Antibacterial effect of aqueous leaf extracts of five spices

Introduction: Antimicrobial drug resistance has increased dramatically in the past years. Therefore, the urge to discover alternative natural antimicrobial agents has increased. Plants used in traditional medicine can be identified as potential candidates for the synthesis of novel drug compounds to act against antibiotic-resistant bacteria. This study aims to determine the potential antibacterial effects of aqueous extracts of five Sri Lankan medicinal plants against two human bacterial pathogens.
Methods: Trachyspermum roxburghianum L. (Ajwain), Murraya koenigii L. (Curry leaves), Pandanus amaryllifolius Roxb. (Screw pine), Cymbopogon citratus Stapf. (Lemongrass), and Coriandrum sativum L. (Coriander) were used in the study. Plant extracts were tested against two clinically important bacterial strains: Staphylococcus aureus (ATCC 25923) and Escherichia coli (ATCC 25922). The antibacterial activity of the plant extracts was evaluated using the agar well diffusion method. Eight concentrations of each extract were tested to determine the minimum inhibitory concentration (MIC) by a 2-fold serial dilution of the original extract.
Results: Aqueous extracts of T. roxburghianum. gave the zones of inhibition of 9.67 ± 0.1 mm, MIC values of 400 mg/ml, and MBC values of 800 mg/ml respectively, against S. aureus. Aqueous extracts of C. citratus gave the maximum zones of inhibition of 10.67 ± 1.1 mm, MIC value 400 mg/ml, and MBC value 800 mg/ml, respectively, against Escherichia coli. None of the other plants were effective against either of the microorganisms used for the study.
Conclusions: T. roxburghianum and C. citratus aqueous extracts exhibit significant invitro antibacterial activity against S. aureus and E. coli respectively under the tested conditions, and the active compounds from them can be potential sources for the synthesis of alternative antibacterial drugs.