Antimicrobial activity of fungal secondary metabolites isolated from pearl millet on gut microflora
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Date
2022
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University of Namibia
Abstract
Pearl millet also known as mahangu in Namibia is a crop commonly found regions in the Northern part of Namibia such as Zambezi and Ohangwena region. Pearl millet is a common staple food of a certain percentage of Namibians. Traditional methods used for processing millet comprise of threshing, cleaning, washing, soaking, germination, wet and dry milling and fermentation. The fungal species gain access to grain matrices, depending on the type of environmental conditions certain secondary metabolites are generated this may occur during the pre-harvest, storage, transportation, processing, and marketing stages. Hazardous secondary metabolites with antimicrobial properties for instance polyketide, non-ribosomal peptides, alkaloids, and terpenes are produced by fungi and can cause food poisoning and possibly affect the microflora in the gut. It is important to identify and document whether fungi that produce antimicrobial secondary metabolites are present in mahangu that may affect the microflora. Even though sophisticated machinery exist, traditional methods of food storage and preparation are still being used in certain parts of the country. These traditional methods are seldom done in unhygienic conditions resulting in contamination of the food. The effect of food poisoning by fungi in Namibia is unknown, to the best of my knowledge there are fewer studies in Namibia that focused on the effect of antimicrobial fungi secondary metabolites on the microflora found in the gut. For this reason this study focused on isolating fungal species from pearl millet and testing their antimicrobial ability on four gut microflora E. coli ATCC 33849, K. pneumoniae ATCC BAA- 2146, L. monocytogenes and L. plantarum ATCC 8014. The pearl millet was bought from the local market and serial dilution was performed using distilled water. The solution of pearl millet with a dilution of 1:100 000 was plated on Sabouraud Dextrose Agar, it was then sub cultured until pure fungal isolates was obtained. Fungi were identified on the basis of colony characteristics and microscopic examinations. The following six types of fungi were identified Aspergillus flavus, Aspergillus niger, Saccharomyces sp., Rhodotorula sp., Trichosporon sp. and Saccharomyces sp. Ethyl acetate was used for extraction of the secondary metabolites and agar well diffusion was used to test for ii antimicrobial activity. Then Minimum Inhibitory Concentration was carried out only with fungi which produced zones of inhibition against the selected bacteria, lastly Minimum Bactericidal Concentration was carried out. The analytic test used showed that there was a significant difference in the antimicrobial activity among different fungal species p= 0.019. The fungus A. niger did not show any form of antimicrobial activity while Saccharomyces sp. showed the highest inhibitory effects with a mean value of 12.16 ± 0.21. The fungus A. flavus showed more inhibitory activity against the following bacterial strain L. plantarum, L. monocytogenes and K. pneumoniae at 7.5 mg/ml when MIC was carried out. The extract from A. flavus was the only extract exhibiting bactericidal effects and this was seen against K. pneumoniae and L. plantarum. It is evident that gut microflora can be affected by secondary metabolites of fungi from pearl millet which can lead to detrimental effects in humans. Further studies are required to detect secondary metabolites that could cause harm to the gut microflora also what dosage level is required to cause an effect in vivo on gut microflora.
Description
A mini thesis submitted in partial fulfilment of the requirements for the Degree of Master of Science (Microbiology)
Keywords
Pearl millet, Secondary metabolites, Antimicrobial activity, Gut Microflora