Average Minimum Inhibitory Concentration Research Articles

Is There Evidence for Resistance of Ocular Chlamydia trachomatis to Azithromycin After Mass Treatment for Trachoma Control?

Trachoma, caused by repeated infections with ocular Chlamydia trachomatis, is targeted for elimination using multiple annual rounds of mass drug administration (MDA) in endemic communities. Infection rates do not decline as expected in some communities, leading to concerns about azithromycin resistance. After 3 yearly MDAs in 32 communities in Tanzania, 107 children were identified 1 year later with infection. All were provided MDA again, and 90 were seen again at 2 months, of whom 30 had infection. Chlamydia trachomatis isolates were obtained before and after MDA in 15 paired samples and were tested for antimicrobial susceptibility. The infectious load of C. trachomatis before MDA was determined in 30 children who had infection at both times and 60 whose infection cleared. The median load was 8.6 genome copies per polymerase chain reaction in the consistently infected, and 8.4 in those whose infection cleared (P = .86). For the consistently infected, the average minimum inhibitory concentration was 0.26 µg/mL for azithromycin before and 0.20 µg/mL after MDA. All isolates had minimum inhibitory concentration ≤0.50 µg/mL. There is no evidence that continued infection after MDA was due either to resistance to azithromycin or to a heavier load of organism before treatment. Other potential causes of persistent infection need to be evaluated.

Antimicrobial activity and cytotoxicity of the ethanol extract, fractions and eight compounds isolated from Eriosema robustum (Fabaceae)

BackgroundThe aim of this study was to evaluate the antimicrobial activity and the cytotoxicity of the ethanol crude extract, fractions and isolated compounds from the twigs of Eriosema robustum, a plant used for the treatment of coughs and skin diseases.MethodsColumn chromatographic and spectroscopic techniques were used to isolate and identify eight compounds, robusflavones A (1) and B (2), orostachyscerebroside A (3), stigmasterol (4), 1-O-heptatriacontanoyl glycerol (5), eicosanoic acid (6), 3-O-β-D-glucopyranoside of sitosterol (7) and 6-prenylpinocembrin (8), from E. robustum. A two-fold serial microdilution method was used to determine the minimum inhibitory concentration (MIC) against fungi and bacteria, and the 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide reduction assay was used to evaluate the cytotoxicity.ResultsFraction B had significant antimicrobial activity against Aspergillus fumigatus and Cryptoccocus neoformans (MIC 0.08 mg/ml), whilst the crude extract and fraction A had moderate activity against A. fumigatus and Candida albicans (MIC 0.16 mg/ml). Fraction A however had excellent activity against Staphylococcus aureus (MIC 0.02 mg/ml), Enterococcus faecalis and Escherichia coli (MIC 0.04 mg/ml). The crude extract had significant activity against S. aureus, E. faecalis and E. coli. Fraction B had good activity against E. faecalis and E. coli (MIC 0.08 mg/ml). All the isolated compounds had a relatively weak antimicrobial activity. An MIC of 65 μg/ml was obtained with robusflavones A (1) and B (2) against C. albicans and A. fumigatus, orostachyscerebroside A (3) against A. fumigatus, and robusflavone B (2) against C. neoformans. Compound 8 had the best activity against bacteria (average MIC 55 μg/ml). The 3 fractions and isolated compounds had LC50 values between 13.20 to > 100 μg/ml against Vero cells yielding selectivity indices between 0.01 and 1.58.ConclusionThe isolated compounds generally had a much lower activity than expected based on the activity of the fractions from which they were isolated. This may be the result of synergism between different compounds in the complex extracts or fractions. The results support the traditional use of E. robustum to treat infections. The crude extract had a good activity and low preparation cost, and may be useful in topical applications to combat microbial infections.

