There are reports on the biological activities of
Scutellaria genus essential oils, and most of the studies have investigated the antimicrobial activity of essential oils from this genus. The antimicrobial activity of these oils could be due to the components such as linalool, eugenol, and other long-chain alcohols (
73). Moreover, other compounds such as thymol and alpha-terpineol could also contribute to the antimicrobial activity of the essential oil (
74,
75). Yu et al. (2004) investigated the antibacterial activities of
S. barbata essential oils against 17 microorganisms (
Enterococcus faecalis, Staphylococcus aureus, Serratia marcescens, Escherichia coli, Stenotrophomonas maltophila, Pseudomonas aeruginosa, Staphylococcus heamolyticus, Staphylococcus epidermidis, Candida tropicalis, Staphylococcus simulans, Citrobacter freundii, Salmonella paratyphi-A, Shigella flexneri, Klebsiella pneumoniae, Salmonella typhi, Serratia liquefaciens, and
Candida albicans) using the disc diffusion and broth microdilution methods. According to their results, the essential oil demonstrated a strong bactericidal effect;
S. epidermidis was the most sensitive microorganism (29 mm inhibition zone and 0.77 mg/mL MBC), and
C. albicans was the most resistant to the extract (7 - 9 mm and 24.50 mg/mL MBC) (
69). Based on the results reported by Zhu et al. (2016), the essential oils from
S. strigillosa had higher antimicrobial effects on gram-positive bacteria than gram-negative bacteria and fungus (
53). Another study by Pant et al. (2012) demonstrated that the essential oils of
S. grossa had significant antibacterial activity against
B. subtilis, E. faecalis, K. pneumonia, and
S. enterica (
65). Skaltsa (2005) reported a moderate activity against
S. aureus and
B. cereus for the essential oils of
S. rupestris and
S. sieberi that were collected from Greece (
28). In a study by Skaltsa et al. (2000), it was revealed that the essential oil of
S. albida subsp albida was moderately active against
E. coli, S. aureus, B. subtilis, P. aeruginosa, and
S. cerevisiae, which can be attributed to high levels of linalool and nerolidol content (
27). Dereboylu et al. (2012) investigated the antimicrobial activities of the volatile compounds of
S. sibthorpii, S. cypria var. cypria, and
S. cypria var. elatior against 7 bacteria and one fungis (
S. aureus, B. subtilis, S. typhimurium, E. faecalis, E. coli, P. aeruginosa, K. pneumonia, and
C. albicans) and reported that S. aureus was the most sensitive microorganism (
58). The antibacterial activity of
S. repens essential oil was tested on
S. aureus, E. faecalis, A. tumefac iens, E. chrysanthemi, X. phaseoli, E. coli, S. enterica, K. pneumoniae, and
P. multocida (
67), and according to the results, the essential oil showed a high level of antibacterial activity. The maximum zone of inhibition was 23 mm for
E. coli, 18 mm for
E. faecalis, 15 mm for
K. pneumonia, and 12 mm for
B. subtilis (
67). The antimicrobial activities of
Scutellaria essential oils are summarized in
Table 2.