Abstract

ABSTRACT
BACKGROUND: Endophytes are microorganisms that live inside plants without causing harm. They have been shown to produce biologically active metabolites of great interest in drug discovery. In this era of antibiotic resistance, endophytes offer an innovative and eco-friendly niche of potentially new compounds, whose efficacy and yield can be enhanced by cultural optimisation.
METHODS: Ageratum conyzoides plant was harvested, washed, cut and surface-sterilised. The sterilised pieces of all parts were seeded on solid media and incubated. Endophytes were isolated and re-streaked continuously till uniform colonies of bacteria or mycelia of fungi were obtained. The pure endophytes were fermented in liquid media, and crude extracts were obtained by solvent extraction using a mixture of Dichloromethane and methanol. These extracts were screened at 200µg/ml against resistant isolates of Escherichia coli, Pseudomonas aeruginosa, Proteus mirabilis and Acinetobacter sp. using the broth microdilution method. The endophytes producing the most active extracts were identified using MALDI-TOF MS. These endophytes were fermented in a series of new media of different properties and for an extended time. The extracts obtained were screened pharmacologically, and their yield and MIC were determined.
RESULTS: 33 morphotypes were isolated from the leaves, flowers, stems, and roots of A. conyzoides, with 75% of the crude extracts showing antibacterial activity. The selected bacterial endophytes NPMRU805, NPMRU814, and NPMRU825, each active on at least two pathogenic bacteria isolates, were tentatively identified as Bacillus cereus, Bacillus subtilis, and Bacillus cereus, respectively. They were cultured in new media and produced crude extracts with increased action spectrum inhibiting P. aeruginosa, P. mirabilis and Acinetobacter sp., with MICs from 200µg/ml of extracts from 18 days fermentation, nitrogen sources, and salts.
Conclusion: To the best of our reading, This study highlights for the first time the potential of endophytes inhabitation A. conyzoides as sources of extracts with antibacterial.

Key words: Ageratum conyzoides, endophytes, antibacterial, culture optimisation