吸水链霉菌BS-112产生的抗真菌活性物质的分离纯化与结构鉴别

【目的】分离纯化吸水链霉菌(Streptomyces hygroscopicus)BS-112产生的抗真菌活性物质,究明各活性组分的结构,测定其对黄曲霉的抑制作用,为该菌株及其产生的抗真菌活性物质的应用提供依据。【方法】通过大孔吸附树脂柱层析、硅胶柱层析及制备HPLC等方法,对该菌株产生的抗真菌活性物质进行分离纯化;利用质谱(MS)和核磁共振谱(NMR)解析各活性组分的结构;采用微量液体稀释法测定各活性组分对黄曲霉的最小抑菌浓度(MIC)和最小杀菌浓度(MFC)。【结果】从BS-112菌株发酵液中分离获得4个抗真菌活性组分,利用波谱技术确定其结构分别为Tetrins A和B、Tetramycins A和B。96孔板法测得这4个化合物对黄曲霉的MIC分别为3.13μg/mL、12.56μg/mL、1.56μg/mL、6.25μg/mL,MFC分别为6.25μg/mL、25.0μg/mL、3.13μg/mL、12.56μg/mL。【结论】BS-112菌株产生的抗真菌活性物质由Tetrins A和B、Ttramycins A和B 4个化合物组成,它们对黄曲霉均具有良好的抑制作用。     

Pyrrolnitrin Production by Biological Control Agent Pseudomonas cepacia B37w in Culture and in Colonized Wounds of Potatoes

Bacterial strain B37w (= NRRL B-14858), an isolate noteworthy because it inhibits the growth of the bioherbicide fungus Colletotrichum truncatum, was selected for further studies of bacterial antifungal properties. This isolate was identified as a Pseudomonas cepacia strain by performing carbohydrate utilization and fatty acid profile analyses, as well as other biochemical and physiological tests. Petri plate assays revealed that strain B37w exhibited antifungal activity against the potato dry rot fungus Fusarium sambucinum. Using bioautography, we correlated antifungal activity with production of a specific compound. Isolation from strain B37w and identification of the antifungal antibiotic pyrrolnitrin are described. A whole-potato assay revealed B37w's ability to colonize potato wounds. Wounded potatoes were inoculated with B37w, and pyrrolnitrin was detected in these potatoes by thin-layer chromatography-bioautography at a concentration on the order of nanograms per wound. We performed an assay in which we examined efficacy against F. sambucinum-incited potato dry rot and found that B37w inhibited disease development. This is the first report of P. cepacia or pyrrolnitrin activity against the economically important potato pathogen F. sambucinum.     

In vitro development and transfer of resistance to chlortetracycline in Bacillus subtilis

The present criteria and rules controlling the approval of the use of probiotics are limited to antibiotic resistance patterns and the presence of antibiotic resistance genes in bacteria. There is little information available in the literature regarding the risk of the usage of probiotics in the presence of antibiotic pressure. In this study we investigated the development and transfer of antibiotic resistance in Bacillus subtilis selected in vitro by chlortetracycline in a stepwise manner. Bacillus subtilis was exposed to increasing concentrations of chlortetracyclineto induce in vitro resistance to chlortetracycline, and the minimal inhibitory concentrations were determinedfor the mutants. Resistant B. subtilis were conjugated with Escherichia coli NK5449 and Enterococcus faecalis JH2-2 using the filter mating. Three B. subtilis tetracycline resistant mutants (namely, BS-1, BS-2, and BS-3) were derived in vitro. A tetracycline resistant gene, tet (K), was found in the plasmids of BS-1 and BS-2. Three conjugates (BS-1N, BS-2N, and BS-3N) were obtained when the resistant B. subtilis was conjugated with E. coli NK5449. The conjugation frequencies for the BS-1N, BS-2N, and BS-3N conjugates were 4.57×10^?7, 1.4×10^?7, and 1.3×10^?8, respectively. The tet(K) gene was found only in the plasmids of BS-1N. These results indicate that long-term use of probiotics under antibiotic selection pressure could cause antibiotic resistance, and the resistance gene could be transferred to other bacteria. The risk arising from the use of probiotics under antibiotic pressure should be considered in the criteria and rules for the safety assessment of probiotics.     

