Minimum Inhibitory Activity Research Articles

Quantitative antifungal activity of reuterin against food isolates of yeasts and moulds and its potential application in yogurt

Reuterin is an antimicrobial agent produced by conversion of glycerol and excreted by several bacterial species including the food grade lactic acid bacterium Lactobacillus reuteri. Several inhibitory activities have been reported to reuterin against a broad range of Gram-positive and Gram-negative bacteria, bacterial spores, moulds, yeasts and protozoa. However, the antifungal and anti-yeast activity of reuterin is poorly documented.The aim of the current work was:1) To quantify the minimum inhibitory activity (MIC) and the minimum fungicidal activity (MFC) of reuterin against a representative panel of the most abundant fungi and yeast species associated with food contamination; 2) To investigate the application of reuterin as antifungal agent for biopreservation of yogurt.Reuterin was produced by L. reuteri ATCC 53608 in MRS and glycerol solution then purified before using. Our data showed that purified reuterin inhibited the growth of tested microorganisms at a concentration of 11 mM or less. Moreover, reuterin showed a fungicidal activity (killed 99.9% of all tested microorganisms) at concentrations equal or below 15.6 mM as indicated by MFC. Values of MFC were comprised between 1.0 and 4.8 of the MIC values, suggesting a potent fungicidal mechanism on both yeasts and filamentous moulds with one exception only. In yogurt, reuterin showed a fungistatic effect at a concentration of 1.38 mM while a fungicidal effect was obtained at 6.9 mM. Therefore, reuterin has a high potential as a food preservative, particularly owing to its biochemical properties and antibacterial and antifungal activities.

Antifungal properties of soleshine - An in vitro study

Background: Soleshine is a polyherbal formulation meant to be used to heal cracks on heels, protecting sole from chaffs, marketed by Rumi Herbal Pvt Ltd., Chennai. The active ingriedients are Azadirachta indica, Lawsonia alba, Shorea robusta, Ricinus communis, and Sesamum indicum, which were well known for their antimicrobial activity. Aim and Objectives: The aim of this study is to evaluate the antifungal activity of the ingredients and to evaluate the synergistic activity present in the preparation. Materials and Methods: The plant materials were procured, dried, powdered, and sequentially extracted. The organisms were collected and evaluated the antifungal activity with disc diffusion method for all individual extracts and in combination of different extracts. Sabouraud dextrose agar, culture medium was used for the growth of fungal organism. The minimum inhibitory activity was observed with resazurin method. Clotrimazole, an antifungal drug, belongs to azole group was taken as a standard negative control. Results: The zone of inhibition was determined by disc diffusion method where it shows the inhibition of growth of fungal organism. The same experiment was repeated totally for 6 times and analyzed with SPSS software in May 2017, found that significant (P < 0.05). The minimum amount of extract required to inhibit the growth was determined by resazurin dye method where the color change (oxidation-reduction reaction) implies the viability of fungi. Conclusion: The formulation has an antifungal activity in all the extracts and maximum activity was with aqueous extract, and also, it shows synergistic activity in combination which quotes the additive effect.

The antibacterial activities of six organic solvent extracts of Salicornia iranica against Salmonella typhimurium

The overuse of antibiotics in poultry industries may lead to a rise in antibiotic-resistance, in humans and animals. Natural antibiotics degrade in living tissues, and therefore, they do not induce antibiotic-resistance. In this study, the antibacterial activity of six organic solvent extracts of S. iranica were investigated against S. typhimurium. The results indicate a significant antibacterial activity of S. iranica extracts against S.typhimurium (p < 0.01). The maximum and minimum inhibitory activity of organic solvent extracts compared with 0.5 mg/ml of tetracycline were detected for butanol and acetyl acetate (50 mg/ml) treatments, respectively.

