The purposeful development of synthetic antibacterial compounds requires an understanding of the relationship between effects of compounds and their chemical structure. This knowledge can be obtained by studying changes in bacteria ultrastructure under the action of antibacterial compounds of a certain chemical structure. Our study was aimed at examination of ultrastructural changes in S. aureus cells caused by polycationic amphiphile based on 1,4‒diazabicyclo[2.2.2]octane (DL₄12), ciprofloxacin and their hybrid (DL₅Cip6); the samples were incubated for 15 and 45 min. DL₄12 first directly interacted with bacterial cell wall, damaging it, then penetrated into the cell and disrupted cytoplasm. Ciprofloxacin penetrated into cell without visually damaging the cell wall, but altered the cell membrane and cytoplasm, and inhibited the division of bacteria. The ultrastructural characteristics of S. aureus cells damaged by the hybrid clearly differed from those under ciprofloxacin or DL₄12 action. Signs associated with ciprofloxacin predominated in cell damage patterns from the hybrid. We studied the effect of ciprofloxacin, DL₄12 and their hybrid on S. aureus biofilm morphology using paraffin sections. Clear differences in compound effects on S. aureus biofilm (45 min incubation) were observed. The results obtained allow us to recommend this simple and cheap approach for the initial assessment of antibiofilm properties of synthesized compounds.

The aim: Design and synthesis of new compounds with antibacterial activity. Determination of the minimum inhibitory and minimum bactericidal concentration of conjugates of cationic amphiphiles based on quaternary salts of 1,4-diazabicyclo[2.2.2]octane with ciprofloxacin. Materials and methods: The article is dedicated to the synthesis and primary assessment of antibacterial activity in vitro of conjugates of cationic amphiphiles based on quaternary salts of 1,4-diazabicyclo[2.2.2]octane with ciprofloxacin against gram-negative and gram-positive microorganisms. Results: The present work provides hybrid structures which include the widely used antibiotic ciprofloxacin and tetra-cationic DABCO derivatives. The last ones previously showed a wide spectrum of antimicrobial activity as well as primary studies of their antibacterial activity against gram-positive and gram-negative microorganisms in vitro. There was a high in vitro antibacterial activity against gram-negative pathogens, moderate against Staphylococcus aureus and low against Enterococcus faecalis. Conclusions: A range of amphiphilic polycationic compounds based on quaternary salts of 1,4-diazabicyclo[2.2.2]octane (DABCO) was synthesized and their biological activity was studied. The compounds have demonstrated high antibacterial activity. We assume that they can serve as a basis for the development of new antibacterial drugs.

The cationic amphiphile DL ₄ 12, has been synthesized, possessing ribonuclease activity (D—DABCO (1,4-diazabicyclo[2.2.2]octane); L ₄ is a tetramethylene linker; 12 is a dodecyl residue) and pronounced antibacterial properties. A suspension of Salmonella enterica ATCC 14028 cells was incubated in 5 μM DL ₄ 12 solution for 15 and 30 min or 5 μM ciprofloxacin solution (comparison drug); intact cells served as a control. Samples were fixed with 4% formaldehyde and 1% OsO ₄ or by the Ryter-Kellenberger method with 1% OsO ₄ post-fixed with 0.5% uranyl acetate, then dehydrated and embedded in an epoxy resin mixture. The obtained ultrathin sections were examined in a Jem 1400 electron microscope. After 15 min of incubation with the DL ₄ 12 compound, visible ribosomes disappeared from the entire cytoplasm of S. enterica cells. A homogeneous substance of medium electron density appeared in the periplasmic space, capable of penetrating into the cytoplasm, in which polymorphic inclusions were formed. Pronounced ultrastructural changes were observed in the nucleoids of the bacteria: they were rounded, and the DNA strands “glued” together into bundles. The structure of the outer membrane has not change. The observed changes in the structure of S. enterica were similar when fixed by different methods and were due to a combination of ribonuclease activity and the amphiphilic properties of DL ₄ 12. The ultrastructural changes we identified have not been described in the scientific literature. This study is the first to visualize the effects of ribonuclease and the amphiphilic component of the DL ₄ 12 compound in bacterial 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.

An Erratum to this paper has been published: https://doi.org/10.1134/S0003683825090030

Background/Objectives: The rapid emergence and spread of antibiotic-resistant bacterial strains represent a major global health threat, requiring the development of novel broad-spectrum antimicrobial agents. This study aims to design, synthesize, and evaluate a novel series of multitarget amphiphilic carvacrol derivatives to combat molecular resistance mechanisms by combining a natural monoterpene with polycationic ribonuclease scaffolds. Methods: A series of 16 dimeric carvacrol–1,4-diazabicyclo[2.2.2]octane (DABCO) hybrids, including both novel and previously reported derivatives, with varying central and lateral linkers were synthesized. In vitro antibacterial activity was evaluated against Gram-positive (S. aureus) and Gram-negative (E. coli, S. enterica, C. freundii, P. aeruginosa, A. baumannii) strains. Antibacterial action was examined through a time-kill kinetic assay against S. aureus at minimum inhibitory concentrations (MICs). RNA-hydrolyzing efficiency (using a FAM-labeled 17-mer ribooligonucleotide), hemolytic activity on rabbit red blood cells, and cytotoxicity (MTT assay) against RPMI8226, LMTK, and MEF cell lines were assessed. Results: Several compounds exhibited potent antibacterial activity, with MIC values ranging from 4 to 63 µM against most strains. The most active hybrid, DL4CAR-6, demonstrated broad-spectrum efficacy (MIC 4–16 µM against most strains) and outperformed the reference amphiphile DL4-12 against P. aeruginosa eightfold. Bacterial growth inhibition kinetic assay revealed that the cationic amphiphiles eradicate S. aureus faster than the reference antibiotic, indicating rapid membrane disruption. Most hybrids demonstrated pronounced RNA-hydrolyzing activity (up to 60% cleavage). The hemolytic assay showed less than 10% hemolysis for most compounds even at 500 µM. Furthermore, DL4CAR-6 displayed low cytotoxicity (IC₅₀ 114–250 µM), with safety thresholds exceeding effective antibacterial doses. Conclusions: The newly developed carvacrol–DABCO amphiphilic hybrids represent a promising class of multitarget antibacterial agents. Their broad-spectrum efficacy, bactericidal kinetics, RNA-cleaving activity, low hemolytic toxicity, and favorable selectivity indices support their potential for further in vivo evaluation.