Isolation of Bacterial Antagonists of Aspergillus flavus from Almonds

Bacteria were isolated from California almond orchard samples to evaluate their potential antifungal activity against aflatoxin-producing Aspergillus flavus. Fungal populations from the same samples were examined to determine the incidence of aflatoxigenic Aspergillus species. Antagonistic activities of the isolated bacterial strains were screened against a nonaflatoxigenic nor mutant of A. flavus, which accumulates the pigmented aflatoxin precursor norsolorinic acid (NOR) under conditions conducive to aflatoxin production. Using solid and liquid media in coculture assays, 171 bacteria isolated from almond flowers, immature nut fruits, and mature nut fruits showed inhibition of A. flavus growth and/or inhibition of NOR accumulation. Bacterial isolates were further characterized for production of extracellular enzymes capable of hydrolyzing chitin or yeast cell walls. Molecular and physiological identification of the bacterial strains indicated that the predominant genera isolated were Bacillus, Pseudomonas, Ralstonia, and Burkholderia, as well as several plant-associated enteric and nonenteric bacteria. A set of 20 isolates was selected for further study based on their species identification, antifungal phenotypes, and extracellular enzyme production. Quantitative assays using these isolates in liquid coculture with a wild-type, aflatoxin-producing A. flavus strain showed that a number of strains completely inhibited fungal growth in three different media. These results indicate the potential for development of bacterial antagonists as biological control agents against aflatoxigenic aspergilli on almonds.     

Lactobacillus coryniformis subsp. coryniformis Strain Si3 Produces a Broad-Spectrum Proteinaceous Antifungal Compound

The antifungal activity spectrum of Lactobacillus coryniformis subsp. coryniformis strain Si3 was investigated. The strain had strong inhibitory activity in dual-culture agar plate assays against the molds Aspergillus fumigatus, A. nidulans, Penicillium roqueforti, Mucor hiemalis, Talaromyces flavus, Fusarium poae, F. graminearum, F. culmorum, and F. sporotrichoides. A weaker activity was observed against the yeasts Debaryomyces hansenii, Kluyveromyces marxianus, and Saccharomyces cerevisiae. The yeasts Rhodotorula glutinis, Sporobolomyces roseus, and Pichia anomala were not inhibited. In liquid culture the antifungal activity paralleled growth, with maximum mold inhibition early in the stationary growth phase, but with a rapid decline in antifungal activity after 48 h. The addition of ethanol to the growth medium prevented the decline and gave an increased antifungal activity. The activity was stable during heat treatment and was retained even after autoclaving at 121°C for 15 min. Maximum activity was observed at pH values of between 3.0 and 4.5, but it decreased rapidly when pH was adjusted to a level between 4.5 and 6.0 and was lost at higher pH values. The antifungal activity was fully regained after readjustment of the pH to the initial value (pH 3.6). The activity was irreversibly lost after treatment with proteolytic enzymes (proteinase K, trypsin, and pepsin). The antifungal activity was partially purified using ion-exchange chromatography and (NH₄)₂SO₄ precipitation, followed by gel filtration chromatography. The active compound(s) was estimated to have a molecular mass of approximately 3 kDa. This is the first report of the production of a proteinaceous antifungal compound(s) from L. coryniformis subsp. coryniformis.     

The inhibitory effect of Bacillus megaterium on aflatoxin and cyclopiazonic acid biosynthetic pathway gene expression in Aspergillus flavus

