Plants from Puerto Rico with anti-Mycobacterium tuberculosis properties

This study assesses the antitubercular potential of natural products obtained from plants reputed to have medicinal properties and collected from the tropical flora of Puerto Rico.

The increase in persons infected with Mycobacterium tuberculosis (MTB) the world over and the development of resistance to antibiotics by this microbe and other infectious bacteria has created the need for new drugs to replace those which have lost effectiveness.

In Phase I of this study, ethanolic leaf extracts of fifty local plants were submitted to preliminary screening to assess their in vitro Mycobacterium smegmatis inhibitory activity using the Bauer-Kirby disk diffusion method. In Phase II, the definitive screening of the six most promising extracts which inhibited M. smegmatis were assayed for their MTB inhibitory activity using the BACTEC 460 susceptibility test method. The brine shrimp bioassay was used as a toxicity bioassay and the mice inoculation test was used to determine mice tolerance to the effect of the daily intraperitoneal inoculations of the plant extracts.

MTB showed varying degrees of susceptibility to each plant extract. This effect was dependent upon the plant species, dose and time of exposure. Evidence is provided suggesting that: (1) Six crude plant extracts (12%) tested possessed inhibitory capacity at the amount of 500 micrograms per disc; (2) Mammea americana extract yielded the strongest inhibitory effect at 50 micrograms per disc, followed by Marchantia polymorpha, Mangifera indica, Callistemon citrinus, Syzygium jambos and Momordica charantia; (3) the bactericidal inhibitory pattern of MTB growth, exposed to Mammea americana extract, was comparable to streptomycin; and (4) the transitory reduction pattern of MTB growth, produced by Callistemon citrinus, Marchantia polymorpha extracts at 100 micrograms and 250 micrograms, was similar to that of bacteriostatic agents.

Of 50 plants screened six extracts tested for their anti-MTB activity yielded positive results with varying degrees of inhibition. Mammea americana showed the greatest inhibitory activity suggesting that certain plant species yield valuable anti-Mycobacterium tuberculosis substances. The procedures employed in this study, including the BACTEC 460 modified method, are useful for in vitro screening of plant extracts with potential antitubercular activity.