Effect of neem leaf extract and neem oil on Penicillium growth, sporulation, morphology and ochratoxin A production

Genome analysis of Pseudomonas strain 4B with broad antagonistic activity against toxigenic fungi

Pseudomonas sp. 4B isolated from the effluent pond of a bovine abattoir was investigated as antifungal against toxigenic fungi. The complete genome of Pseudomonas 4B was sequenced using the Illumina MiSeq platform. Phylogenetic analysis and genome comparisons indicated that the strain belongs to the Pseudomonas aeruginosa group. In silico investigation revealed gene clusters associated with the biosynthesis of several antifungals, including pyocyanin, rhizomide, thanamycin, and pyochelin. This bacterium was investigated through antifungal assays, showing an inhibitory effect against all toxigenic fungi tested. Bacterial cells reduced the diameter of fungal colonies, colony growth rate, and sporulation of each indicator fungi in 10-day simultaneous growing tests. The co-incubation of bacterial suspension and fungal spores in yeast extract-sucrose broth for 48 h resulted in reduced spore germination. During simultaneous growth, decreased production of aflatoxin B1 and ochratoxin A by Aspergillus flavus and Aspergillus carbonarius, respectively, was observed. Genome analysis and in vitro studies showed the ability of P. aeruginosa 4B to reduce fungal growth parameters and mycotoxin levels, indicating the potential of this bacterium to control toxigenic fungi. The broad antifungal activity of this strain may represent a sustainable alternative for the exploration and subsequent use of its possible metabolites in order to control mycotoxin-producing fungi.

Comparative evaluation of physicochemical and antimicrobial properties of rubber seed oil from different regions of Bangladesh

In Bangladesh, the annual production of rubber seeds is typically left untapped although the seeds contained a high percentage of oil but underutilized without any value-added utilization. This study aims to evaluate the geographical effect on physicochemical properties, fatty acid composition and the antimicrobial activity of oil extracted from rubber seeds. Seeds were collected from three different regions of Bangladesh and the oil was extracted by the soxhlet method using n-hexane as a solvent. Results demonstrated that the geographical regions have some significant effect on the properties of rubber seed oil (RSO). The physicochemical properties of RSO varied from region to region. For example, the percent of yield, higher heating value, and flash point varied from 50.0 to 50.8 %, 31.8-33.3 kJ/g, and 237-245 °C, respectively. The chemical parameters, such as acid value, iodine value, and hydroxyl value varied from 13.3 to 18.2 mg KOH/g, 132-137 g I2/100g, and 47.7-55.8 mg KOH/g, respectively. Chromatographic analysis showed that RSO mainly contains palmitic, linoleic, linolenic, and stearic acid. Regional variations were also seen in the composition of these fatty acids. Most notably, regardless of the rubber seeds collected from various locations, RSO exhibited inhibitory activity against only gram positive bacteria. The zone of inhibition range for different tested gram positive bacteria was 2.33-11.17 mm irrespective of different RSO samples.

Antifungal Activity of Thymol against Aspergillus awamori and Botrytis aclada Isolated from Stored Onion Bulbs

The antifungal activity of thymol against Aspergillus awamori F23 and Botrytis aclada F15 in onions was examined through direct treatment with amended media and gaseous treatment with I-plates (plastic plates containing central partitions). The protective and curative control efficacy of thymol was examined 24 h before and after the inoculation of onion bulbs with the fungal isolates. Mycelial growth, sporulation, and spore germination of the isolates were inhibited on potato dextrose agar amended with various concentrations of thymol or acetic acid (positive control). Overall, thymol produced a stronger inhibitory effect on the mycelial growth and development of the isolates than acetic acid. Following gaseous treatment in I-plates, mycelial growth, sporulation, and spore germination of the isolates were inhibited at higher concentrations of thymol or acetic acid; however, acetic acid showed a little effect on the sporulation and spore germination of the isolates. Following the treatment of onion bulbs with 1000 mg L^-1 of thymol 24 h before and after fungal inoculation, lesion diameter was greatly reduced compared with that following treatment with 0.5% ethanol (solvent control). Onion bulbs sprayed with thymol 24 h before fungal inoculation generally showed reduced lesion diameters by isolate F23 but not in isolate F15 compared with those sprayed 24 h after fungal inoculation. Collectively, thymol effectively inhibited the growth and development of A. awamori and B. aclada on amended media and in I-plates. In addition, spraying or fumigation of thymol is more desirable for effectively controlling these postharvest fungal pathogens during long-term storage conditions.

New solutions using natural products

Most antibiotics are derived from natural products, like penicillin, as well as recent insecticides, like pyrethroids. Secondary metabolites are produced by plants as ecological chemical mediators, and can therefore possess intrinsic physiological properties against other organisms. These benefits are far from being fully explored. In particular, attention is here focused on the multipurpose neem tree (Azadirachta indica), reporting several experiments of applications in the field of seed oil and neem cake. The latter product seems to be promising because of the low cost, the possible production on a large scale, and the selection of effects in favor of beneficial organisms. Neem cake is able to act on different sites, as required by integrated pest management. Several utilizations of neem products are reported and their potentiality evidenced. Some considerations in this chapter may appear distant from the title of the book, but only by applying the general natural rules can the reason of the single phenomenon be understood. Other studies on resistance mechanisms of Plasmodium are enabling new possible methods of control always based on natural products activity.

