Azole susceptibility and resistance in Candida dubliniensis

Candidiasis and Mechanisms of Antifungal Resistance

Candidiasis can be present as a cutaneous, mucosal or deep-seated organ infection, which is caused by more than 20 types of Candida sp., with C. albicans being the most common. These are pathogenic yeast and are usually present in the normal microbiome. High-risk individuals are patients of human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS), organ transplant, and diabetes. During infection, pathogens can adhere to complement receptors and various extracellular matrix proteins in the oral and vaginal cavity. Oral and vaginal Candidiasis results from the overgrowth of Candida sp. in the hosts, causing penetration of the oral and vaginal tissues. Symptoms include white patches in the mouth, tongue, throat, and itchiness or burning of genitalia. Diagnosis involves visual examination, microscopic analysis, or culturing. These infections are treated with a variety of antifungals that target different biosynthetic pathways of the pathogen. For example, echinochandins target cell wall biosynthesis, while allylamines, azoles, and morpholines target ergosterol biosynthesis, and 5-Flucytosine (5FC) targets nucleic acid biosynthesis. Azoles are commonly used in therapeutics, however, because of its fungistatic nature, Candida sp. evolve azole resistance. Besides azoles, Candida sp. also acquire resistance to polyenes, echinochandins, and 5FC. This review discusses, in detail, the drug resistance mechanisms adapted by Candida sp.

Uncommon opportunistic fungal infections of oral cavity: A review

The majority of opportunistic oral mucosal fungal infections are due to Candida albicans and Aspergillus fumigatus species. Mucor and Cryptococcus also have a major role in causing oral infections, whereas Geotrichum, Fusarium, Rhodotorula, Saccharomyces and Penicillium marneffei are uncommon pathogens in the oral cavity. The broad spectrum of clinical presentation includes pseudo-membranes, abscesses, ulcers, pustules and extensive tissue necrosis involving bone. This review discusses various uncommon opportunistic fungal infections affecting the oral cavity including their morphology, clinical features and diagnostic methods.

Candida dubliniensis encrustation of an obstructing upper renal tract calculus

We present the case of a 53-year-old man, with a history of alcohol abuse, requiring intensive care unit admission, with an obstructing right upper renal calculus and Klebsiella pneumoniae urosepsis. Ureteroscopic treatment of this obstruction displayed a small calculus within the renal pelvis completely encapsulated within a fungal bezoar. Laboratory analysis of the fungal mass found it to be Candida dubliniensis.

Performance comparison of phenotypic and molecular methods for detection and differentiation of Candida albicans and Candida dubliniensis

BACKGROUND

Candida albicans is the most pathogenic Candida species but shares many phenotypic features with Candida dubliniensis and may, therefore, be misidentified in clinical microbiology laboratories. Candidemia cases due to C. dubliniensis are increasingly being reported in recent years. Accurate identification is warranted since mortality rates are highest for C. albicans infections, however, C. dubliniensis has the propensity to develop resistance against azoles more easily. We developed a duplex PCR assay for rapid detection and differentiation of C. albicans from C. dubliniensis for resource-poor settings equipped with basic PCR technology and compared its performance with three phenotypic methods.

METHODS

Duplex PCR was performed on 122 germ tube positive and 12 germ tube negative isolates of Candida species previously identified by assimilation profiles on Vitek 2 ID-YST system. Typical morphologic characteristics on simplified sunflower seed agar (SSA), and reaction with a commercial (Bichro-Dubli) latex agglutination test were also performed. The assay was further applied on 239 clinical yeast and yeast-like fungi and results were confirmed by DNA sequencing of internal transcribed spacer (ITS) region of rDNA.

RESULTS

The results of duplex PCR assay for 122 germ tube positive and 12 germ tube negative isolates of Candida species were comparable to their identification by Vitek 2 ID-YST system, colony characteristics on SSA and latex agglutination test. Application of duplex PCR also correctly identified all 148 C. albicans and 50 C. dubliniensis strains among 239 yeast-like fungi.

CONCLUSIONS

The data show that both, duplex PCR and Bichro-Dubli are reliable tests for rapid (within few hours) identification of clinical yeast isolates as C. dubliniensis or C. albicans. However, duplex PCR may be applied directly on clinical yeast isolates for their identification as C. dubliniensis or C. albicans as it does not require prior testing for germ tube formation or latex Candida agglutination.

