The Interactive Antimicrobial Activity of Terminalia ferdinandiana Exell. Extracts and Conventional Antibiotics against Bacterial Triggers of Some Autoimmune Diseases

Autoimmune inflammatory diseases are debilitating conditions for which limited safe and effective therapeutic options exist. A re-examination of traditional medicines may highlight leads for therapies against those diseases. Terminalia ferdinandiana has strong antibacterial activity against several bacterial pathogens, and has noteworthy COX-2 and iNOS inhibitory activity. However, the effects of Terminalia ferdinandiana extracts on bacterial triggers of autoimmune inflammatory diseases is relatively unexplored, and the extracts have not been tested in combinations with conventional antibiotics. Terminalia ferdinandiana leaf, fruit and seed extracts were screened for growth inhibitory activity against bacterial triggers of selected autoimmune inflammatory diseases and the activity was quantified using disc diffusion and liquid dilution MIC assays. Toxicity was evaluated using the Artemia nauplii cytotoxicity assay and therapeutic indexes were calculated. The methanolic, aqueous and ethyl acetate T. ferdinandiana leaf and fruit extracts displayed noteworthy growth inhibitory activity against some bacterial triggers of rheumatoid arthritis (RA), ankylosing spondylitis (AS) and multiple sclerosis (MS), with MIC values as low as 90 μg/mL. Thus, the T. ferdinandiana leaf and fruit extracts have potential to treat RA, AS and MS when used alone. However, the methanolic T. ferdinandiana extracts also potentiated the antibacterial activity of conventional antibiotics substantially when tested in combination. In total, nine combinations were synergistic, with seven of these combinations synergistic against Proteus mirabilis. Thus, those combinations may be particularly useful in preventing and treating RA. Notably, none of the extracts or extract-antibiotic combinations were toxic in the Artemia nauplii assay, indicating that they may be safe for therapeutic use, although this needs to be confirmed in mammalian cell lines and in in vivo toxicity assays. Further in vivo studies to determine the anti-inflammatory and antibacterial mechanisms are warranted.