*2.4.3.2 Antiviral activity*

*Essential Oils - Bioactive Compounds, New Perspectives and Applications*

valuable drugs used in the treatment include vinblastine, vincristine, camptothecin, and Taxol [89]. Many studies pointed out the anticancer properties of plants. Over 500 research papers are published on the anticancer activity of EOs [90–93], even though, till date, there are no scientific studies showing that aromatherapy can cure or prevent cancer. Most promising research results obtained from in vitro studies revealed that EOs were found to affect cancer cell lines in petri dishes. EOs are well known for their anti-inflammatory activity; hence it appeared that EOs could also have anticancer effects as there is a relationship between the production of reactive oxygen species to the origin of oxidation and inflammation that can lead to cancer. More than 100 EOs from more than 20 families of plants have been tested on more than 20 different types of cancers in the past 10 years [94]. Bourgou and collaborators showed that the EO from seeds of black cumin (*Nigella sativa* L.) significantly inhibits the growth of A-549 and DLD-1 cancer cell lines with IC50 values of 43.0 and 46.0 μg/mL, respectively [95]. In 2012, Wang and collaborators reported the toxicology potential of EO of *Rosmarinus officinalis* L. and its three main components (including *α*-pinene, *β*-pinene, and 1,8-ceneole) toward three human cancer cell lines: the EO showed a strong cytotoxicity toward the three cancer cells with IC50 values of 0.025, 0.076, and 0.13‰ (v/v) on SK-OV-3, HO-8910, and Bel-7402,

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* 

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* 

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*

**86**

respectively [96].

*fluorescens* [101].

*alba*) > sage (*Salvia officinalis*) [102].

*2.4.3.1 Antibacterial and antifungal activities*

*2.4.3 Antimicrobial activity*

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].
