In vitro and In vivo Anti-Microbial Effects of Nigella sativa Linn. Seed Extracts Against Clinical Isolates from Skin Wound Infections

Problem statement: The developing microbial resistance to the existing anti-microbial agents has become a real challenge and a serious problem facing patients suffering from skin infections. Seeds of Nigella sativa have been used for a long time in folk medicine for the treatment of such infections. Production of new potent agents is urgently needed, especially for hospitals and health centers. Therefore, the anti-microbial effect of aqueous, diethyl ether, chloroform and petroleum ether extracts of the seeds against four standard microbial strains and seven clinical isolates from patients with skin wound infections were investigated. Approach: The in vitro anti-microbial effect of the extracts at a concentration of 20% on standard strains and clinical isolates was assessed and compared with standard drugs, chloramphenicol and amphotericin B using agar well diffusion assay. The in vivo anti-bacterial effect of petroleum ether extract was studied in male BALB/c mice infected subcutaneously with S. aureus (ATCC 25923) or a clinical isolate (0.1 mL from 10⁹ colony forming units mL^-1 suspension) and immediately treated at the infected site by subcutaneous injection of 0.1 mL of pure extract (fixed oil) or chloramphenicol or normal saline. Counts of viable bacteria present in the skin area corresponding to the infected site were determined, after 24 and 48 h of infection and treatment. Results: The aqueous extract did not show any inhibitory effect against all the tested microorganisms. The diethyl ether and chloroform extracts indicated significant inhibitory effect only against Gram-positive bacteria. However, petroleum ether extract was proved to be the most powerful one against these bacteria and also against other clinical isolates like one Gram-negative bacterium (Klebsiella pneumonia) and the yeast (Candida albicans). Moreover, the extract revealed a superior effect over the standard drug, chloramphenicol, on the clearance of subcutaneous staphylococcal infection in mice when injected at the site of infection. Counts of viable bacteria were decreased at highly significant level in mice infected with S. aureus (ATCC 25923) or a clinical isolate. Conclusion/Recommendations: The results of this study revealed clear potentiality of N. sativa fixed oil as a source for anti-microbial drugs and support its use in folk medicine for the treatment of microbial skin infections.