Antibacterial Activity of Harpagophytum procumbens (Burch.) DC. ex Meisn. Root Extracts against Gastrointestinal Pathogens and Bacterial Triggers of Autoimmune Diseases

Background: Recent increases in the numbers of antibiotic resistant bacteria and corresponding decreases in antimicrobial discovery have focussed drug discovery efforts towards plant based medicines. Harpagophytum procumbens has been used in southern African traditional medicine for a variety of conditions including inflammation, and to treat bacterial infections. Despite this, investigations of the antibacterial activity of H. procumbens root extracts have been relatively neglected. Materials and Methods: The antimicrobial activity of H. procumbens root extracts was assessed using disc diffusion and liquid dilution minimum inhibitory concentration (MIC) assays against gastrointestinal pathogens and bacterial triggers of some autoimmune diseases. The toxicity of the individual samples was assessed using the Artemia nauplii lethality assay (ALA) and an MTS HDF cell viability assay. Results: Harpagophytum procumbens root extracts displayed notable antibacterial activity against several bacterial triggers of autoimmune diseases, and against several gastrointestinal bacterial pathogens. The methanolic and aqueous extracts were particularly good inhibitors of Proteus spp. (MIC 125-313 μg/mL), K. pneumonia (MIC 313 μg/mL), P. aeruginosa (MIC 625 μg/mL) and S. pyogenes (MIC 313 μg/mL). Substantially higher MIC values were recorded against A. baylyi and the gastrointestinal bacteria. None of the extracts were toxic in the ALA or MTS assays, indicating their suitability for therapeutic use. Conclusion: The H. procumbens root extracts were effective inhibitors of the growth of several bacterial triggers of autoimmune inflammatory diseases and had noteworthy activity against some gastrointestinal bacteria. Isolation and identification of the bioactive compounds may be beneficial in the development of new antibiotic drugs.