Ultrastructural Study of the Effects of Hybrid Compounds of Natural Monoterpene Carvacrol and Synthetic Cationic Amphiphile DL412 on S. aureus and E. faecalis Cells

Ultrastructure changes in <i>S. aureus</i> and <i>E. faecalis</i> bacteria incubated with synthetic cationic amphiphile DL₄12 and its hybrids with the natural monoterpene carvacrol were studied. The hybrid compounds DL₄CAR-6, DL₅CAR-6, DLpCAR-6, and DLoCAR-6 contained two carvacrol molecules and differed in central linker structure. The study was conducted on ultrathin sections of bacteria fixed by the Ryter-Kellenberger method and on a Jem 1400 transmission electron microscope (Jeol, Tokyo, Japan). Ultrastructure changes in <i>S. aureus</i> and <i>E. faecalis</i> incubated with compound DL₄12 were species-specific. Destructive changes in <i>S. aureus</i> cells when exposed to DL₄12 compound and all DL₄12-carvacrol hybrids did not differ. DL₄12 and DL₄12-carvacrol hybrids in <i>E. faecalis</i> cells damaged all structures except the cell wall. Compound DL₄12 and its hybrids disrupted the ultrastructure of nucleoid and DNA strands in both bacterial species. Complete disorganization of ribosomes in cells of both bacteria occurred upon incubation with compound DL₄12 and its carvacrol-bearing analog DL₄CAR-6. Inclusions in bacterial cells exposed to all compounds had the same ultrastructure. The study showed that all compounds used possess multitarget properties; the structure of the central linker of hybrid compounds plays a significant role in the nature of their damaging effect on <i>S. aureus</i> and <i>E. faecalis</i> cells.