Inhibition of Candida species via Proteosome Inhibitor MG-262 (ZL3B)

Backround: Candida species take the fourth place among the microorganisms which cause hospital infections. New therapeutic agents are needed because of rapidly increasing resistance rates. Boric acid preparations are preferred in local treatment especially in resistant cases while azole formulations are the first choice in oral treatment. The only boric acid analog that was approved by FDA (Food and Drug Administration) for systemic use is Bortezomib (Velcade). Bortezomib is a proteasome inhibitor and proteasome inhibitors cause apoptosis of eukaryotic cells. Although the yeast also has a well preserved 20S proteasome region, the studies on the effects of proteasome inhibitors on the yeast are limited. In this study, the effects of the one of the most potent proteasome inhibitor, MG-262, on Candida spp. were investigated. Methods: C. albicans ATCC 90028, C. krusei ATCC 6258 and C. glabrata (clinical strain) strains were used in our study. Antifungal susceptibilities of the strains against MG-262 and effects of MG-262 on oxidative metabolism, proteasome activity and apoptosis as well as virulence factors such as hyphal transformation, pseudohypha, germ tube and biofilm formation were investigated. CLSI (Clinical and Laboratory Standards Institute) guidelines were used for antifungal susceptibility tests. The effect on hypha and pseudohypha formation and germ tube were determined with conventional tests. Biofilm formation was detected according to the microplate method. Oxidative metabolism experiments, proteosome activity and apoptosis tests were performed with Alamarblue dye, fluorogenic peptides and DNA ladder assays, respectively. Findings: MG-262 exhibited minimum inhibitory activity at 25 μg/ml concentration for C. albicans ATCC 90028 and at 50 μg/ml concentration for C. krusei ATCC 6258 and C. glabrata. Minimum fungicidal concentrations for all species were 50 μg/ml. Hypha, pseudohypha, germ tube and biofilm formation, proteosome activity and oxidative metabolism were all inhibited at 50 μg/ml and higher concentrations. The apoptosis was detected at 200 μg/ml. Conclusion: MG-262 caused apoptosis by inhibiting oxidative metabolism and showed fungicidal activity. It also inhibited the virulence factors such as hypha, pseudohypha germ tube and biofilm formation. Inhibition of proteasome is promising in terms of discovery of a new generation antifungal agent.

Amycolatopsis sp. KCTC 29142로부터 유래된 siderochelin A의 다제 내성 균주에 대한 항균활성

본 연구에서는 신규 Amycolatopsis 균주 KCTC 29142를 분리하여 형태학적 관찰, 계통분석 및 화학분류학적 분석 등 다상 분류분석을 통해 분석하였다. KCTC 29142 균주의 에틸아세테이트추출물은 강한 항균활성을 나타났고, 활성물질은 철 이온 킬레이트 물질인 siderochelin A로 동정되었다. 본 연구에서 분리된 siderochelin A는 다제내성균인 Acinetobacter baumanii, methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Staphylococcus aureus (VRSA), 및 Escherichia coli (E. coli)에 대해 강한 활성을 보였고, 임상에서 분리된 다제내성균에 대한 MIC를 결정하였다. A novel Amycolatopsis strain KCTC 29142 was isolated and characterized based on the polyphasic taxonomic analysis including morphological observation, phylogenetic analysis, physiological and chemotaxonomic characteristics. The ethyl acetate extract of strain KCTC 29142 culture broth showed strong antibacterial activity and the active compound was identified as siderochelin A, a ferrous-ion chelating compound. In this study, siderochelin A showed good activity against multi-drug resistant pathogens, including Acinetobacter baumanii, methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Staphylococcus aureus (VRSA), and Escherichia coli (E. coli). The minimum inhibitory activity against clinical isolates was also determined.

Synthesis and Evaluation of in vitro Antibacterial Properties of Secoisolariciresinol Diglucoside

In the present study, Secoisolariciresinol diglucoside (SDG) was synthesized from commercially available 3,4-dimethoxytoluene, butanediol and penta acetyl glucose. This includes bromination, alkylation, glycosylation, deacetylation and demethylation reactions to yield the interested title compound (SDG), further the assignment of the chemical structure of the synthetic SDG was performed with IR, MS-TOF, 1H and 13C NMR. The antibacterial property of the synthetic SDG was investigated against seven different Gram positive and Gram negative bacteria. The results of the present study proved that SDG can be obtained with good yield (56.2%) under this scheme. Moreover, it exerts an exceptional antibacterial activity where it showed maximum zone of inhibition with 30 and 27.3 mm against E. coli and minimum 7 and 6.1 mm against S. pyogens and S. typhimurium in agar well and disk diffusion respectively. It also showed maximum activity (18 mm at MIC 200 ppm) against S. typhimurium, while minimum inhibitory activity was 4 mm with MIC at 300 ppm against S. pyogens. The scheme of synthesis was found to be an efficient method and the synthetic SDG was also proved to possess a broad spectrum of activity against a panel of bacteria responsible for causing most common diseases.

