Characterization and structure identification of an antimicrobial peptide, hominicin, produced by Staphylococcus hominis MBBL 2-9

Hominicin, antimicrobial peptide displaying potent activity against Staphylococcus aureus ATCC 25923, methicillin-resistant S. aureus (MRSA) ATCC 11435 and vancomycin-intermediate S. aureus (VISA) CCARM 3501, was purified by chloroform extraction, ion-exchange column chromatography and reverse-phase HPLC from culture supernatant of Staphylococcushominis MBBL 2-9. Hominicin exhibited heat stability up to 121 °C for 15 min and activity under both acidic and basic conditions (from pH 2.0 to 10.0). Hominicin was cleaved into two fragments after treatment with proteinase K, resulting in the loss of its antibacterial activity, while it was resistant to trypsin, α-chymotrypsin, pepsin and lipase. The molecular mass of hominicin determined by mass spectrometry was 2038.4 Da. LC-mass spectrometry and NMR spectroscopy analyses of the two fragments revealed the sequence of hominicin as DmIle-Dhb-Pro-Ala-Dhb-Pro-Phe-Dhb-Pro-Ala-Ile-Thr-Glu-Ile-Dhb-Ala-Ala-Val-Ile-Ala-Dmp, which had no similarity with other antimicrobial peptides previously reported. The present study is the first report of this novel antimicrobial peptide, which has uncommon amino acid residues like the ones in Class I group and shows potent activity against clinically relevant S. aureus, MRSA and VISA.     

Antimicrobial Potential of Endophytic Fungi Derived from Three Seagrass Species: Cymodocea serrulata,Halophila ovalis and Thalassia hemprichii

Endophytic fungi from three commonly found seagrasses in southern Thailand were explored for their ability to produce antimicrobial metabolites. One hundred and sixty endophytic fungi derived from Cymodocea serrulata (Family Cymodoceaceae), Halophila ovalis and Thalassia hemprichii (Family Hydrocharitaceae) were screened for production of antimicrobial compounds by a colorimetric broth microdilution test against ten human pathogenic microorganisms including Staphylococcus aureus ATCC 25923, a clinical isolate of methicillin-resistant S. aureus, Escherichia coli ATCC 25923, Pseudomonas aeruginosa ATCC 27853, Candida albicans ATCC 90028 and NCPF 3153, Cryptococcus neoformans ATCC 90112 and ATCC 90113 and clinical isolates of Microsporum gypseum and Penicillium marneffei . Sixty-nine percent of the isolates exhibited antimicrobial activity against at least one test strain. Antifungal activity was more pronounced than antibacterial activity. Among the active fungi, seven isolates including Hypocreales sp. PSU-ES26 from C . serrulata , Trichoderma spp. PSU-ES8 and PSU-ES38 from H . ovalis , and Penicillium sp. PSU-ES43, Fusarium sp. PSU-ES73, Stephanonectria sp. PSU-ES172 and an unidentified endophyte PSU-ES190 from T . hemprichii exhibited strong antimicrobial activity against human pathogens with minimum inhibitory concentrations (MIC) of less than 10 µg/ml. The inhibitory extracts at concentrations of 4 times their MIC destroyed the targeted cells as observed by scanning electron microscopy. These results showed the antimicrobial potential of extracts from endophytic fungi from seagrasses.     

High expression of a plectasin-derived peptide NZ2114 in Pichia pastoris and its pharmacodynamics, postantibiotic and synergy against Staphylococcus aureus

