Standardisation of Antimicrobial Compounds from Aspergillus flavus against the Escherichia coli and Staphylococcus aureus: An In-vitro Analysis

Introduction: The increasing prevalence of antibiotic resistance among pathogenic microorganisms poses a significant challenge to global public health. Previously effective treatments against common pathogens such as Escherichia coli (E.coli) and Staphylococcus aureus (S.aureus) are becoming progressively less effective. These organisms are responsible for a wide spectrum of diseases, ranging from minor infections to severe systemic illnesses. As resistance to conventional antibiotics continues to rise, the need for novel antimicrobial agents has become increasingly urgent. Natural products have long served as a rich source of antimicrobial substances, and among them, fungi are well recognised for their ability to produce a diverse array of bioactive metabolites with potential therapeutic applications. Aim: The aim of the current study was to isolate and identify bioactive metabolite-producing Aspergillus flavus (A.flavus) strains from soil samples and to evaluate their antimicrobial activity against clinical isolates of E.coli and S.aureus. Materials and Methods: The present in-vitro experimental study was conducted in the Department of Microbiology, SRM Medical College Hospital and Research Centre, Kattankulathur, Tamil Nadu, India, from January to December 2023. The current study involved the isolation of A.flavus from soil samples collected from dump yards and the isolation of E.coli and S.aureus from clinical specimens. The total sample size was 50, comprising 25 E.coli and 25 S.aureus isolates obtained from various clinical samples, including urine, pus, sputum, blood, ear swabs, wound swabs, tracheal aspirates, and tissue samples. Soil samples were collected from four different dump yard sites surrounding the SRM Medical College Hospital and Research Centre. Only A.flavus was isolated from soil samples using the spot method, while E.coli and S.aureus isolated from clinical samples were included in the study. Other fungal and bacterial isolates were excluded. Antimicrobial activity was assessed using the perpendicular cross-streaking method and the agar well diffusion method. Bioactive compounds were extracted through fermentation, followed by separation using Thin-Layer Chromatography (TLC). Compound identification was performed using Gas Chromatography-Mass Spectrometry (GC-MS). Statistical analysis was carried out using Statistical Package for Social Sciences (SPSS) software, and all data were expressed as mean±standard deviation. Results: The isolated A.flavus strains demonstrated antimicrobial activity against both E.coli and S.aureus. TLC analysis revealed four distinct bioactive compounds with Rf values of 0.70, 0.80, 0.87, and 0.89. GC-MS analysis identified a total of 23 volatile compounds. The antimicrobial activity produced Zones Of Inhibition (ZOI) ranging from 23 to 18 mm against E.coli and from 16 to 24 mm against S.aureus. Conclusion: The bioactive compounds extracted from A.flavus exhibited significant antibacterial activity, particularly against the Gram-positive organism S.aureus. These findings highlight the potential of A.flavus as a promising source of novel antimicrobial agents, especially in the context of increasing antibiotic resistance. Further studies are warranted to optimise the production and purification of these compounds and to explore their potential clinical applications.