Aspergillus flavus is one of the major moulds that colonize peanut in the field and during storage. The impact to human and animal health, and to the economy in agriculture and commerce, is significant since this mold produces the most potent known natural toxins, aflatoxins, which are carcinogenic, mutagenic, immunosuppressive, and teratogenic. A strain of marine Bacillus megaterium isolated from the Yellow Sea of East China was evaluated for its effect in inhibiting aflatoxin formation in A. flavus through down-regulating aflatoxin pathway gene expression as demonstrated by gene chip analysis. Aflatoxin accumulation in potato dextrose broth liquid medium and liquid minimal medium was almost totally (more than 98 %) inhibited by co-cultivation with B. megaterium. Growth was also reduced. Using expression studies, we identified the fungal genes down-regulated by co-cultivation with B. megaterium across the entire fungal genome and specifically within the aflatoxin pathway gene cluster (aflF, aflT, aflS, aflJ, aflL, aflX). Modulating the expression of these genes could be used for controlling aflatoxin contamination in crops such as corn, cotton, and peanut. Importantly, the expression of the regulatory gene aflS was significantly down-regulated during co-cultivation. We present a model showing a hypothesis of the regulatory mechanism of aflatoxin production suppression by AflS and AflR through B. megaterium co-cultivation.     

Evaluation of (4-aminobutyloxy)quinolines as a novel class of antifungal agents

Antifungal assessment of eighteen 5-, 6- and 8-(4-aminobutyloxy)quinolines revealed a significant susceptibility of the tested fungi and yeast strains (Candida albicans, Rhodotorula bogoriensis, Aspergillus flavus and Fusarium solani) toward different halo-substituted 8-(4-aminobutyloxy)quinolines. The six most potent compounds displayed antifungal activities similar to those of established antifungal agents such as Amphotericin B, Fluconazole and Itraconazole, and one representative also showed a promising broad-spectrum antifungal profile. The introduction of an aminoalkoxy side chain at the 8-position of a halo-substituted quinoline core might thus provide a new class of lead structures in the search for novel antifungal agents.     

Antifungal activity in vitro of Baccharis glutinosa and Ambrosia confertiflora extracts on Aspergillus flavus, Aspergillus parasiticus and Fusarium verticillioides

The aims of this study were to evaluate the antifungal properties of Baccharis glutinosa and Ambrosia confertiflora extracts against Aspergillus flavus, A. parasiticus and Fusarium verticillioides, and to isolate the group of compounds that are responsible for the antifungal activity. Samples of aerial parts from each plant were extracted with 70% methanol and sequentially partitioned with hexane, ethyl acetate, and n-butanol. The partitioned fractions were evaluated in their capacity to inhibit the radial growth of the three species of fungi. The active fraction was used for an assay-guided chromatography of antifungal extracts. The results showed that the extract from B. glutinosa partitioned in ethyl acetate (Bea) showed the highest antifungal activity against the three fungi. Bea completely inhibited the growth of F. verticillioides at 0.8 mg/ml, whereas the radial growth of A. flavus and A. parasiticus was inhibited 70% at 1.5 mg/ml. The purified antifungal fraction from Bea showed 72, 54, and 52% of antifungal activity, respectively.     

Effect of essential oil from fresh leaves of Ocimum gratissimum L. on mycoflora during storage of peanuts in Benin

The aim of this study was to evaluate the effect of essential oil from fresh leaves of Sweet Fennel (Ocimum gratissimum) on mycoflora and Aspergillus section Flavi populations in stored peanuts. Aspergillus, Fusarium and Mucor spp. were the most common genera identified from peanuts at post-harvest in Benin by using a taxonomic schemes primarily based on morphological characters of mycelium and conidia. The isolated fungi include Aspergillus niger, A. parasiticus, A. flavus, A. ochraceus, Fusarium graminearum, F. solani, F. oxysporum and Mucor spp. The most prevalent fungi recorded were A. niger (94.18 %), A. flavus (83.72 %), A. parasiticus (77.90 %), A. ochraceus (72.09 %), F. graminearum (59.30 %) and F. oxysporum (51.16 %). Antifungal assay, performed by the agar medium assay, indicated that essential oil exhibited high antifungal activity against the growth of A. flavus, A. parasiticus, A. ochraceus and F. oxysporium. The minimal inhibitory concentration (MIC) of the essential oil was found to be 7.5 μl/ml for A. flavus and A. parasiticus and 5.5 μl/ml for A. ochraceus and F. oxysporium. The minimal fungicidal concentration (MFC) was recorded to be 8.0 μl/ml for A. flavus and A. parasiticus, 6,5 μl/ml for A. ochraceus and 6.0 μl/ml for F. oxysporium. The essential oil was found to be strongly fungicidal and inhibitory to aflatoxin production. Chemical analysis by GC/MS of the components of the oil led to the identification of 31 components characterized by myrcene (6.4 %), α-thujene (8.2 %), p-cymene (17.6 %), γ-terpinene (20.0 %), and thymol (26.9 %) as major components. The essential oil of Sweet Fennel, with fungal growth and mycotoxin inhibitory properties, offers a novel approach to the management of storage, thus opening up the possibility to prevent mold contamination in stored peanuts.     

