## 4 Discussion  
The emergence of resistant bacteria is of imperative significance for public health safety [40]. The observed evolution of drug resistance is the end-result of long term selective pressure applied to  
Figure 3: Time-kill kinetics for origanum oil, basil oil, tea tree oil, and thyme oil on the MRSA no. 4 clinical isolate (isolated from wound swab). Figure 2: Time-kill kinetics for origanum oil, basil oil, tea tree oil, and thyme oil on a vancomycin resistant _E. fecium_ (VRE no. 2) clinical isolate (isolated from wound swab). bacteria due to inconsiderate exploitation of the drug use. The appearance of drug-resistance leads to decrease of the existing therapeutic options thus implying the urgency for the development of new antimicrobials [35]. For centuries it has been well acknowledged the potential of medicinal plants to produce a wide range of phytochemicals, mostly alkaloids, phenolic compounds, polyacetylenes and polypeptides [2; 35; 41]. In particular, essential oils have been studied for antimicrobial properties against various non-pathogenic microorganisms and to a lesser extent against pathogenic microorganisms. Although their activity against bacteria of the same genera and species appears to be comparable, yet drug-resistant clinical isolates may show different response from the usually used reference strains [42; 43]. Therefore, to better document the antimicrobial performance of essential oils, it is essential to test drug-resistant isolates from different sources (diseased humans, animals, food, water, environment) in order to have a realistic indication of their antimicrobial effect [35]. In the available literature the majority of the published papers employ reference strains, or non-pathogenic strains and scarcely multi-drug resistant isolates. This variety in the used strains and the diversity of the employed methods produces variable findings and the comparative assessment of the published results is difficult. Regarding the essential oils and the bacterial isolates employed in the present study the literature search revealed only a few publications relating to drug-resistant clinical strains. However, there are variations in the methodological approach that make any comparison of their findings with our results rather inaccurate. A study on the antimicrobial activity of origanum (_Origanum vulgare_) and basil (_Ocimum basilicum_) oils against clinical strains of _S. aureus_ showed that only origanum essential oil was effective and concluded that wild clinical strains are less sensitive to essential oils compared to prototype strains but no data on the strain susceptibility are presented [29]. [PERSON] et al. (2004) using the agar diffusion method, have evaluated the MIC values of origanum oil (_O. vulgare_, thymol chemotype) at a range of 0.063 to 0.125% (_v/v_) against methicillin-resistant _S. aureus_ and methicillin-resistant _S. epidermidis_ strains and at 0.125% (_v/v_) against _S. aureus_ ATCC 25923, _S. aureus_ ATCC 43300 and _S. epidermidis_ ATCC 12228 [44]. Although [PERSON] et al., have used the same ATCC strains which we used in our study too, the methodological approach is different justifying the observed discrepancies (Table 3). [PERSON] et al. (2005) report that the MIC of _S. aureus_ ATCC 33591 to origanum oil, determined by a broth macrodilution method, was 0.5% (_v/v_), but here again this is a different reference strain [45]. [PERSON] et al. (1999), using the broth microdilution method, evaluated the MIC of tea tree oil, basil oil, origanum oil, and thyme oil against _S. aureus_ National Collection of Type Cultures (NCTC) 6571 at concentrations 0.5%, 2%, 0.12% and 0.25% (_v/v_) respectively [46], while [PERSON] et al. (2002) report that the MIC and MBC of tea tree oil against _S. aureus_ ATCC 9144 were determined at concentrations 0.25% and 0.5% (_v/v_) respectively [47], but a different reference strain was used and no clinical drug-resistant isolates were tested.