Biological Control of Citrus Postharvest Phytopathogens

Citrus are vulnerable to the postharvest decay caused by Penicillium digitatum, Penicillium italicum, and Geotrichum citri-aurantii, which are responsible for the green mold, blue mold, and sour rot post-harvest disease, respectively. The widespread economic losses in citriculture caused by these phytopathogens are minimized with the use of synthetic fungicides such as imazalil, thiabendazole, pyrimethanil, and fludioxonil, which are mainly employed as control agents and may have harmful effects on human health and environment. To date, numerous non-chemical postharvest treatments have been investigated for the control of these pathogens. Several studies demonstrated that biological control using microbial antagonists and natural products can be effective in controlling postharvest diseases in citrus, as well as the most used commercial fungicides. Therefore, microbial agents represent a considerably safer and low toxicity alternative to synthetic fungicides. In the present review, these biological control strategies as alternative to the chemical fungicides are summarized here and new challenges regarding the development of shelf-stable formulated biocontrol products are also discussed.

Nontoxic concentrations of OTA aggravate DON-induced intestinal barrier dysfunction in IPEC-J2 cells via activation of NF-κB signaling pathway

Deoxynivalenol (DON) is well-known enteropathogenic mycotoxin which can alter intestinal barrier functions. Consistently, Ochratoxin A (OTA) ingestion has been found to induce intestinal injuries, including inflammation and diarrhea. However, little is known whether OTA aggravates DON-induced toxicity. This study is designed to explore the effects of OTA on DON-induced intestinal barrier function and involved mechanism. Our results showed either DON or OTA could disrupt intestinal barrier function in a time- and dose-dependent manner, as demonstrated by decreased transepithelial electrical resistance (TEER) and increased paracellular permeability to 4 kDa dextran. However, to eliminate the involvement of cell death, nonlethal concentrations of DON and OTA were used in following experiments. The nontoxic concentration of OTA was observed to aggravate DON-induced intestinal barrier dysfunction, accompanied with tight junction disruption (Claudin-3 and Claudin-4). Moreover, nontoxic concentrations of OTA aggravated DON-induced up-regulation of pro-inflammatory cytokines expression and activated nuclear factor-κB (NF-κB) in IPEC-J2 cells. Adding NF-κB inhibitor (PDTC) alleviated the aggravating effects of nontoxic concentrations of OTA on DON-induced intestinal barrier dysfunction and inflammation. These findings indicate that nontoxic concentrations of OTA promoted DON-induced barrier dysfunction via NF-κB signaling pathway. Our experiment suggests that exposure to nontoxic concentrations of toxins also poses potentially harmful effects.

Modelling the sporulation of some fungi associated with cheese, at different temperature and water activity regimes

The objectives of this study were to determine, in-vitro, the influence of temperature (T; 10-30 °C, step 5°), water activity (a_w, 0.83-0.99; step 0.04) and time on sporulation (SPO) of some cheese-related fungi belonging to Penicillium spp. and A. versicolor. Overall, sporulation started rapidly (8 h in optimal conditions); it was significantly influenced by T and a_w and the fungi studied were clearly distinguished based on their thermo-hydro adaptation. Boundary conditions for sporulation were defined for all the fungi considered and the sporulation rate was successfully modelled, especially based on T and time regimes. Penicillium crustosum, P. nordicum and P. verrucosum showed optimum for SPO at T between 20 and 25 °C and their sporulation continued up to a_w = 0.87 (a_w = 0.83 for P. nordicum). They resulted the fungi best adapted to the environmental conditions of ripening grana cheese storehouses; therefore, it is expected they dominate on the grana cheese surface. Studies on cheese are necessary to validate these results obtained on artificial media and without fungi co-occurrence.

Apoptotic activity and gene responses in Drosophila melanogaster S2 cells, induced by azadirachtin A

BACKGROUND

Azadirachtin has been used as an antifeedant and growth disruption agent for many insect species. Previous investigations have reported the apoptotic effects of azadirachtin on some insect cells, but the molecular mechanisms are still not clear. This study investigated the underlying molecular mechanisms for the apoptotic effects induced by azadirachtin on Drosophila melanogaster S2 cells in vitro.

RESULTS

The results of the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide assay demonstrated that azadirachtin exhibited significant cytotoxicity to S2 cells in a time- and dose-dependent manner. The changes in cellular morphology and the DNA fragmentation demonstrated that azadirachtin induced remarkable apoptosis of S2 cells. Expression levels of 276 genes were found to be significantly changed in S2 cells after exposure to azadirachtin, as detected by Drosophila genome array. Among these genes, calmodulin (CaM) was the most highly upregulated gene. Azadirachtin was further demonstrated to trigger intracellular Ca(2+) release in S2 cells. The genes related to the apoptosis pathway, determined from chip data, were validated by the real-time quantitative polymerase chain reaction method.

