Encyclopedia
Please note this is an old version of this entry, which may differ significantly from the current revision.
Subjects:
Plant Sciences
Fungi from the genus Candida are very important human and animal pathogens. Many strains can produce biofilms, which inhibit the activity of antifungal drugs and increase the tolerance or resistance to them as well.
- Candida
- biofilm
- treatment
- antifungals
- natural compounds
- essential oil
- extract
- minimal inhibitory concentration (MIC)
1. Introduction
The genus Candida contains about 150 species; however, most are environmental organisms. The most medically important is Candida albicans, which accounts for about 80% of infections. C. albicans causes more than 400,000 cases of bloodstream life-threatening infections annually, with a mortality rate of about 42% [1]. Candida non-albicans species that are mainly responsible for infections are C. glabrata, C. parapsilosis, C. tropicalis, C. krusei, and C. dubliniensis [2]. Less frequently identified are C. guilliermondii, C. lusitaniae, C. rugosa, C. orthopsilosis, C. metapsilosis, C. famata, C. inconspicua, and C. kefyr [3].
C. albicans is a member of the commensal microflora. It colonizes the oral mucosal surface of 30–50% of healthy people. The rate of carriage increases with age and in persons with dental prostheses up to 60% [4,5,6]. Opportunistic infection caused by Candida species is termed candidiasis. At least one episode of vulvovaginal candidiasis (or thrush) concerns 50 to 75% of women of childbearing age [7]. Candidiasis can also affect the oral cavity, penis, skin, nails, cornea, and other parts of the body. In immunocompromised persons, untreated candidiasis poses the risk of systemic infection and fungemia [5,8]. Candida can be an important etiological factor in the infection of chronic wounds that are difficult to treat; this is mainly related to the production of biofilm [9].
Treatment of candidiasis depends on the infection site and the patient’s condition. According to guidelines, vulvovaginal candidiasis should be treated with oral or topical fluconazole; however, regarding C. glabrata infection, topical boric acid, nystatin, or flucytosine is suggested. In oropharyngeal candidiasis, the treatment options include clotrimazole, miconazole, or nystatin, and in severe disease, fluconazole or voriconazole. In candidemia and invasive candidiasis, the drugs of choice are echinocandins (caspofungin, micafungin, anidulafungin), fluconazole, or voriconazole; in resistant strains, amphoteticin B is used. In selected cases of candidemia caused by C. krusei, voriconazole is recommended [10,11,12]. More details can be found in the Guidelines of the Infectious Diseases Society of America [12] and the European Society of Clinical Microbiology and Infectious Diseases [11]. Increasingly, Candida species are becoming resistant to drugs. Marak and Dhanashree [13] tested the resistance of 90 Candida strains isolated from different clinical samples, such as pus, urine, blood, and body fluid. Their study revealed that about 41% of C. albicans strains are resistant to fluconazole and voriconazole. Simultaneously, about 41% of C. tropicalis strains are resistant to voriconazole and about 36% of strains to fluconazole. In strains of C. krusei, about 23% are resistant to fluconazole and about 18% to voriconazole. Rudramurthy et al. [14] studied resistance in C. auris, which is considered a multiresistant pathogen. Among 74 strains obtained from patients with candidemia, over 90% of strains were resistant to fluconazole and about 73% to voriconazole. Virulence factors of Candida species include the secretion of hydrolases, the transition of yeast to hyphae, phenotypic switching, and biofilm formation [15,16]. All microorganisms in biofilm form are more resistant to antimicrobial and host factors, which leads to difficulties in eradication [17]. It has also been shown that resistance to drugs increases significantly in the case of Candida biofilm occurrence. Biofilm prevents the spread of antifungals; moreover, fluconazole is bound by the biofilm matrix [18]. The formation of a Candida biofilm during infection increases mortality, length of hospital stay, and cost of antifungal therapy [19].
