VVC is a widespread fungal infection that is induced primarily by C. albicans and affects reproductive-age women . Although VVC is primarily a challenging therapy worldwide, some socioeconomic factors could affect its incidence . Besides, service planning managers should utilize updated epidemiological data from across the world.
In the recent decade, the amount of fungal resistance to antifungal drugs has increased and has led to therapeutic problems . In the present study, the 50 C. albicans isolates that were tested for susceptibility to antifungals belonged to the polyenes group (amphotericin B) and azoles group (fluconazole, voriconazole, itraconazole, and clotrimazole) via the microdilution method. The results obtained from amphotericin B exhibited an excellent susceptibility to all C. albicans isolates. This finding agrees with the results reported in studies by Eski et al. and Mohammadi et al. concerning an absence of amphotericin B-resistant isolates [23, 24]. Besides, susceptibility to different azoles drugs varied among C. albicans isolates, with lower susceptibility of C. albicans isolates to fluconazole (36%) followed by clotrimazole(52%). Meanwhile, itraconazole and voriconazole (68%) exerted similar effects.
Many studies have highlighted the resistance of C. albicans to azole antifungal drugs, especially fluconazole [2, 20–24]. A previous study conducted by Mohammadi et al. found the highest resistance to fluconazole (76%) compared to other antifungals (itraconazole 62%, ketoconazole 72%, clotrimazole 55%, voriconazole 6%, posuconazole7%, nystatin1%, and amphotericin B 0%) .
Lower susceptibility rates of C. albicans to fluconazole have been reported from Brazil (68%; 2011), India (48%; 2013), and Egypt (89%; 2016), respectively [26, 29, 30].
The widespread use of fluconazole against prophylaxis and Candida infections may be one of several factors contributing to antifungal resistance. C. albicans has developed multiple resistance mechanisms against azole antifungal drugs, leaving the way open to only a few antifungal agents available . Therefore, it is of particular importance to investigate the mechanisms and patterns of antifungal resistance. In the current study, the analyses of the association between risk factors and incidence of fluconazole resistance showed higher rates of anti fungal resistance in women with a history of vaginitis. Moreover, the patients who had used a contraception method were at a greater risk to develop drug resistance (Table 2). As a result, the history of infection indicates that a failure in the treatment of primary infection leads to the emergence of resistant species. Also, any factor that predisposes to infection can lead to the emergence of resistant species.
Findings that arise from such research can contribute to designing and developing alternative therapeutic strategies. Additionally, understanding the molecular mechanism of antifungal resistance and the role of genes relevant to drug resistance can be used to diagnose resistant isolates via molecular diagnostic tools.
Previous research has reported overexpression of ATP-binding cassette transporters, which are encoded by different genes, primarily CDR1 and CDR2, in C. albicans. TAC1 gene is the first transcription factor that regulates efflux pump family genes [32, 33]. However, it is well documented that the most significant factor involved in C. albicans resistance to azole antifungal agents is the overexpression of the ERG11 gene [34, 35].
According to our results, TAC1 gene expression was not merely increased in fluconazole-resistant isolates; it was also abserved in sensitive isolates. The TAC1gene was found to have overexpression rates in resistant and sensitive isolates, respectively, with statistically significant differences between the two groups (P < 0.001). Moreover, fluconazole-sensitive isolates had ERG11 gene overexpression. In fact, all resistant isolates had ERG11 gene overexpression at significantly higher levels than the ATCC 10231 strain. Based on the results, we witnessed an overexpression of ERG11 and TAC1 in susceptible isolates. Despite the increase in gene expression in susceptible isolates, these isolates are sensitive to fluconazole.
In a previews study by Riberio et al. after fluconazole treatment, they observed ERG11gene overexpression in fluconazole-sensitive C. albicans isolates. They concluded that the overexpression of the ERG11 gene is accompanied by the overexpression of other efflux pump genes and that the ERG11 expression is not the only cause of increased resistance to fluconazole . Teimouri et al. detected ERG11 gene overexpression in eight resistant isolates of C. albicans from infants . Another study conducted by Sasse et al. evaluated the expression of TAC1 and MRR1 transcription factors . They investigated mutations in the gene sequence after they observed an increase in the expression of TAC1 and MRR1 genes. The results of this study showed that the increase in TAC1 gene expression is sometimes up to 500-fold in the development of fluconazole resistance, arguably due to mutations in this gene. Shi et al. investigated the expression rates of efflux genes (CDR1, CDR2, MDR1, Erg11, and TAC1) in the biofilm formation process on fluconazole-resistant isolates of C. albicans . The results showed that the increase in TAC1 expression occurred in the early stages (first 8 hours) and that the expression increase was nearly two-fold. In a study by Chen 2010 and Xu in 2008, over 143 mutations,contributing to increased ERG11 gene expression, were reported in fluconazole-resistant C. albicans isolates [40, 41].
The results obtained from this study, indicate that the occurrence of drug resistance can be directly related to increased expression of TAC1 which as transcription gene. In addition to increasing the expression of drug resistance genes, the incidence of drug resistance can be directly related to patient risk factors such as the use of broad-spectrum antibiotics, immune system function, and underlying diseases such as diabetes . As observed, there is a significant relationship between the resistance to azole resistance and history of infection or the use of contraceptive methods.
This study has some limitations. In this study, the mutations of the studied genes were not investigated due to limited facilities. Therefore, future research may aim to detect the frequency of definite mutations in the C. albicans ERG11 and TAC1 genes and its targets in resistant isolates.