Identification and characterization of a novel Bacillus subtilis strain with potent antifungal activity of a flagellin-like protein

The filamentous fungus Botrytis cinerea is an important agricultural pathogen affecting a wide range of cultivated plants. Since World War II, chemical fungicides have been the go-to method for agricultural pathogen control. However, the potential adverse environmental and health effects of these chemicals have led to an increasing demand for alternative methods of pathogen control, including biological control agents. In this study, we identified a bacterial isolate with strong antagonistic activity against B. cinerea. An analysis of the 16S rRNA gene sequence for this isolate identified it as a novel strain of Bacillus subtilis. Culture media from this isolate were harvested and fractionated using ion exchange and gel filtration chromatography. The fraction exhibiting the highest level of antifungal activity was identified, and its sequence determined by electrospray tandem mass spectrometry had significant similarity to flagellin. This flagellin-like protein was exogenously expressed in Escherichia coli, and screened for antifungal activity against B. cinerea. This flagellin-like protein demonstrated clear antifungal activity of inhibiting B. cinerea growth.     

Biocontrol of toxinogenic Aspergillus flavus and Fusarium oxysporum f. sp. albedinis by two rare Saharan actinomycetes strains and LC-ESI/MS-MS profiling of their antimicrobial products

Fungi colonizing fruits in the field and post-harvest constitute a major threat to the global food sector. This study focuses on the biocontrol of Aspergillus flavus (aflatoxin-producing mold considered carcinogenic by IARC) and Fusarium oxysporum f. sp. albedinis (FOA) (phytopathogenic agent, causal of El Bayoud in the Algerian and Moroccan Sahara). These molds have a significant economic impact and pose a serious human health problem. The aim of this work is to study the antifungal activity of two rare actinomycetes strains; Saccharothrix sp. COL22 and Actinomadura sp. COL08 strains against toxinogenic A. flavus and F. oxysporum f. sp. albedinis. The strains are isolated from Citrullus colocynthis rhizosphere on different media: ISP2, GLM, TSA, Starch-casein-agar and WYE and with different treatments of the samples (physical, chemical treatment and enrichment). The antifungal tests against the pathogenic microorganisms were performed on ISP2, GLM and TSA medium by means of the agar cylinders method. The kinetics of antibiotic production were performed on ISP medium over 16 days. The characterization of the antimicrobial compounds by LC-ESI/MS-MS showed that the bacterial extracts contain Antibiotic SF 2738C, Tetrodecamycin and Aplysillamide B. The phenotypic and molecular studies showed that Saccharothrix sp. COL22 is closely related to the Saccharothrix longispora strain type and that Actinomadura sp. COL08 is closely related to the Actinomadura hibisca strain type. The two strains are rare and showed an interesting activity against toxinogenic A. flavus and F. oxysporum f. sp. albedinis.     

