Anti-Salmonella activity on multidrug-resistant strains and cytotoxicity of extracts and constituents of Garcinia brevipedicellata and Garcinia epunctata

Abstract

The morbidity of Salmonella infections remains high partly due to emergence of multidrug-resistant (MDR) strains. Garcinia species have demonstrated activity against a wide range of infectious organisms including bacteria. Two species, Garcinia brevipedicellata and G. epunctata were investigated for activity against MDR clinical isolates of Salmonella. Methanol extracts of the leaves of both plants were serially re-extracted using ethyl acetate (EtOAc), acetone (Ace) and methanol (MeOH); and the three extracts tested for antibacterial activity by disc diffusion and microdilution methods, and cytotoxicity effects against monkey kidney epithelial (LLCMK2) cells. Five of eighteen pure compounds isolated, identified and tested for activity include β-sitosterol (1), stigmasterol (2), epunctosides A (3), B (4) from G. epunctata and brevipedicelone D (5) from G. brevipedicellata; among which three are new compounds (3, 4 and 5). The EtOAc extract of G. epunctata and brevipedicelone D (5), recorded maximum diameters of zones of inhibition of 18 and 17 mm respectively corresponding to moderate activity. All the four crude extracts recorded the lowest minimum inhibitory concentration (MIC) of 0.125 µg/mL, corresponding to high activity against MDR Salmonella isolates and control strains. Brevipedicelone D (5) showed moderate activity with the lowest MIC of 16 µg/mL. All the crude extracts and compound 5 were not cytotoxic (CC50 = 250 - 809µg/mL). Low minimum bactericidal concentrations (≤ 2 mg/mL) were recorded against most bacteria strains which may indicate bactericidal activity. This is the first report of moderate to high activity against MDR Salmonella and no cytotoxicity of the leaves and pure compounds from G. brevipedicellata and G. epunctata; hence, the leaves should be further investigated as a potential alternative treatment for infections of these strains and source of an antibacterial natural product lead.