Susceptibility of Staphylococcus aureus Clinical Isolates to Propolis Extract Alone or in Combination with Antimicrobial Drugs

The objective of this study was to assess in vitro the antimicrobial activity of ethanolic extract of Polish propolis (EEPP) against methicillin-sensitive Staphylococcus aureus (MSSA) and methicillin-resistant Staphylococcus aureus (MRSA) clinical isolates. The combined effect of EEPP and 10 selected antistaphylococcal drugs on S. aureus clinical cultures was also investigated. EEPP composition was analyzed by a High Performance Liquid Chromatography (HPLC) method. The flavonoid compounds identified in Polish Propolis included flavones, flavonones, flavonolols, flavonols and phenolic acids. EEPP displayed varying effectiveness against twelve S. aureus strains, with minimal inhibitory concentration (MIC) within the range from 0.39 to 0.78 mg/mL, determined by broth microdilution method. The average MIC was 0.54 ± 0.22 mg/mL, while calculated MIC50 and MIC90 were 0.39 mg/mL and 0.78 mg/mL, respectively. The minimum bactericidal concentration (MBC) of the EEPP ranged from 0.78 to 3.13 mg/mL. The in vitro combined effect of EEPP and 10 antibacterial drugs was investigated using disk diffusion method-based assay. Addition of EEPP to cefoxitin (FOX), clindamycin (DA), tetracycline (TE), tobramycin (TOB), linezolid (LIN), trimethoprim+sulfamethoxazole (SXT), penicillin (P), erythromycin (E) regimen, yielded stronger, cumulative antimicrobial effect, against all tested S. aureus strains than EEPP and chemotherapeutics alone. In the case of ciprofloxacin (CIP) and chloramphenicol (C) no synergism with EEPP was observed.

Combined effect of Zn2+ and Mn2+ on physiology of wood-rotting basidiomycetes

The effect of pure Zn2+ and combined Zn2+ and Mn2+ supplements on the growth and ligninolytic activity of wood-rotting basidiomycetes was studied. Based on measurements of minimum inhibitory concentration and minimum decolourisation-inhibiting concentration available from cultures of Inocutis sp., Trametes versicolor and Gloeophyllum trabeum, and a comparison of such results with those obtained in previous work for P. chrysosporium and P. atropurpurascens, metal supplements were shown to inhibit fungal physiology at concentrations within the study range. Average minimum inhibitory concentration values were consistently lower for ZnSO4 than for ZnSO4/MnSO4 (2 mM Zn2+), demonstrating the antagonistic effect of the tested cations. Furthermore, because the ligninolytic system of P. atropurpurascens had shown a high tolerance to metals, its ligninolytic and germinative behaviour was compared with that of P. chrysosporium. Conidial germination was inhibited at 1 mM of Zn2+ in the two strains, whereas extracellular activity was inhibited at concentrations above 2 mM.

Antimicrobial activity of natural antimicrobial substances against spoilage bacteria isolated from fresh produce

The aim of this study was to investigate the efficacy of natural antimicrobial substances for inhibiting vegetable spoilage bacteria. Natural antimicrobial compounds (carvacrol, thymol, eugenol, cinnamic acid, nisin, and chitosan), organic acids (acetic acid and lactic acid), and chemical sanitizers (sodium hypochlorite and chlorine dioxide) were evaluated for their antibacterial activities, as single and combination treatments, against 15 spoilage bacteria isolated from vegetables, using the agar disc diffusion and broth dilution methods. Carvacrol, thymol, and eugenol showed strong inhibitory effects compared to those of the other antimicrobial substances, and their average minimum inhibitory concentration (MIC) values against 15 spoilage bacteria were 167, 648, and 168 μg/ml, respectively. When they were combined, four kinds (carvacrol + thymol, carvacrol + eugenol, thymol + eugenol, and carvarol + thymol + eugenol) of the combination formulas showed higher antibacterial effect than others against spoilage bacteria, with average MIC values of 47, 43, 59, and 42 μg/ml, respectively. However, two combinations (carvacrol + thymol, and carvacrol + thymol + eugenol) showed the strongest inhibitory effects against bacteria in fresh vegetables among all treatments. These results could be used for the development of new sanitation or preservation methods to improve freshness and to extend the shelf-life of fresh produce.

