Formulation and Evaluation of a Nigella sativa Oil-Based Emulsion as a Potential Hand Sanitizer Against Methicillin-Susceptible and Methicillin-Resistant Staphylococcus aureus.

BACKGROUND

Hand hygiene is key to controlling healthcare-associated infections. Staphylococcus aureus is a critical pathogen in wound infections and infection prevention is compromised by methicillin-resistant S. aureus (MRSA) because of the ability of this pathogen to resist antimicrobial agents. In this study, the efficacy of Nigella sativa oil-based emulsion against clinical S. aureus strains separated from wound samples, including methicillin-resistant strains, was studied.

METHODS

This in vitro experimental study examined the properties of crude N. sativa oil, its preliminary oil emulsions, and the final emulsions made by mixing with either distilled water or carbomer 940 gel. The identification of wound strains was performed using culturing and different tests like Gram staining, catalase, coagulase, and performance of the phenotypic test for methicillin-resistant strains using cefoxitin disk diffusion. The results of antibacterial activity testing were obtained by using agar well diffusion. The obtained results were compared to those of broth-dilution MIC. The characterization included physicochemical parameters such as quality of oil, size of droplets in emulsion, viscosity of gel, and pH. All results were analyzed statistically and no duplicates were included in the analyses.

RESULTS

The tested 13 S. aureus strains are listed in the table containing the results of the antibacterial efficacy comparison. Undiluted N. sativa oil is suggested to have shown antibacterial activity against 11 (84.6%) of the S. aureus isolates, with the measured inhibition zones ranging from 24 to 38 mm. On the basis of the susceptibility data presented in the paper and CLSI interpretation standard, three strains from the total number of tested strains belong to MRSA. Of these three strains, two strains are susceptible to undiluted N. sativa oil. The average inhibition zone when using N. sativa oil was recorded at 27.5 ± 13.0 mm, although the inhibition ring average in the case of cefoxitin usage made 21.5 ± 8.1 mm, although the statistical difference in results was insignificant (paired t test, P = 0.100). The active solution of the emulsion at the concentration of 50% produced inhibition effects on seven studied S. aureus strains. As for other concentrations, the lowest one producing measurable effects on all studied S. aureus strains made 10% w/w with water, or 5% w/w with carbomer gel. As for the carbomer gel S1 studied in terms of viscosity, it was shown that its viscosity amounted to 2050 poise and the pH level was 7.6. The initial studies of the emulsion based on N. sativa showed droplet diameters equal to 0.25-0.29 µm.

CONCLUSION

The conducted research shows that it is worthwhile to study different formulations on the basis of N. sativa. Nonetheless, the research has several limitations, such as lack of in vivo studies and lack of any time stability testing.