Abstract:
Tuberculosis (TB) is currently the deadliest human disease caused by a single infectious agent. Mycobacterium tuberculosis, the causative TB pathogen, infects over 10 million people and kills over 1 million people annually. Successful TB treatment requires lengthy courses of several antibiotics over many months. Opportunistic infections caused by nontuberculous mycobacteria (NTM) are also increasing in frequency. The appearance of infections caused by mycobacteria that are resistant to antibiotics is increasing while the arsenal of useful antibiotics is quickly diminishing. We need new antibiotics with new modes of action to fight against the inevitable threat of untreatable mycobacterial infections. Many bioactive agents, including some anti-mycobacterial agents in use today, derive from compounds produced by microorganisms. Recent evidence suggests that continued prospection of microbes in uncharted territories can still prove fruitful in the ongoing hunt for new antibiotics. In this project I sought to validate a novel way to screen fungi for anti-mycobacterial activity using a 24-well plate as culture vessel for growing and screening fungi isolated from New Zealand. This format allowed me to screen multiple fungal cultures in multiple media to increase the chemical diversity of the metabolites produced by these cultures. This screen utilised strains of bioluminescent M. abscessus and M. marinum to detect whether cocultivation significantly inhibited mycobacterial growth, which suggests the production of anti-mycobacterial compounds. I screened 40 untested New Zealand fungi, nearly all of which produced considerable anti-mycobacterial activity in at least one medium. I cultured a subset of these active fungi for chemical extraction and fractionation. Many of these extracts retained activity. Most of this activity was due to the known anti-mycobacterial compound linoleic acid. The extract fractions with the highest anti-mycobacterial activity came from an unspeciated Xylariales isolate cultured on malt extract and oatmeal agars. Analysis of these fractions by Nuclear Magnetic Resonance spectroscopy revealed that the activity from this isolate cultured on oatmeal was most likely due to a novel macrolide compound. This research validates the use of a novel screening method for anti-mycobacterial activity and reinforces the notion that useful novel compounds remain to be discovered from microbes isolated from unexplored habitats.