Detection and genotyping of vancomycin-resistant Enterococcus spp. by multiplex polymerase chain reaction in Korean aquatic environmental samples

The distribution characteristics of Enterococcus spp., which are indicators of fecal pollution, were investigated at 33 sites within the 3 major water systems of Korea. Enterococci were detected at concentrations ranging from 1 to 37 CFU/100mL in 41 of 132 samples (31.1%) from the 3 major water systems. The overall average detected concentration was 1.2 CFU/100mL, while the average concentration for all detection sites was 5.3 CFU/100mL. After optimized multiplex polymerase chain reaction (PCR) was performed with newly developed VanA, VanB, VanC-1, and VanC-2/3 primers, concentrations of vancomycin-resistant Enterococcus spp. (VRE) ranging from 1 to 23 CFU/100mL were detected in 17 of 132 samples (12.9%). Of 216 individual enterococcal colonies, 64 (29.6%) displayed the VanC genotype. The results of a susceptibility test to vancomycin showed that the range of the minimal inhibitory concentration (MIC), an indicator of bacterial resistance, was 4 to 24μg/mL, with the average MIC at 9.2±4.5μg/mL. Of the bacterial isolates, 1 colony with the VanC-1 genotype was identified as E. gallinarum by 16S rDNA sequencing, whereas the other 63 colonies had the VanC-2/3 genotype and were identified as E. casseliflavus. Although these results imply that the major head bays of Korea are not contaminated with the highly vancomycin-resistant VanA- or VanB-type VREs, the misuse of antibiotics should be prohibited to minimize the presence of VREs and to maintain a safe water supply for protecting the health of the general population. Based on the study results, we also recommend the implementation of a continuous, broad-spectrum inspection program for Enterococcus spp. and VRE contamination in the major head bays. Furthermore, the multiplex PCR method described in this study can be used effectively for this purpose.

Antibiotic resistance in triclosan tolerant fecal coliforms isolated from surface waters near wastewater treatment plant outflows (Morris County, NJ, USA)

Triclosan (TCS) is a common antimicrobial agent that has been detected in wastewater treatment plant (WWTP) effluent outflows. A link between TCS exposure and increased antibiotic resistance in microbes has been postulated. The purpose of this study was to evaluate whether fecal coliforms (FC) isolated from surface waters located near (WWTP) outflows display TCS resistance and, if so, whether such organisms exhibit increased resistance to antibiotics. Water samples were collected at two streams in Morris County, NJ that receive WWTP effluent: Loantaka Brook and the Whippany River. Water samples were collected at three sites within each location near the WWTP effluent outflow. Abiotic river parameters were measured and FCs were enumerated for each sample. River parameters were analyzed to determine if TCS or antibiotic resistance was correlated to water quality. Triclosan resistance levels were determined for individual isolates, and isolates were screened against seven classes of antibiotics at clinically relevant levels to assess cross-resistance. At Loantaka Brook, 78.8% of FC isolates were resistant to TCS with an average minimum inhibitory concentration (MIC) of 43.2μgml−1. In addition, 89.6% of isolates were resistant to four classes of antibiotics and all were identified as Citrobacter freundii. There was a significant effect of stream location on mean TCS MIC values in the Loantaka Brook, with effluent isolates maintaining significantly higher MIC values compared to upstream isolates. At Whippany River sites, TCS resistant isolates were detected on 94% of sampling dates with a significant relationship between TCS resistance and multiple antibiotic resistances (≥three antibiotic classes, p<0.001). TCS resistant isolates were significantly more resistant to chloramphenicol (p=0.007) and to nitrofurantoin (p=0.037) when compared to TCS sensitive isolates. Environmental FC isolates resistant to high level TCS included species of Escherichia, Enterobacter, Serratia and Citrobacter. There was no correlation between river water quality and resistance of isolates to TCS. Presence of isolates not resistant to TCS, but resistant to other antibiotics, were significantly correlated to increased river flow, precipitation, and decreased nutrient levels, suggesting that observed resistance is due to run-off events. This study demonstrates that TCS resistant FC are common in river systems receiving WWTP effluent and display multiple drug resistance.

