Novel two-chain fatty acid-based lipids for development of vancomycin pH-responsive liposomes against Staphylococcus aureus and methicillin-resistant Staphylococcus aureus (MRSA)

Abstract

The development of bacterial resistance against antibiotics is attributed to poor localisation of lethal antibiotic dose at the infection site. This study reports on the synthesis and use of novel two-chain fatty acid-based lipids (FAL) containing amino acid head groups in the formulation of pH-responsive liposomes for the targeted delivery of vancomycin (VAN). The formulated liposomes were characterised for their size, polydispersity index (PDI), surface charge and morphology. The drug-loading capacity, drug release, cell viability, and in vitro and in vivo efficacy of the formulations were investigated. A sustained VAN release profile was observed and in vitro antibacterial studies against S. aureus and MRSA showed superior and prolonged activity over 72?h at both pH 7.4 and 6.0. Enhanced antibacterial activity at pH 6.0 was observed for the DOAPA-VAN-Lipo and DLAPA-VAN-Lipo formulations. Flow cytometry studies indicated a high killing rate of MRSA cells using DOAPA-VN-Lipo (71.98%) and DLAPA-VN-Lipo (73.32%). In vivo studies showed reduced MRSA recovered from mice treated with formulations by four- and two-folds lower than bare VN treated mice, respectively. The targeted delivery of VAN can be improved by novel pH-responsive liposomes from the two-chain (FAL) designed in this study.     

Antibacterial effects of 18 medicinal plants used by the Khyang tribe in Bangladesh

Context: The resistance of bacteria to antibiotics is raising serious concern globally. Asian medicinal plants could improve the current treatment strategies for bacterial infections. The antibacterial properties of medicinal plants used by the Khyang tribe in Bangladesh have not been investigated.

Objective: The present study examines the antibacterial properties of 18 medicinal plants used by the Khyang tribe in day-to-day practice against human pathogenic bacteria.

Materials and methods: Leaves, bark, fruits, seeds, roots and rhizomes from collected plants were successively extracted with hexane, ethyl acetate and ethanol. The corresponding 54 extracts were tested against six human pathogenic bacteria by broth microdilution assay. The antibacterial mode of actions of phytoconstituents and their synergistic effect with vancomycin and cefotaxime towards MRSA was determined by time-killing assay and synergistic interaction assay, respectively.

Results and discussion: Hexane extract of bark of Cinnamomum cassia (L.) J. Presl. (Lauraceae) inhibited the growth of MRSA, Enterococcus faecalis, Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae and Acinetobacter baumannii with MIC values below 100 µg/mL. From this plant, cinnamaldehyde evoked at 4?×?MIC in 1?h an irreversible decrease of MRSA count Log10 (CFU/mL) from 6 to 0, and was synergistic with vancomycin for MRSA with fractional inhibitory concentration index of 0.3.

Conclusions: Our study provides evidence that the medicinal plants in Bangladesh have high potential to improve the current treatment strategies for bacterial infection.     

Antibacterial activities of chemical constituents from the aerial parts of Hedyotis pilulifera

Context: Hedyotis pilulifera (Pit.) T.N. Ninh (Rubiaceae) has been used in Vietnamese ethnomedicine; the methanol extract exhibited antibacterial activity in our preliminary screening.

Objectives: In this study, compounds from H. pilulifera were isolated and their antibacterial activity in vitro was evaluated.

Materials and methods: The aerial parts of H. pilulifera (1.4?kg) were extracted with MeOH, suspended in water and ethyl acetate extract was chromatographed on a silica gel column. The structures of isolated compounds were elucidated by the combination analyses of spectroscopy including 1D-, 2D-NMR, HRMS and in comparison with the reported NMR data in the literature. All isolated compounds were evaluated for inhibitory effect using the microdilution method toward Staphylococcus aureus, Bacillus subtilis and Mycobacterium smegmatis, and MIC values were determined.

