A.M. Viljoen

Osmitopsis asteriscoides(Asteraceae)-the antimicrobial activity and essential oil composition of a Cape-Dutch remedy

The essential oil composition and antimicrobial activity of Osmitopsis asteriscoides, a medicinal plant used in traditional herbal preparations in South Africa has been investigated. Three different antimicrobial methods (disc diffusion, minimum inhibitory concentration by micro-titer plate and time-kill studies) were comparatively evaluated against Candida albicans, Staphylococcus aureus and Pseudomonas aeruginosa. A preliminary screening was done using the disc diffusion method on nine bacterial and four fungal isolates. Minimum inhibitory concentrations showed some correlation with the disc diffusion method. However, time-kill studies appear to be a more superior method for determining antimicrobial activity of volatile compounds such as essential oils. Two moderately susceptible and one resistant organism were selected to further demonstrate the variability between the three methods. The antimicrobial activity of the essential oil, tested by means of time-kill methodology at concentrations ranging from 0.5 to 2% (v/v) indicate a strong fungicidal activity against Candida albicans and the oil was also found to be bacteriostatic against Staphylococcus aureus in a concentration-dependent manner. The essential oil rapidly reduced viable counts of Pseudomonas aeruginosa, but regrowth was noted after 240 min. The results have been generated in duplicate in separate microbiology laboratories using different time-kill methods and the results are congruent. The two major essential oil components camphor and 1,8-cineole were investigated indicating the positive antimicrobial efficacy of 1,8-cineole independently and in combination with camphor. In addition to (-)-camphor and 1,8-cineole, 40 compounds were identified by GC-MS in the hydro-distilled essential oil. The high concentration of cineole and camphor and their synergistic effect is presented as a possible explanation for the traditional use of Osmitopsis asteriscoides for treating microbe-related illnesses.

In vitro activity of Aloe extracts against Plasmodium falciparum

The antiplasmodial activity and toxicity data of 34 Aloe species and their main constituents were determined. A number of the methanol extracts possessed antimalarial activity where 50% of the parasite growth was inhibited (IC50 value) by 32 to 77xa0μgxa0ml-xa01 of the extract. The chemical common to the most active species is the anthrone C-glucoside homonataloin which inhibited the chloroquine-resistant Plasmodium falciparum strain with an IC50 value of 13.46xa0±xa01.36xa0μgxa0ml-xa01. Homonataloin was a more potent inhibitor of parasite growth than aloin (IC50 value of 107.20xa0±xa04.14xa0μgxa0ml-xa01). The Aloe extracts tested did not exhibit any toxicity towards transformed human kidney epithelium cells at the concentrations (0.5-50xa0μgxa0ml-xa01) used in the antimalarial assay.

Experimental design for the formulation and optimization of novel cross-linked oilispheres developed for in vitro site-specific release ofMentha piperita oil

A Plackett-Burman design was employed to develop and optimize a novel crosslinked calcium-aluminum-alginatepectinate oilisphere complex as a potential system for the in vitro site-specific release ofMentha piperita, an essential oil used for the treatment of irritable bowel syndrome. The physicochemical and textural properties (dependent variables) of this complex were found to be highly sensitive to changes in the concentration of the polymers (0%–1.5% wt/vol), crosslinkers (0%–4% wt/vol) and crosslinking reaction times (0.5–6 hours) (independent variables). Particle size analysis indicated both unimodal and bimodal populations with the highest frequency of 2 mm oilispheres. Oil encapsulation ranged from 6 to 35 mg/100 mg oilispheres. Gravimetric changes of the crosslinked matrix indicated significant ion sequestration and loss in an exponential manner, while matrix erosion followed Higuchis cube root law. Among the various measured responses, the total fracture energy was the most suitable optimization objective (R2 =0.88, Durbin-Watson Index=1.21%, Coefficient of Variation (CV)=33.21%). The Lagrangian technique produced no significant differences (P>.05) between the experimental and predicted total fracture energy values (0.0150 vs 0.0107 J). Artificial Neural Networks, as an alternative predictive tool of the total fracture energy, was highly accurate (final mean square error of optimal network epoch≈0.02). Fused-coated optimized oilispheres produced a 4-hour lag phase followed by zero-order kinetics (n>0.99), whereby analysis of release data indicated that diffusion (Fickian constantk1=0.74 vs relaxation constantk2=0.02) was the predominant release mechanism.