Mycoplasma infection of ducks and geese

Production of ducks and geese in certain parts of the world is very important. Mycoplasma diseases cause significant losses to the duck and goose industry. This review summarizes the epidemiological, clinical, and pathomorphological characteristics of mycoplasma diseases of ducks and geese and the involvement of the various mycoplasma species in their pathogenesis. The role of mycoplasma infections in the development of clinical signs, pathological lesions, and mortality of challenged birds is demonstrated in challenge experiments. Transmission of mycoplasma in the ovary and eggs resulting in the reduction of egg production and an increase of embryo mortality has been shown in challenge experiments as well as in field studies. The susceptibility of many mycoplasma isolates of the most important mycoplasma species of duck and goose origin were tested and showed relatively high average minimum inhibitory concentrations of lincomycin, tilosin, oxytetracycline, chlortetracycline, and enrofloxacin but not for tiamulin. The successful treatment of mycoplasma infections with antibiotics in ducks and geese should be selected based on the minimum inhibitory concentration values against the mycoplasmas isolated from the flock.

Mechanisms, clinically curative effects, and antifungal activities of cinnamon oil and pogostemon oil complex against three species of Candida

The anti-fungus mechanisms and curative effects of cinnamon oil and pogostemon oil complexes towards intestinal Candida infections were investigated. We measured the minimal inhibitory concentration (MIC) values of the complexes against Candida using proportionally-diluted test-tube medium, and examined the evolution of the morphology and structures of Candida albicans using scanning electronic microscopy (SEM) and transmission electronic microscopy (TEM). We found that the average MIC values of the complexes against the fungi were 0.064 mg/mL (cinnamon oil), 0.032 mg/mL (pogostemon oil) for Candida albicans, 0.129 mg/mL (cinnamon oil), 0.064 mg/mL (pogostemon oil) for Candida tropicalis, and 0.129 mg/mL (cinnamon oil), 0.064 mg/mL (pogostemon oil), for Candida krusei. SEM examination over a 24–48 h period showed that the morphology of Candida albicans cells changed significantly. Irregular hollows appeared on the surfaces, inside organelles were destroyed and the cells burst after treatment. TEM examination over a 48 – 72 h period indicated that the cell walls were damaged, organelles were destroyed and most cytoplasms became empty bubbles. Sixty intestinal Candida-infected patients were treated with a capsule containing cinnamon and pogostemon oil. The curative ratio was 71.67% (43/60), and the improvement ratio was 28.33% (17/60), giving a total ratio of 100%. Thus, the cinnamon oil and pogostemon oil complexes had strong anti-fun-guseffectsagainst Candida albican, Candida tropicalis, and Candida krusei. They impacted the morphology and sub-micro structures of the fungus within 48–72 h, and eventually denatured and killed the cells. The complexes have also shown considerable curative effects to intestinal Candida infections.

Preliminary screening of some fractions of Loxostylis alata (Anacardiaceae) for antimicrobial and antioxidant activities

An acetone extract of Loxostylis alata was separated into six fractions based on polarity by a solventsolvent fractionation procedure and the different fractions were screened for antimicrobial and antioxidant activities. The number of antimicrobial compounds in the carbon tetrachloride (CCl 4 ), chloroform (CC), aqueous methanol (AM) and butanol (BT) fractions were determined by bioautography. Each fraction was loaded onto thin layer chromatography (TLC) plates and eluted using two different mobile solvent systems, namely chloroform/ethyl acetate/formic acid (5:4:1): (CEF) and ethyl acetate/methanol/water (40:5.4:5) (EMW). Relative front (R f ) values of active compounds against bacteria ranged from 0.4 - 0.9 in CEF and EMW solvent system. Similarly, the Rf values of compounds active against fungi were in the range of 0.7 - 0.9. Hexane, carbon tetrachloride, chloroform, aqueous methanol and butanol fractions showed areas of inhibition against bacterial organisms, while only hexane and carbon tetrachloride fractions depicted areas of fungal growth inhibition on their chromatograms. The CCl 4 extract was active against six out of the nine microbial strains used and was particularly active against Staphylococcus aureus, Enterococcus faecalis, Aspergillus fumigatus, Candida albicans, Cryptococcus neoformans and Microsporum canis with minimum inhibitory concentration (MIC) of 0.04, 0.04, 0.1, 0.1, 0.06 and 0.03 mg/ml, respectively. M. canis was the most sensitive organism with the lowest average MIC of 0.16 mg/ml. Qualitative antioxidation using diphenylpicryl- hydrazyl (DPPH) and qualitative assay using both 2,2'-azinobis-3-ethylbenzothiazoline-6- sulfonate (ABTS) and DPPH radicals revealed the presence of three antioxidant compounds in the AM and BT fractions, while the water fraction had only one antioxidant compound. However, the concentration of the antioxidant compounds was more in the AM and BT fractions as revealed by their pronounced colour intensity on the TLC plates. The water fraction had more free radical scavenging effect against DPPH with EC 50 value of 0.62 ± 0.03 μg/ml. The lower the EC 50 value of an extract, the more effective its antioxidant activity. In a similar manner, TEAC value of water fraction was 2.97, which further indicates superior free radical scavenging effect of the fraction against ABTS radical. The greatest reduction of reactive oxygen species (ROS) production induced by diclofenac was also achieved by the water fraction which on overall shows that the water fraction contains more antioxidants. The presence of antimicrobial and antioxidant activities in the fractions of L. alata suggests that this plant may be a source of pharmacologically active substances with beneficial actions towards disease control and treatment in animals and humans. Key words : Medicinal plant, antibacterial, antifungal, serial microdilution, minimum inhibitory concentration, antioxidants.