[Virulence of Candida dubliniensis in comparison with Candida albicans using an experimental model of mouse oral candiddiasis]

Certain species of Candida are known as opportunistic fungal pathogens and Candida albicans has especially been isolated oral candidiasis patients at high frequency as a result of its strong pathogenicity. Recently C. dubliniensis is isolated mainly from immunocompromised patients, but is also detected from healthy persons. C. dubliniensis has similar cell morphology and molecular biological properties to C. albicans. Thus, in order to clarify the pathogenicity of C. dubliniensis, the activities of two extracellular enzymes, phospholipase (PL) and proteinase (PT), were measured, and pathological features were compared using mice. PL activity was examined in the improved Price's PL activity assay. In brief, the white precipitation zone was detected by spraying NaCl on egg yold plates without NaCl after colonies had grown. PL activity was no detected in any of the 31 C. dubliniensis strains tested. On the other hand, PT acitivty of C. dubliniensis was almost equivalent to that of C. albicans. Although we attempted to make an experimental model of mouse oral candidiasis using C. dubliniensis in yeast form as an inoculum following the conventional method, oral candidiasis did not develop in any mice. Thrush was successfully developed after inoculation with mycelial form cells, and there was no significant difference in histopathological findings of the thrush in comparison with C. albicans. These results strongly suggest that the two enzymes, PT and PL, do not play a crusial role in the establishment of mouse oral experimental candidiasis by C. dubliniensis.

Biofilm formation and adhesive/invasive properties of Candida dubliniensis in comparison with Candida albicans

Candida dubliniensis and Candida albicans are closely related spp. exhibiting differences in their virulence potency. This study compared clinical isolates of C. dubliniensis with C. albicans from HIV patients with oropharyngeal candidiasis (OPC) and standard strains in power to form biofilm and their adhesive and invasive properties. Members of both spp. were able to form strong biofilms. However, SEM microscopy confirmed that C. albicans undergoes the more effective yeast-to-hyphae transition than C. dubliniensis with prevalent yeast form and limited ability to form filaments. Kinetic patterns indicated that while the first 30 min are critical for sufficient attachment to a polystyrene surface, adhesion to human carcinoma cell lines (Caco-2 and TR 146) needs additional time with maximal saturation observed at 240 min for both spp. The invasion process was tested on 3D RHE (reconstituted human epithelium) with Caco-2 or TR 146 on the collagen surface. C. albicans rapidly produced hyphae that penetrated the tissue layer, demonstrating substantive invasion within 21 h. In contrast, C. dubliniensis attached to the tissue surface and proliferated, suggesting the formation of a biofilm-like structure. After 21 h, C. dubliniensis was able to penetrate the RHE layer and invade unusually, with a cluster of the yeast cells.

Identification of Candida albicans by using different culture medias and its association in potentially malignant and malignant lesions

BACKGROUND AND OBJECTIVE

The present study evaluates the association of Candida albicans with normal control group, potentially malignant and malignant lesions of oral cavity by using two different liquid culture media.

MATERIALS AND METHODS

Saliva was collected and biopsy was taken only from those clinically suspected potentially malignant and malignant lesions for histopathological diagnosis. Saliva samples were inoculated for fungal growth in Sabouraud's dextrose agar and culture-positive samples had undergone for Germ tube test. Germ tube-positive samples were further taken for quantification of chlamydospore production in liquid media at 8 and 16 hours.

RESULTS

In normal control groups no fungus growth was found; however, potentially malignant and malignant cases showed fungus growth, positive germ tube test and chlamydospore formation. The result also showed rapid and quantitatively more chlamydospore formation in corn meal broth + 5% milk in comparison to serum milk culture media.

CONCLUSION

The oral mucosa is compromised in potentially malignant lesions, it can be argued that this species may be involved in carcinogenesis by elaborating the nitrosamine compounds which either act directly on oral mucosa or interact with other chemical carcinogens to activate specific proto-oncogenes and thereby initiate oral neoplasia.