Phytochemical Screening and Antimicrobial Activity of Tamarindus indica

The method of cold maceration was used in the extraction by serial exhaustive extraction method which involves successive extraction with solvents of increasing polarity from a non polar (hexane) to a more polar solvent (methanol) to ensure that a wide polarity range of compound could be extracted. The phytochemical screening of crude yields of the chemical constituents of Tamarindus indica showed that alkaloids, flavonoids, and tannins are present in all the extracts are present in all the leaf extracts. Activity of the crude hexane, chloroform, ethyl acetate acetone and methanol extracts from the leaf of Tamarindus indica were tested on five clinical isolates; Pseudomonas aeuroginosa, Staphylococcus aureus, Escherichia coli, Aspergillus niger and penicillium spp Augmentin and mycotin were used as control drugs. All the crude extracts of the leaf inhibited or exhibited antibacterial activity against all the bacteria pathogens tested with a diameter that ranged between 8 – 26 mm. All the crude extracts of the leaf inhibited or exhibited antifungal activity against Penicillium Spp with a diameter that ranged between 8 – 13 mm but did not show significant inhibition against A. niger. The minimum inhibitory activity (MIC) of the extracts of Tamarindus indica against tested microbes ranges from 400 to 100 mg/ml in all the extracts against the tested bacteria. The minimum inhibitory activity (MIC) of the extracts of Tamarindus indica against tested microbes ranges from 400 to 200 mg/ml in almost all the extracts for the tested fungi.

Chemical composition profiling and antifungal activity of the essential oil and plant extracts of Mesembryanthemum edule (L.) bolus leaves.

Essential oil from Mesembryanthemum edule leaves have been used by the Eastern Cape traditional healers for the treatment of respiratory tract infections, tuberculosis, dysentery, diabetic mellitus, laryngitis and vaginal infections. The investigation of bioactive compounds in the essential oil of this plant could help to verify the efficacy of the plant in the management or treatment of these illnesses. Various concentrations of the hydro-distilled essential oil, ranging from 0.005-5 mg/ml, were tested against some fungal strains, using the micro-dilution method. Minimum inhibitory activity was compared with four other different crude extracts of hexane, acetone, ethanol and aqueous samples from the same plant. The chemical composition of the essential oil, hexane, acetone and ethanol extracts was determined using GC-MS. GC/MS analysis of the essential oil resulted in the identification of 28 compounds, representing 99.99% of the total oil. Phytoconstituents of hexane, acetone and ethanol extracts yielded a total peak chromatogram of fifty nine compounds. A total amount of 10.6% and 36.61% of the constituents were obtained as monoterpenes and oxygenated monoterpenes. Sesquiterpene hydrocarbons (3.58%) were relatively low compared to the oxygenated sesquiterpenes (9.28%), while the major concentrated diterpenes and oxygenated diterpenes were 1.43% and 19.24 %, respectively and phytol 12.41%. Total amount of fatty acids and their methyl esters content, present in the oil extract, were found to be 19.25 %. Antifungal activity of the oil extract and four solvent extracts were tested against five pathogenic fungal strains. The oil extract showed antifungal activity against Candida albican, Candida krusei, Candida rugosa, Candida glabrata and Cryptococcus neoformans with MIC ranges of 0.02 0.31 mg/ml. Hexane extract was active against the five fungal strains with MICs ranging between 0.02-1.25 mg/ml. Acetone extracts were active against C. krusei only at 0.04mg/ml. No appreciable antifungal activity was found in either ethanol or water extracts when compared with commercial antibiotics. The profile of chemical constituents found in M. edule essential oil and its antifungal properties support the use of M. edule by traditional healers as well as in the pharmaceutical and food industries as a natural antibiotic and food preservative.

The inhibitory effect of Mesembryanthemum edule (L.) bolus essential oil on some pathogenic fungal isolates.

