An Examination of the Antioxidant Capacity, Antibacterial Activity and Toxicity of Commercial Kale and Spirulina Powders

Introduction: The development of antibiotic resistant bacteria has resulted in treatment failure for the current antibiotic regimen against many bacteria. A corresponding decrease in the development of new antibiotic therapies has highlighted the urgent need for the discovery of new antibiotics. An examination of ‘superfoods’ is an attractive option due to the high antioxidant capacities and beneficial secondary compounds reported in many ‘superfoods’. This study was undertaken to test kale and spirulina extracts for the ability to inhibit the growth of a panel of bacterial pathogens of human importance. Methods: Commercially sourced kale and spirulina powders were extracted and tested for antimicrobial activity using modified disc diffusion and liquid dilution MIC methods. Toxicity was evaluated using an Artemia franciscana nauplii bioassay. Results: The methanolic and aqueous extracts of kale and spirulina displayed noteworthy growth inhibitory activity against P. mirabilis. The aqueous spirulina extract was a particularly good inhibitor of P. mirabilis, with MIC values as low as 220μg/mL. In contrast, all extracts were ineffective or of low inhibitory activity against all other bacteria tested. All extracts were non-toxic in the Artemia nauplii bioassay, confirming their suitability as natural antibacterial therapies. Conclusion: These studies indicate that aqueous kale and spirulina extracts are promising inhibitors of P. mirabilis growth and may be useful in the prevention and treatment of rheumatoid arthritis, as well as other diseases caused by that bacterium.