Results: Twenty compounds were isolated, including five triterpenoids, two steroids, two aromatic compounds, three fatty acids, one quinone derivative, one lignan glycoside, one ceramide and five glycolipids. Among these, oleanolic acid showed significant antibacterial activity against M. smegmatis with the MIC value of 2.5?μg/mL. Remarkably, rotungenic acid showed strong activity against S. aureus, B. subtilis, M. smegmatis with MIC values of 2.5, 2.5 and 1.25?μg/mL, respectively. Rotundic acid exhibited significant antibacterial activity against B. subtilis with the MIC value of 5?μg/mL. To the best of our knowledge, the antibacterial activity of rotungenic acid, stigmast-4-ene-3,6-dione and (2S,3S,4R,2′R)-2-(2′-hydroxytetracosanoylamino) octadecane-1,3,4-triol was reported for the first time.

Conclusions: Oleanolic acid, rotungenic acid, and rotundic acid were considered to be useful for developing new antimicrobial therapeutic agents for human.     

Synergistic effect of artocarpin on antibacterial activity of some antibiotics against methicillin-resistant Staphylococcus aureus,Pseudomonas aeruginosa,and Escherichia coli

Context: Antibacterial resistance has dramatically increased and resulted in serious health problems worldwide. One appealing strategy to overcome this resistance problem is the use of combinations of antibacterial compounds to increase their potency.

Objective: The objective of this study is to determine the synergistic effects of artocarpin for ampicillin, norfloxacin, and tetracycline against methicillin-resistant Staphylococcus aureus (MRSA) as well as the Gram-negative bacteria Pseudomonas aeruginosa and Escherichia coli.

Materials and methods: A broth microdilution method (1.95–250?µg/mL) was used to determine the minimum inhibitory concentration (MIC) of artocarpin and the antibiotics. Any synergistic effects were evaluated at their own MIC using the checkerboard method and a time-kill assay at 37?°C for 24?h.

Results and discussion: Artocarpin showed antibacterial activity against MRSA and E. coli with an MIC value of 62.5?µg/mL, and against P. aeruginosa with an MIC value of 250?µg/mL. The interaction of artocarpin with all tested antibiotics produced synergistic effects against MRSA with a fractional inhibitory concentration index (FICI) of 0.15–0.37. In addition, a combination of artocarpin and norfloxacin showed a synergistic effect against E. coli with an FICI value of 0.37, while the combinations of artocarpin and tetracycline as well as artocarpin and norfloxacin exhibited synergy interactions against P. aeruginosa with FICI values of 0.24 and 0.37, respectively. Time-kill assays indicated that artocarpin enhanced the antimicrobial activities of tetracycline, ampicillin, and norfloxacin against MRSA as well as Gram-negative bacteria.     

Antibacterial assay-guided isolation of active compounds from Artocarpus heterophyllus heartwoods

Abstract

Context: Preparations from Artocarpus heterophyllus Lam. (Moraceae) heartwoods are used in the traditional folk medicine for the treatment of inflammation, malarial fever, and to prevent bacterial and fungal infections.

Objective: The objective of this study was to isolate pure antibacterial compounds from A. heterophyllus heartwoods.

Materials and methods: The dried and powdered A. heterophyllus heartwoods were successively extracted with the following solvents: hexane, ethyl acetate, and methanol. Each of the extracts was screened for their antibacterial activities using a disc diffusion method (10?mg/disc). Their minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) were determined using a broth microdilution method. The extract that showed the strongest antibacterial activities was fractionated to isolate the active compounds by an antibacterial assay-guided isolation process.

Results and discussion: The ethyl acetate extract exhibited the strongest antibacterial activities against Streptococcus mutans, S. pyogenes, and Bacillus subtilis with MIC values of 78, 39, and 9.8?µg/mL, respectively. Based on an antibacterial assay-guided isolation, four antibacterial compounds: cycloartocarpin (1), artocarpin (2), artocarpanone (3), and cyanomaclurin (4) were purified. Among these isolated compounds, artocarpin exhibited the strongest antibacterial activity against Gram-positive bacteria, including S. mutans, S. pyogenes, B. subtilis, Staphylococcus aureus, and S. epidermidis with MICs of 4.4, 4.4, 17.8, 8.9, and 8.9?µM, respectively, and MBCs of 8.9, 8.9, 17.8, 8.9, and 8.9?µM, respectively, while artocarpanone showed the strongest activity against Escherichia coli, a Gram-negative bacteria with MIC and MBC values of 12.9 and 25.8?µM, respectively. Only artocarpin showed inhibitory activity against Pseudomonas aeruginosa with an MIC of 286.4?µM.     

