Checkerboard and Isobologram Analysis of the Interaction between Black Cumin and Clove Essential Oils against Multidrug-Resistant Nosocomial Pathogens.

Nosocomial infections, those acquired during receiving healthcare services, represent a significant public health challenge, particularly when caused by multidrug-resistant (MDR) bacteria. While natural products have been widely investigated for their antibacterial properties, many show limited efficacy against nosocomial pathogens and fail to adequately address the escalating problem of antimicrobial resistance. Moreover, research on the antibacterial effects of natural product combinations remains scarce. This study investigates the antibacterial activity of black cumin (Nigella sativa) essential oil (NSE) combined with clove (Syzygium aromaticum) essential oil (SAE) against key nosocomial pathogens, including methicillin-resistant Staphylococcus aureus (MRSA), Acinetobacter baumannii, Escherichia coli, and Bacillus sp. A descriptive, observational, and experimental approach was employed, incorporating FTIR spectroscopy, the checkerboard microdilution assays, and isobologram methods. Antibacterial interactions were also assessed using the fractional inhibitory concentration index (FICI), which quantifies the nature of the combined effect. The results revealed synergistic interactions between NSE and SAE against MRSA, A. baumannii, and Bacillus sp., highlighting their potential as a natural alternative in the management of nosocomial infections. While, NSE exhibited no inhibitory activity against E.coli. These findings underscore the value of essential oil combinations in enhancing antibacterial efficacy and offer a promising strategy to help curb the emergence of antibiotic resistance driven by overuse.