Proliferation of intracellular structure corresponding to reduced affinity of fluconazole for cytochrome P-450 in two low-susceptibility strains of Candida albicans isolated from a Japanese AIDS patient

Detection of ERG11 point mutations in Iranian fluconazole-resistant Candida albicans isolates

Background and Purpose

Candidiasis is referred to a group of superficial and deep-tissue fungal infections often caused by Candida albicans. The superficial infections affect the oral, oropharynx, esophagus, and vaginal mucosa. The treatment of choice for these infections is the use of azoles, such as fluconazole. However, the increased use of these antifungal agents has led to the emergence of azole-resistant isolates of C. albicans. Different mechanisms have been suggested for the development of drug resistance, such as mutations in the encoding gene ERG11. Mutations in ERG11 result in changes in the ERG11p spatial construction and reduce the affinity between the protein and azole. This study aimed to determine the susceptibility profile of C. albicans clinical isolates to fluconazole using microdilution method. The present research was also targeted toward the detection of mutations that might be related to fluconazole resistance by the amplification and sequencing of ERG11 gene.

Materials and Methods

This study was conducted on a total of 216 clinical isolates obtained from Mashhad, Isfahan, and Tehran cities in Iran, during 2016-2018. The clinical isolates were identified using molecular techniques. Furthermore, minimum inhibitory concentration (MICs) was determined according to the clinical and laboratory standards institute M27-A3 and M27-S4 documents. The concentration range for fluconazole was obtained as 0.063-64 μg/ml. In the resistant strains, ERG11 genes were amplified by specific primers. Subsequently, cycle sequencing reactions were performed on purified polymerase chain reaction (PCR) products in forward and reverse directions. Finally, the results were analyzed by MEGA (version 7) and Gene Runner software (version 6.5.30).

Results

Out of 216 strains, 100 (46.3%) species were identified as C. albicans. The MIC values for fluconazole had a range of 0.125-16 μg/ml with the MIC50 and MIC90 values of 0.5 and 1 μg/ml, respectively. Totally, 41 nucleotide changes were detected among 4 resistant isolates. In this regard, 4 out of 41 mutations in codons caused changes in ERG11p; however, these mutations did not lead to fluconazole resistance.

Conclusion

Fluconazole resistance among clinical isolates is not merely due to the changes in ERG11p. This resistance may be also related to some other mechanisms, such as the prevention of the intracellular accumulation of the antifungal agent and alteration of the target enzyme to diminish drug binding.

Genome sequence of the opportunistic human pathogen Magnusiomyces capitatus

The yeast Magnusiomyces capitatus is an opportunistic human pathogen causing rare yet severe infections, especially in patients with hematological malignancies. Here, we report the 20.2 megabase genome sequence of an environmental strain of this species as well as the genome sequences of eight additional isolates from human and animal sources providing an insight into intraspecies variation. The distribution of single-nucleotide variants is indicative of genetic recombination events, supporting evidence for sexual reproduction in this heterothallic yeast. Using RNAseq-aided annotation, we identified genes for 6518 proteins including several expanded families such as kexin proteases and Hsp70 molecular chaperones. Several of these families are potentially associated with the ability of M. capitatus to infect and colonize humans. For the purpose of comparative analysis, we also determined the genome sequence of a closely related yeast, Magnusiomyces ingens. The genome sequences of M. capitatus and M. ingens exhibit many distinct features and represent a basis for further comparative and functional studies.

In silico analysis of cytochrome P450 monooxygenases in chronic granulomatous infectious fungus Sporothrix schenckii: Special focus on CYP51

Sporotrichosis is an emerging chronic, granulomatous, subcutaneous, mycotic infection caused by Sporothrix species. Sporotrichosis is treated with the azole drug itraconazole as ketoconazole is ineffective. It is a well-known fact that azole drugs act by inhibiting cytochrome P450 monooxygenases (P450s), heme-thiolate proteins. To date, nothing is known about P450s in Sporothrix schenckii and the molecular basis of its resistance to ketoconazole. Here we present genome-wide identification, annotation, phylogenetic analysis and comprehensive P450 family-level comparative analysis of S. schenckii P450s with pathogenic fungi P450s, along with a rationale for ketoconazole resistance by S. schenckii based on in silico structural analysis of CYP51. Genome data-mining of S. schenckii revealed 40 P450s in its genome that can be grouped into 32 P450 families and 39 P450 subfamilies. Comprehensive comparative analysis of P450s revealed that S. schenckii shares 11 P450 families with plant pathogenic fungi and has three unique P450 families: CYP5077, CYP5386 and CYP5696 (novel family). Among P450s, CYP51, the main target of azole drugs was also found in S. schenckii. 3D modeling of S. schenckii CYP51 revealed the presence of characteristic P450 motifs with exceptionally large reductase interaction site 2. In silico analysis revealed number of mutations that can be associated with ketoconazole resistance, especially at the channel entrance to the active site. One of possible reason for better stabilization of itraconazole, compared to ketoconazole, is that the more extended molecule of itraconazole may form a hydrogen bond with ASN-230. This in turn may explain its effectiveness against S. schenckii vis-a-vis resistant to ketoconazole. This article is part of a Special Issue entitled: Cytochrome P450 biodiversity and biotechnology, edited by Erika Plettner, Gianfranco Gilardi, Luet Wong, Vlada Urlacher, Jared Goldstone.

