FTIR analysis of the metabolomic stress response induced by N-alkyltropinium bromide surfactants in the yeasts Saccharomyces cerevisiae and Candida albicans

The activity of surfactants against fungal cells has been studied less than against bacteria, although the medical and industrial importance of the former is of paramount importance. In this paper the surfactant biocidal effect was measured in the yeasts Saccharomyces cerevisiae and Candida albicans with a previously described FTIR bioassay which estimates the stress level as function of the FTIR spectra variation of the cells upon exposition to the chemicals. N-tetradecyltropinium bromide was chosen as stressing agent on the basis of previous preliminary study demonstrating its ability to kill prokaryotic and especially eukaryotic cells at concentration around or over the critical micellar concentration (c.m.c.). Here we show that this surfactant is able to inactivate S. cerevisiae cells at 0.4 mM and C. albicans cells at 0.6 mM after 1 h exposition. FTIR analysis revealed that the surfactant induced metabolomics reactions of S. cerevisiae cells in the regions of amides (W2) and fatty acids (W1). In the same way C. albicans cells showed the maximum stress response in amides (W2) and mixed (W3) regions. Variations of the hydrophobic tail of this surfactant produced a reduced level of cell stress with both the 12C and 16C variants; although these two compounds were more effective in inducing cell mortality in S. cerevisiae but not in C. albicans. In conclusion, this paper has shown that, for this surfactant, the n-alkyl chain must vary between 12C and 16C and that the hydrophilic head size is not as critical as the tail length.