The composition and antimicrobial activity of the essential oil of the resurrection plant Myrothamnus flabellifolius

An investigation of the antibacterial and antifungal activity of Myrothamnus flabellifolius against eleven different pathogens showed inhibition of all micro-organisms except for Salmonella typhimurium and Alternaria alternata. A preliminary screening was done by the disc diffusion method and three susceptible organisms were selected to demonstrate the rapid onset of antimicrobial activity using time-kill methodology. Essential oil concentrations, ranging from 0.0625% to 2%, exhibited strong fungicidal activity against Candida albicans and were found to be bacteriostatic against Staphylococcus aureus with microbiocidal effects increasing in a concentration-dependant manner. Essential oil rapidly reduced viable counts of Pseudomonas aeruginosa but regrowth was noted after 24 hours. The results have been generated in duplicate in two separate microbiology laboratories using different time-kill methods and the results are in agreement. Eighty-five compounds were identified by GC-MS in the hydro-distilled essential oils which contained pinocarvone and trans-pinocarveol as the major terpenoids. The antimicrobial properties of the essential oil are presented as a possible rationale for the traditional use of the resurrection bush, Myrothamnus flabellifolius in African herbal medicinal preparations.

Antimicrobial activity of Eriocephalus L. species

The genus Eriocephalus, commonly known as ‘wild rosemary’, ‘Cape snow bush’, ‘kapokbos’ or ‘asmabossie’, belongs to the family Asteraceae, of the tribe Anthemideae. It is endemic to southern Africa and is comprised of 32 species, of which several are economically important as traditional herbal remedies and as perfumes in fragrance industries. The species may be an important potential source for new and novel drugs for the treatment of various diseases, hence warrants further research. An investigation into the antimicrobial activity of the genus Eriocephalus using the disc diffusion assay against a range of Gram-positive and Gram-negative bacteria as well as a few selected fungi was carried out. The study included 15 Eriocephalus species with 113 essential oil and acetone leaf extract samples. Preliminary screening was carried out using 16 test pathogens: Bacillus cereus, B. subtilis, Staphylococcus aureus (four strains), S. epidermidis, Klebsiella pneumoniae, Escherichia coli, Pseudomonas aeruginosa, Yersinia enterocolitica, Salmonella typhimurium, S. enteriditis, Proteus vulgaris, Serratia odorifera, Enterococcus faecalis, Cryptococcus neoformans, Candida albicans and Alternaria alternata. From the preliminary screening, the most susceptible test pathogens selected for further study were: Bacillus cereus, B. subtilis, Staphylococcus aureus (one strain), Klebsiella pneumoniae, Escherichia coli, Cryptococcus neoformans and Candida albicans. The Gram-positive bacteria and two fungal pathogens showed inhibition for most of the essential oils and the leaf extracts while there was very little activity noted on the Gram-negative bacteria. Intra- and inter-population variation as well as inter-specific variation was observed in the antimicrobial activity for some species of Eriocephalus. The major variation was mainly observed in the activity of the essential oils and the leaf extracts against the yeast, Cryptococcus neoformans and the Gram-positive bacteria, Bacillus cereus, B. subtilis and Staphylococcus aureus. From the results obtained from the disc diffusion assay, the most active species were selected to determine the minimum inhibitory concentration against two Gram-positive and two Gram-negative bacteria and two fungal strains. The acetone extracts of E. aromaticus from Swartberg produced the most promising activity for all species studied with MIC values of 400μg ml−xa01 and 200μg ml−xa01 for B. cereus and S. aureus respectively.

The essential oil composition of the roots and rhizomes of Siphonochilus aethiopicus

The composition of the essential oil obtained through hydrodistillation is reported for the roots and rhizomes of Siphonochilus aethiopicus. The major compounds in both the roots and the rhizomes are 1,8-cineole, (E)-β-ocimene, cis-alloocimene, together with the recently reported furanoterpenoid (4aα,5β,8α)-3,5,8a-trimethyl-4,4a,9-tetrahydo-naphtho[2,3-b]-furan-8(5H)-one which is the major compound in both plant organs. The roots and rhizomes are virtually identical in composition and provide a chemical rationale to promote plant part substitution as a method to conserve this endangered South African medicinal plant.