三色拟迷孔菌Daedaleopsis tricolor抗真菌活性成分的研究

在对多孔菌发酵产物进行的活性筛选中,发现三色拟迷孔菌具有抗白假丝酵母、酿酒酵母、烟曲霉、黄曲霉等目标真菌活性。通过应用萃取、柱层析及HPLC等分离手段对其活性组分进行分离纯化,共获得3个化合物。根据波谱数据,化合物1-3的结构分别被鉴定为4-乙二醇基-8-羟基异香豆素、4- (2-羟乙酰基)-8-羟基异香豆素及4-乙二醇基-5,8-二羟基异香豆素。这3个异香豆素首次从拟迷孔菌属中分离得到,且化合物2为其活性成分。     

三色拟迷孔菌Daedaleopsis tricolor抗真菌活性成分的研究

在对多孔菌发酵产物进行的活性筛选中,发现三色拟迷孔菌具有抗白假丝酵母、酿酒酵母、烟曲霉、黄曲霉等目标真菌活性。通过应用萃取、柱层析及HPLC等分离手段对其活性组分进行分离纯化,共获得3个化合物。根据波谱数据,化合物1-3的结构分别被鉴定为4-乙二醇基-8-羟基异香豆素、4- (2-羟乙酰基)-8-羟基异香豆素及4-乙二醇基-5,8-二羟基异香豆素。这3个异香豆素首次从拟迷孔菌属中分离得到,且化合物2为其活性成分。     

Isolation and identification of antifungal peptides from Bacillus BH072, a novel bacterium isolated from honey

A bacterial strain BH072 isolated from a honey sample showed antifungal activity against mold. Based on morphological, biochemical, physiological tests, and analysis of 16S rDNA sequence, the strain was identified to be a new subspecies of Bacillus sp. It had a broad spectrum of antifungal activity against various mold, such as Aspergillus niger, Pythium, and Botrytis cinerea. Six pairs of antifungal genes primers were designed and synthesized, and ituA, hag, tasA genes were detected by PCR analysis. The remarkable antifungal activity could be associated with the co-production of these three peptides. One of them was purified by 30–40% ammonium sulfate precipitation, Sephadex G-75 gel filtration and anion exchange chromatography on D201 resin. The purified peptide was estimated to be 35.615 kDa and identified to be flagellin by micrOTOF-Q II. By using methanol extraction, another substance was isolated from fermentation liquor, and determined to be iturin with liquid chromatography–mass spectrometry (LC–MS) method. The third possible peptide encoded by tasA was not isolated in this study. The culture liquor displayed antifungal activity in a wide pH range (5.0–9.0) and at 40–100 °C. The result of the present work suggested that Bacillus BH072 might be a bio-control bacterium of research value.     

The major volatile compound 2-phenylethanol from the biocontrol yeast,Pichia anomala,inhibits growth and expression of aflatoxin biosynthetic genes of Aspergillus flavus

Aspergillus flavus is a ubiquitous saprophyte that is able to produce the most potent natural carcinogenic compound known as aflatoxin B₁ (AFB₁). This toxin frequently contaminates crops including corn, cotton, peanuts, and tree nuts causing substantial economic loss worldwide. Consequently, more than 100 countries have strict regulations limiting AFB₁ in foodstuffs and feedstuffs. Plants and microbes are able to produce volatile compounds that act as a defense mechanism against other organisms. Pichia anomala strain WRL-076 is a biocontrol yeast currently being tested to reduce AF contamination of tree nuts in California. We used the SPME-GC/MS analysis and identified the major volatile compound produced by this strain to be 2-phenylethanol (2-PE). It inhibited spore germination and AF production of A. flavus. Inhibition of AF formation by 2-PE was correlated with significant down regulation of clustering AF biosynthesis genes as evidenced by several to greater than 10,000-fold decrease in gene expression. In a time-course analysis we found that 2-PE also altered the expression patterns of chromatin modifying genes, MYST1, MYST2, MYST3, gcn5, hdaA and rpdA. The biocontrol capacity of P. anomala can be attributed to the production of 2-PE, which affects spore germination, growth, toxin production, and gene expression in A. flavus.     