Perfil fenotípico e susceptibilidade antimicrobiana de Streptococcus equi isolados de equinos da região Sul do Brasil

As características fenotípicas [morfológicas, bioquímicas, susceptibilidade aos antimicrobianos, índice de resistência múltipla aos antimicrobianos (IRMA), concentração inibitória mínima (CIM) e concentração bactericida mínima (CBM) da benzilpenicilina] de 38 isolados de Streptococcus equi oriundos de amostras clínicas de animais com adenite equina foram alvo deste estudo. A fenotipia demonstrou três padrões de colônias, três biotipos de fermentação de carboidratos e variação de 0 a 0,4 no IRMA. Todos os isolados de S. equi demonstraram sensibilidade à penicilina, tanto pelo método de disco difusão quanto pelo método de microdiluição. A CIM e CBM média de benzilpenicilina foi de 0,0095μg/mL e 0,0267μg/mL para S. equi subesp. equi e de 0,0128μg/mL e 0,0380μg/mL para S. equi subesp. zooepidemicus. Os valores de CIM e CBM diferiram entre as subespécies (p&lt;0,05). O diâmetro do halo de inibição de penicilina demonstrou relação com a CIM (ì=0,03638 - 0,00072x) para S. equi subesp. equi. Também foi demonstrada relação entre o diâmetro do halo de inibição de penicilina com a CBM para S. equi subesp. equi (ì=0,10931- 0,00223x). Entretanto para as amostras de S. equi subesp. zooepidemicus esta relação somente foi verificada para a CBM (ì=0,1322 - 0,00271x). A CIM de benzilpenicilina frente às amostras isoladas da região Central, Planalto e Sul do estado do Rio Grande do Sul foram estatisticamente semelhantes, mas diferiram do isolado do estado do Paraná, sugerindo o caráter atípico desta cepa. Todos os isolados de S. equi são sensíveis à penicilina e sulfazotrim, confirmando a eleição destes antimicrobianos para o tratamento das infecções por este agente na clínica veterinária. Os resultados obtidos não dispensam a utilização prudente dos antimicrobianos.

Evaluation of the antibacterial and anticancer activities of some South African medicinal plants.

BackgroundSeveral herbs are traditionally used in the treatment of a variety of ailments particularly in the rural areas of South Africa where herbal medicine is mainly the source of health care system. Many of these herbs have not been assessed for safety or toxicity to tissue or organs of the mammalian recipients.MethodsThis study evaluated the cytotoxicity of some medicinal plants used, inter alia, in the treatment of diarrhoea, and stomach disorders. Six selected medicinal plants were assessed for their antibacterial activities against ampicillin-resistant and kanamycin-resistant strains of Escherichia coli by the broth micro-dilution methods. The cytotoxicities of methanol extracts and fractions of the six selected plants were determined using a modified tetrazolium-based colorimetric assay (3-(4, 5-dimethylthiazol)-2, 5-diphenyl tetrazolium bromide (MTT) assay).ResultsThe average minimum inhibitory concentration (MIC) values of the plants extracts ranged from 0.027 mg/mℓ to 2.5 mg/mℓ after 24 h of incubation. Eucomis autumnalis and Cyathula uncinulata had the most significant biological activity with the least MIC values. The in vitro cytotoxicity assay on human hepatocarcinoma cell line (Huh-7) revealed that the methanol extract of E. autumnalis had the strongest cytotoxicity with IC50 of 7.8 μg/mℓ. Ethyl acetate and butanol fractions of C. uncinulata, Hypoxis latifolia, E. autumnalis and Lantana camara had lower cytotoxic effects on the cancer cell lines tested with IC50 values ranging from 24.8 to 44.1 μg/mℓ; while all the fractions of Aloe arborescens and A. striatula had insignificant or no cytotoxic effects after 72 h of treatment.ConclusionsOur results indicate that the methanol fraction of E. autumnalis had a profound cytotoxic effect even though it possessed very significant antibacterial activity. This puts a query on its safety and hence a call for caution in its usage, thus a product being natural is not tantamount to being entirely safe. However, the antibacterial activities and non-cytotoxic effects of A. arborescens and A. striatula validates their continuous usage in ethnomedicine.

