Changes in the Ultrastructure of Candida albicans Treated with Cationic Peptides

Abstract

Candida albicans is becoming increasingly harmful for humans, which determines the need for new effective antifungal preparations. Currently, when testing antifungals, various morphological methods are used, among which transmission electron microscopy (TEM) is not the leading one. In this work, we used TEM to study the submicroscopic changes in C. albicans cells induced by cationic peptides R9F2 and (KFF)3K. Studies were performed on C. albicans-34 strain from the Collection of EMTC of ICBFM SB RAS in logarithmic phase. R9F2 and (KFF)3K showed an antifungal effect (MIC 10 and 20 μM) and suppressed fungal hyphal growth. Semithin and ultrathin sections of fungal suspensions incubated with 10 μM of peptides were studied at regular intervals from 15 min to 24 h. The first target of both peptides was plasmalemma, and its “alignment” was the only common morphological manifestation of their effect. Other changes in the plasmalemma and alteration of the vacuole and cell wall ultrastructure distinctly differed in cells treated with R9F2 and (KFF)3K peptides. In general, our work has shown pronounced differences of the temporal and morphologic characteristics of the effect of peptides, evidently related to their physicochemical properties. The benefit of TEM studies of ultrathin sections for understanding the mechanisms of action of antifungal drugs is shown.

Candida albicans Reactive Oxygen Species (ROS)-Dependent Lethality and ROS-Independent Hyphal and Biofilm Inhibition by Eugenol and Citral

“…4 ). Similar findings have been reported for C. albicans exposed to known membrane disruptors such as Amp B ( 41 ), cationic peptides ( 54 ), clove, thyme ( 55 ) rosemary and its major components ( 41 ).…”

Changes in the Ultrastructure of Staphylococcus aureus Treated with Cationic Peptides and Chlorhexidine

“…Mesosomes in S. aureus cells were the most striking and common feature of action of R9F2 and (KFF)3K peptides, ultrathin sections of all cells showed the presence of these membranous structures and many of them had a high electron density. Similar osmiophilic multimembrane structures have been observed in C. albicans cells; however, their formation followed damage to the cytoplasmic membranes or cell membrane [ 19 ], whereas in S . aureus cells, mesosomes were formed first, and osmiophilia appeared later.…”

“…The different character of ultrastructural changes after 1 min of incubation proved a specificity of reagents action. Fast effects were observed when R9F2 and (KFF)3K peptides attacked cells of C. albicans [ 19 ]. Both C. albicans and S. aureus showed damage of cell membrane as a first event in the interaction with R9F2 and (KFF)3K, and this evidence suggests that the cell wall did not protect microorganisms from peptide action, regardless of cell wall thickness and chemical composition.…”

“…Thus, we revealed a different pattern in damage to the S. aureus cell wall by the R9F2 and (KFF)3K peptides and chlorhexidine, the latter causing significantly more pronounced changes. The cell wall of C. albicans also were affected by chlorhexidine, and ultrastructural changes clearly differed from those caused by R9F2 and (KFF)3K peptides [ 19 ]. Thus, the changes in cell wall ultrastructure upon treatment with chlorhexidine were different in S. aureus and C. albicans , which is apparently due to the different chemical composition of the walls.…”

“…Earlier we synthesized and characterized two cationic AMPs, highly amphiphilic R9F2 and moderately amphiphilic peptide (KFF)3K, and showed their antibacterial effect, as well as the absence of cytotoxicity for eukaryotic cells [ 18 ]. We applied TEM of ultrathin sections for examination of successive changes in Candida albicans ultrastructure under the influence of R9F2 and (KFF)3K peptides and found clear differences in their effects [ 19 ]. C. albicans is an eukaryotic microorganism with a thick cell wall, mainly composed of highly mannosylated glycoproteins [ 20 ], and it was interesting to compare its damage by R9F2 and (KFF)3K peptides with their effects on prokaryotic microorganisms enclosed in a cell wall, such as S. aureus .…”