NZ2114, a new variant of plectasin, was overexpressed in Pichia pastoris X-33 via pPICZαA for the first time. The total secreted protein of fermentation supernatant reached 2,390 mg/l (29 °C) and 2,310 mg/l (25 °C), and the recombinant NZ2114 (rNZ2114) reached 860 mg/l (29 °C) and 1,309 mg/l (25 °C) at 96 h induction in a 5-l fermentor, respectively.The rNZ2114 was purified by cation exchange chromatography, and its yield was 583 mg/l with 94.8 % purity. The minimal inhibitory concentration (MIC) of rNZ2114 to four ATCC strains of Staphyloccocus aureus was evaluated from 0.028 to 0.90 μM. Meanwhile, it showed potent activity (0.11–0.90 μM) to 20 clinical isolates of MRSA. The rNZ2114 killed over 99.9 % of tested S. aureus (ATCC 25923 and ATCC 43300) in Mueller-Hinton medium within 6 h when treated with 4?×?MIC. The postantibiotic effect of rNZ2114 to S. aureus ATCC 25923 and ATCC 43300 was 18.6–45.6 and 1.7–3.5 h under 1×, 2×, and 4× MIC, respectively. The fractional inhibitory concentration index (FICI) indicated a synergistic effect between rNZ2114 and kanamycin, streptomycin, and vancomycin against S. aureus ATCC 25923 (FICI?=?0.125), and additivity between rNZ2114 and ampicillin, spectinomycin (FICI?=?0.625), respectively. To S. aureus ATCC 43300 [methicillin-resistant S. aureus (MRSA)], rNZ2114 showed a synergistic effect (FICI?=?0.125–0.3125) with kanamycin, ampicillin, streptomycin, and vancomycin, and antagonism with spectinomycin (FICI?=?8.0625). The rNZ2114 caused only less than 0.1 % hemolytic activity in the concentration of 128 μg/ml, and showed a good thermostability from 20 to 80 °C. In addition, it exhibited the highest activity at pH 8.0. These results suggested that large-scale production of NZ2114 is feasible using the P. pastoris expression system, and it could be a new potential antimicrobial agent for the prevention and treatment of S. aureus especially for MRSA infections.     

Neolignans from Callistemon lanceolatus

Two neolignans, named callislignan A and B together with known C-methyl-flavonoids, a lignan and pentacyclic triterpenoid esters were isolated from the leaves of Callistemon lanceolatus. Their structures were characterized by spectroscopic methods. Callislignan A and B had antibacterial activity against Staphylococcus aureus ATCC25923 and MRSA SK1 with callislignan B having an MIC of 8 μg/mL.     

Pharmacological synergism of bee venom and melittin with antibiotics and plant secondary metabolites against multi-drug resistant microbial pathogens

The goal of this study was to investigate the antimicrobial activity of bee venom and its main component, melittin, alone or in two-drug and three-drug combinations with antibiotics (vancomycin, oxacillin, and amikacin) or antimicrobial plant secondary metabolites (carvacrol, benzyl isothiocyanate, the alkaloids sanguinarine and berberine) against drug-sensitive and antibiotic-resistant microbial pathogens. The secondary metabolites were selected corresponding to the molecular targets to which they are directed, being different from those of melittin and the antibiotics.The minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) were evaluated by the standard broth microdilution method, while synergistic or additive interactions were assessed by checkerboard dilution and time-kill curve assays. Bee venom and melittin exhibited a broad spectrum of antibacterial activity against 51 strains of both Gram-positive and Gram-negative bacteria with strong anti-MRSA and anti-VRE activity (MIC values between 6 and 800 µg/ml). Moreover, bee venom and melittin showed significant antifungal activity (MIC values between 30 and 100 µg/ml). Carvacrol displayed bactericidal activity, while BITC exhibited bacteriostatic activity against all MRSA and VRE strains tested (reference strains and clinical isolates), both compounds showed a remarkable fungicidal activity with minimum fungicidal concentration (MFC) values between 30 and 200 µg/ml. The DNA intercalating alkaloid sanguinarine showed bactericidal activity against MRSA NCTC 10442 (MBC 20 µg/ml), while berberine exhibited bacteriostatic activity against MRSA NCTC 10442 (MIC 40 µg/ml).Checkerboard dilution tests mostly revealed synergism of two-drug combinations against all the tested microorganisms with FIC indexes between 0.24 and 0.50, except for rapidly growing mycobacteria in which combinations exerted an additive effect (FICI = 0.75–1). In time-kill assays all three-drug combinations exhibited a powerful bactericidal synergistic effect against MRSA NCTC 10442, VRE ATCC 51299, and E. coli ATCC 25922 with a reduction of more than 3log₁₀ in the colony count after 24 h. Our findings suggest that bee venom and melittin synergistically enhanced the bactericidal effect of several antimicrobial agents when applied in combination especially when the drugs affect several and differing molecular targets. These results could lead to the development of novel or complementary antibacterial drugs against MDR pathogens.     

