Potential of a methanolic extract of Lawsonia inermis (L.) leaf as an alternative sanitiser in the time of COVID-19 Pandemic and beyond

Abstract

To harness the antimicrobial properties of a crude methanolic extract of Henna (Lawsonia inermis) leaf as a potential alternative sanitiser, there is the need to test its performance in different solutions. In this work, the effects of distilled water (dH20), Acetate-HCL (AH) Buffer (pH 4.6), Phosphate Buffer Saline (PBS) (pH 7.2) and Tris-HCL (TBH) Buffer (pH 8.6) on the antibacterial and antiviral activity of the extract were assessed. Through standard phytochemical screening and HPLC-MS (LCMS STANDARD 7.M), it was found that the extract consisted of about 30 different compounds including flavonoids. The extent of the antimicrobial activity of the extract in solutions was in the increasing order of AH > dH2O >>>> TBH > PBS. Under the same conditions, reduced antibacterial activity and complete cessation of the antiviral activity of the extract in TBH and PBS was observed. However, in AH and dH20, within 1-5 min, 1 mg ml^-1, 0.125 mg ml^-1 and 0.0625 mg ml^-1 of the extract caused complete inactivation of E.coli (reductions of 8.2 log CFU ml^-1), B. subtilis (reductions of 8.2 log CFU ml^-1) and MS2 (reductions of 9.7 log PFU ml^-1) respectively. The fluorescence microscopy images of the live/dead staining of the inactivated bacterial samples validated the extent of the inactivation. The broad spectrum and high antimicrobial activity of the extract, coupled with the plant not a staple food, has long history of safe use by humans as a medicine and cosmetic, cheaply available in abundance in many regions of the world, thus making the extract a potential candidate as an alternative sanitiser in the time of COVID-19 Pandemic and beyond.

Keywords: AH, Acetate-HCl buffer; Antibacterial; Antiviral; Henna; LM, methanolic extract of Lawsonia inermis leaf; Lawsonia inermis; Methanolic extract; PBS, Phosphate Buffer Saline; S, solution; Sanitiser; TBH, Tris Base-HCl buffer; dH2O, distilled water.

Fig. 1

Inactivation of E. coli using different concentrations of the LM extract in different solutions. (A) Inactivation of E.coli in different solution; (B) LM concentration dependent inactivation of E.coli in AH buffer; (C) LM concentration dependent inactivation of dH20. AH, acetate-HCl buffer; dH2O, distilled water; PBS, phosphate buffer saline; TBH, Tris base-HCl buffer; S, solution; LM, methanolic extract of Lawsonia inermis leaf. Data are mean ± SD (n = 3). Error bars show ± SD.

Fig. 2

Fluorescence microscopy images of live/dead staining of the E. coli samples inactivated with 1 mg ml⁻¹ LM in dH20 and AH buffer. AH, acetate-HCl buffer; dH2O, distilled water; LM, methanolic extract of Lawsonia inermis leaf.

Fig. 3

Inactivation of B. subtilis using different concentrations of the LM extract in different solutions. (A) Inactivation of B. subtilis in different solutions; (B) LM concentration dependent inactivation of B. subtilis in AH buffer; (C) LM concentration dependent inactivation of B. subtilis in dH20. AH, acetate-HCl buffer; dH2O, distilled water; PBS, phosphate buffer saline; TBH, Tris base-HCl buffer; S, solution; LM, methanolic extract of Lawsonia inermis leaf. Data are mean ± SD (n = 3). Error bars show ± SD.

Fig. 4

Fluorescence microscopy images of live/dead staining of the B. subtilis samples inactivated with 1 mg ml⁻¹ LM in dH20 and AH buffer. AH, acetate-HCl buffer; dH2O, distilled water; LM, methanolic extract of Lawsonia inermis leaf.

Fig. 5

Inactivation of phage MS2 using different concentrations of the LM extract in different solutions. (A) Inactivation of phage MS2 in different solutions; (B) LM concentration dependent inactivation of phage MS2 in AH buffer; (C) LM concentration dependent inactivation of phage MS2 in dH20. AH, acetate-HCl buffer; dH2O, distilled water; PBS, phosphate buffer saline; TBH, Tris base-HCl buffer; S, solution; LM, methanolic extract of Lawsonia inermis leaf. Data are mean ± SD (n = 3). Error bars show ± SD.