Justice-Alucho, C. H. | Search bioRxiv

bioRxiv2026

Antimicrobial activity of Syzygium aromaticum (clove) against Staphylococcus aureus and Listeria monocytogenes is enhanced by optimized extraction methods

Clove (Syzygium aromaticum) is a food spice rich in phenolic profile with potent antimicrobial properties. However, the influence of solvent extraction efficiency and antimicrobial performance against selected foodborne pathogens needs to be further elucidation. In this study, four solvents (80% ethanol, 80% acetone, 75% methanol, and water) were analyzed for their impact on clove bud extraction yield and antimicrobial activity against Staphylococcus aureus and Listeria monocytogenes. Extraction yield varied significantly across solvents, with 80% acetone producing the highest recovery, while water yielded the lowest, with no significant difference from 75% methanol (p > 0.05). Preliminary agar diffusion screening revealed inhibition zones for all extracts and Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) assays demonstrated that acetone and ethanol extracts exerted the strongest inhibitory effect on S. aureus, whereas ethanol and methanol extracts were most effective against L. monocytogenes. Water extract consistently exhibited the weakest antimicrobial activity. A perfect correlation (r = 1.00) was observed between MIC and MBC for both organisms, and a strong negative correlation existed between extraction yield and antimicrobial thresholds for S. aureus (r = -0.98; p < 0.05), suggesting solvent-driven phytochemical concentration as a determinant of bioactivity. Collectively, these findings reaffirm the critical role of solvent polarity in maximizing phenolic extraction and antimicrobial potency of clove extracts as a promising natural antimicrobial agent for the control of foodborne pathogens.

microbiology↗

bioRxiv2025

Bacterial succession, functional organization, and ecological drivers during spontaneous ukwa (Treculia africana) fermentation

Spontaneous fermentation of ukwa (Treculia africana) involves complex microbial succession that remains poorly characterized. Here, bacterial community dynamics during ukwa fermentation were resolved across six time points using high-throughput 16S rRNA gene sequencing. Fermentation followed a structured, stage-wise trajectory, beginning with plant-associated aerobic taxa, transitioning through a mid-phase dominated by fermentative firmicutes, and culminating in late-stage enrichment of acid-tolerant lactic and acetic acid bacteria. Microbial richness increased progressively during fermentation, while community composition clustered by time and correlated strongly with declining pH and moisture. Multivariate analyses identified these physicochemical gradients as primary drivers of succession. Network analysis further revealed distinct co-occurrence modules, indicating coordinated microbial guilds that underpin functional transitions during fermentation. This study provides the first sequencing-based ecological framework for ukwa fermentation and highlights how environmental filtering and microbial interactions shape community assembly in traditional African solid-state fermentations. These insights provide a basis for improving process control and guiding future starter culture development for ukwa and related fermented foods.

microbiology↗