Inhibition of bacterial triggers of selected autoimmune inflammatory diseases by Harpagophytum procumbens Burch. DC. ex Meisn. fruit extracts

Abstract

Harpagophytum procumbens DC. ex Meisn. (commonly known as ‘devils claw’) is used in traditional South African medicine to treat arthritis and rheumatic diseases. The anti-inflammatory and analgesic properties of the fruit are well documented and have been confirmed in pre-clinical and clinical studies. Despite their direct effects on the inflammatory phases of these diseases, the effects of H. procumbens extracts on the etiological agents remain to be rigorously tested. The current study was undertaken to test H. procumbens extracts for their ability to inhibit the growth of the bacterial triggers of rheumatoid arthritis (Proteus mirabilis), ankylosing spondylitis (Klebsiella pneumoniae), multiple sclerosis (Acinitobacter baylyi and Pseudomonas aeruginosa) and rheumatic fever (Streptococcus pyogenes). Powdered H. procumbens fruit was extracted with solvents of varying polarity and investigated for the ability to inhibit bacterial growth using disc diffusion and liquid dilution MIC techniques. The extracts were subsequently tested for toxicity in the Artemia nauplii bioassay to verify their suitability for therapeutic usage. The H. procumbens extracts were potent inhibitors of most of the bacterial triggers of autoimmune inflammatory diseases. The methanolic extract was a particularly potent inhibitor of P. mirabilis, with low MIC values determined. The methanolic extract was also a potent inhibitor of most of the other bacterial species tested. In contrast, the methanolic extract was a poor inhibitor of P. aeruginosa growth. However, this bacterial strain was also not inhibited significantly by the control antibiotics, indicating that it is a particularly resistant strain. All extracts were shown to be non-toxic in the Artemia nauplii bioassay. The lack of toxicity of these extracts and their growth inhibitory bioactivity against the bacterial triggers of several autoimmune inflammatory diseases indicates their potential for the prevention and treatment of rheumatoid arthritis, ankylosing spondylitis, multiple sclerosis and rheumatic fever.