BackgroundMesembryanthemum edule is a medicinal plant which has been indicated by Xhosa traditional healers in the treatment HIV associated diseases such as tuberculosis, dysentery, diabetic mellitus, laryngitis, mouth infections, ringworm eczema and vaginal infections. The investigation of the essential oil of this plant could help to verify the rationale behind the use of the plant as a cure for these illnesses.MethodsThe essential oil from M. edule was analysed by GC/MS. Concentration ranging from 0.005 - 5 mg/ml of the hydro-distilled essential oil was tested against some fungal strains, using micro-dilution method. The plant minimum inhibitory activity on the fungal strains was determined.ResultGC/MS analysis of the essential oil resulted in the identification of 28 compounds representing 99.99% of the total essential oil. A total amount of 10.6 and 36.61% constituents were obtained as monoterpenes and oxygenated monoterpenes. The amount of sesquiterpene hydrocarbons (3.58%) was low compared to the oxygenated sesquiterpenes with pick area of 9.28%. Total oil content of diterpenes and oxygenated diterpenes detected from the essential oil were 1.43% and 19.24%. The fatty acids and their methyl esters content present in the essential oil extract were found to be 19.25%. Antifungal activity of the essential oil extract tested against the pathogenic fungal, inhibited C. albican, C. krusei, C. rugosa, C. glabrata and C. neoformans with MICs range of 0.02-0.31 mg/ml. the activity of the essential oil was found competing with nystatin and amphotericin B used as control.ConclusionHaving accounted the profile chemical constituent found in M. edule oil and its important antifungal properties, we consider that its essential oil might be useful in pharmaceutical and food industry as natural antibiotic and food preservative.

Antimicrobial activity and qualitative phytochemical analysis of Punica granatum Linn. (PERICARP)

Pomegranate, Punica granatum L. is frequently used for the treatment of gastero-intestinal resistant organisms, oral bacteria, highly pathogenic and antibiotic-resistant organisms (Salmonellae and Pseudomonas aeruginosa) and a few skin infecting pathogens, including fungus and methicillin-resistant Staphylococcus aureus (MRSA). In this study, an in vitroantimicrobial activity and phytochemical analysis of ethanolic pericarp extract of P. granatum was carried out. A total of 21 microorganisms (19 bacteria and 2 fungi) were used for antimicrobial activity by disc diffusion, broth dilution methods and a standard procedure was employed to identify the phytoconstituents. Ethanolic extract of pericarp showed significant bactericidal activity against Yersinia enterocolitica (25.8 mm),Staphylococcus epidermidis (24.6 mm), Salmonella enterica (21.2 mm), Burkholderia cepacia (19.4 mm), S. aureus (19.2 mm), Salmonella paratyphi A (18.8 mm), Salmonella typhimurium (18.6 mm), Escherichia coli (18.4 mm) and P. aeruginosa (18.2 mm) were documented. Based on broth dilution technique, the lowest concentration of ethanolic pericarp extract (512 µg/ml) showed significant inhibitory activity against S. epidermidis andY. enterocolitica and 1,024 µg/ml was observed as a minimum inhibitory concentration (MIC) value against S. aureus, Streptococcus mutans, S. paratyphi A, S. typhimurium,Salmonella brunei, P. aeruginosa and B. cepacia. The results of ethanolic extract of P. granatum pericarp showed significant inhibitory activity when compared with other organisms. The highest minimum inhibitory activity was observed against bacteria when compared with fungi. The inhibitory effect could be due to the presence of some of the secondary metabolites like phenolic compounds, flavonoids, terpenoids, phytosterols, glycosides and tannins detected in the ethanolic pericarp extract of P. granatum. Key words: Punica granatum, phytoconstituents, antimicrobial activity, disc diffusion and broth dilution methods, minimum inhibitory concentration (MIC).

Synthesis and Antitubercular Evaluation of N‐Arylpyrazine and N,N′‐Alkyl‐diylpyrazine‐2‐carboxamide Derivatives

Two series of pyrazinamide (PZA) derivatives have been synthesized and evaluated for their in vitro antibacterial activity against Mycobacterium tuberculosis H37Rv. Some compounds exhibited minimum inhibitory concentration activity of 50–100 μg/mL, greater than the first line antituberculosis drug PZA in Alamar Blue assay (&gt;100 μg/mL). The obtained activities can be considered promising results, which characterizes these compounds as good start points to development of new antitubercular agents.

