Antibacterial activity of three medicinal Thai plants against Campylobacter jejuni and other foodborne pathogens

Abstract

Leaves of Adenanthera pavonina, Moringa oleifera and Annona squamosa are used in traditional Thai medicine to treat dysentery and other diseases. This 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, terpines and tannins, and was the most active extract against Campylobacter jejuni, inhibiting growth at 62.5–125 µg mL⁻¹. The A. squamosa extract contained flavonoids, terpines, 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 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 M. oleifera. The data presented here show that A. pavonina and A. squamosa could potentially be used in modern applications aimed at the treatment or prevention of foodborne diseases.

Keywords:

• Adenanthera pavonina
• Moringa oleifera
• Annona squamosa
• antibacterial
• foodborne pathogen
• Campylobacter jejuni

Acknowledgements

This work was supported by the Office of the Higher Education Commission, Ministry of Education, Thailand, through a CHE PhD scholarship. The authors are very grateful to Ms Suttira Khumkratok for identifying the plant material and assisting with voucher specimen preparation, Dr Wanida Caichompoo for providing bacterial strains, Assistant Professor Uthai Sakee for chemistry advice and Mr Surapong Rattana for assistance with TLC. They also thank the anonymous reviewers of ‘Natural Product Research’ for their constructive comments and suggestions.