Chemical variation, antimicrobial activity and toxicity of three South African species of Salvia used in Cape Herbal Medicine

Salvia is the largest genus in Lamiaceae and includes many species of medicinal and pharmacological value. In South Africa, three blue-flowered species are used in Cape Herbal Medicine, yet S. dentata remains poorly studied. This study profiles and compares the phenolic composition of these three species and evaluates the antimicrobial activity and toxicity of S. dentata. Phenolic compounds were identified using UHPLC-MS, with carnosic acid and carnosol confirmed by NMR. The UHPLC-MS analysis revealed a distinct chemical profile for S. dentata, marked by high levels of rosmarinic acid (7), acetoxycarnosic acid (13), epirosmanol methyl ether (16), carnosol (14), and carnosic acid (18), closely resembling the profile of Mediterranean rosemary (S. rosmarinus). Antimicrobial activity was assessed using the microwell broth dilution assay, and toxicity by the brine shrimp lethality assay. Organic extracts of S. dentata showed notable antimicrobial activity, with MIC values of 0.13 mg/mL (against Streptococcus pyogenes) and 0.15 mg/mL (Enterococcus faecium), and moderate activity against Staphylococcus aureus, Listeria monocytogenes and Streptococcus agalactiae (MIC values of 0.57 mg/mL, 0.25 mg/mL and 0.23 mg/mL respectively). The extract of Salvia dentata was noted to be non-toxic. Out of the three species studied, S. dentata demonstrated the greatest promise as an anti-infective agent. However, the activity is not solely attributed to carnosic acid or carnosol, suggesting synergistic interactions between phenolics. The application of UHPLC-MS was key to revealing the distinct chemical profile of S. dentata, particularly its strong similarity to S. rosmarinus, an important new insight that expands the potential use of S. dentata beyond the traditional role in Cape Herbal Medicine.