Synthesis and Antitubercular Activity of Novel Amino Acid Derivatives

In this work, 17 new N-acylhydrazone derivatives of amino acids have been evaluated for their in vitro antibacterial activity against Mycobacterium tuberculosis H37Rv. The compounds 8b, 8e, 8f, 9a-d, and 10c exhibited an important minimum inhibitory concentration activity between 12.5 and 50 μg/mL, which can be compared with that of the tuberculostatic drug d-cycloserine (20 μg/mL).

Evaluation of botanicals as biopesticides on the growth of Fusarium verticillioides causing rot diseases and fumonisin production of maize

Partially (Pp) and completely purified (Cp) methanolic extracts of leaves of Cassia alata,Cymbopogon citratus (lemongrass), Mangifera indica (mango), Carica papaya (pawpaw),Citrus limon (lemon), fruits of Xylopia aethiopica, seeds of Aframomum melegueta (alligator pepper), Citrus aurantifolia (lime), Garcinia kola (bitter kola), Piper guineense (brown pepper), and rhizome of Zingiber officinale (ginger) were tested for antimicrobial activity using the poisoned medium and disc diffusion assay techniques on maize mycotoxigenic fungus:Fusarium verticillioides. The Pp extracts of P. guineense, G. kola and A. melegueta showed consistent higher growth inhibitions at 2, 5 and 7 days after incubation, while C. papaya and M. indica had the least activities. It was observed that these extracts completely inhibited the mycelial growth of the fungus at 2 days after incubation and produced growth reduction of 82, 80 and 73% respectively. The Cp extracts of P. guineense, G. kola, and A. melegueta also exhibited consistently higher inhibitions at 3, 5, and 7 days after incubation, while C. papaya andM. indica had no inhibitory activity. The three extracts produced reduction of mycelial growth of 76, 54 and 43% respectively. CP extracts of the plant material showed minimum inhibitory activity against F. verticillioides at 10 to 250 mgml-1 concentration level. The thin layer chromatographic analysis of the plant extracts showed different fractions, while 4 and 1 fractions of P. guineense and A. melegueta showed bioactivity respectively, which may be the important factor in causing the inhibitory effect. P. guineense, G. kola and A. meleguetashowed potential and could be successfully used as environmentally-friendly, cheap, available, effective and sustainable alternative biopesticides. Key words: Alternative pesticides, antifungal, Fusarium verticillioides, maize, medicinal plants

Mutual influence of backbone proline substitution and lipophilic tail character on the biological activity of simplified analogues of caspofungin

The echinocandins represent the most recent class of antifungal drugs. Previous structure-activity relationship studies on these lipopeptides have relied mainly upon semisynthetic derivatives due to their complex chemical structures. A successful strategy for the rapid enantioselective synthesis of the branched fatty acid chain of caspofungin and analogues was developed to synthesize several simplified analogues of caspofungin. The specific minimum inhibitory activity of each mimic was determined against a panel of Candida strains. This approach gave access to new fully synthetic derived caspofungin mimics with high and selective antifungal activities against Candida strains. In addition, the data suggested an important role of the hydroxy proline residue in the bioactive conformation of the macrocyclic peptide ring structure.

Antibacterial properties of an Indian traditional medicinal plant, Rhynchosia scarabaeoides (L.) DC. (Fabaceae)