Chemical constituents and biological activities of Albizia myriophylla wood

Context: Albizia myriophylla Benth (Leguminosae) is a medicinal plant widely used in Thailand and other Asian countries as a folk medicine remedy for many ailments.

Objective: The objective of this study is to investigate the chemical compositions, antibacterial activity, and cytotoxicity of A. myriophylla wood.

Materials and methods: The structure identification of the isolated compounds was established using spectroscopic methods. In vitro antibacterial activity against Streptococcus mutans, Staphylococcus aureus, and Bacillus cereus and the cytotoxicity against KB cells of extracts and compounds from A. myriophylla were performed using broth microdilution and resazurin microplate assays, respectively. The lupinifolin content in A. myriophylla extracts was quantified by high-performance liquid chromatography.

Results: A rare flavan-3,4-diol (1) together with eight known compounds (2–9) were isolated from the wood of A. myriophylla. Compounds 4–9 exhibited anti-S. mutans activity, of which lupinifolin (5) was the most potent with an MIC value of 0.98?µg/mL, followed by its dihydroxy derivative 4 with an MIC value of 62.5?µg/mL. Compounds 4 and 5 also displayed marked antibacterial activity against B. cereus and S. aureus (MIC value 15.63–125?µg/mL) and showed strong cytotoxic activity against KB cells (IC₅₀ value 4.95–12.55?µg/mL). The lupinifolin contents in ethanol extracts from two different collections of this plant originating from central and southern Thailand were 93.85 and 0.04?mg/g, respectively.

Conclusion: This is the first report of compounds 1–4 from A. myriophylla. Compounds 4 and 5 showed potent antibacterial and cytotoxic activities compared with other isolates. The anti-S. mutans activity of A. myriophylla extracts seems to be related to the lupinifolin content.     

Antimicrobial activities of some Thai traditional medical longevity formulations from plants and antibacterial compounds from Ficus foveolata

Context: Medicinal plants involved in traditional Thai longevity formulations are potential sources of antimicrobial compounds.

Objective: To evaluate the antimicrobial activities of some extracts from medicinal plants used in traditional Thai longevity formulations against some oral pathogens, including Streptococcus pyogenes, Streptococcus mitis, Streptococcus mutans, and Candida albicans. An extract that possessed the strongest antimicrobial activity was fractionated to isolate and identify the active compounds.

Materials and methods: Methanol and ethyl acetate extracts of 25 medicinal plants used as Thai longevity formulations were evaluated for their antimicrobial activity using disc diffusion (5?mg/disc) and broth microdilution (1.2–2500?µg/mL) methods. The ethyl acetate extract of Ficus foveolata Wall. (Moraceae) stems that exhibited the strongest antibacterial activity was fractionated to isolate the active compounds by an antibacterial assay-guided isolation process.

Results and discussion: The ethyl acetate extract of F. foveolata showed the strongest antibacterial activity with minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values of 19.5–39.0 and 39.0–156.2?µg/mL, respectively. On the basis of an antibacterial assay-guided isolation, seven antibacterial compounds, including 2,6-dimethoxy-1,4-benzoquinone (1), syringaldehyde (2), sinapaldehyde (3), coniferaldehyde (4), 3β-hydroxystigmast-5-en-7-one (5), umbelliferone (6), and scopoletin (7), were purified. Among these isolated compounds, 2,6-dimethoxy-1,4-benzoquinone (1) exhibited the strongest antibacterial activities against S. pyogenes, S. mitis, and S. mutans with MIC values of 7.8, 7.8, and 15.6?µg/mL, and MBC values of 7.8, 7.8, and 31.2?µg/mL, respectively. In addition, this is the first report of these antibacterial compounds in the stems of F. foveolata.     

Effects of β-caryophyllene and Murraya paniculata essential oil in the murine hepatoma cells and in the bacteria and fungi 24-h time–kill curve studies

Context: Orange Jessamine [Murraya paniculata L. (Rutaceae)] has been used worldwide in folk medicine as an anti-inflammatory, antibiotic and analgesic.

