The antimicrobial activity of five novel SQ109 derivatives including SQ109 against bacteria, yeast and filamentous fungi is reported herein. Using broth microdilution techniques, compounds 2 and 3 were found to be active against most tested fungi and bacteria, with minimum inhibitory concentrations (MICs) ranging from 0.98 to 31 lg ml -1 , except for Klebsiella pneumonia where the MIC was 250 lg ml -1 . SQ109 and derivative 4 did not show any significant activity against most of the organisms used. However, their reduced derivatives 1 and 5 showed promising activity with MICs between 0.49 and 62.5 lg ml -1 against most of the microorganisms used.
Aspergillus flavus is a cosmopolitan fungal pathogen that is often implicated in food spoilage and in aspergillosis infections in immunocompromised individuals. The current study was undertaken to assess the effect of aqueous bulb extracts of Tulbaghia violacea on A. flavus spore survival. The broth dilution assay was used to determine that the minimum inhibitory concentration (MIC) of the extract against A. flavus was 15 mg/mL and that the minimum fungicidal concentration (MFC) was 20 mg/mL. During well diffusion assays A. flavus was inhibited by a minimal extract concentration of 60 mg/mL. As expected, inhibition zones during well diffusion assays increased with increasing extract concentrations. The 2,3‐bis(2‐methoxy‐4‐nitro‐5‐sulfophenyl)‐5‐([phenylamino] carbonyl)‐2H‐tetrazolium hydroxide (XTT) assay showed a direct proportional decrease in metabolic activity of A. flavus with an increase in extract concentration. Inhibition of metabolic activity was quantifiable as early as 12 h after spore inoculation. This was in contrast to the broth dilution assay where inhibition only became clearly observable 48 h after spore inoculation. The antifungal nature of T. violacea aqueous bulb extracts against A. flavus 2527 shown here for the first time indicates a potential use of this extract as an effective antifungal agent against Aspergillus species. The extract could possibly be used in the future for reducing Aspergillus contamination of plant‐derived foods. PRACTICAL APPLICATIONS Tulbaghia violacea (wild garlic) is a well‐known, indigenous ornamental plant in South Africa whose biological activities including a reduction in blood pressure has been previously documented. It is often eaten by African people for alleviating symptoms of high blood pressure including headaches. The plant is therefore safe to consume and appears to have no toxicological effects. With an ever‐increasing population and increasing cost of maintaining a constant and effective food supply, the natural antifungal agents found in aqueous extracts of T. violacea may provide an inexpensive means of reducing food spoilage by Aspergillus spp.
The broad spectrum activity and the efficacy of aqueous T. violacea plant extract on both β-glucan and chitin synthesis may limit the potential of the fungus developing resistance towards it and therefore the extract is an ideal candidate for use as a potential antifungal agent.
Aspergillus flavus and Aspergillus parasiticus are important plant pathogens and causal agents of pre- and postharvest rots of corn, peanuts, and tree nuts. These fungal pathogens cause significant crop losses and produce aflatoxins, which contaminate many food products and contribute to liver cancer worldwide. Aqueous preparations of Tulbaghia violacea (wild garlic) were antifungal and at 10 mg/ml resulted in sustained growth inhibition of greater than 50% for both A. flavus and A. parasiticus. Light microscopy revealed that the plant extract inhibited conidial germination in a dose-dependent manner. When exposed to T. violacea extract concentrations of 10 mg/ml and above, A. parasiticus conidia began germinating earlier and germination was completed before that of A. flavus, indicating that A. parasiticus conidia were more resistant to the antifungal effects of T. violacea than were A. flavus conidia. At a subinhibitory extract dose of 15 mg/ml, hyphae of both fungal species exhibited increased granulation and vesicle formation, possibly due to increased reactivity between hyphal cellular components and T. violacea extract. These hyphal changes were not seen when hyphae were formed in the absence of the extract. Transmission electron microscopy revealed thickening of conidial cell walls in both fungal species when grown in the presence of the plant extract. Cell walls of A. flavus also became considerably thicker than those of A. parasiticus, indicating differential response to the extract. Aqueous preparations of T. violacea can be used as antifungal treatments for the control of A. flavus and A. parasiticus. Because the extract exhibited a more pronounced effect on A. flavus than on A. parasiticus, higher doses may be needed for control of A. parasiticus infections.
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