Antimicrobial Activity of Plants Collected from Serpentine Outcrops in Sri Lanka

Abstract

Thirty-two plant species collected from serpentine (ultramafic) soils in Sri Lanka were screened for antimicrobial properties against three Gram-positive and two Gramnegative bacteria, a non-acid fast bacterium, and the yeast, Candida albicans. Methanol extracts of 29 species belonging to 12 families were active against at least one microorganism. Activity against the Gram-positive and non-acid fast bacteria was common, however, only two taxa, Lantana camara L. (Verbenaceae) and a species of Phyllanthus L. (Euphorbiaceae), were active against the Gram-negative bacterium Pseudomonas aeruginosa. None of the species was active against the other Gram-negative bacterium, Escherichia coli, or C. albicans. Photoactivity was observed from extracts of 10 species belonging to 10 families, including Convolvulaceae, Lamiaceae, and Rhamnaceae where photoactivity has not been previously reported. Interestingly, Leucas zeylanica (L.) R. Br. (Lamiaceae), one of only three species collected from more than one site, showed population-level variation in photoactivity. This is the first study where plants from highly stressful serpentine environments have been tested for antimicrobial activity. Our findings suggest that plants from serpentine environments may have altered antimicrobial activities when compared to their relatives from non-serpentine environments, urging the need to pay attention to substrate, habitat, etc., when collecting plants to test for antimicrobial properties.