TAGRA 2025

The rapid rise of antibiotic-resistant bacteria and the limited development of new antimicrobial agents highlight the urgent need for alternative therapeutic strategies. One promising approach is the use of synergistic combinations of antibiotics and essential oils, which may enhance antibacterial efficacy through complementary mechanisms. Essential oils, known for their broad-spectrum activity, have gained increasing attention as potential adjuvants capable of improving antibiotic performance and reducing the required drug dose. This study evaluated the synergistic antibacterial effects of Black seed (Nigella sativa) essential oil in combination with two antibiotics—Oxolinic acid (2 µg) and Netilmicin (30 µg)—against Klebsiella pneumoniae ATCC 70063 and Acinetobacter baumannii. Disk diffusion assays were used to measure inhibition zone diameters for antibiotics alone and in combination with black seed essential oil. For A. baumannii, netilmicin alone produced a 2.0 mm inhibition zone, which increased to 2.3 mm when combined with the essential oil. Oxolinic acid showed a 1.0 mm inhibition zone that rose to 1.1 mm with the addition of black seed oil. For K. pneumoniae, netilmicin increased from 2.4 mm to 2.7 mm in the presence of essential oil. Similarly, oxolinic acid increased from 0.9 mm to 1.1 mm when combined with the oil. Overall, black seed essential oil showed limited yet notable synergistic potential with both antibiotics, particularly against Gram-negative bacteria. Such combinations may offer a strategy to enhance antimicrobial activity and help mitigate resistance development.