In vitro antimicrobial, antibiofilm and antioxidant activities of six South African plants with efficacy against selected foodborne pathogens

Abstract

Foodborne pathogens are a major cause of concern as they are responsible for food spoilage or microbial diseases, leading to economic loss to the food industry as well as health issues. The problem of increased resistance to available antimicrobial agents, and the ability of the microorganisms to form protective biofilms, strengthens their capacity to resist treatment. The antimicrobial, anti-biofilm and antioxidant activities and cytotoxicity of six South African plants, Carpobrotus edulis, Vachellia rehmanniana, Vachellia xanthophloea, Kigelia africana, Elephantorrhiza elephantina and Ochna pretoriensis, were investigated. Plants were selected based on traditional use against foodborne diseases or known antimicrobial activity. Serial microdilution and crystal violet assays were used to assess the antimicrobial and anti-biofilm potential of the extracts. Antioxidant activity of the extracts was determined against free radicals in vitro, and a tetrazolium-based cell viability assay was used to investigate cytotoxicity. Extracts were active against microorganisms implicated in causing foodborne diseases, with minimum inhibitory concentration (MIC) values ranging from 0.02 to 2.5 mg/ml. Acetone extracts of V. xanthophloea and C. edulis had noteworthy MIC values of 0.02 mg/ml against Enterobacter cloacae. Most extracts selectively reduced biofilm growth by at least 50% against the foodborne pathogens. The acetone extract of V. xanthophloea had the most significant anti-biofilm activity against Salmonella Typhimurium. The methanol extract of V. xanthophloea and the acetone extract of C. edulis had good antioxidant activity. Leaf extracts of the selected plants have useful bioactivities coupled with low cytotoxicity, providing impetus for further studies on possible development of these plants as protective food additives against microbial attack or oxidation.