# Chemical Composition and Biological Activities of Oregon and Lavender Essential Oils
## 4 Discussion
Damage to treated cells is also suggested by the appearance of the bacterial cytoplasm. In fact, the cytoplasm of the treated bacteria lost its typical grainy appearance and developed large moderately dense areas, which suggests cytoplasm degeneration. Furthermore, observations of the external curly filaments suggest development of an external capsule, which could be induced by the essential oil exposure. It was demonstrated in _K. pneumoniae_ that the construction of a capsule is upregulated by antimicrobial peptides [60]. The safety of the tested substances has been evaluated by the cell viability test. It clearly showed that the essential oils tested did not have cytotoxicity activity against human lymphocytes under the used MTT test. Instead, _O. glandulosum_ essential oils even activated the lymphocyte compared to the untreated ones. In the case of cytotoxic compounds, this phenomenon can be interpreted as a rescue mechanism. At low subtoxic concentrations, cells escape detrimental stimuli by the induction of proliferation, while at higher concentrations, this defense mechanism is overridden by the cytotoxic effects [61]. The respiratory chain, other electron transport systems, and cell enzymes convert the MTT and other tetrazolium salts into formazan crystals. The quantity of these crystals can be determined by spectrophotometry and is used to estimate the number of mitochondria and, thus, the number of viable cells in the sample. Our results are consistent with those in the literature, reporting no cytotoxicity on several cell lines treated with the essential oils of several plant species, such as _Thymus zygis_ subsp. _sylvestris_[49], _Aniba canellilla_[62], and _Salvia officinalis_[63]. However, testing cytotoxicity is essential, especially in the case of substances with good profiles of biological activities. In fact, lemon myrtle oil has been shown to have significant antimicrobial activity against different organisms, but in vitro cytotoxicity tests indicated a very toxic effect against primary cell cultures of fibroblasts of human skin [49]. [PERSON] et al. [64] detected a reduction in viability of human lymphocytes treated with the essential oils of palmarosa, citronella, lemongrass, and vevier, including loss of integrity of the plasma membrane associated with necrosis. Another study showed that lavender oil is cytotoxic in vitro on human skin cells (endothelial cells and fibroblasts) at a concentration of 0.25% (\(v/v\)) [65]. In addition, carvacrol is known to be toxic to mammalian cells at high concentrations; on the other hand, protective effects on DNA have been observed with carvacrol on mammalian cells cultured in vitro [49]. The excessive ROS production is deleterious for cells and tissues since they change the structure and function of biomolecules. _O. glandulosum_ and _L. dentata_ extracts displayed inhibitory effects on leukocyte ROS production compared to untreated control cells. Thus, these extracts can act as antiinflammatory agents as may be efficient in protecting the organism from excess ROS production via radical scavenging activity. The test of ROS generation confirms the activation of the lymphocytes under the essential oil treatments. The activity on lymphocytes is very interesting because these cells play a crucial role in the immune system. Hence, the essential oils, in addition to fighting bacterial infections, could also be able to activate the immune system. It should be noted that a reduction in (excessive) ROS production can indeed reduce tissue damage/inflammation on one side, but that this may be at the expense of the antibacterial efficacy of the cells via ROS, but the strong direct effect of essential oils could compensate for this reduction. Concluding, the in vitro results of the essential oils showed interesting activities. _O. glandulosum_ and _L. dentata_ show remarkable antibacterial and bactericidal activity against antibiotic-resistant _K. pneumoniae_ strains, with no cytotoxicity on human lymphocytes. Instead, they could even potentiate the immune response.