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Abstract

Staphylococcus aureus is a pathogenic bacterium associated with severe infections in humans and animals, with increasing resistance to commonly used antibiotics such as erythromycin. This study aimed to evaluate the antibacterial efficacy of aqueous extracts of Nigella sativa compared with erythromycin against S. aureus isolated from naturally infected Cyprinus carpio. Bacterial identification was carried out using standard microbiological and biochemical methods, followed by Gram staining and in vitro susceptibility testing. The antibacterial activity of N. sativa was assessed through the agar well diffusion method at different concentrations (0.75–1.5 mg/ml), and results were compared with erythromycin as a control. The extract exhibited a dose-dependent inhibitory effect, with the largest inhibition zone observed at 1.5 mg/ml (30.2 mm). In contrast, erythromycin showed no activity, indicating resistance of the tested isolate. The findings demonstrate that N. sativa possesses strong antibacterial potential, even against drug-resistant S. aureus, likely due to bioactive phytochemicals such as thymoquinone. These results support the use of N. sativa as a promising phytotherapeutic alternative and suggest its possible application in aquaculture and clinical settings to reduce reliance on conventional antibiotics. Further in vivo studies and phytochemical analyses are recommended to validate its therapeutic efficacy and safety.