Creeping baselines and adaptive resistance to antibiotics

The introduction of antimicrobial drugs in medicine gave hope for a future in which all infectious diseases could be controlled. Decades later it appears certain this will not be the case, because antibiotic resistance is growing relentlessly. Bacteria possess an extraordinary ability to adapt to environmental challenges like antimicrobials by both genetic and phenotypic means, which contributes to their evolutionary success. It is becoming increasingly appreciated that adaptation is a major mechanism behind the acquisition and evolution of antibiotic resistance. Adaptive resistance is a specific class of non-mutational resistance that is characterized by its transient nature. It occurs in response to certain environmental conditions or due to epigenetic phenomena like persistence. We propose that this type of resistance could be the key to understanding the failure of some antibiotic therapy programs, although adaptive resistance mechanisms are still somewhat unexplored. Similarly, hard wiring of some of the changes involved in adaptive resistance might explain the phenomenon of "baseline creep" whereby the average minimal inhibitory concentration (MIC) of a given medically important bacterial species increases steadily but inexorably over time, making the likelihood of breakthrough resistance greater. This review summarizes the available information on adaptive resistance.

Bactericidal Capacity of Silver Nanoparticles Associated with Gantrez S-97 on Streptococcus Mutans

Dental caries is a worldwide public health problem. S mutans plays an important role in the etiology of caries. There have been studies that showed the antimicrobial properties of silver nanoparticles are an effective agent to diminish S. mutans. The objective of this study was to evaluate the bactericidal and bacteriostatic effects of silver nanoparticles in addition to the Gantrez S-27 copolymer, on S mutans. We performed an in vitro experimental study using the liquid microdilution method in order to find the minimum inhibitory concentrations (MICs) and the minimum bactericidal concentrations (MBCs) with the subcultures obtained. The mixture was obtained by preparing 98 microg/mL of silver nanoparticles (10(3)mol) with Gantrez S-27 2%, in distilled water The readings were performed 24 hours after incubation and on 3 consecutive days. The results showed an average MTC of 6.12 microg /mL and MBC of 6.12 microg /mL. The addition of Gantrez 2% to silver nanoparticles does not alter its antimicrobial effect.

Antimycobacterial evaluation of fifteen medicinal plants in South Africa

Fifteen plant species were collected from the Nelspruit Botanical Garden based on a list of plants provided by Phytomedicine Programme at the University of Pretoria and their ethnopharmacological information. Hexane, dichloromethane (DCM), acetone and methanolic extracts were screened for antimycobacterial activity against Mycobacterium smegmatis. The acetone extract of Milletia stulhimannii was the most active, showing activity against Mycobacterium smegmatis with minimum inhibitory concentration (MIC) value of 0.13 mg/ml. Acetone extracts for all plants had lower MIC values ranging between 0.11-1.25 mg/ml against M. smegmatis. Milletia stulhimannii, Albizia gummifera, Xanthocercis zambesiaca and Barringtonia racemosa have shown great potential as anti-tuberculosis agents. They were active against M. smegmatis with average MIC values of acetone extracts of 0.13 mg/ml.