Objective: The objective of this study is to investigate the in vitro antioxidant, cytotoxic, antibacterial and antifungal activity and the time-kill curve studies of orange jessamine essential oil and β-caryophyllene, as well as the chemical composition of the essential oil.

Material and methods: The cytotoxic activity of M. paniculata and β-caryophyllene (7.8–500?μg/mL) was evaluated using the MTT assay on normal fibroblasts and hepatoma cells. The minimal inhibitory concentration and time–kill curves (24?h) were evaluated against those of Staphylococcus aureus, Escherichia coli, Salmonella typhimurium, Enterococcus faecallis, Aspergillus (niger, fumigates and parasiticum) and F. solani by the broth microdilution method. The antioxidant activity was measured by the DPPH and ABTS assays. Chemical composition was evaluated by GC/MS analyses.

Results: GC/MS analyses identified 13 compounds, with β-caryophyllene as the major compound. The oil exhibited moderate antibacterial activity (MIC <1.0?mg/mL) and strong antifungal activity. Time–kill curve studies showed that either the essential oil or β-caryophyllene presented rapid bacterial killing (4?h for S. aureus) and fungicidal effect (2-4?h for F. solani); however, both displayed weak free radical scavenger capacity. The cytotoxic activity exhibited a prominent selective effect against hepatoma cancer cells (IC₅₀ value =63.7?μg/mL) compared with normal fibroblasts (IC₅₀ value =195.0?μg/mL), whereas the β-caryophyllene showed low cytotoxicity.

Discussion and conclusion: The experimental data suggest that the activities of M. paniculata essential oil are due to the synergistic action among its components.     

Antibacterial Activity of Xanthones from Guttiferaeous Plants against Methicillin-resistant Staphylococcus aureus

Extracts of Garcinia mangostana (Guttiferae) showing inhibitory effects against the growth of S. aureus NIHJ 209p were fractionated according to guidance obtained from bioassay and some of the components with activity against methicillin-resistant Staphylococcus aureus (MRSA) were characterized. One active isolate, α-mangostin, a xanthone derivative, had a minimum inhibitory concentration (MIC) of 1.57?12.5 μg mL^?1. Other related xanthones were also examined to determine their anti-MRSA activity. Rubraxanthone, which was isolated from Garcinia dioica and has a structure similar to that of α-mangostin, had the highest activity against staphylococcal strains (MIC = 0.31?1.25 μg mL^?1), an activity which was greater than that of the antibiotic vancomycin (3.13?6.25 μg mL^?1). The inhibitory effect against strains of MRSA of two of the compounds when used in conjunction with other antibiotics was also studied. The anti-MRSA activity of α-mangostin was clearly increased by the presence of vancomycin; this behaviour was not observed for rubraxanthone. The strong in-vitro antibacterial activity of xanthone derivatives against both methicillin-resistant and methicillin-sensitive Staphylococcus aureus suggests the compounds might find wide pharmaceutical use.     

In vitro antibacterial activity and in vivo therapeutic effect of Sesbania grandiflora in bacterial infected silkworms

Context: Antibiotic resistance is a serious problem worldwide. Searching for new potential agents is, therefore, essential. The bark of Sesbania grandiflora (L.) Pers. (Fabaceae) has been used in folk medicine against various diseases.

Objective: To investigate the antibacterial activity of S. grandiflora bark and explore the therapeutic effect of the highest potent fraction.

Materials and methods: Bacteria and healthy silkworms were exposed to three fractionated extracts (3.1–400?mg/mL) of S. grandiflora bark from hexane (HXF), chloroform (CFF), and ethyl acetate (EAF). The sets of bacteria were incubated at 37?°C while silkworms were kept at 27?°C for 24?h. To evaluate the therapeutic effect, silkworms infected with bacteria were exposed to the extracts (0.5–60?mg/mL) and incubated at 27?°C for 52?h. Qualitative analysis of the most potent extract was done using HPLC.

