## 2 Results and Discussion
### Unlocking Antimicrobial Potential of the Essential Oil  
The essential oil of _C. erythraea_ showed different antimicrobial potential towards the bacterial species tested. In general, Gram-negative bacteria (_E. coli_ and _S. enteritidis_) were the most sensitive species to the oil, while there was no effect to _P. fluorescens_ growth. Ampicillin (10 \(\upmu\)g), norfloxacin (10 \(\upmu\)g), ofloxacin (5 \(\upmu\)g) and tetracycline (30.5 \(\upmu\)g) were used as positive reference standards to determine the sensitivity of bacterial strains tested. Although applied antibiotics possessed in general strongest antibacterial activity, the activity of _C. erythraea_ to _E. coli_ was almost identical to the inhibition zones of ampicillin (Table 3). Antibiotics are molecules with selective activity towards the cells of microorganisms while essential oils are compounds with many different and, often, variable components that attack different parts of cell structures. It is extremely hard to compare zones of inhibition produced by antibiotics and bioactive compounds since they differ in nature and mechanism of the inhibition. Nevertheless, antibiotics are used as controls in any compound testing to ensure information about sensitivity of tested strains and internal control. Observed higher antimicrobial activity is presumably related to the oil principal constituents, although part of the activity could result from the presence of oil minor constituents. In general, the most active essential oils (principally composed of carvacrol, thymol, citral, eugenol and their precursors [20; 21; 22]) against the strains of _E. coli_ are: the oil of oregano (_Origanum vulgare_), thyme (_Thymus vulgaris_), bay (_Pimenta racemosa_) and clove (_Eugenia caryophyllata_). The oil of _C. erythraea_ contained thymol and carvacrol as major constituents and exhibited noticed activity against _E. coli_. Menthol is abundant in _C. erythraea_ oil and the MICs demonstrated [23] that menthol is more toxic against _E. coli_ than thymol. The antimicrobial activity mechanism of thymol, carvacrol and menthol is well known (alteration of membrane permeability [23]). In addition, strong antimicrobial activity of basil (_Ocinum basilicum_) oil (major constituents were linalool and 1,8-cineole) against _S. enteritidis_ is known [24] and linalool was present in _C. erythraea_ oil that exhibited activity against _S. enteritidis_. However, there is evidence that total essential oil is more strongly antimicrobial than is accounted for the additive effect of their major antimicrobial components; minor components appear, therefore, to play a significant role [25]. Gram-positive bacteria demonstrated increased resistance to _C. erythraea_ oil, compared to Gram negative ones. To _L. monocytogenes_, the essential oil exhibited no inhibitory effect, while weak inhibitory zones (7 and 8 mm, respectively), were observed to _B. cereus_ and _S. aureus_ growth. \begin{table}
\begin{tabular}{|c|c|c|c|c|c|c|} \hline  & & **Culture** & **Essential** & \multicolumn{4}{c|}{**Antibiotics**} \\ \cline{3-6}  & & **oil** & **Ampicillin** & **Norfloxacin** & **Ofloxacin** & **Tetracycline** \\ \hline \multirow{4}{*}{**C. coli**} & _Escherichia coli_ & \(13\pm 0.577\) * & \(15\pm 2.828\) & \(26\pm 0\) & \(25\pm 0\) & \(20\pm 1.414\) \\ \cline{2-6}  & _Pseudomonas_ & \multirow{2}{*}{\(0\pm 0\)} & **\(\ast\)** & \(40\pm 5.657\) & \(31\pm 0\) & \(22\pm 1.414\) \\ \cline{1-1} \cline{3-6}  & _Salmonella enteritidis_ & \(13\pm 1\) & \(24\pm 0\) & \(27\pm 0\) & \(26.5\pm 0.707\) & \(24.5\pm 0.707\) \\ \hline \multirow{4}{*}{**C. coli**} & _Bacillus cereus_ & \(7\pm 0.693\) & \(13\pm 0.707\) & \(22\pm 0\) & \(24\pm 0.707\) & \(22\pm 0.707\) \\ \cline{2-6}  & _Listeria monocytogenes_ & \(0\pm 0\) & \(37\pm 0\) & \(30.5\pm 0.707\) & \(28.5\pm 0.707\) & \(37.5\pm 2.121\) \\ \cline{1-1} \cline{2-6}  & _Staphylococcus aureus_ & \(8\pm 0.289\) & \(45\pm 1.414\) & \(29.5\pm 3.536\) & \(29.5\pm 2.121\) & \(30.5\pm 3.536\) \\ \hline \end{tabular}  
* = no inhibition.  
\end{table}