Antibacterial Effects of New Zealand Plant Extracts against Mycobacteria

Mycobacterium tuberculosis, the causative agent of tuberculosis (TB) has infected approximately 1/3 of the world population, with 9.4 million new TB cases in 2008. In addition to increased cases of drug-resistant strains it is vital that novel antitubercular compounds are discovered in order to treat infections and reduce the time of current TB therapy courses. Natural resources such as plants are now being considered as the focus for discovering new compounds. Plants have long been investigated as a source of antibiotics for the treatment of human disease. New Zealand (NZ) contains a unique and diverse flora; however, to current knowledge no native plants have been examined for antimycobacterial activity. Using ethnobotany as a basis for selection, a total of 58 native plant samples were collected and tested for direct antimycobacterial activity. Samples were extracted with sterile distilled water (SDW), ethanol (EtOH) or methanol (MeOH) and screened for inhibition against the surrogate species, Mycobacterium smegmatis. Active plant samples were then validated for bacteriostatic activity towards M. bovis BCG and M. tuberculosis H37Ra as well as other clinically-important species. Nine extracts from the species Laurelia novae-zelandiae, Lophomyrtus bullata, Metrosideros excelsa, Myoporum laetum, Pittosporum tenuifolium, Pseudopanax crassifolius and Pseudowintera colorata were found to be active against M. smegmatis. Two active extracts were the bark and cambium extracts of Laurelia novae-zelandiae (Pukatea), which were reportedly used by indigenous Māori for the treatment of tubercular lesions. Upon further investigation these extracts also demonstrated bactericidal activity towards M. smegmatis as well as bacteriostatic activity towards the slow-growing species M. bovis BCG and M. tuberculosis. Purification techniques were then performed to improve the efficiency of activity and initial exploration of delivery systems was also examined. The bioactive extracts determined in this research offer a starting point for identifying their chemical basis of antimycobacterial activity with the objective of potentially discovering new anti-tubercular drugs.