24-Branched Δ5 sterols from Laurencia papillosa red seaweed with antibacterial activity against human pathogenic bacteria

Methanol extract of thirty-eight seaweeds samples were first screened against Gram-positive (Staphylococcus aureus ATCC 25923 and Bacillus subtilis ATCC 6051) and -negative (Escherichia coli ATCC 8739 and Pseudomonas aerugenosa ATCC 9027) bacteria. Laurencia papillosa (Ceramiales, Rhodomelaceae, Rhodophyta) gave maximum antimicrobial activity against these bacteria. It was finally tested against four clinical Gram-negative isolates (E. coli, P. aerugenosa, Klebsiella pneumoniae and Shigella flexineri) and exhibited antibacterial activity. The extract was fractionated by column chromatography and the active fraction was identified as a cholesterol derivative, 24-propylidene cholest-5-en-3β-ol using gas chromatography mass spectrometry (GC–MS). The electrospray ionization mass spectrometry (ESI-MS) and FT-IR spectroscopic analysis also supported the structure of the compound. The minimum inhibitory concentration ranged from 1.2 to 1.7 μg/mL (IC₅₀) against clinical isolates. This is the first report of antibacterial activity of this cholesterol derivative. This compound could be exploited as potential lead molecule against broad spectrum drug development. The results also affirm the potential of seaweeds as an important natural source of antimicrobial compounds for pharmaceutical industries.     

Screening of Indonesian peat soil bacteria producing antimicrobial compounds

The development and world-wide spread of multidrug-resistant (MDR) bacteria have a high concern in the medicine, especially the extended-spectrum of beta-lactamase (ESBL) producing Escherichia coli and methicillin-resistant Staphylococcus aureus (MRSA). There are currently very limited effective antibiotics to treat infections caused by MDR bacteria. Peat-soil is a unique environment in which bacteria have to compete each other to survive, for instance, by producing antimicrobial substances. This study aimed to isolate bacteria from peat soils from South Kalimantan Indonesia, which capable of inhibiting the growth of Gram-positive and Gram-negative bacteria. Isolates from peat soil were grown and identified phenotypically. The cell-free supernatant was obtained from broth culture by centrifugation and was tested by agar well-diffusion technique against non ESBL-producing E. coli ATCC 25922, ESBL-producing E. coli ATCC 35218, methicillin susceptible Staphylococcus aureus (MSSA) ATCC 29,213 and MRSA ATCC 43300. Putative antimicrobial compounds were separated using SDS-PAGE electrophoresis and purified using electroelution method. Antimicrobial properties of the purified compounds were confirmed by measuring the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). In total 28 isolated colonies were recovered; three (25PS, 26PS, and 27PS) isolates produced proteins with strong antimicrobial activities against both reference strains. The substance of proteins from three isolates exerted strong antimicrobial activity against ESBL-producing E. coli ATCC 35,218 (MIC = 2,80 µg/mL (25PS), 3,76 µg/mL (26PS), and 2,41 µg/mL (27PS), and MRSA ATCC 43,300 (MIC = 4,20 µg/mL (25PS), 5,65 µg/mL (26PS), and 3,62 µg/mL (27PS), and also had the ability bactericidal properties against the reference strains. There were isolates from Indonesian peat which were potentials sources of new antimicrobials.     

Evaluation of antimicrobial activity of bacterial symbionts isolated from wild field cockroach Blattella vaga from Saudi Arabia

Drug-resistant pathogens form the main threat to global health during the current century. Annually, a lot of patients die in hospitals due to infection with one or more drug-resistant bacteria especially Staphylococcus aureus (MRSA). In the absence of new effective antimicrobial drugs, the number of deaths said to be increased. Searching for new antibiotics in our backyard form a part of scientist strategies to solve such serious health problem. Insects consider one of such interesting sources of the new era of antimicrobial drugs. Cockroaches as an example can live and adapt in a polluted area for a long time, so through this work field cockroach, Blattella vaga was collected from two semi-wild areas around Riyadh, Saudi Arabia for isolation of gut bacteria searching for new antimicrobial agents. Three species of bacteria were identified from field cockroach gut: Bacillus licheniformis, Bacillus subtilis, and Kocuria rosea. The three species were isolated, purified, and tested for their antimicrobial activity against four drug-resistant pathogens (three bacteria: Salmonella enterica (ATCC25566), Staphylococcus aureus (MRSA) (Clinical strain), and Streptococcus mutans (RCMB 017(1) ATCC ® 25175™) and one fungus: Candida albicans (RCMB005003(1) ATCC® 10231™)). The results show no antimicrobial activity of Bacillus subtilis and very good activity Bacillus licheniformis and Kocuria rosea. Bacillus licheniformis gives very effective activity against Candida albicans while Kocuria rosea is effective against MRSA and Streptococcus mutans. None of the gut isolated bacteria show any activity against Salmonella enterica. Such results revealed that the metabolites of these bacteria could be used as substitutes to the already used antibiotics to overcome the problem of multidrug-resistant human pathogens.     