Results: EAF showed the highest activity with MIC against methicillin resistant Staphylococcus aureus (MRSA) and vancomycin resistant enterococci (VRE) of 1.6 and 0.4?mg/mL, respectively, and against Gram-negative Escherichia coli and Pseudomonas aeruginosa of 6.2 and 3.1?mg/mL, respectively. It is nontoxic to silkworms with LC₅₀?>400?mg/mL and has high therapeutic effect on infected silkworms with EC₅₀ of 1.9?mg/mL. EAF consists of at least five major compounds, one of them is gallic acid. The activity of EAF is higher than the sum of individual activities of separated compounds.

Discussion and conclusion: These results suggest that EAF is a promising antibacterial extract, suitable for further investigation in rodents infected with drug resistant bacteria.     

Solid lipid nanoparticles-loaded topical gel containing combination drugs: an approach to offset psoriasis

Aim: The primary aim of present work was to develop effective combination drug therapy for topical treatment of psoriasis.

Methods: Betamethasone dipropionate and calcipotriol loaded solid lipid nanoparticles (CT-BD-SLNs) were prepared by hot melt high shear homogenization technique, which were then incorporated in Carbopol gel matrix. The anti-psoriatic potential was tested by sequential in vitro (skin permeation and dermal distribution, anti-proliferative effect in HaCaT cells) and in vivo (Draize patch irritation, transepidermal water loss (TEWL) and anti-psoriatic mouse tail studies) experiments.

Results: A negligible amount in receptor compartment, yet confined distribution of drugs to epidermal and dermal region of skin was observed in case of SLNs, which is essential for safe and effective anti-psoriatic therapy. Draize patch test and TEWL demonstrated negligible skin irritation and better skin tolerability of SLNs. The in vitro HaCaT cell line study demonstrated that SLNs delayed the abrupt growth of keratinocytes, while in vivo mouse tail model showed that SLNs gel significantly decreased the epidermal thickness and increased melanocyte count in comparison to commercial Daivobet® ointment.

Conclusions: The developed SLNs gel is expected to be potential strategies for treatment of psoriasis and other topical diseases.     

Evaluation of in vitro antioxidant,anticancer and in vivo antitumour activity of Termitomyces clypeatus MTCC 5091

Context: Termitomyces clypeatus (Lyophyllaceae) is a filamentous edible mushroom, having ethnomedicinal uses. However, information about the antioxidant, anticancer and antitumour properties of this mushroom remains to be elucidated.

Objective: The study examines the in vitro antioxidant, anticancer and in vivo antitumour activity of T. clypeatus.

Materials and methods: Antioxidant activity was evaluated with seven in vitro assays. Cytotoxicity of T. clypeatus was tested against a panel of cancer cells lines including U373MG, MDA-MB-468, HepG2, HL-60, A549, U937, OAW-42 and Y-79 using MTT assay. The antitumour activity of aqueous extract was evaluated against Ehrlich ascites carcinoma (EAC) tumour model in Swiss albino mice.

Results: HPLC analysis of aqueous extract revealed the presence of sugar entities. Termitomyces clypeatus showed excellent in vitro antioxidant activity. Termitomyces clypeatus was found cytotoxic against all cancer cells, among which it showed higher activity against U937 (IC₅₀ 25?±?1.02?μg/mL). Treatment of EAC-bearing mice with varied doses of aqueous extract significantly (p?<?0.01) reduced tumour volume, viable tumour cell count and improved haemoglobin content, RBC count, mean survival time, tumour inhibition and % increase life span. The enhanced antioxidant status in treated animals was evident from the decline in the levels of lipid peroxidation, increased levels of glutathione, catalase and superoxide dismutase.

Discussion: The analyzed data indicate that the aqueous extract of T. clypeatus exhibits significant antitumour activity, which might be due to the antioxidant effects on EAC bearing hosts.

Conclusion: Termitomyces clypeatus possesses anticancer activity, valuable for application in food and drug products.     

Potential anti-inflammatory,antioxidant and antimicrobial activities of Sambucus australis

Context: Sambucus australis Cham. &; Schltdl. (Adoxaceae) is used in Brazilian folk medicine to treat inflammatory disorders.

Objective: To evaluate the in vitro anti-inflammatory, antioxidant and antimicrobial properties of S. australis.

