The cytotoxicity assays of the EO and its fractions are shown
in Table 3. A relationship between cytotoxicity and antimicrobial
activity was established through the selectivity index (SI). The SI
values were calculated by the logarithm of the ratio of the CC50
and the MIC value for microorganisms (SI = log [CC50]/[MIC]). Positive
values represent elevated selectivity against microorganisms,
whereas negative values indicate elevated toxicity towards HeLa
cells (Case et al., 2006). The SI for the EO at inhibitory concentrations
of 400 and 100 g mL−1 were −0.46 and 0.14, respectively. The positive
value found for the concentration of 100 g mL−1 indicates
that the EO is more selective against P. nigrescens and P. gingivalis
than HeLa cells. On the other hand, the antimicrobial activity of
the EO was moderated (400 g mL−1), and the SI indicated higher
toxicity to HeLa cells.
W