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 S. aureus and E. faecalis 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 S. aureus and E. faecalis incubated with compound DL412 were species-specific. Destructive changes in S. aureus cells when exposed to DL412 compound and all DL412-carvacrol hybrids did not differ. DL412 and DL412-carvacrol hybrids in E. faecalis 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 S. aureus and E. faecalis cells.