Antimicrobial properties of Lawsonia inermis : a review

Australian Journal of Medical Herbalism, Fall, 2007 by O.A. Habbal, A.A. Al-Jabri, A.G. El-Hag

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Our results demonstrated that the most striking antimicrobial effect of henna was the inhibitory effect of all dilutions on both Shigella sonnei and Staphylococcus aureus (Fig 2 and Table 1). This is reassuring since certain henna ingredients such as flavonoids, quinones and simple phenols have been reported to have antimicrobial activity on Shigella sonnei (Vijaya 1995) which supports our own findings.

The dry leaves seemed to have stronger activity on the Shigella sonnei than the fresh leaves, which were shown to be more effective at higher concentrations. This may be due to the presence of certain natural constituents in the fresh leaves such as chlorophyll and water.

We noticed that the antimicrobial activity of the henna sample was generally more evident in the leaves of the plant rather than the seeds, the latter having only demonstrated a limited antibacterial activity and at higher concentrations. The anti Candida albicans activity is self evident as it demonstrated sensitivity to the leaves but not the seeds. It is the presence of quinones in henna which gives that material its dyeing properties (Fessenden 1998).

The switch between diphenol (or hydroquinone) and diketone (or quinone) occurs easily through oxidation and reduction reactions. The individual redox potential of the particular quinone hydroquinone pair is very important in many biological systems. Hydroxilated amino acids may be made into quinones in the presence of suitable enzymes such as a polyphenoloxidase (Thastrup 1985). In addition to providing a source of stable free radicals, quinones are known to complex irreversibly with nucleophilic amino acids in proteins (Stern 1985) often leading to inactivation of the protein and loss of function.

For that reason the potential range of quinone antimicrobial effects is great. Portable targets in the microbial cell are surface exposed adhesions, cell wall polypeptides, and membrane bound enzymes. Quinones may also render substrates unavailable to the microorganism. In addition they were shown to inhibit cell growth in culture (Kamei 1998).

Leaves of the henna are strikingly most effective against the spectrum of bacteria we tested compared to seeds. This is probably due to the inherent characteristics of the fully grown plant and the maturity of its chemically active constituents such as quinones. Such constituents would not have been established in seeds. Although fresh leaves did demonstrate bacteriostatic activity in general, this was less evident when compared with the effect of dry leaves. It is possible that the drying effect on the plant causes the active ingredients to be more concentrated than those in the green leaves, where water and other constituents are still present.

Table 1 elucidates our findings of antimicrobial activities of henna both against a wide spectrum of bacterial strains and against Candida albicans. Work is underway in our laboratory to test henna against a wider spectrum of bacterial strains and other microbes.