Principles of a New Protocol for Prediction of Azole Resistance in Candida albicans Infections on the Basis of ERG11 Polymorphisms

In recent years, Candida albicans infections treatment has become a growing problem because, among others, pathogenic strains are capable to develop resistance to the administered drugs. The elaboration of rapid and accurate method of resistance assessment is an important goal of many studies. They aim to avoid inappropriate dosage or drug choice, which may be life threatening in case of severe candidiasis. Here we propose a new protocol to predict C. albicans infections. The resistance prediction is based on high-resolution melt (HRM) analysis of ERG11 gene, especially, at the particularly unstable regions. Two statistically significant nucleotide polymorphisms were detected among twenty-seven strains isolated from saliva, one of which was silent mutation (Glu266Asp, Leu480Leu). We propose also HRM analysis as a convenient, simple and inexpensive method of preliminary selection of C. albicans DNA samples that vary in ERG11 nucleotide sequence within presumed region. Taken together, our study provides firm basis for the development of fast, simple and reliable methodology for diagnosis of C. albicans infections.

Investigation of mutations in Erg11 gene of fluconazole resistant Candida albicans isolates from Turkish hospitals

Widespread use of fluconazole has resulted in resistance in strains of Candida. The aim of our study was to investigate Y132H and other mutations in the ERG11 gene in conferring fluconazole resistance to C. albicans isolates. Seven fluconazole-resistant (R)/susceptible dose-dependent (SDD)/trailing and 10 fluconazole-susceptible (S) isolates were included. Restriction enzyme analysis was performed on all isolates for Y132H mutation and sequence analysis was performed for other mutations in the ERG11 gene. None of our strains had Y132H mutation. One single mutation (D153E, E266D, D116E, V437I) was detected in isolates 348, 533, 644, 1453, 2157, while the others had more than one nucleotide change. D116E and E266D, which were two mutations found in fluconazole R/SDD/trailing isolates with the highest frequency, were also detected in azole S strains. K143R, G464S, G465S and V488I mutations were determined in three of the R/SDD isolates. S412T and R469K mutations were detected only in this group of strains by sequence analysis. Mutations such as K143R, G464S, G465S, V488I, S412T and R469K in the ERG11 gene were determined to be effective mechanisms in our fluconazole R/SDD C. albicans isolates. Other mechanisms of resistance, such as overexpression of ERG11 and efflux pumps and mutations in the ERG3 gene should also be investigated.

Screening for amino acid substitutions in the Candida albicans Erg11 protein of azole-susceptible and azole-resistant clinical isolates: new substitutions and a review of the literature

For several years, azole antifungal drugs have been a treatment option for potentially life-threatening Candida infections. However, azole resistance can occur through various mechanisms such as alterations in ERG11, encoding lanosterol 14alpha-demethylase (CYP51). In this study, we investigated the antifungal susceptibility to fluconazole, itraconazole, and voriconazole of 73 clinical isolates of Candida albicans. Screening for amino acid substitutions in Erg11 was performed on each of the 73 isolates. Twenty isolates displayed a marked decrease in azole susceptibility. Amino acid substitutions were detected in more than two-thirds of the strains. In all, 23 distinct substitutions were identified. Four have not been described previously, among which N136Y and Y447H are suspected to be involved in azole resistance. We suggest that the high genetic polymorphism of ERG11 must be considered in the rationale design of new azole compounds targeting lanosterol 14alpha-demethylase. A review of all Erg11 amino acid polymorphisms described to date is given.

Resistance mechanisms in fluconazole-resistant Candida albicans isolates from vaginal candidiasis

Candida albicans is the most frequently identified yeast species causing mycotic vaginitis. A significant number of vaginal yeast isolates are resistant to azole antifungal agents in vitro. Here we investigated the molecular mechanisms of resistance in 22 randomly selected fluconazole-resistant vaginal C. albicans isolates. Twelve isolates in this collection were found to be cross-resistant to itraconazole and 15 to voriconazole. Most of them also displayed decreased susceptibility to terbinafine. Northern blot analyses revealed overexpression of the MDR1 gene in all isolates, which in some isolates was accompanied by elevated levels of CDR1/CDR2 and ERG11 expression. Sequence analysis of the polymerase chain reaction-amplified ERG11 gene of selected azole-resistant isolates identified D116E and V488I amino acid alterations in Erg11p that are known to be conserved in fluconazole-resistant strains. The results demonstrate that decreased susceptibilities of vaginal yeast isolates to clinically used azole derivatives are the result of a combination of several molecular mechanisms involving drug efflux and alterations in the structure or cellular amount of 14-alpha-lanosterol demethylase.