Interactive Antibacterial Activity and Toxicity Profiles of Selected Pure Plant Compounds and Conventional Antibiotics Against Bacterial Triggers of Some Autoimmune Diseases

Background: Curcumin, lupeol and piperine are plant compounds that have been reported to be effective against numerous medical conditions, including inflammation and against pathogenic infections. However, these compounds are yet to be tested for the ability to inhibit the growth of bacterial triggers of rheumatoid arthritis, ankylosing spondylitis and multiple sclerosis. Materials and Methods: Antimicrobial activity was assessed using disc diffusion and liquid dilution minimum inhibitory concentration (MIC) assays against a panel of bacterial triggers of autoimmune diseases. Interactions between the pure plant compounds and conventional antibiotics were studied and classified using the sum of the fractional inhibitory concentration (ΣFIC). The toxicity of the individual samples and the combinations was assessed using the Artemia lethality assay (ALA) assay. Results: Curcumin, lupeol and piperine (in 3% DMSO) displayed clinically relevant antibacterial activity against P. mirabilis and K. pneumoniae when tested alone, but were ineffective against A. baylyi and P. aeruginosa. However, the inhibitory effects were potentiated against A. baylyi and P. aeruginosa by several plant compound-antibiotic combinations. None of the individual components (nor the combinations) were toxic in the ALA assay. Conclusion: The antibacterial activity of curcumin, lupeol and piperine against some triggers of autoimmune diseases and their lack of toxicity indicates that these compounds may provide leads in the development of new therapies to prevent and treat the autoimmune diseases rheumatoid arthritis and ankylosing spondylitis.