Validating the in vitro antimicrobial activity of Artemisia afra in polyherbal combinations to treat respiratory infections

Artemisia afra is one of the most widely used medicinal plants in African traditional medicine and is commonly administered in polyherbal combinations to treat respiratory infections. Focussing on plant volatiles, the aim of this study was to provide scientific evidence for the antimicrobial activity of A. afra (principle plant) in combination with essential oils from three medicinal aromatic plants; Agathosma betulina, Eucalyptus globulus and Osmitopsis asteriscoides. In vitro minimum inhibitory concentration (MIC) assays were undertaken on four pathogens (Enterococcus faecalis ATCC 29212, Moraxella catarrhalis ATCC 23246, Klebsiella pneumoniae NCTC 9633 and Cryptococcus neoformans ATCC 90112) to determine antimicrobial efficacy of the oils and their combinations. The fractional inhibitory concentration (FIC) and isobolograms were used to interpret pharmacodynamic interactions such as synergy, antagonism or additive profiles. The antimicrobial activity of the individual oils mostly displayed moderate activity. Predominantly, additive interactions were noted. The most prominent synergistic interaction (FIC value of 0.5) was observed when A. afra was combined with O. asteriscoides in the 8:2 ratio (eight parts A. afra with two parts O. asteriscoides) against C. neoformans. No antagonistic interactions were evident.     

Synthesis and on-target antibacterial activity of novel 3-elongated arylalkoxybenzamide derivatives as inhibitors of the bacterial cell division protein FtsZ

Novel 3-elongated arylalkoxybenzamide derivatives were designed, synthesized and evaluated for their cell division inhibitory activity and antibacterial activity. Among them, the subseries of 3-alkyloxybenzamide derivatives exhibited greatly improved on-target activity against Bacillus subtilis and Staphylococcus aureus, and remarkably increased antibacterial activity against B. subtilis ATCC9372, penicillin-susceptible S. aureus ATCC25923, methicillin-resistant S. aureus ATCC29213 (MRSA) and penicillin-resistant S. aureus PR compared with 3-methoxybenzamide. In contrast, the subseries of 3-phenoxyaklyloxybenzamide, 3-heteroarylalkyloxybenzamide and 3-heteroarylthioalkyloxybenzamide derivatives only showed a significant improvement in on-target activity and antibacterial activity against B. subtilis ATCC9372.     

The Diversity and Antimicrobial Activity of Preussia sp. Endophytes Isolated from Australian Dry Rainforests

Limited knowledge currently exists regarding species diversity and antimicrobial activity of endophytic isolates of Preussia within Australia. This report describes endophytic Preussia species that were identified through molecular analysis of the internal transcribed spacer region. Screening for antimicrobial secondary metabolites was determined by testing crude ethyl acetate (EtOAc) extracts derived from fungal mycelia against a panel of ATCC type strains which included Bacillus cereus, Escherichia coli, Enterococcus faecalis, Pseudomonas aeruginosa, Serratia marcescens, methicillin-resistant Staphylococcus aureus (MRSA) and the opportunist yeast pathogen Candida albicans. Subsequently, high-performance liquid chromatography generated fractions of bioactive EtOAc extracts which were subject to confirmatory testing using the Clinical and Laboratory Standards Institute reference microdilution antimicrobial activity assay. A total of 18 Preussia were isolated from nine host plants with 6/18 having a <97 % sequence similarity to other known species in Genbank, suggesting that they are new species. In preliminary screening, 13/18 Preussia isolates revealed antimicrobial activity against at least one of the microbes tested, whilst 6/18 isolates, including 4/6 putative new species showed specific antimicrobial activity against MRSA and C. albicans. These results highlight the antimicrobial potential of Australian Preussia spp. and also the importance of Australian dry rainforests as an untapped repository of potentially significant bioactive compounds.     

