Antibacterial Activity of Terpenes and Terpenoids Present in Essential Oils

Abstract

Background: The antimicrobial activity of essential oils has been reported in hundreds of studies, however, the great majority of these studies attribute the activity to the most prevalent compounds without analyzing them independently. Therefore, the aim was to investigate the antibacterial activity of 33 free terpenes commonly found in essential oils and evaluate the cellular ultrastructure to verify possible damage to the cellular membrane. Methods: Screening was performed to select substances with possible antimicrobial activity, then the minimal inhibitory concentrations, bactericidal activity and 24-h time-kill curve studies were evaluated by standard protocols. In addition, the ultrastructure of control and death bacteria were evaluated by scanning electron microscopy. Results: Only 16 of the 33 compounds had antimicrobial activity at the initial screening. Eugenol exhibited rapid bactericidal action against Salmonella enterica serovar Typhimurium (2 h). Terpineol showed excellent bactericidal activity against S. aureus strains. Carveol, citronellol and geraniol presented a rapid bactericidal effect against E. coli. Conclusions: The higher antimicrobial activity was related to the presence of hydroxyl groups (phenolic and alcohol compounds), whereas hydrocarbons resulted in less activity. The first group, such as carvacrol, l-carveol, eugenol, trans-geraniol, and thymol, showed higher activity when compared to sulfanilamide. Images obtained by scanning electron microscopy indicate that the mechanism causing the cell death of the evaluated bacteria is based on the loss of cellular membrane integrity of function. The present study brings detailed knowledge about the antimicrobial activity of the individual compounds present in essential oils, that can provide a greater understanding for the future researches.

Efficacy and Mechanism of Traditional Medicinal Plants and Bioactive Compounds against Clinically Important Pathogens

“…Coumarins (12) are benzo-α-pyrones known to stimulate macrophages, which could have an adverse effect on infections [7,120]. Terpenes are organic compounds containing isoprene subunits, which involve microbial membrane disruption [121,122]. Thymol (13), eugenol (14), Cinnamaldehyde (15), carvone (16), and carvacrol (17) (Figure 2) disintegrate the external membrane of various Gram-negative bacteria, releasing LPS and increasing the permeability [123][124][125].…”

Antibacterial Activity and Mode of Action of β-caryophyllene on Bacillus cereus

“…Terpenoids are derived from terpenes with the modification through the addition or removal of functional groups (Mahizan et al 2019). Terpenes can have different chemical functional groups including alcohol, aldehyde, phenol, ketone, ether, and hydrocarbon groups (Guimarães et al 2019). These terpenes and terpenoids are secondary metabolites, which are often used as a functional food, food additives, medicines, nutritional supplements, and in the manufacture of cosmetics because they exhibit antibacterial, antioxidant, and anti-inflammatory properties (Zengin and Baysal 2014).…”

Absolute quantification of terpenes in conifer-derived essential oils and their antibacterial activity

“…The microorganisms are susceptible to various terpenes since investigated EOs differ in their antibacterial profile. In general, the oxygenated terpenes exhibited better antibacterial activity than the hydrocarbon congeners (Nazzaro et al 2013;Guimaraes et al 2019;Iseppi et al 2019;Dahham et al 2015;Hong et al 2004). As described previously, terpenes have several targets in the bacterial membrane and in the cytoplasm of bacterial cell (Burt 2004;Nazzaro et al 2013).…”