Materials and methods: The anti-in?ammatory activity of ethanol extracts of the leaf and bark of S. australis (1–100?μg/mL) were studied in lipopolysaccharide/interferon γ stimulated murine macrophages RAW 264.7 cells (24?h incubation) by investigating the release of nitric oxide (NO) and tumour necrosis factor-alpha (TNF-α) and in the TNF-α-induced nuclear factor kappa (NF-κB) assay. Minimum inhibitory concentration (MIC) was determined by the microdilution test (24?h incubation). Antioxidant activity was determined by 2,2-diphenyl-1-picrylhydrazyl (DPPH), ferric reducing antioxidant power (FRAP) and the NO scavenging assays. Chemical composition was assessed by LC-MS/MS.

Results: Antioxidant activities in the DPPH (IC₅₀ 43.5 and 66.2?μg/mL), FRAP (IC₅₀ 312.6 and 568.3?μg/mL) and NO radical scavenging assays (IC₅₀ 285.0 and 972.6?μg/mL) were observed in the leaf and bark ethanol extracts, respectively. Solely the leaf extract showed significant inhibition of NO and TNF-α production in RAW264.7 cells at concentrations of 2 and 100?μg/mL, respectively, and suppression of TNF-α inhibition of NF-κB by 12.8 and 20.4% at concentrations of 50 and 100?μg/mL, respectively. The extract also exhibited antibacterial activity against Salmonella typhimurium (MIC 250?μg/mL) and Klebsiella pneumoniae (MIC 250?μg/mL). LC-MS/MS revealed the presence of chlorogenic acid and rutin as major compounds.

Discussion and conclusion: The results indicate that the ethanol leaf extract of S. australis exhibit prominent anti-in?ammatory effects.     

Ceftaroline for complicated skin and skin-structure infections

Importance of the field: A dramatic increase in infections caused by methicillin-resistant Staphylococcus aureus (MRSA) has been observed, in part as a result of the epidemic of community-associated MRSA skin and skin-structure infections (SSSIs). Simultaneously, decreasing sensitivities of S. aureus to vancomycin have been reported and invasive infections caused by these strains have been associated with worse clinical outcomes. Clearly, new agents active against MRSA are needed. Ceftaroline is a new cephalosporin active against MRSA and many Gram-negative bacteria, though it is not active against Pseudomonas spp. and extended spectrum β-lactamase producers (ESBL).

Areas covered in this review: In this review we focus on the properties of ceftaroline such as in vitro activity, the pharmacokinetic and pharmacodynamic characteristics, and its efficacy and safety observed in the clinical trials of patients with SSSI. Finally, we provide an overview of the possible future role of ceftaroline and other compounds in development for the treatment of SSSIs. The literature search was based on PubMed articles plus review of the abstracts presented in the most important international conferences in the field.

What the reader will gain: The reader will gain clear concepts to understand the value that ceftaroline might have in the treatment of SSSIs, including those caused by MRSA.

Take home message: Ceftaroline has shown bactericidal activity against common pathogens associated with SSSIs including MRSA, noninferiority in clinical trials of patients with complicated SSSI (cSSSI), and a favorable safety profile.     

Topical hyaluronan alone promotes corneal epithelial cell migration whereas combination with benzalkonium chloride impairs epithelial wound healing

Abstract

Purpose: To evaluate the effects of topical hyaluronan (HA) on corneal epithelial wound healing when administered with or without benzalkonium chloride (BAC).

Methods: A cultured human corneal epithelial cell line (HCE-T) was subjected to in vitro scratch assays and in situ epithelial migration was evaluated in organ-cultured rabbit corneas. The corneal epithelium of C57BL/6J mice was also evaluated to determine in vivo wound healing. An in vivo imaging system was also used to evaluate the effects of HA on eye drop retention on the ocular surface.

Results: The findings revealed the promotion of HCE-T migration, in situ rabbit corneal epithelial migration, and in vivo wound healing in mouse corneal epithelium by HA. Pre-treatment with HA also protected against delayed epithelial wound healing in BAC in vitro. However, pre-treatment with 3?mg/mL HA did not show a protective effect against BAC in vivo, but instead delayed epithelial wound healing and increased detection of cleaved caspase-3. This suggested that HA promotes the retention of BAC on the ocular surface. The instilled HA was retained after 15?min, at a significantly higher rate than for phosphate-buffered saline.