Expression of Paenibacillus polymyxa β-1,3-1,4-glucanase in Streptomyces lydicus A01 improves its biocontrol effect against Botrytis cinerea

Streptomyces lydicus strain A01, which can produce natamycin and chitinase, has a significant inhibition effect on gray mold disease caused by Botrytis cinerea. However, it has no detectable glucanase activity. Strain A21 isolated from the snow covered high altitude area in Tibet, China, also has a high antagonistic activity against B. cinerea. It displayed an obvious halo on lichen polysaccharides plates by congo red staining, indicating a strong glucanase activity. A21 was identified as Paenibacillus polymyxa using 16S rDNA gene analysis and biochemical and physiological analysis. To obtain the synergistic antifungal effects of natamycin, chitinase, and glucanases on B. cinerea, this study transformed the β-1,3-1,4-glucanase gene from P. polymyxa A21 to S. lydicus A01. The engineered S. lydicus AG01 showed substantially high glucanase activity, and had similar natamycin production and chitinase activity as the wild-type strain A01. Compared to the wild-type strain A01, the antifungal effects of S. lydicus AG01 on B. cinerea, including inhibition of spore germination and mycelial growth, were highly improved. The improved biocontrol effect of S. lydicus AG01 is likely attributed to the heterologous expression of glucanase from P. polymyxa, which acted synergistically with natamycin and chitinase to increase the antifungal activity of the strain.     

Purification of an antifungal compound,cyclo(l-Pro-d-Leu) for cereals produced by Bacillus cereus subsp. thuringiensis associated with entomopathogenic nematode

Mold spoilage is the main cause of substantial economic loss in cereals and might also cause public health problems due to the production of mycotoxins. The aim of this study was to separate and purify and to identify antifungal compounds of bacterium associated with novel entomopathogenic nematode and check the antifungal property of identified compound in particular food model systems. The antifungal compound was purified using silica gel column chromatography, TLC and HPLC and its structure was elucidated using NMR (¹H NMR, ¹³C NMR, ¹H–¹H COSY, ¹H–¹³C HMBC), HRMS and Marfey's method. Based on the spectral data, the active compounds were identified as diketopiperazine [cyclo(l-Pro-d-Leu)]. The antifungal activity of cyclo(l-Pro-d-Leu) was studied by MIC and paper disk assay against Aspergillus flavus MTCC 277 and Aspergillus niger MTCC 282 and best MIC value of 8 μg/ml was recorded against A. flavus. Cyclo(l-Pro-d-Leu) strongly inhibit mycelia growth of fungus and thereby affecting aflatoxin production. To investigate the potential application of the cyclo(l-Pro-d-Leu) and to eliminate fungal spoilage in food and feed, soybean and peanut were used as models. White mycelia and dark/pale green spores of A. flavus were observed in the control soybeans after 2-day incubation. However the fungal growth was not observed in soybeans treated with cyclo(l-Pro-d-Leu). Almost the same result was observed for peanuts treated with cyclo(l-Pro-d-Leu) for A. niger. The cyclo(l-Pro-d-Leu) was nontoxic to two normal human cell lines (FS normal fibroblast and L231 lung epithelial) up to 200 μg/ml. Thus the diketopiperazine derivative identified in the study may be a promising alternative to chemical preservatives as a potential biopreservative which prevent fungal growth and mycotoxin formation in food and feed.     

Lethal destructive sinusopathy due to amphotericin B-resistant Aspergillus flavus: A case report

BackgroundThe prevalence of pulmonary aspergillosis and the importance of its early diagnosis are recognized. However, non-pulmonary involvement, including the sinuses region, is not frequently reported, and an infection in this area can affect all paranasal sinuses (pansinusopathy), being a rare pathology that affects immunocompromised hosts. Recent studies have highlighted the occurrence of Aspergillus flavus resistant to antifungal therapy. Therefore, a nasal sinus infection by resistant Aspergillus strains in immunocompromised patients may be linked to a high risk of lethality.Case reportWe are reporting a resistant A. flavus infection in an allogeneic hematopoietic stem cell transplant recipient with episodes of febrile neutropenia, and prolonged use of various antibacterial drugs and antifungal prophylaxis. The patient underwent brain magnetic resonance, which showed the presence of pansinusopathy, and presented necrosis in the left nasal region. Direct microscopic examination of a sample taken from the nasal mucosa revealed the presence of septate hyphae and conidiophores resembling those of A. flavus, that species being the identification achieved with MALDI-TOF MS. Antifungigram was performed by microdilution in broth (EUCAST-E.DEF. 9.3.2) and E-test, and resistance to amphotericin B was shown in both tests. The patient died after septic shock and hemorrhage.ConclusionsInvasive fungal infections due to amphotericin-B resistant A. flavus may lead to the death of the patient due to an ineffective therapeutic management. Therefore, antifungal susceptibility testing are of utmost importance for administering the proper treatment.     

