* values, and increased a* and ΔE* values. Therefore, our findings showed that EUMFE had a good antibacterial effect on S. aureus, and provided a theoretical basis for the application of EUMFE as a natural preservative in the preservation of cooked beef.

Comparative Evaluation of Piper nigrum, Rosmarinus officinalis, Cymbopogon citratus and Juniperus communis L. Essential Oils of Different Origin as Functional Antimicrobials in Foods.

Essential oils can be used as preservatives in foods because of their ability to inhibit bacteria growth in low concentration, which does not influence on foods' organoleptic properties and does not generate the resistance mechanisms in cells. The aim of that work was to compare the effectiveness of commercial oils from black pepper (Piper nigrum), rosemary (Rosmarinus officinalis), lemongrass (Cymbopogon citratus) and juniper (Juniperus communis L.) with oils obtained in our laboratory. The typical cultivation method was supported by the flow cytometry to detect the cells of very low physiologic and metabolic activity. Our investigation demonstrated that both types of oils can effectively inhibit the growth of saprophytic bacteria P. orientalis. The oils distilled in our laboratory had a bacteriostatic effect at a lower concentration, which is important for application in the food industry. Flow cytometry analyzes and confirmed the thesis that essential oils do not have a germicidal effect on bacteria cells.

The Influence of Selected Plant Essential Oils on Morphological and Physiological Characteristics in Pseudomonas Orientalis.

The aim of this work was to estimate the antibacterial activity of selected essential oils on Pseudomonas orientalis strains isolated from foods. An attempt was also made to identify the mechanisms of the action of the plant oils. Classical methods of assessment of the effectiveness of antimicrobial activity of oils were linked with flow cytometry. It was observed that bergamot, lemongrass, bitter orange, juniper, and black pepper oils have bacteriostatic effect against P. orientalis P49. P. orientalis P110 is sensitive to lime, lemongrass, juniper, rosemary, and black pepper oils. Additionally, plant oils with biostatic effect on P. orientalis limited the intracellular metabolic activity of cells; this was closely linked with the ability of plant oils' bioactive components to interact with bacteria cell membrane, causing the release of membrane proteins. As a result, the selective permeability of the cell membranes were damaged and the bacterial shape was transformed to coccoid in form.