## 3 Discussion
cereus_[35], was also in harmony with our findings on _B. thuringiensis_. From among the most effective bactericidal EOs (thyme, cinnamon and lemongrass), lemongrass was chosen for further studies because of the following practical considerations: _B. thuringiensis_--a recently identified causative agent of PK--is a spore-forming bacterium. Although a recent study has shown that cinnamon, thyme, and lemongrass EOs were all able to reduce the number of viable spores, this effect was the most pronounced in the case of lemongrass EO [18; 36]. Furthermore, cinnamon could cause contact dermatitis if exposed to the skin surface [37]. Percentage-based compound composition results, obtained by HS-SPME/GC-MS analysis, were in agreement with previous studies [38; 39; 40]. A former study has reported that West Indian lemongrass EO (Cymbopogon citratus (DC). [PERSON]) contains about 77% citral. Natural citral is a mixture of two geometric isomers: geranial (citral \(a\), \(\ell\)- or \(\alpha\)-citral) and neral (citral b, (Z)- or \(\beta\)-citral). In the case of West Indian lemongrass EO, their percentage distribution is usually as follows: geranial 36.7-55.9% and neral 25.0-35.2% [41]. Similarly, our results showed that neral comprised 26.1% and geranial comprised 34.5% of the EO. Generally, some discrepancies among EO compound compositions in publications are apparent due to multiple factors, including geographic localization and temperature [42; 43]. It was not surprising that citral showed a characteristic inhibition zone (white spots on Figures 5 and 6) on the TLC-based bioautographic silica plate as this feature has been previously published in the cases of other bacterium species [44]. Our results further support that lemongrass EO is effective against hitherto uncharacterized bacterium species, including the potential aetiological agents of PK. Beyond citral, \(\alpha\)-terpineol also induced antibacterial effects. In order to reveal other potential compounds with antibacterial features in lemongrass EO, HS-SPME/GC-MS analysis was used. The SPME method is an anhydrous sampling technique that involves the use of a fibre-coated extraction phase. In contrast to steam distillation, this technique works at a lower temperature, meaning that the compounds do not decompose or transform, and the proportion of more volatile components increases compared to the less volatile components [45]. Unfortunately, in the frame of this study we could not identify if \(\gamma\)-cadinence and calamenene were antibacterial as these compounds were not available from any supplier. We could only speculate if these EO compounds could also contribute to the antibacterial feature represented by a white spot on the TLC plate (Figures 5C(4),D(4) and 6C(4)) or not. Further studies addressing this issue in the future could clarify this question. The low MIC and MBC values (0.1 mg/mL) of all three tested bacteria (Table 4) confirmed the strong antibacterial activity of citral, similar to recent findings [35] using _B. cereus_ (0.15 mg/mL). Although the antibacterial feature of \(\alpha\)-terpineol was less pronounced (Tables 3 and 4), results from the drop plate method, MIC and MBC tests indicate that this compound--together with cadinence and calamenene--might also contribute to the antibacterial feature of the spot that was analysed by HS-SPME/GC-MS.  
Our results highlight the potential of therapeutics based on West Indian lemongrass EO in the treatment of PK and possibly other superficial skin infections, and revealed the presence of specific compounds with potential therapeutic value.