**Acknowledgements**

*Essential Oils - Oils of Nature*

**8.1 Lavender essential oil**

**8.2 Cinnamon bark essential oil**

bacteria [104].

**8.3 Peppermint essential oil**

**9. Future perspectives**

**8. Synergistic activity of essential oil**

The synergistic effects between the EOs and antibiotics against the MDR bacteria have been investigated [97]. The synergistic effect can be defined as the ability of EO components to act together with the antibiotic component to increase the activity of the EO against MDR bacteria [98]. This is important because it will help to reduce the use of antibiotics and decrease the rates of antibiotic resistance [97]. Some studies have been done to assess the combinatory activities of lavender, cinnamon bark, peppermint, and other EOs against bacteria, and the results show there is a synergistic

The lavender EO is used in traditional medicine as well as in cosmetic products; this oil is believed to have sedative, anti-inflammatory, and antimicrobial effects [99]. Lavender EO shows a synergistic effect when combined with piperacillin antibiotic against beta-lactamase-producing *Escherichia coli* under study with fractional inhibitory concentration (FIC) index between 0.26 and 0.5 [97]. This finding shows that it's possible to use the lavender EO as an agent in modifying the antibiotic resistance [97]. Another study which aimed to compare the antimicrobial efficacy of four types of lavender oil on MSSA and MSRA shows that by direct contact the oil inhibits the growth of these microbes [100]. Fusidic acid is one of the compounds within this oil which gives it the antimicrobial activity, the mechanism of which is

effect [97]. Some of these EOs will be discussed in the following sections.

to cause bacterial cell damage by reducing synthesis of proteins [101].

The cinnamon bark EO can be obtained from different parts of the tropical evergreen tree, which is important for human health and agriculture uses [102]. Previously, a study reported that a combination of cinnamon bark EO with piperacillin resulted in a synergistic relationship with FIC ≤ 0.5, and this result indicates the possibility of using cinnamon bark EO as a resistance-modifying agent against MDR bacteria [97, 103]. Cinnamon bark oil contains cinnamaldehyde which is one of the compounds that inhibit the activity of amino acid decarboxylase; this compound with others within the oil gives this oil the ability to inhibit some pathogenic

Peppermint EO is significant in inhibiting the microbial growth and increasing the shelf-life of food by preventing food spoilage [105]. Combination of piperacillin and peppermint EOs with FIC in the range 0.26–0.5 was found showing a synergistic effect that is absent in 31 other combination pairs that were studied, indicating a promising alternative to reduce the use of antibiotic and achieve the reverse betalactam antibiotic resistance [91]. The antibacterial activity for this oil is associated

Research about the reversal antibiotic resistance is important to preserve the healthy microbial ecosystem in the human host. It is imperative to understand the cause of antimicrobial resistance and to find solutions to alleviate the present

with menthol and ethyl acetate in high concentrations [106].

**58**

The authors would like to thank the HCT Research Grants from the Higher Colleges of Technology, UAE for supporting this work.