Conclusions: The combination of HA and BAC impaired wound healing in the corneal epithelium.     

Antibacterial and cytotoxic activity from the extract and fractions of a marine derived bacterium from the Streptomyces genus

Abstract

Context: Marine natural products are a rich source of potent, selective, and structurally novel compounds. Marine bacteria are considered the most promising source of biologically active compounds which can be applied to treat a wide range of diseases.

Objective: The current study was designed to establish the bases for a future marine exploration in the Ecuadorian coast based on the molecular identification of a marine bacterium and its potential use as an antibacterial or cytotoxic compounds source.

Materials and methods: Isolation and characterization of the marine bacterium were carried out through microbiological methods from desiccated sediment. Molecular identification was made by means of 16S rDNA analysis. MIC was measured by the microdilution broth method against six pathogenic bacteria: two Gram positive and four Gram negative strains. Cytotoxicity was evaluated by Crystal violet assay against breast adenocarcinoma (MCF7) and ductal carcinoma (T47D and ZR-75-30).

Results: Our present study has shown that EtOAc extract and fraction A1 obtained from marine Streptomyces sp. revealed the maximal antibacterial and cytotoxic activity. Enterococcus faecalis was found to be more sensitive strain (MIC 0.78?μg/ml) than the other five bacteria tested. ZR-75-30 and T47D cell lines were found to be more sensitive (IC₅₀ value, 31.88?±?0.05 and 68.35?±?0.12?μg/ml) than adenocarcinoma MCF7 (IC₅₀ value was 83.65?±?0.06?μg/ml).

Discussion and conclusion: The results obtained herein indicate that EtOAc extract of Streptomyces sp. has shown a strong antibacterial activity as well as moderate cytotoxic activity which make it a good candidate for metabolite isolation.     

Chemical composition and bioactivity of the volatile oil from leaves and stems of Eucalyptus cinerea

Context: Eucalyptus cinerea F. Muell. ex Benth. (Myrtaceae) is a medium-sized tree cultivated in Egypt.

Objective: First, to determine the chemical composition of the volatile oil of the juvenile leaves and stems of E. cinerea to identify its chemotype. Second, to study the in vivo antioxidant activity and in vitro antimicrobial activity of the studied volatile oils against selected Gram-positive, Gram-negative bacteria, yeast, and mycelia fungi.

Materials and methods: The volatile oil was prepared by hydrodistillation and then identified by GC/MS analysis. Broth microdilution and agar dilution methods were applied for determining the MIC. The antioxidant activity was studied by determination of glutathione level in blood of alloxan-induced diabetic rats.

Results: The yield of the volatile oil hydrodistilled from the juvenile leaves and stems of E. cinerea was 4.5 and 0.5%, respectively. 1,8-Cineole was the major identified oxygenated monoterpenoid (84.55% and 60.15% in the juvenile leaves and stems, respectively). The antibacterial activity of the oil of the juvenile leaves was more potent against all the tested organisms than that of the stems. The (MIC) of volatile oil of the juvenile leaves against Escherichia coli, Pseudomonas aeruginosa, Streptococcus faecalis, Candida albicans, and Aspergillus flavus were 5.2, 5.6, 4, 4.8, and 12.8?μg/ml, respectively. Also, the juvenile leaves’ oil was more active as an antioxidant than that of the stems. They restored glutathione level by 33.7?±?1.1 and 29.6?±?0.7?mg/dl, respectively, compared with vitamin E (35.9?±?1.2?mg/dl) which was used as a reference.

Discussion and conclusion: Results suggest that the volatile oil is 1,8-cineole chemotype. Moreover, the oil of the juvenile leaves of E. cinerea might find usefulness as a therapeutic agent following further development.     

Investigation of the antifungal activity of carvacrol against strains of Cryptococcus neoformans

Background: Cryptococcus neoformans is the etiologic agent of opportunistic systemic fungal infection cryptococcosis, which affects individuals with compromised immune systems. Thus, natural products research has become important, since monoterpenes such as carvacrol, a promising molecule in the search antifungal agents, have shown significant biological activity.