&lt;em&gt;Rhynchosia scarabaeoides &lt;/em&gt;(L.) DC plant parts are extensively used by traditional healers in India to treat a variety of bacterial diseases, such as dysentery, diarrohea and skin disorders. This article reports the antibacterial activities of n-hexane, ethyl acetate and ethanol extracts belonging to the leaf, stem and root parts of &lt;em&gt;R. scarabaeoides&lt;/em&gt; against five bacterial strains, &lt;em&gt;Bacillus subtilis&lt;/em&gt;, &lt;em&gt;Escherichia coli&lt;/em&gt;, &lt;em&gt;Klebseilla pneumonia&lt;/em&gt;, &lt;em&gt;Proteus vulgaris&lt;/em&gt; and &lt;em&gt;Staphylococcus aureus&lt;/em&gt;, using an agar gel diffusion method. The range of inhibition zone (IZ) was found to be 15-24 mm and the minimum inhibitory activity (MIC) was found to be 1 mL/well. The IZ was found to be higher in ethyl acetate extracts while this was moderate in ethanol extracts, and no activity was seen with n-hexane extracts or root extracts. The MIC value of leaf ethyl acetate extract was found to be 1 mg against bacterial strains &lt;em&gt;P. vulgaris&lt;/em&gt; and &lt;em&gt;S. aureus&lt;/em&gt;, whereas 2 mg was found against &lt;em&gt;B. subtilis&lt;/em&gt;, &lt;em&gt;K. pneumoniae&lt;/em&gt; and &lt;em&gt;E. coli&lt;/em&gt;. These results support the traditional usage of R. scarabaeoides plant parts in the treatment of bacterial infections. Interestingly, this plant was screened for antibacterial activity for the first time and was found to be active. Detailed chemical investigations are, therefore, warranted.

Antimicrobial Efficacy of Metal-Barbiturate Conjugates Against Pathogenic Strains of Escherichia coli and Staphylococcus aureus

Resistance to commercially available antimicrobials is increasing at alarming rate therefore there is an urgent need of new antimicrobial compounds and materials with novel modes of action to tackle the problem of resistance in pathogenic gram positive and gram negative bacteria. The current study involves the design and synthesis of new molecular structures which should not resemble the basic molecular structures of the existing classes of antimicrobial agents in order to avoid the risks of cross resistance development. A total of 14 metal-barbiturate complexes (newly synthesized compounds) were evaluated for their antimicrobial properties against multiple drug resistance clinical isolates of S. aureus and E. coli. Broth dilution method was used to determine minimum inhibitory and bactericidal activity of the newly synthesized compounds. The results showed that the metal-barbiturate complexes with cobalt ions were more effective against E. coli and S. aureus as compared to other compounds. Moreover the activity of these compounds was higher against S. aureus as compared to E. coli which indicates species specific variable antimicrobial effects of these compounds. Keywords: Antimicrobial, Barbiturate Complexes, Drug resistance, E. coli, S. aureus, Antimicrobial resistance, Staphylococcus aureus, Staphylococcal infections, P. aeruginosa, metal-barbiturate complex, MRSA, fluphenazine, fluoroquinoline-resistant, Prochlorperazine, Urinary Tract Infections

Synthesis and evaluation of novel macrocyclic antifungal peptides

Echinocandins are a novel class of macrocyclic antifungal peptides that act by inhibiting the β-(1,3)-d-glucan synthase complex, which is not present in mammalian cells. Due to the large number of hydroxyl groups present in these complex macrocyclic lipopeptides, most structure–activity relationship studies have relied upon semisynthetic derivatives. In order to probe the influence of the cyclic peptide backbone on the antifungal activity we developed a successful strategy for the synthesis of novel echinocandins analogues by on-resin ring closing metathesis or disulfide formation. The specific minimum inhibitory activity of each mimic was determined against Candida albicans. Our results indicate that ring size is an important factor for antifungal activity.

Some toxicological impacts and invitro antibacterial activity of Datura innoxia extract in rats

The study was carried out to investigate some toxicological effects and in-vitro antibacterial activity of Datura innoxia dried leaves.The yield percentage of Datura innoxia 95% ethyl alcohol leaves extract was 19%. Phytochemicals analysis of both Datura innoxia leaves powder and alcoholic extract, indicated the presence of alkaloids, phenols, glycosides, tannins, resins, saponins, flavonoids and steroids which are responsible for toxic and therapeutic effects. The acute toxicological effect of Datura innoxia ethanolic extract in male rats was determined by estimation the oral median lethal dose (LD50) by up and down method was 1214 mg/kg. BW. The in-vitro antibacterial activity of Datura innoxia ethanolic extract and its minimum inhibitory concentration activity (MIC) showed that E. coli was more sensitive to D.I ethanolic extract than Staph. aureus, the MIC for D.I extract against E. coli was less than MIC against Staph. aureus which was 5 and 10 mg/ml respectively, also E. coli was more sensitive to ciprofloxacin .