Lactic acid bacteria against post-harvest moulds and ochratoxin A isolated from stored wheat

A total of 54 lactic acid bacteria (LAB) were isolated from stored wheat samples sourced from grain silos in North Tunisia. Fifteen representative isolates were identified by 16S rDNA sequencing as Pediococcus pentosaceus, Lactobacillus plantarum, Lactobacillus graminis, Lactobacillus coryniformis and Weissella cibaria. These isolates were screened for antifungal activity in dual culture agar plate assay against eight post-harvest moulds (Penicillium expansum, Penicillium chrysogenum, Penicillium glabrum, Aspergillus flavus, Aspergillus niger, Aspergillus carbonarius, Fusarium graminearum and Alternaria alternata). All LAB showed inhibitory activity against moulds, especially strains of L. plantarum which exhibited a large antifungal spectrum. Moreover, LAB species such as L. plantarum LabN10, L. graminis LabN11 and P. pentosaceus LabN12 showed high inhibitory effects against the ochratoxigenic strain A. carbonarius ANC89. These LAB were also investigated for their ability to reduce A. carbonarius ANC89 biomass and its ochratoxin A (OTA) production on liquid medium at 28 and 37 °C and varied pH conditions. The results indicated that factors such as temperature, pH and bacterial biomass on mixed cultures, has a significant effect on fungal inhibition and OTA production. High percentage of OTA reduction was obtained by L. plantarum and L. graminis (>97%) followed by P. pentosaceus (>81.5%). These findings suggest that in addition to L. plantarum, L. graminis and P. pentosaceus strains may be exploited as a potential OTA detoxifying agent to protect humans and animals health against this toxic metabolite.     

Screening the antifungal activity of essential oils against decay fungi from palmyrah leaf handicrafts

Background

The whitish tender leaves of Palmyrah are used for making handicrafts. The problem with these articles is discolouration with time and become more brittle due to fungal attack. This could be prevented by some protective coating. Instead of expensive and harmful chemicals we decided to test natural plant essential oils to control fungal attack. Palmyrah leaf article decay fungi were isolated from two different sites of Jaffna peninsula. In this investigation Antifungal Activity of different plant essential oils from neem (Azadirachta indica), castor (Ricinus communis), citronella (Cymbopogon sp) and camphor (Cinnamomum camphora) obtained from local market have been evaluated against isolated fungi. For screening of Antifungal activity, tests and controls were set to determine minimum inhibitory concentration (MIC) and Percentage of Growth Inhibition.

Results

Morphologically three different types of Palmyrah leaf decay fungi were isolated and characterized as Aspergillus niger, Aspergillus flavus and Penicillium sp. Neem and castor oils have recorded no significant (0.05 > P) antifungal activity while citronella and camphor oils showed significantly different antifungal activity compared with control. Camphor oil and Citronella oil showed 100, 58.13% of average growth inhibition for A. niger. 96.38, 51.32% for A.flavus and 84.99, 72.76% for Penicillium sp respectively. Camphor oil showed highest percentage of growth inhibition at lowest minimum inhibitory concentration compared with citronella oil. Camphor oil was found to be highly antifungal and most effective against A niger, and A. flavus, compared with Penicillium sp and gave 100 percentage of growth inhibitions at 5, 1 and 15 ml/dl minimum inhibitory concentration respectively.

Conclusion

Significantly higher broad-spectrum of antifungal activity was observed in camphor oil than other tested oils because it showed highest percentage of growth inhibition at lowest inhibitory concentration. Therefore it could be used for the development of new environmental friendly antifungal agent for the preservation of leafy handicrafts. Further formulation, field experiments are necessary to achieve this target.