Antimicrobial, Antioxidant, and Cytotoxic Activities of Ocimum forskolei and Teucrium yemense (Lamiaceae) Essential Oils

Abstract

<b>Background:</b><i>Ocimum forskolei</i> and <i>Teucrium yemense</i> (Lamiaceae) are used in traditional medicine in Yemen. <b>Methods:</b> The chemical composition, antimicrobial, antioxidant and cytotoxic activities of the essential oils isolated from the leaves of <i>Ocimum forskolei</i> Benth. (EOOF) and two different populations of <i>Teucrium yemense</i> Deflers., one collected from Dhamar province (EOTY-d), and another collected from Taiz (EOTY-t) were investigated. The antimicrobial activities of the oils were evaluated against several microorganisms with the disc diffusion test or the broth microdilution test. The essential oils were screened for <i>in-vitro</i> cytotoxic activity against human tumor cells. EOOF and EOTY-d were screened for free-radical-inhibitory activity using the DPPH radical scavenging assay. <b>Results:</b> Sixty-four compounds were identified in (EOOF) representing 100% of the oil content with <i>endo</i>-fenchol (31.1%), fenchone (12.2%), τ-cadinol (12.2%), and methyl (<i>E</i>)-cinnamate (5.1%) as the major compounds. In EOTY-d, 67 compounds were identified, which made up 91% of the total oil. The most abundant constituents were (<i>E</i>)-caryophyllene (11.2%), α-humulene (4.0.%), γ-selinene (5.5%), 7-<i>epi</i>-α-selinene (20.1%), and caryophyllene oxide (20.1%), while the major compounds in EOTY-t were α-pinene (6.6%), (<i>E</i>)-caryophyllene (19.1%) α-humulene (6.4%), δ-cadinene (6.5%), caryophyllene oxide (4.3%), α-cadinol (9.5%), and shyobunol (4.6%). The most sensitive microorganisms for EOOF were <i>B. subtilis</i>, <i>S. aureus</i>, and <i>C. albicans</i> with inhibition zones of 34, 16, and 24 mm and MIC values of, 4.3 mg/mL, 4.3 mg/mL, and 8.6 mg/mL, respectively. EOTY-t showed antimicrobial activity against <i>S. aureus</i>, <i>B. cereus</i>, <i>A. niger</i>, and <i>B. cinerea</i> with MIC values of 0.156, 0.156, 0.313 and 0.313 mg/mL, respectively. Neither essential oil showed remarkable radical inhibition (IC₅₀ = 31.55 and 31.41 μL/mL). EOTY-d was active against HT-29 human colorectal adenocarcinoma cell lines with IC₅₀ = 43.7 μg/mL. Consistent with this, EOTY-t was active against both MCF-7 and MDA-MB-231 human breast adenocarcinoma cells. <b>Conclusions:</b> The antimicrobial activity of <i>Ocimum forskolei</i> essential oil against <i>B. subtilis</i> and <i>C. albicans</i> is consistent with its traditional use in Yemeni traditional medicine to treat skin infections. Both <i>O. forskolei</i> and <i>T. yemense</i> show wide variations in their respective essential oil compositions; there remains a need to investigate both species botanically, genetically, and phytochemically more comprehensively.