*2.4.3 Antimicrobial activity*

EOs are well-kwon as antimicrobial agents and are well documented in numerous research works. Their antimicrobial activity depends not only on the presence of the main active compounds but also on the interaction between different components which can have synergistic or antagonistic actions. It also depends on the content, concentration, interaction between main active components, and susceptibility of microorganisms [97, 98]. The inactive compounds might influence resorption, the rate of the reactions, as well as biological activities of active compounds. The combination of both major and minor components can thus modify the activity to exert significant synergistic or antagonistic effect [99, 100]. EOs extracted from cinnamon, oregano, and thyme showed significant antibacterial activities against *Escherichia coli*, *Bacillus thermosphacta*, *Listeria monocytogenes*, and *Pseudomonas fluorescens* [101].

In general, EOs in decreasing order of antimicrobial activities are reportedly as follows: oregano (*Origanum vulgare*) > clove (*Syzygium aromaticum*) > coriander (*Coriandrum sativum*) > cinnamon (*Cinnamomum cassia*) > thyme (*Thymus vulgaris*) > mint (*Mentha*) > rosemary (*Salvia rosmarinus*) > mustard (*Sinapis alba*) > sage (*Salvia officinalis*) [102].

### *2.4.3.1 Antibacterial and antifungal activities*

Antibiotic resistance is one of the most serious health burdens worldwide due to the continuous appearance of antibiotic-resistant bacterial strains. The bacteria that cause the most major clinical problems are *Klebsiella* and *Enterobacter* species, *Staphylococcus aureus*, *Enterococcus faecium*, *Clostridium difficile*, *Acinetobacter baumannii*, *Pseudomonas aeruginosa*, and *Escherichia coli* [103]. Generally, EOs are more active on gram-positive bacteria due to the presence of peptidoglycan layer, which lies outside the outer membrane. In gram-negative bacteria, the outer membrane is composed of a double layer of phospholipids, which is linked to the inner membrane by lipopolysaccharide [104]. Several studies on the bioactivity of EOs have revealed their antibacterial and antifungal potential on different pathogen microorganisms [105–108]. Previous studies revealed that the EOs from *Piper guineense*

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*Terpenoids as Important Bioactive Constituents of Essential Oils DOI: http://dx.doi.org/10.5772/10.5772/intechopen.91426*

*2.4.3.2 Antiviral activity*

*2.4.4 Anti-inflammatory activity*

*2.4.5 Miscellaneous activities*

macrophages than to parasites [115].

**2.5 Composition of essentials oils**

two or three appearing to be major ones [116, 117]:

• Aromatic and phenolic components

• Straight-chain compounds not containing any side chain

*zeamais* adults [114].

• Terpenoids

• Sulfured derivatives

and γ [113].

fruit and *P. caldense* roots were active against the gram-negative bacteria *E. coli* and *P. aeruginosa* [109, 110]. EOs have been reported to possess potent antimicrobial activity, exhibiting bacteriostatic and bactericidal effects against tested pathogens.

New agents that are effective against common pathogens are needed particularly for those resistant to conventional antiviral agents. The ability of viruses to persist in fresh products, as well as their low infectious dose, could lead to serious foodborne problems [111]. Plants and plant-derived natural products provide unlimited opportunities for new antiviral drugs. Many EOs have been investigated in recent years toward their antiviral activity. As conclusion of their work, Reichling and collaborators reported that particular free viruses are very sensitive to EOs [112].

Most of EOs have been firstly identified and used for the treatment of inflammatory and oxidative diseases. *Cymbopogon citratus* (Lemongrass) is a popular herb used as analgesic and anti-inflammatory agent. It has been reported that its EO suppresses COX-2 expression promoter activity; citral was identified as the major component responsible for suppressing COX-2 expression and for activating PPARα

The insect repellent activity of EOs is well studied and many research papers have been published. The EOs of *Hyptis spicigera* Lamarck and *Hyptis suaveolens* (L) Poitier and *Lavandula angustifolia* (Miller) showed repellent activity on *Sitophilus* 

EOs of the leaves of *Endlicheria bracteolate* was tested against *Leishmania amazonensis* by Rottini and collaborators. The antileishmanial activity was evaluated against promastigotes and intracellular amastigotes, and cytotoxicity was performed with J774.G8, which were incubated with different concentrations of *E. bracteolate*. Promastigote forms showed *E. bracteolate* EO IC50 value of 7.945 μg/mL (24 h). The IC50 value was 15.14 μg/mL showing that *E. bracteolate* EO is less toxic to

EOs are generally very complex mixture (60–300) of nonpolar and semipolar lipophilic constituents of low molecular weight, at different concentrations with

The variation in odor and taste of EO depends on the plants variety, the harvest-

ing seasons, the geographical location, the drying methods, and the extraction

fruit and *P. caldense* roots were active against the gram-negative bacteria *E. coli* and *P. aeruginosa* [109, 110]. EOs have been reported to possess potent antimicrobial activity, exhibiting bacteriostatic and bactericidal effects against tested pathogens.
