Phytochemical Analysis and Antimicrobial Activity of Pakistani Medicinal Plants used as Antibacterial Agents Against Escherichia coli O157:H7

Abstract

Medicinal Plants are a rich source of bioactive compounds having anti-microbial properties and effectiveness against infectious diseases, have a greater affinity to mitigate antibiotic resistance, and to produce alternative, economical veterinary therapeutics. This study aimed to determine the phytochemical composition of Azadirachta Indica, Melia Azedarach, Withania Coagulans, and Nigella Sativa, and their antimicrobial properties against E. coli O157:H7. The plants were sequentially extracted using hydro-methanolic solvent. Phenolic acids (Gallic acid, Sinapic acid, Caffeic acid) and Flavonols (Myricetin, Quercetin, Kaempferol) were quantified using Reverse-Phase High-Performance Liquid Chromatography (RP-HPLC). Antibacterial activity was assessed using the Agar Well diffusion assay at concentrations of 100–400 mg/mL, with ciprofloxacin as the positive control. HPLC revealed gallic acid as the predominant phenolic compound in A. indica (83.28%), M. azedarach (83.36%), and W. coagulans (98.61%), while sinapic acid dominated in N. sativa (74.59%). Flavonol composition varied, with kaempferol highest in A. indica (80.84%), myricetin in M. azedarach (63.08%) and N. sativa (100%), and quercetin in W. coagulans (65.92%). Antibacterial activity was dose-dependent, with the hydro-methanolic extract showing the highest activity at 400 mg/mL.  M. azedarach exhibited the largest inhibition zone (12.21 ± 1.16 mm), followed by N. sativa (9.03 ± 1.47 mm), A. indica (8.98 ± 1.97 mm), and W. coagulans (8.81 ± 1.39 mm). The study concluded that the medicinal plants used were rich in phenolic compounds, showing strong antimicrobial properties against E. coli O157:H7, and can be used as a promising candidate for an affordable antibiotic alternative.