CONCLUSION

The results showed that azadirachtin-mediated intracellular Ca(2+) release was the primary event that triggered apoptosis in Drosophila S2 cells through both pathways of the Ca(2+) -CaM and EcR/Usp signalling cascade. © 2015 Society of Chemical Industry.

Inhibition of mycotoxin-producing fungi by Bacillus strains isolated from fish intestines

Bacillus strains isolated from the aquatic environment of the Brazilian Amazon region were tested for their activity against mycotoxigenic fungi. All tested bacteria showed antifungal activity, inhibiting at least 7 indicator fungi. Four Bacillus strains showing promising antifungal results were subsequently evaluated for their activity in reducing mycelial growth rate, sporulation, spore germination percentage, and mycotoxin production. Bacillus sp. P1 and Bacillus sp. P11 had a remarkable antifungal effect on toxigenic fungi. Washed bacterial cell suspension of strains P1 and P11 (10⁷CFU/ml) reduced by >70% the fungal colony diameters, including a complete inhibition of ochratoxin A (OTA) producing Aspergillus spp. Significant reduction of growth rate, sporulation and spore germination were also observed. The bacteria influenced the production of mycotoxins, causing a reduction around 99 and 97% in AFB1 and OTA concentration, respectively. Chromatographic analysis revealed the presence of lipopeptides (iturin A and surfactin isomers) in butanol extracts of cell-free supernatants and cell pellets of strains P1 and P11. Furthermore, antifungal activity of these extracts was confirmed against A. flavus A12 and A. carbonarius ITAL293, producers of AFB1 and OTA, respectively. These bacterial strains could be promising biocontrol agents against toxigenic fungi.

Inhibiting Microbial Toxins Using Plant-Derived Compounds and Plant Extracts

Many pathogenic bacteria and fungi produce potentially lethal toxins that cause cytotoxicity or impaired cellular function either at the site of colonization or other locations in the body through receptor-mediated interactions. Various factors, including biotic and abiotic environments, competing microbes, and chemical cues affect toxin expression in these pathogens. Recent work suggests that several natural compounds can modulate toxin production in pathogenic microbes. However, studies explaining the mechanistic basis for their effect are scanty. This review discusses the potential of various plant-derived compounds for reducing toxin production in foodborne and other microbes. In addition, studies highlighting their anti-toxigenic mechanism(s) are discussed.

Neem (Azadirachtaindica A. Juss) Oil: A Natural Preservative to Control Meat Spoilage

Plant-derived extracts (PDEs) are a source of biologically-active substances having antimicrobial properties. The aim of this study was to evaluate the potential of neem oil (NO) as a preservative of fresh retail meat. The antibacterial activity of NO against Carnobacterium maltaromaticum, Brochothrix thermosphacta, Escherichia coli, Pseudomonas fluorescens, Lactobacillus curvatus and L. sakei was assessed in a broth model system. The bacterial growth inhibition zone (mm) ranged from 18.83 ± 1.18 to 30.00 ± 1.00, as was found by a disc diffusion test with 100 µL NO. The bacterial percent growth reduction ranged from 30.81 ± 2.08 to 99.70 ± 1.53 in the broth microdilution method at different NO concentrations (1:10 to 1:100,000). Viable bacterial cells were detected in experimentally-contaminated meat up to the second day after NO treatment (100 µL NO per 10 g meat), except for C. maltaromaticum, which was detected up to the sixth day by PCR and nested PCR with propidium monoazide (PMA™) dye. In comparison to the previously published results, C. maltaromaticum, E. coli, L. curvatus and L. sakei appeared more susceptible to NO compared to neem cake extract (NCE) by using a broth model system.

Fabrication and Antifungal Activity of Cellulose Acetate-Based Fibers Encapsulating Natural Neem Seed Oil

Due to an attempt to increase the economic value of Thai neem (Azadirachta indica A. Juss. var. siamensis Valeton) as well as a concern on biosafety and environmental friendliness of a material that can be used for shelf-life extension of foods and perishable crops, this work was conducted to evaluate the antifungal property of NSO (NSO) and to fabricate and investigate the antifungal activity of NSO encapsulated in bio-based fibrous films. Natural cold-pressed NSO was first stabilized in micelles structure of sodium dodecyl sulfate (SDS) and then embedded in a composite matrix of cellulose acetate (CA) and poly (ethylene oxide) (PEO) via needleless electrospinning technique. The effects of SDS and NSO ratios in the electrospinning solution on the micelles size distribution, which in turn influenced the morphology of the e-spun fibers and payload of the encapsulated NSO, were investigated. Morphology of the fiber samples was examined via scanning electron microscopy (SEM). Fibrous films were selected to test for their in vivo antifungal property with wounded-inoculated and healthy tomatoes; Alternaria alternata was chosen as a tested fungus. As indicated by SEM images, an average fiber diameter was 900 nm. The results also showed that as the NSO ratio increased, the fibers tended to exhibit rice-grain-on-string microstructure. Electrospun fibrous film containing 50% NSO exhibited antifungal effect on wounded-inoculated tomatoes at a utilized weight ratio of the film to tomato of 125 mg film/1 kg tomato (in a 100% relative humidity controlled closed chamber).