Antimicrobial activity, cytotoxicity evaluation and heavy metal content of five commonly used South African herbal mixtures

Abstract

Herbal mixtures are becoming highly used in South Africa to treat several ailments such as cough, diarrhoea, fever, sexually transmitted diseases, cancer and diabetes. This study was aimed at evaluating some of the claimed biological activities and safety of five commonly used South African herbal mixtures. Five herbal mixtures obtained from herbal stores within Gauteng Province were evaluated for antimicrobial activities using micro-dilution method against Candida albicans, Neisseria gonorrhoeae, Escherichia coli, Klebsiella pneumoniae and Staphylococcus aureus. The cytotoxicity of the herbal mixtures was tested using Human Embryonic Kidney (HEK) 293 cells. Their heavy metal concentration was analysed using Inductively Coupled Plasma-Mass Spectrometry. All the herbal mixtures demonstrated weak antimicrobial activity against the micro-organisms used. The lowest minimum inhibitory concentration (MIC) was found in the case of 'All Rounders Special mixture' against E. coli. Both 'Knock out Special mixture' and 'Vultures Special mixture' had an MIC of 6.3 mg/ml against N. gonorrhoeae and E. coli while the latter mixture also had an MIC of 6.3 mg/ml against C. albicans. High concentrations of chromium and cadmium (except in 'All Rounders Special mixture') far exceeding the maximum permissible limits in herbal products as recommended by the World Health Organization (WHO) were found in all the mixtures. In addition, the levels of arsenic, mercury and lead in 'Knock out Special mixture' were above WHO recommended permissible limits in herbal products. Nonetheless, all the mixtures displayed no cytotoxic effect against HEK cells. High concentrations of some toxic metals found in these herbal mixtures raise serious concerns related to the quality of the herbal preparations, source of starting plant materials used in product manufacturing and consumer safety.