Antifungal and Anti-Virulent Activity of Origanum majorana L. Essential Oil on Candida albicans and In Vivo Toxicity in the Galleria mellonella Larval Model.

Banu Kaskatepe,Sukran Ozturk,Ivan Kosalec,Sinem Aslan Erdem,Mehmet Koyuncu,Zehra Safi Oz,Eldan Subasi,Josipa Vlainić

doi:10.3390/molecules27030663

Abstract

The aim of this study was to investigate and compare in detail both the antifungal activity in vitro (with planktonic and biofilm-forming cells) and the essential oil composition (EOs) of naturally growing (OMN) and cultivated (OMC) samples of Origanum majorana L. (marjoram). The essential oil composition was analyzed using GC-MS. The major constituent of both EOs was carvacrol: 75.3% and 84%, respectively. Both essential oils showed high antifungal activity against clinically relevant Candida spp. with IC50 and IC90 less than or equal to 0.5 µg mL−1 and inhibition of biofilm with a concentration of 3.5 µg mL−1 or less. Cultivated marjoram oil showed higher anti-biofilm activity against C. albicans. In addition, OMC showed greater inhibition of germ-tube formation (inhibition by 83% in Spider media), the major virulence factor of C. albicans at a concentration of 0.125 µg mL−1. Both EOs modulated cell surface hydrophobicity (CSH), but OMN proved to be more active with a CSH% up to 58.41%. The efficacy of O. majorana EOs was also investigated using Galleria mellonella larvae as a model. It was observed that while the larvae of the control group infected with C. albicans (6.0 × 108 cells) and not receiving treatment died in the controls carried out after 24 h, all larvae in the infected treatment group survived at the end of the 96th hour. When the treatment group and the infected group were evaluated in terms of vital activities, it was found that the difference was statistically significant (p < 0.001). The infection of larvae with C. albicans and the effects of O. majorana EOs on the hemocytes of the model organism and the blastospores of C. albicans were evaluated by light microscopy on slides stained with Giemsa. Cytological examination in the treatment group revealed that C. albicans blastospores were phagocytosed and morphological changes occurred in hemocytes. Our results indicated that the essential oil of both samples showed strong antifungal activities against planktonic and biofilm-forming C. albicans cells and also had an influence on putative virulence factors (germ-tube formation and its length and on CSH).

Highlights

Herbs and spices are very well known over the world and have been used since ancient times for flavoring, coloring, and preserving food, as well as for medicinal and cosmetic purposes [1,2]
The yieldBsootfhesosielsntwiaelroeilrsicwheirne ofoxuyngdentaotebde hmigohneort,earps e5n.3e%s, and 6th.3e%m. ain constituents of the two EBOotsh foroilms wOeMreNricahndinOoMxyCgewnaetreedcamrvonacortoelr,paecnceosu, natnindgthfoerm7a5i.n3%coannsdtit8u4e%nt,saonfdthpetwo essential oil composition (EOs) from OMN and OMC were carvacrol, accounting for 75.3% and 84%, and p-. Both oils were rich in oxygenated monoterpenes, and the main constituents of the two EOs from OMN and OMC were carvacrol, accounting for 75.3% and 84%, and p-cymene, accounting for 7.1% and 4.8%, respectively
Our results showed for the first time that in addition to the antifungal activity of O. majorana EOs against clinically important Candida spp. in planktonic form, both oils inhibited biofilm formation (Figure 1)

Summary

Introduction

Herbs and spices are very well known over the world and have been used since ancient times for flavoring, coloring, and preserving food, as well as for medicinal and cosmetic purposes [1,2]. The antimicrobial properties of marjoram essential oil are well known and have been studied, no research work has been found on its inhibitory effect on the virulence of Candida albicans and the larval model of Galleria mellonella. G. mellonella is one of the preferred in vivo models to determine the pathogenesis of infections and the virulence factors of the microorganisms and to identify effective treatment options. It is used in areas such as determining fungal and bacterial loads and evaluating antimicrobial peptides [25,26]. It is emphasized that this organism is a reliable model for both bacterial and fungal pathogenicity studies [33,34,35,36]

Objectives

Methods

Results

Conclusion