Synergistic Effects of Black Seed Oil, Fresh Clove Extracts, and Amoxicillin Against Bacterial Skin Pathogens: An In Vitro Experimental Study

Background The rising prevalence of antimicrobial resistance has reduced the clinical efficacy of commonly prescribed antibiotics, including amoxicillin. Plant-derived extracts used as adjuvants to conventional antibiotics have emerged as a potential strategy to enhance antibacterial activity. This study evaluated the antimicrobial effects of ethanol-based extracts of black seed oil and fresh clove, individually and in combination with amoxicillin, against reference microbial strains associated with skin and soft tissue infections. Methods Ethanolic extracts of black seed oil and fresh clove were prepared using 70% ethanol, 100% ethanol, and ultrasonic-assisted extraction techniques. Antimicrobial activity was assessed against 10 reference microbial strains using the disc diffusion method according to the Clinical & Laboratory Standards Institute guidelines. Zones of inhibition (ZOIs) were measured in millimeters. Statistical analysis was performed using one-way ANOVA after confirming normality of the data. Results Both plant extracts exhibited measurable antimicrobial activity, with clove extract showing broader inhibitory effects than black seed oil when tested alone. Combinations of plant extracts with amoxicillin produced larger ZOI, particularly against Staphylococcus aureus, Streptococcus pyogenes, and Enterococcus faecalis. Sonicated ethanolic extracts demonstrated slightly enhanced antibacterial activity compared to non-sonicated preparations. Normality testing confirmed parametric data distribution, and comparative analysis revealed statistically significant differences between combination formulations and individual agents (p < 0.05). Conclusions Ethanolic extracts of black seed oil and clove exhibit antimicrobial activity and demonstrate synergistic effects when combined with amoxicillin against selected skin pathogens. These findings support the potential use of plant-derived extracts as natural adjuvants to β-lactam antibiotics. Further quantitative and clinical studies are needed to validate their therapeutic applicability.