## 3 Results  
The antimicrobial susceptibility of the tested isolates is presented in Table 2. Both MRSA and VRE were identified as multidrug-resistant (resistance to 3 or more antibiotics classes tested). MIC values of selected essential oils against MRSA, VRE and ATCC strains are presented in Figure 1. Origanum, thyme, tea tree and basil oils demonstrated antibacterial activity, while MIC values were higher on the wild MRSA isolates than on the reference strains _S. aureus_ ATCC 29213, _S. aureus_ ATCC 43300 and _S. epidermidis_ ATCC 12228 as well. In general, chamomile oil demonstrated no antibacterial action. The only exception was one sensitive MRSA strain in which both low bacteriostatic (MIC = 2% _v/v_) and bactericidal (MBC = 2% _v/v_) efficacy was occurred (Figure 1A). Origanum, thyme, and tea tree oils demonstrated great antimicrobial activity against enterococci, while basil and chamomile oils presented weak and no antimicrobial properties, respectively (Figure 1B). The range of MIC and MBC values of the tested essential oils against the selected isolates are presented in Table 3. The mean values of the MICs \(\pm\) SD (% _v/v_) reported for MRSA were 0.25 \(\pm\) 0.14 for origanum oil, 0.41 \(\pm\) 0.27 for thyme oil, 0.56 \(\pm\) 0.30 for tea tree oil, and 1.42 \(\pm\) 1.43 for basil oil. Regarding enterococci, origanum oil demonstrated the most significant antimicrobial activity (0.58 \(\pm\) 0.28), followed by thyme oil (1.22 \(\pm\) 0.60) and tea tree oil (2 \(\pm\) 1.22). \begin{table}
\begin{tabular}{c c c} \hline \hline
**Antibiotics \(\ddagger\)/Bacteria** & _S. aureus (n = 16)_ & _Enterococcus_ spp. (n = 9)_ \\ \hline PEN & 16 (100\%) & 9 (100\%) \\ AMP & - & 9 (100\%) \\ VAN & 3 (18.7\%) & 9 (100\%) \\ TEC & 4 (25\%) & 9 (100\%) \\ ERY & 11 (68.7\%) & - \\ CC & 11 (68.7\%) & - \\ GEN & 4 (25\%) & - \\ FOX & 16 (100\%) & - \\ CIP & 11 (68.7\%) & 7 (77.7\%) \\ QD & 4 (25\%) & 9 (100\%) \\ LZD & - & 6 (66.6\%) \\ TET & - & 5 (55.5\%) \\ \hline \hline \end{tabular} \(\ddagger\) PEN, penicillin G; AMP, ampicillin; VAN, vancomycin; TEC, teicoplanin; ERY, erythromycin; CC, clindamycin; GEN, gentamicin; FOX, cefoxitin; CIP, ciprofloxacin; QD, quinupristin/dalfopristin; LZD, linezolid; TET, tetracycline.  
\end{table} 
Table 2: Antimicrobial resistance (%) of the strains used in this study. In Figures 2 and 3 the time-kill assays of each essential oil at concentrations ranging from 0.125% up to 4% (_v/v_) against two of the tested clinical isolates (one VRE and one MRSA) are presented. In these two assays, in contrast to the majority of the tested bacteria, the presented VRE isolate (VRE no. 2) exhibited bactericidal response to tea tree and thyme oils at 1% (_v/v_) and 0.5% (_v/v_) concentrations respectively at 48 h, while the total reduction of viable cells was achieved at higher concentrations at 24 h (Figure 2). However, the activity of the afore-mentioned oils was reduced at 48 h on three clinical MRSA isolates and the bactericidal values were one dilution higher than the displayed values at 24 h. Figure 3 presents an example of one clinical MRSA strain (MRSA no. 4) isolated from wound swab, which demonstrated bactericidal response at 1% (_v/v_) and 2% (_v/v_) to tea tree oil and at 0.12% (_v/v_) and 0.25% (_v/v_) to thyme oil, after 24 h and 48 h of incubation, respectively.