Positive effects of Moringa oleifera and Moringa stenopetala seed and leaf extracts against selected bacteria

Moringa oleifera is hailed as the “miracle tree” for its impressive catalog of nutritional, medicinal, and water purification benefits. A (sub)tropical plant with a rapid growth rate (3–5 m in a single season), Moringa has proven beneficial in multiple ways in developing regions around the world. In addition to its high nutrient content and water clarifying properties, Moringa seed and leaf extracts have shown potential as natural antibacterial agents. Based on this, we anticipated that extracts from multiple species of Moringa would exhibit potentially useful antibacterial properties against a range of bacterial species. To explore this, both disk diffusion and minimum inhibitory concentration (MIC) culture techniques were employed to assess the inhibitory effects of seed and leaf extracts from M. oleifera and M. stenopetala against species of bacteria commonly used in research and teaching laboratories. Aqueous seed extracts from both Moringa species showed broad-spectrum activity but were especially effective at inhibiting the growth of Gram-positive bacteria, including species of Staphylococcus, Streptococcus, and Bacillus. Moringa leaf extracts also exhibited antibacterial activity, with ethanolic leaf extracts showing greater efficacy than aqueous leaf extracts in disk-diffusion assays. Temporary acidification (1 h at pH 2) of Moringa seed and leaf extracts had a detrimental effect on their antibacterial activity. MIC assays using Moringa leaf extracts also showed more pronounced inhibition of Gram-positive bacteria (MIC = 12.5% v/v) versus Gram-negative species (MIC = 25% v/v). These results are of particular relevance in tropical areas where pharmaceutical drugs are scarce but Moringa is widely available and often used as a nutritional supplement. Moreover, the rising threat of multi-drug resistant pathogens lends greater importance to the study of antibacterial plant products that ultimately may find application in the clinical setting.