Synergistic interactions in two-drug and three-drug combinations (thymol,EDTA and vancomycin) against multi drug resistant bacteria including E. coli

Combinations of two or more drugs, which affect different targets, have frequently been used as a new approach against resistant bacteria. In our work we studied the antimicrobial activity (MIC, MBC) of individual drugs (the phenolic monoterpene thymol, EDTA and vancomycin), of two-drug interactions between thymol and EDTA in comparison with three-drug interactions with vancomycin against sensitive and resistant bacteria. Thymol demonstrated moderate bactericidal activity (MBC between 60 and 4000 μg/ml) while EDTA only exhibited bacteriostatic activity over a range of 60–4000 μg/ml. MICs of vancomycin were between 0.125 and 16 μg/ml against Gram-positive and between 32 and 128 μg/ml against Gram-negative bacteria. Checkerboard dilution and time-kill curve assays were performed to evaluate the mode of interaction of several combinations against Methicillin-resistant Staphylococcus aureus (MRSA NCTC 10442) and Escherichia coli (ATCC 25922). Checkerboard data indicate indifferent interaction against Gram-positive (FICI = 1–1.3) and synergy against Gram-negative bacteria (FICI ≈ 0.4), while time kill analyses suggest synergistic effect in different combinations against both types of bacteria. It is remarkable that the combinations could enhance the sensitivity of E. coli to vancomycin 16-fold to which it is normally insensitive. We have provided proof for the concept, that combinations of known antibiotics with modern phytotherapeutics can expand the spectrum of useful therapeutics.     

Effect of Ottoman Viper (Montivipera xanthina (Gray, 1849)) Venom on Various Cancer Cells and on Microorganisms

Cytotoxic and antimicrobial effects of Montivipera xanthina venom against LNCaP, MCF-7, HT-29, Saos-2, Hep3B, Vero cells and antimicrobial activity against selected bacterial and fungal species: Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922, E. coli O157H7, Enterococcus faecalis 29212, Enterococcus faecium DSM 13590, Staphylococcus epidermidis ATCC 12228, S. typhimirium CCM 5445, Proteus vulgaris ATCC 6957 and Candida albicans ATCC 10239 were studied for evaluating the potential medical benefit of this snake venom. Cytotoxicity of venom was determined using MTT assay. Snake venom cytotoxicity was expressed as the venom dose that killed 50 % of the cells (IC₅₀). The antimicrobial activity of venom was studied by minimal inhibitory concentration (MIC) and disc diffusion assay. MIC was determined using broth dilution method. The estimated IC₅₀ values of venom varied from 3.8 to 12.7 or from 1.9 to 7.2 μg/ml after treatment with crude venom for 24 or 48 h for LNCaP, MCF-7, HT-29 and Saos-2 cells. There was no observable cytotoxic effect on Hep3B and Vero cells. Venom exhibited the most potent activity against C. albicans (MIC, 7.8 μg/ml and minimal fungicidal concentration, 62.5 μg/ml) and S. aureus (MIC, 31.25 μg/ml). This study is the first report showing the potential of M. xanthina venom as an alternative therapeutic approach due to its cytotoxic and antimicrobial effects.     

The Antibacterial Properties of 4, 8, 4′, 8′-Tetramethoxy (1,1′-biphenanthrene) -2,7,2′,7′-Tetrol from Fibrous Roots of Bletilla striata

Biphenanthrene compound, 4, 8, 4′, 8′-tetramethoxy (1, 1′-biphenanthrene)—2, 7, 2′, 7′-tetrol (LF05), recently isolated from fibrous roots of Bletilla striata, exhibits antibacterial activity against several Gram-positive bacteria. In this study, we investigated the antibacterial properties, potential mode of action and cytotoxicity. Minimum inhibitory concentrations (MICs) tests showed LF05 was active against all tested Gram-positive strains, including methicillin-resistant Staphylococcus aureus (MRSA) and staphylococcal clinical isolates. Minimum bactericidal concentration (MBC) tests demonstrated LF05 was bactericidal against S. aureus ATCC 29213 and Bacillus subtilis 168 whereas bacteriostatic against S. aureus ATCC 43300, WX 0002, and other strains of S. aureus. Time-kill assays further confirmed these observations. The flow cytometric assay indicated that LF05 damaged the cell membrane of S. aureus ATCC 29213 and B. subtilis 168. Consistent with this finding, 4 × MIC of LF05 caused release of ATP in B. subtilis 168 within 10 min. Checkerboard test demonstrated LF05 exhibited additive effect when combined with vancomycin, erythromycin and berberine. The addition of rat plasma or bovine serum albumin to bacterial cultures caused significantly loss in antibacterial activity of LF05. Interestingly, LF05 was highly toxic to several tumor cells. Results of these studies indicate that LF05 is bactericidal against some Gram-positive bacteria and acts as a membrane structure disruptor. The application of biphenanthrene in the treatment of S. aureus infection, especially local infection, deserves further study.     

