Antimicrobial Activity of Persea americana Mill (Lauraceae) (Avocado) and Gymnosperma glutinosum (Spreng.) Less (Asteraceae) Leaf Extracts and Active Fractions Against Mycobacterium tuberculosis

Tuberculosis is considered a re-emerging disease and one of the most important health problems worldwide. It causes approximately three million deaths every year. In the last decades multi-drug resistant Mycobacterium tuberculosis has been detected, exacerbating the situation. The main objective of this research was to test the effect of Persea americana and Gymnosperma glutinosum (commonly used in Mexico to treat diverse diseases) leaf extracts and active fractions against M. tuberculosis H37Ra and H37Rv strains. Colonyforming units method was used to determine the MICs of plant extracts, active fractions and clofazimine against the mycobacterial strains. Methanol extracts from both plants were observed to possess antimycobacterial activity; however, P. americana extracts possessed higher antimicrobial activity against such mycobacteria strains than those of G. glutinosum, as determined by their respective MICs of 125 μg/ml versus 250 μg/ml against H37Ra strain, respectively, and 62.5μg/ml versus 250 μg/ml against H37Rv strain respectively. It was also observed that hexane fraction of P. americana extract caused MICs of 31.2 μg/ml against H37Ra and H37Rv strains, whereas G. glutinosum GGF5 hexane extract fraction induced MICs of 125 μg/ml against H37Ra strain, fraction GGF6 caused MICs of 250 μg/ml against H37Ra and H37Rv strains, and fraction GGF7 induced MICs of 125 μg/ml against H37Ra and H37Rv strains. MICs of control clofazimine were 0.31 μg/ml against H37Ra and H37Rv strains respectively. We have experiments underway to elucidate the putative antimycobacterial active molecule (s) present in both plants.