Objective: The study aimed to investigate the antifungal activity and mode of action of carvacrol against strains of C. neoformans.

Methods: The minimum inhibitory concentration (MIC) was determined by microdilution method. Minimum fungicidal concentration (MFC) was performed by seeding technique on solid media. Studying the mode of action was performed using broth microdilution.

Results: The MIC ranged from 25 to 81?μg/mL and the MFC ranged from 25 to 102?μg/mL. Carvacrol bonded to exogenous ergosterol and cholesterol.

Discussion: The results suggest that carvacrol has antifungal activity against C. neoformans and its mode of action is related to fungal membrane instability.

Conclusions: The phytoconstituent carvacrol may eventually become a drug; however, further studies are needed to elucidate its mechanism.     

Antimalarial and antiplasmodial activity of husk extract and fractions of Zea mays

Context: Zea mays L. (Poacae) husk decoctions are traditionally used in the treatment of malaria by various tribes in Nigeria.

Objective: To assess the antimalarial and antiplasmodial potentials of the husk extract and fractions on malaria parasites using in vivo and in vitro models.

Materials and methods: The ethanol husk extract and fractions (187–748?mg/kg, p.o.) of Zea mays were investigated for antimalarial activity against Plasmodium berghei using rodent (mice) malaria models and in vitro activity against chloroquine sensitive (Pf 3D7) and resistant (Pf INDO) strains of Plasmodium falciparum using the SRBR green assay method. Median lethal dose and cytotoxic activities against HeLa and HEKS cells were also carried out. The GCMS analysis of the most active fraction was carried out.

Results: The husk extract (187–748?mg/kg, p.o.) with LD₅₀ of 1874.83?mg/kg was found to exert significant (p?P. berghei infection in suppressive, prophylactive and curative tests. The crude extract and fractions also exerted prominent activity against both chloroquine sensitive (Pf 3D7) and resistant (Pf INDO) strains of P. falciparum with the ethyl acetate fraction exerting the highest activity with IC₅₀ values of 9.31?±?0.46?μg/mL (Pf 3D7) and 3.69?±?0.66?μg/mL (Pf INDO). The crude extract and fractions were not cytotoxic to the two cell lines tested with IC₅₀ values of?>100?μg/mL against both HeLa and HEKS cell lines.

Discussion and conclusion: These results suggest that the husk extract/fractions of Zea mays possesses antimalarial and antiplasmodial activities and these justify its use in ethnomedicine to treat malaria infections.     

Eradication of methicillin-resistant Staphylococcus aureus infection by nanoliposomes loaded with gentamicin and oleic acid

Context: Methicillin-resistant Staphylococcus aureus (MRSA) infection with its high incidence is responsible for nosocomial infections. MRSA strains resistant to multiple antibiotics have emerged increasingly. Recently, combination therapy and efficient drug delivery systems are developed to treat infections.

Objective: The aim of the present study was to evaluate antibacterial activities of combination of oleic acid and gentamicin against MRSA, in both free and liposomal forms, and in comparison with vancomycin.

Materials and methods: The antibacterial activities against MRSA ATCC 43300 were assessed by the determination of minimum inhibitory concentration (MIC), MBC, and Fractional Inhibitory Concentration Index (FICI). The time-kill assays were performed to evaluate the potency of antibacterial agents. Nanoliposomal formulations of gentamicin, oleic acid, and combination of gentamicin with oleic acid were prepared by the dehydration–rehydration (DRV) method and characterized for size, zeta potential, and encapsulation efficiency.

Results: MIC values of gentamicin and oleic acid were 19.5 and >250?µg/ml, respectively. Synergetic effects were observed by the gentamicin and oleic acid combination; FICI was 0.5. Following incorporation of gentamicin into liposomal gentamicin and liposomal combination, the MIC values were reduced 15- and 27-fold, respectively. In comparison with vancomycin, liposomal combination was more effective in bacterial inhibition and killing. Liposomal combination was the most effective formula in time-kill study.

Discussion and conclusion: Liposomal formulation showed a higher antibacterial activity in comparison with the free forms and vancomycin. These carriers can improve antimicrobial activity as well as reducing the effective concentration required and inducing rapid bacterial clearance.