Contribution of bovine lactoferrin inter-lobe region to iron binding stability and antimicrobial activity against <Emphasis Type="Italic">Staphylococcus aureus</Emphasis>

The investigation of the recombinant bovine lactoferrin-derived antimicrobial protein (rBLfA) demonstrates that the inter-lobe region of bovine lactoferrin contributes to iron binding stability and antimicrobial activity against Staphylococcus aureus. rBLfA containing N-lobe (amino acid residues 1–333) and inter-lobe region (residues 334–344) was expressed in Pichia pastoris at shaking flask and fermentor level. The recombinant intact bovine lactoferrin (rBLf) and N-lobe (rBLfN) were expressed in the same system as control. The physical–chemical parameters of rBLfA, rBLfN and rBLf including amino acid residues, molecular weight, isoelectric point, net positive charge and instability index were computed and compared. The simulated tertiary structure and the calculated surface net charge showed that rBLfA maintained original structure and exhibited a higher cationic feature than rBLf and rBLfN. The three proteins showed different iron binding stability and antimicrobial activity. rBLfA released iron in the pH range of 7.0–3.5, whereas rBLfN lost its iron over the pH range of 7.0–4.0 and iron release from rBLf occurred in the pH range of 5.5–3.0. However, the minimum inhibition concentration of rBLfA against S. aureus ATCC25923 was 6.5 μmol/L, compared with 12.5 and 25 μmol/L that of rBLfN and rBLf, respectively. These results revealed that S. aureus was more sensitive to rBLfA than rBLfN and rBLf. It appeared that the strong cationic character of inter-lobe region related positively to the higher anti-S. aureus activity.     

Computational Ranking of Yerba Mate Small Molecules Based on Their Predicted Contribution to Antibacterial Activity against Methicillin-Resistant Staphylococcus aureus

The aqueous extract of yerba mate, a South American tea beverage made from Ilex paraguariensis leaves, has demonstrated bactericidal and inhibitory activity against bacterial pathogens, including methicillin-resistant Staphylococcus aureus (MRSA). The gas chromatography-mass spectrometry (GC-MS) analysis of two unique fractions of yerba mate aqueous extract revealed 8 identifiable small molecules in those fractions with antimicrobial activity. For a more comprehensive analysis, a data analysis pipeline was assembled to prioritize compounds for antimicrobial testing against both MRSA and methicillin-sensitive S. aureus using forty-two unique fractions of the tea extract that were generated in duplicate, assayed for activity, and analyzed with GC-MS. As validation of our automated analysis, we checked our predicted active compounds for activity in literature references and used authentic standards to test for antimicrobial activity. 3,4-dihydroxybenzaldehyde showed the most antibacterial activity against MRSA at low concentrations in our bioassays. In addition, quinic acid and quercetin were identified using random forests analysis and 5-hydroxy pipecolic acid was identified using linear discriminant analysis. We also generated a ranked list of unidentified compounds that may contribute to the antimicrobial activity of yerba mate against MRSA. Here we utilized GC-MS data to implement an automated analysis that resulted in a ranked list of compounds that likely contribute to the antimicrobial activity of aqueous yerba mate extract against MRSA.     

Antimicrobial lignans derived from the roots of Streblus asper

Four new lignans, (7′R,8′S)-4,4'-Dimethoxy-strebluslignanol (1), 3'-Hydroxy-isostrebluslignaldehyde (2), 3,3'-Methylene-bis(4-hydroxybenzaldehyde) (3), and 4-Methoxy-isomagnaldehyde (4), and six known lignans (5–10), were isolated from the roots of Streblus asper. The structures of these molecules were elucidated through various spectroscopic methods of analysis, including 1D and 2D NMR. The stereochemistry at the chiral centres was determined using the CD spectrum and from coupling constant and optical rotation data. Compounds 1–6 showed good antimicrobial activity against Saccharomyces cerevisiae (ATCC 9763), Bacillus subtilis (ATCC 6633), Pseudomonas aeruginosa (ATCC 9027), Escherichia coli (ATCC 11775), and Staphylococcus aureus (ATCC 25923), with MIC values ranging from 0.0150 to 0.0940 μM.     