Antifungal efficacy of ten selected South African plant species against Cryptococcus neoformans

Fungal infections are a major threat to public health care. Cryptococcosis in humans and animals, caused by Cryptococcus neoformans, is a life-threatening disease. In a random antifungal screening of acetone leaf extracts of 400 tree species against Cryptococcus neoformans, the following plant species had good activity: Zanthoxylum capense (Thunb.) Harv. (Rutaceae), Morusmesozygia Stapf (Moraceae), Calodendrum capense (L.f.) Thunb. (Rutaceae), Catha transvaalensis Codd (Celastraceae), Cussonia zuluensis Strey (Araliaceae), Ochna natalitia (Meisn.) Walp. (Ochnaceae), Croton sylvaticus Hochst. ex C. Krauss (Euphorbiaceae), Maytenus undata (Thunb.) Blakelock (Celastraceae), Celtis africana Burm.f. (Ulmaceae), and Cassine aethiopica Thunb. (Celastraceae). Hexane, dichloromethane, acetone, and methanol extracts of these 10 plants were tested against Cryptococcus neoformans using bioautography and microdilution assays. Acetone extracted the highest quantity of plant material. Dichloromethane and hexane extracts of Maytenus undata showed clear bands in bioautography while the other species did not produce good results in bioautography. Maytenus undata extracts had promising antifungal activity against C. neoformans, with average minimum inhibitory concentration (MIC) of 0.09 mg/mL after 24 h and 0.18 mg/mL after 48 h incubation. Croton sylvaticus and Catha transvaalensis extracts also had good activity, with average MIC values of 0.07 mg/mL and 0.09 mg/mL, respectively. Because of the clear bands on bioautograms and low MIC values compared to the other plant species investigated, M. undata was identified as a good candidate for further studies.

Biosynthesis of Antimicrobial Silver Nanoparticles by The Endophytic Fungus Aspergillus Clavatus

To induce the biosynthesis of silver nanoparticles (AgNPs) using Aspergillus clavatus and evaluate their antimicrobial potential. Aspergillus clavatus (AzS-275), an endophytic fungus isolated from sterilized stem tissues of Azadirachta indica A. Juss., was challenged with 1 mM AgNO(3) solution. The characterization of the AgNPs was carried out by x-ray diffraction spectrometry, transmission-electron microscopy and atomic force microscopy. The synthesized AgNPs were found to be extracellular, polydispersed spherical or hexagonal particles ranging from 10 to 25 nm in size. Antimicrobial activity was performed using a disc-diffusion method against Candida albicans, Pseudomonas fluorescens and Escherichia coli. The results showed an average minimum inhibitory concentration of 5.83 microg ml(-1) and minimum fungicidal concentration of 9.7 microg ml(-1) against C. albicans. AgNPs can be mycosynthesized extracellularly using A. clavatus as the fungal system, which is highly advantageous over chemical synthesis not only because it can be synthesized on a large scale, but because of the ease of downstream processing and its biomedical application in antimicrobial activity.

Antifungal and antibacterial activities of different extracts of Harungana madagascariensis stem bark

The antifungal and antibacterial effects of the stem bark extracts of Harungana madagascariensis Lam. ex Poir. (Clusiaceae) were examined against nine microbial pathogens causing infections in both man and animals. Hexane (H), dichloromethane (D), chloroform (C), ethyl acetate (E), acetone (A), methanol (M), and water (W) extracts were tested in vitro through bioautography and minimum inhibitory concentrations (MIC) determination using the serial micro-dilution assays. Bioautographic results revealed the presence of eight different spots. Extract A exhibited the lowest MIC of 0.04 mg/mL against Microsporum canis, while water extract (W) and methanol (M) showed the highest MIC of 2.5 mg/mL against at least one of the tested fungi when compared to amphotericin B with 0.0625–1 g/mL. Sporotrichum schenckii was the most susceptible fungal pathogen with average MIC of 0.06 mg/mL, while the acetone extract (A) was the most active against three fungal organisms when compared with other extracts. Similarly, extracts D, C, E and A exhibited very high activity with low MIC values of 0.156–0.62 mg/mL, while M and W gave the highest values of 0.31–2.5 mg/mL on bacterial pathogens as compared to gentamicin (0.02–0.62 8 g/mL). The dichloromethane extract is the most active against bacteria with average MIC of 0.19 mg/mL, while Staphylococcus aureus is the most sensitive organism; that shows susceptibility at an average MIC of 0.34 mg/mL. These results provide promising information for the potential use of the crude extracts from the stem-bark of H. madagascariensis in the treatment of bacterial and fungal infections similar to what was obtained in the leaves.