The Chemotaxonomic Value of Two Cinnamoyl Chromones, Aloeresin E and F, in Aloe (Aloaceae)

A chemotaxonomic study of the genus Aloe indicates a remarkable quantitative and qualitative similarity in leaf exudate composition between 12 species. The diagnostic leaf exudate profile found in all representatives of this group a combination of homonataloin A and B with either or both of two recently described cinnamoyl chromones, aloeresin E and F, together with various coumaroyl chromones may serve as a fingerprint. Taxonomic assessment and cladistic analysis of both morphological and chemical data support the transfer of A. pearsonii, previously misplaced in A. ser. Macrifoliae, to A. ser. Mitriformes, and are consistent with the broadening of the circumscription of the latter to include 5 anomalous species: A. angelica, A. yavellana, A. peglerae, A. melanacantha, and A. erinacea.

Cyclooxygenase inhibitory activity of Aloe species

Aloes are used in traditional medicine for arthritis and to treat skin irritations. These indications could point to the plants having anti-inflammatory activity. Methanolic extracts of dried leaves of 53 Aloe species were tested in the cyclooxygenase-1 assay. Cyclooxygenase is one of the key enzymes in the biosynthesis of prostaglandins that are implicated in inflammatory processes. The selected species are representative of all chemotypes identified for the genus. The grass-like and scandent aloes accumulate flavonoids in co-occurrence with the anthrone isomers aloin A and B (A. boylei). This group is considered to be basal in Aloe and with the exception of A. ciliaris, members of this chemo type showed high values of inhibition. The flavanone producing species (A. pratensis, A. humilis and A. pretoriensis) also exhibited high values. These high values are similar to those recorded for aloes which accumulate anthrones and chromones (A. wickensii). The two main anthrone chemotypes in Aloe are represented by homonataloin and aloin accumulating species. No significant differences could be observed between species accumulating aloin (A. ferox) when compared to the homonataloin-producing species (A. mitriformis). It is interesting to note that species with similar exudate profiles (A. mitriformis and A. comptonii) showed similar values of inhibition.

Essential oil composition and in vitro antimicrobial and anti-inflammatory activity of South African Vitex species

The essential oil composition of Vitex pooara, V. rehmannii, V. obovata ssp. obovata, V. obovata ssp. wilmsii and V. zeyheri was determined using gas chromatography and mass spectrometry. The in vitro antimicrobial activity of the essential oils was assessed on Staphylococcus aureus, Bacillus cereus and Escherichia coli and the minimum inhibitory concentration values recorded. All essential oils were moderately active with V. zeyheri being the most active (8, 4 and 16mg ml−xa01 for S. aureus, B. cereus and E. coli respectively). The in vitro anti-inflammatory activity of the essential oils was evaluated using a 5-lipoxygenase assay and all essential oils effectively inhibited 5-lipoxygenase, a key enzyme in the inflammatory cascade with V. pooara producing the most promising activity (IC50 value of 25ppm). Using the essential oil data matrix, chemotaxonomic evidence is presented which supports the infrageneric placement of V. pooara in subgenus Vitex while the other four above mentioned taxa are placed in subgenus Holmskiodiopsis.

In vitro 5-lipoxygenase and anti-oxidant activities of Warburgia salutaris and drimane sesquiterpenoids

The purpose of this investigation was to determine the in vitro 5-lipoxygenase inhibitory and anti-oxidant activities of Warburgia salutaris . Aqueous and methanol extracts of the leaves of W . salutaris were obtained and subjected to the 5-lipoxygenase assay and the 2,2- diphenyl-1-picrylhydrazyl (DPPH) assay to determine their anti-inflammatory and anti-oxidant activities, respectively. Furthermore, drimane sesquiterpenoids, mukaadial and warburganal, isolated from the same plant, were subjected to the same biological tests. The methanol extract of the leaves of W . salutaris displayed promising in vitro anti-inflammatory activity with an IC 50 value below 33xa0μgxa0ml -1 , while the aqueous extract of the same plant exhibited no activity in the same assay. The aqueous and methanol extracts of W . salutaris displayed promising anti-oxidant activities with IC 50 values of 34.43xa0+xa00.74xa0μgxa0ml -1 and 15.38xa0±xa00.20xa0μgxa0ml -1 , respectively. The compounds mukaadial and warburganal displayed 5-lipoxygenase inhibitory activity and contribute to the in vitro anti-inflammatory activity of the crude extract of the same plant. Anti-oxidant activity of W . salutaris did not appear to be confined to the drimane sesquiterpenoids tested.