Design, expression, and characterization of a novel targeted plectasin against methicillin-resistant Staphylococcus aureus

A novel specifically targeted antimicrobial peptide (STAMP) that was especially effective against methicillin-resistant Staphylococcus aureus (MRSA) was designed by fusing the AgrD1 pheromone to the N-terminal end of plectasin. This STAMP was named Agplectasin, and its gene was synthesized and expressed in Pichia pastoris X-33 via pPICZαA. The highest amount of total secreted protein reached 1,285.5 mg/l at 108 h during the 120-h induction. The recombinant Agplectasin (rAgP) was purified by cation exchange chromatography and hydrophobic exchange chromatography; its yield reached 150 mg/l with 94 % purity. The rAgP exhibited strong bactericidal activity against S. aureus but not Staphylococcus epidermidis or other types of tested bacteria. A bactericidal kinetics assay showed that the rAgP killed over 99.9 % of tested S. aureus (ATCC 25923 and ATCC 43300) in both Mueller–Hinton medium and human blood within 10 h when treated with 4× minimal inhibitory concentration. The rAgP caused only approximately 1 % hemolysis of human blood cells, even when the concentration reached 512 μg/ml, making it potentially feasible as a clinical injection agent. In addition, it maintained a high activity over a wide range of pH values (2.0–10.0) and demonstrated a high thermal stability at 100 °C for 1 h. These results suggested that this STAMP has the potential to eliminate MRSA strains without disrupting the normal flora.     

Design,synthesis and antistaphylococcal activity of marine pyrrole alkaloid derivatives

Abstract

A novel set of 16 hybrids of bromopyrrole alkaloids with aroyl hydrazone were designed, synthesized and evaluated for antibacterial and antibiofilm activities against methicillin-resistant Staphylococcus aureus (MRSA; ATCC 43866), methicillin-susceptible Staphylococcus aureus (MSSA; ATCC 35556) and Staphylococcus epidermidis (SE, S. epidermidis ATCC 35984). Of the 16 tested hybrids, 14 exhibited equal or superior antibiofilm activity against MSSA and MRSA relative to standard vancomycin. Compound 4m showed highest potency with antibiofilm activity of 0.39?µg/mL and 0.78?µg/mL against MSSA and MRSA, respectively. Thus, this compound could act as a potential lead for further development of new antistaphylococcal drugs.     

Assessment of synergistic antibacterial activity of combined biosurfactants revealed by bacterial cell envelop damage

Besides potential surface activity and some beneficial physical properties, biosurfactants express antibacterial activity. Bacterial cell membrane disrupting ability of rhamnolipid produced by Pseudomonas aeruginosa C2 and a lipopeptide type biosurfactant, BS15 produced by Bacillus stratosphericus A15 was examined against Staphylococcus aureus ATCC 25923 and Escherichia coli K8813. Broth dilution technique was followed to examine minimum inhibitory concentration (MIC) of both the biosurfactants. The combined effect of rhamnolipid and BS15 against S. aureus and E. coli showed synergistic activity by expressing fractional inhibitory concentration (FIC) index of 0.43 and 0.5. Survival curve of both the bacteria showed bactericidal activity after treating with biosurfactants at their MIC obtained from FIC index study as it killed > 90% of initial population. The lesser value of MIC than minimum bactericidal concentration (MBC) of the biosurfactants also supported their bactericidal activity against both the bacteria. Membrane permeability against both the bacteria was supported by amplifying protein release, increasing of cell surface hydrophobicity, withholding capacity of crystal violet dye and leakage of intracellular materials. Finally cell membrane disruption was confirmed by scanning electron microscopy (SEM). All these experiments expressed synergism and effective bactericidal activity of the combination of rhamnolipid and BS15 by enhancing the bacterial cell membrane permeability. Such effect of the combination of rhamnolipid and BS15 could make them promising alternatives to traditional antibiotic in near future.