Evaluation of several tree species for activity against the animal fungal pathogen Aspergillus fumigatus

Aspergillus fumigatus causes severe problems in poultry production systems. Seven South African tree species were selected from the database of the Phytomedicine Programme based on its antifungal activity against the fungus Cryptococcus neoformans. The acetone leaf extracts of the selected species had minimum inhibitory concentrations (MICs) of 0.16 mg/ml and lower in the preliminary screening. The antibacterial and antifungal activities of hexane, dichloromethane, acetone and methanol extracts of the leaves were determined using a two-fold serial microdilution method against a range of commonly encountered animal pathogenic fungi ( A. fumigatus, Candida albicans, C. neoformans, Microsporum canis and Sporothrix schenckii) and four nosocomial bacteria ( Staphylococcus aureus, Enterococcus faecalis, Escherichia coli and Pseudomonas aeruginosa). The plant species investigated were Combretum vendae (A.E. van Wyk) (Combretaceae), Commiphora harveyi (Engl.) Engl. (Burseraceae), Khaya anthotheca (Welm.) C.DC (Meliaceae), Kirkia wilmsii Engl. (Kirkiaceae), Loxostylis alata A. Spreng. ex Rchb. (Anacardiaceae), Ochna natalitia (Meisn.) Walp. (Ochnaceae) and Protorhus longifolia (Bernh.) Engl. (Anacardiaceae). All the extracts had activity against at least one of the test organisms over an incubation period of 24 or 48 h. The MIC values of the non-polar and intermediate polarity extracts of O. natalitia, K. anthotheca, C. vendae, C. harveyi, and P. longifolia had MICs as low as 0.08 mg/ml against at least one of the tested bacteria. Furthermore, the acetone extracts of L. alata, K. wilmsii, O. natalitia and C. vendae had antifungal activities with MIC values ranging from 0.04 to 0.08 mg/ml against at least one of the tested fungi. The average MIC values of the plant extracts against the different bacteria ranged from 0.17 to 2.11 mg/ml, while the range was 0.23–1.98 mg/ml for fungi. The Gram-positive bacteria ( S. aureus and E. faecalis) were more susceptible to the plant extracts than the Gram-negative bacteria ( E. coli and P. aeruginosa). E. faecalis was the most susceptible microbe and C. vendae extracts were the most active against nearly all the bacteria tested. The acetone extract of L. alata was the most active against fungal pathogens, with activity against at least 3 fungal organisms. L. alata was selected for further work to isolate compounds active against A. fumigatus and other fungal pathogens.

The activity of extracts of seven common invasive plant species on fungal phytopathogens

Acetone extracts from different parts of seven common invasive plant species occurring in South Africa were studied as potential sources of antifungal agents for selected phytopathogenic fungi (Penicillium janthinellum, Penicillium expansum, Aspergillus niger, Aspergillus parasiticus, Colletotrichum gloeosporioides, Fusarium oxysporum, Trichoderma harzianum, Phytophthora nicotiana, Pythium ultimum and Rhizoctonia solani. The invasive plant species were Cestrum laevigatum (flowers and leaves), Nicotiana glauca (flowers, leaves and seeds), Solanum mauritianum (fruits and leaves), Lantana camara (fruits, flowers and leaves), Datura stramonium (seeds), Ricinus communis (leaves) and Campuloclinium macrocephalum (leaves and flowers). All extracts exhibited moderate to good activities on all tested fungi with minimum inhibitory concentrations (MICs) ranging from 0.08 mg/ml to 2.5 mg/ml. In all cases leaf extracts were more active than seed or flower extracts. The growth of A. niger, P. expansum and R. solani was the most sensitive to all the extracts tested, with average MICs of 0.81, 0.83 and 0.84 mg/ml respectively. C. macrocephalum leaf extract was the most active against C. gloeosporioides with an MIC of 0.05 mg/ml. If extracts of these species do not have deleterious effects against plants infected by the fungi or the environment, it may be useful to protect organically grown crops.