Design, synthesis, characterization, and antibacterial activity of {5-chloro-2-[(3-substitutedphenyl-1,2,4-oxadiazol-5-yl)-methoxy]-phenyl}-(phenyl)-methanones

In the present investigation, a series of novel {5-chloro-2-[(3-(substitutedphenyl)-1,2,4-oxadiazol-5-yl)-methoxy]-phenyl}-(phenyl)-methanones ( 3a– i) have been synthesized from 5-(chloromethyl)-3-substitutedphenyl-1,2,4-oxadiazole ( 2a– i). The newly synthesized compounds were characterized by IR, NMR ( 1H and 13C), mass spectral and elemental analysis. The title compounds were investigated for in-vitro qualitative (zone of inhibition) and quantitative (MIC) antibacterial activity by agar cup plate and microtitration methods, respectively. The minimum inhibitory concentration and structure activity relationships (SARs) were evaluated. Amongst the synthesized compounds in this series, {5-chloro-2-[(3-(2,5-difluoro-4-methyl-phenyl)-1,2,4-oxadiazol-5-yl)-methoxy]-phenyl}-(phenyl)-methanone ( 3d) was found to exhibit significant activity with MICs of 21.5, 22.4, 29.8 and 30.6 μg/mL against Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Klebsiella pneumoniae, respectively.

The major differences in chemical composition and antibacterial activity of two closely related Leonotis species (Lamiaceae) may have taxonomic value

Several Leonotis species are used widely for medicinal purposes in Africa. There have been drastic changes in the taxonomic treatment of Leonotis species during the past decade. Two species, L. dysophylla and L. microphylla occurring in Pretoria have been considered as varieties of the same species and as different species by different authors. Because Leonotis species are used widely as medicinal plants inter alia against bacterial infections, we decided to compare the chemical composition and antibacterial activity of four plants from each of two populations of the species. The chemical composition of acetone extracts of finely ground leaves was determined by thin layer chromatography followed by spraying with vanillin-sulphuric acid. There were hardly any differences between plants from the same population. There were major differences between the two species in the composition of pigments separated by thin layer chromatography and for compounds visualized with the vanillin-sulphuric acid spray reagent. This supported the viewpoint that the two species should not be considered as varieties. The major differences found in chemical composition indicate that chemical parameters may play an important role in resolving taxonomic differences. Because such a small quantity of material is needed, it may be feasible to analyze one or two leaves obtained from herbarium sheets as an additional taxonomic parameter. The antibacterial activity of the acetone extracts was determined using a two-fold serial dilution microplate method with tetrazolium violet as indicator of growth. The specific strains of the four most important nosocomial bacterial pathogens suggested by the United States National Committee for Clinical Laboratory Standards were used: Staphylococcus aureus (American Type Culture Collection 29213), Pseudomonas aeruginosa (ATCC 27853), Escherichia coli (ATCC 25922) and Enterococcus faecalis (ATCC 21212). The minimum inhibitory activity of the crude extract of L. microphylla was 58, 33, 113 and 15 µg/ml against the four pathogens respectively. The MIC of the L. dysophylla extracts were 110, 95, 113 and 63 µg/ml respectively. If the total activity was calculated by dividing the quantity in mg extracted from one gram of each species with the MIC, the following values were obtained against the respective bacteria using the L. microphylla extract: 700, 1400, 381 and 2100 ml/g. The values for the L. dysophylla extract were 381, 420, 420 and 700 ml/g. This means that if one gram of dried leaves of L. microphylla were extracted with acetone it could be diluted to 2100 ml and it would still kill E. faecalis. These results not only prove the possible use of chemical and biological activity as taxonomic markers, but also the potential value of L. microphylla acetone extracts in treating infections with P. aeruginosa and E. faecalis. The activity of the crude extract against P. aeruginosa was as good as or better than the activity of ampicillin, gentamicin, nitrofurantoin, trimethroptin or sulfi soxazole. The activity against E. faecalis was as good as or better than ampicillin, gentamicin, nitrofurantoin or sulfi soxazole. If the acetone leaf extract of L. microphylla is stable and not toxic there is a good possibility of developing a commercially useful antibacterial product from it. The results indicate the taxonomic value of chemical parameters and biological activity and support the view that the two taxa should be considered as different species.