Pharmacognostic and Antibacterial Effect of <i>Citrullus lanatus</i> Leaves against Selected Respiratory Tract Pathogens

Abstract

Bacterial species have been reported to develop resistance to antibiotics commonly prescribed for respiratory tract infections. Therefore, the need to search for natural products for the remedy of this problem cannot be overemphasized. The extraction of Citrullus lanatus leaves was carried out using cold maceration extraction method. Chemomicroscopical and phytochemical analysis were carried out using the standard methods. Agar well diffusion, agar dilution and spread plate methods were employed to determine the zone of inhibition, minimum inhibitory concentration, minimum bactericidal concentration and rate of kill respectively. Chemomicroscopical evaluation revealed the presence of cellulose, tannins, starch, lignin, calcium oxalate, suberin, aleurone grain and mucilage with the exception of calcium carbonate. Phytochemical screening of Citrullus lanatus revealed the presence of phenolic compounds and flavonoid as secondary metabolites. The antibacterial activity  result indicated that S. aureus showed higher zone of inhibition (20 mm and 24 mm) followed by K.pneumoniae (18 mm and 22 mm) and P. aeruginosa (18 mm and 20 mm) at a concentration of 250 mg/ml in aqueous and methanol extract respectively. The two extracts showed broad spectrum of activity and moderate M.I.C and M.B.C values ranging from 15.625 mg/ml – 31.25 mg/ml respectively. LD₅₀ of both extracts was above 5000 mg/kg and did not cause mortality in all the tested rats. The results of this investigation may be useful for deriving doses that are safe for human consumption medicinally.. This study has justified the traditional use of Citrullus lanatus leaf extract in the treatment of respiratory tract infection caused by bacteria.

Keywords: Agar well diffusion, Chemomicroscopical, Minimum inhibitory concentration, Minimum bactericidal concentration, phytochemical, Citrullus lanatus