Antibacterial activity of three medicinal Thai plants againstCampylobacter jejuniand other foodborne pathogens

Leaves of Adenanthera pavonina, Moringa oleifera, and Annona squamosa are used in traditional Thai medicine to treat dysentery and other diseases. The present study investigated the antibacterial activity of these plants against six species of foodborne pathogen. Methods and solvents employed to extract active constituents were optimised using the disc diffusion assay. Phytochemical analysis of the optimised extracts was performed by thin layer chromatography (TLC). Minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) were determined by broth microdilution. A. pavonina contained flavonoids, terpenes and tannins, and was the most active extract against Campylobacter jejuni, inhibiting growth at 62.5 to 125 µg ml-1. A. squamosa extract contained flavonoids, terpenes, tannins and alkaloids, and had the broadest spectrum of antibacterial activity, inhibiting Bacillus cereus, Listeria monocytogenes, Staphylococcus aureus and C. jejuni between 62.5 and 500 µg ml-1. MBCs were just 2- to 4-fold higher than MICs against C. jejuni and B. cereus, suggesting the extracts are bactericidal against these species. Negligible activity was detected from Moringa oleifera. Data presented here shows that A. pavonina and A. squamosa could potentially be used in modern applications aimed at treatment or prevention of foodborne disease.