2. Plant Preparations That Display Activity against Candida Biofilms
The present review includes 60 articles in which Candida biofilm formation was inhibited by at least 50%. It has been shown that preparations from 34 plants demonstrate activity against Candida biofilms. Among them were 29 essential oils and 16 extracts. The plants from the following families dominated: Lamiaceae (6 species in 5 genera), Myrtaceae (5 species in 4 genera), Asteraceae (4 species in 4 genera), Fabaceae (4 species in 3 genera), and Apiacae (4 species in 2 genera).
Plants from the Lamiaceae family had the best antifungal activity, including Lavandula dentata (0.045–0.07 mg/L) [21], Satureja macrosiphon (0.06–8 mg/L) [22], and Ziziphora tenuior (2.5 mg/L) [23]. Artemisia judaica (2.5 mg/L) from the Asteraceae family [24], Lawsonia inermis (2.5–12.5 mg/L) from the Lythraceae family [25], and Thymus vulgaris (12.5 mg/L) from the Lamiaceae family [26] likewise exhibited good antifungal activity (Table 1). All preparations were essential oils, with the exception of Lawsonia inermis, which was an extract. Most of the plant preparations presented in Table 1 acted on biofilm formation and/or mature biofilms.
Table 1. Antifungal (MICs) and anti-biofilm (inhibition >50%) activity of plant preparations (essential oils or extracts).
Legend: MIC—minimal inhibitory concentration; XTT—reduction assay of 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-5-[carbonyl(phenylamino)]-2H-tetrazolium hydroxide; MTT—reduction assay of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide [54,55].
3. Plant Compounds That Display Activity against Candida Biofilm
It has been shown that 69 compounds obtained from plants demonstrate activity against Candida biofilms (Table 2). Among these, the most common are monotherpenes (20), followed by sesquiterpene lactones (7) and sesquiterpenes (6). Another big group is also phenolic compounds, including phenols (6), phenolic acids (5), phenolic aldehydes (2), polyphenols (2), and phenolic alcohol (1).
Table 2. Antifungal and antibiofilm activity of plant compounds.
In terms of activity, large differences were found, depending on the authors cited. Eugenol and thymol serve as good examples. Both compounds exhibited excellent activity in some studies (from 12.5 mg/L for eugenol [58] and 1.56 mg/L for thymol [26]), and in other studies, the activity was very poor (up to 80,000 for both [59]). These differences may be related, for example, to a different purity of the compound, a different fungal suspension density, or even to the use of other Candida strains with different sensitivities to chemical substances. A number of other factors, such as the type of culture medium, pH of the medium, incubation time, and temperature may likewise influence the antimicrobial activity [20].
According to the European Committee on Antimicrobial Susceptibility Testing (EUCAST), the antifungal clinical breakpoints are between 0.001 mg/L and 16 mg/L [60]. Using EUCAST guidelines in this review, the most active compounds that inhibit (>50%) Candida biofilm formation are lichochalcone A (from 0.2 mg/L) [61], thymol (from 3.12 mg/L) [26], dioscin (from 3.9 mg/L) [31], baicalein (from 4 mg/L) [62], warburganal (4.5 mg/L) [52], pterostilbene, waltheriones and riccardin D (both from 8 mg/L) [63,64,65], polygodial (10.8 mg/L) [52], cannabidiol and eugenol (both from 12.5 mg/L) [58,66], and ivalin (15.4 mg/L) [67]. It is interesting that monotherpenes, which represent the highest percentage of substances listed in Table 2, are not the most active compounds. The two larger groups with the best activity are phenolic compounds (thymol, pterostilbene, and eugenol), and sesquiterpene derivatives (warburganal, polygodial, and ivalin). Single compounds with the highest observed activity belong to chalconoids (lichochalcone A), steroidal saponins (dioscin), flavonoids (baicalein), alkaloids (waltheriones), macrocyclic bisbibenzyls (riccardin D), and cannabinoids (cannabidiol). Most of the compounds presented in Table 2 acted on biofilm formation and/or mature biofilm.
This entry is adapted from the peer-reviewed paper 10.3390/jof7050360
