Bioactive compounds from fermented Vernonia amygdalina leaf: Potent antibiotics against multidrug-resistant Escherichia coli and Salmonella typhi

Antibiotic resistance microorganisms (ARMs), particularly gram-negative bacteria, pose a global health threat. The effects of fermentation on phytochemicals are numerous, and exploring this potential is the focus of drug development. The study investigated the role of fermentation in modifying V. amygdalina leaf secondary metabolites as an effective antibiotic against Escherichia. coli, Bacillus subtilis and Salmonella typhi . This work showed that fermentation increased the content of lycopene, flavonoid and carotenoid compounds but decreased chlorophyll, soluble protein and phenol. Pearson’s correlation heatmap showed a strong correlation between microbial activities and secondary metabolic changes. The methanolic extract of fermented V. amygdalina leaf pulp (at day 9) showed significant antioxidant and anti-inflammatory activities. The GCMS and FTIR results showed unique compounds and structural modifications at different intervals of the fermentation period. In-vitro and in-silico analyses showed that fermentation did not alter the inhibition rate against B. subtilis; however, E. coli and S. typhi were significantly inhibited by fermented V. amygdalina pulp extracts. In-silico analyses showed that 4,6-Cholestadien-3β-ol– a compound present only on the ninth day of fermentation–was responsible for the inhibition of the gram-negative bacteria via the substitution of multiple non-ionic interactions of some key catalytic site residues with non-ionic types, thereby denying ionisation and salt-bridge properties that porins explore to resist antibiotics; and higher binding affinity to OmpC and OmpF than ampicillin. Therefore, this steroid-derived compound may open a new pipeline for developing ion-independent multi-target antibiotics against broad-spectrum multidrug-resistant gram-positive and gram-negative bacteria in food and pharmaceutical purposes.