Antibacterial Activity and Toxicity Profiles of Artemisia annua L. Extracts and Conventional Antibiotics against Bacterial Triggers of Some Autoimmune Diseases

Background: Artemisia annua L. has been used traditionally to treat numerous infectious diseases, including many caused by bacterial pathogens. However, A. annua extracts are yet to be tested for the ability to inhibit the growth of bacterial triggers of autoimmune diseases. Methods: Antimicrobial activity was assessed using disc diffusion and liquid dilution minimum inhibitory concentration (MIC) assays against a panel of bacterial triggers of some autoimmune diseases. Interactions between the A. annua extracts and conventional antibiotics were studied and classified using the sum of the fractional inhibitory concentration (∑FIC). The toxicity of the individual samples and the combinations was assessed using the Artemia lethality assay (ALA) assay. Results: Artemisia annua leaf extracts displayed notable antibacterial activity against the bacterial triggers of rheumatoid arthritis (P. mirabilis and P. vulgaris), ankylosing spondylitis (K. pneumoniae), and one of the triggers of multiple sclerosis (A. baylyi), although they were ineffective against P. aeruginosa. The ethyl acetate extracts were particularly good inhibitors of Proteus spp. growth, whilst the chloroform extract was the best inhibitor of K. pneumoniae (on the basis of MICs). Furthermore, combining the extracts with conventional antibiotics resulted in potentiation of the inhibitory activity for some combinations, particularly those containing chloramphenicol as the antibiotic component. None of the individual components (nor the combinations) were toxic in the ALA assay. Conclusion: The A. annua methanolic and ethyl acetate extracts displayed clinically relevant antibacterial activity against P. mirabilis and P. vulgaris, whilst the chloroform A. annua extract had the best activity against K. pneumoniae when tested alone. The lack of toxicity of the extract and combinations indicates that A. annua extract and antibiotic combinations may provide leads in the development of new therapies to prevent and treat the autoimmune diseases rheumatoid arthritis and ankylosing spondylitis.