An MDR1 promoter allele with higher promoter activity is common in clinically isolated strains of Candida albicans

In the opportunistic fungal pathogen Candida albicans, up-regulation of MDR1, encoding an efflux transporter, leads to increased resistance to the antifungal drug fluconazole. Antifungal resistance has been linked to several types of genetic change in C. albicans, including changes in genome structure, genetic alteration of the drug target, and overexpression of transporters. High-level over-expression of MDR1 is commonly mediated by mutation in a trans-acting factor, Mrr1p. This report describes a second mechanism that contributes to up-regulation of MDR1 expression. By analyzing the sequence of the MDR1 promoter region in fluconazole-resistant and fluconazole-susceptible strains, we identified sequence polymorphisms that defined two linkage groups, corresponding to the two alleles in the diploid genome. One of the alleles conferred higher MDR1 expression compared with the other allele. Strains in which both alleles were of the higher activity type were common in collections of clinically isolated strains while strains carrying only the less active allele were rare. As increased expression of MDR1 confers higher resistance to drugs, strains with the more active MDR1 promoter allele may grow or survive longer when exposed to drugs or other selective pressures, providing greater opportunity for mutations that confer high-level drug resistance to arise. Through this mechanism, higher activity alleles of the MDR1 promoter could promote the development of drug resistance.

Curcumin acts synergistically with fluconazole to sensitize a clinical isolate of Candida albicans showing a MDR phenotype

The primary objective of this work was to evaluate the capability of curcumin, a natural compound found in the Curcuma longa plant, to sensitize a clinical isolate of Candida albicans, which was found to have a high resistance to fluconazole. In addition, we assessed whether the resistance of this isolate was the result of the existence of efflux pumps, which could confer a multiple drug resistance phenotype. To evaluate azole resistance, we used the Clinical Laboratory Standard Institute (CLSI) MIC assays procedures with minor modifications. For evaluation of synergistic interaction of curcumin and fluconazole, checkerboard experiments were employed. Nile red and Rhodamine 6G accumulation assays were used to evaluate efflux pump activity. Curcumin was found to have a great capability to inhibit fluconazole resistance of the isolate of C. albicans. It was capable of restoring its sensitivity to this azole when used at 11 μM. Analysis with different azoles and the two indicated dyes showed that an efflux pump could be acting and contributing to the resistance of this isolate to fluconazole. The results suggest that a major facilitator superfamily (MFS) transporter might be involved in this process.

Longitudinal genotyping of Candida dubliniensis isolates reveals strain maintenance, microevolution, and the emergence of itraconazole resistance

We investigated the population structure of 208 Candida dubliniensis isolates obtained from 29 patients (25 human immunodeficiency virus [HIV] positive and 4 HIV negative) as part of a longitudinal study. The isolates were identified as C. dubliniensis by arbitrarily primed PCR (AP-PCR) and then genotyped using the Cd25 probe specific for C. dubliniensis. The majority of the isolates (55 of 58) were unique to individual patients, and more than one genotype was recovered from 15 of 29 patients. A total of 21 HIV-positive patients were sampled on more than one occasion (2 to 36 times). Sequential isolates recovered from these patients were all closely related, as demonstrated by hybridization with Cd25 and genotyping by PCR. Six patients were colonized by the same genotype of C. dubliniensis on repeated sampling, while strains exhibiting altered genotypes were recovered from 15 of 21 patients. The majority of these isolates demonstrated minor genetic alterations, i.e., microevolution, while one patient acquired an unrelated strain. The C. dubliniensis strains could not be separated into genetically distinct groups based on patient viral load, CD4 cell count, or oropharyngeal candidosis. However, C. dubliniensis isolates obtained from HIV-positive patients were more closely related than those recovered from HIV-negative patients. Approximately 8% (16 of 194) of isolates exhibited itraconazole resistance. Cross-resistance to fluconazole was only observed in one of these patients. Two patients harboring itraconazole-resistant isolates had not received any previous azole therapy. In conclusion, longitudinal genotyping of C. dubliniensis isolates from HIV-infected patients reveals that isolates from the same patient are generally closely related and may undergo microevolution. In addition, isolates may acquire itraconazole resistance, even in the absence of prior azole therapy.

Comparative transcript profiling of Candida albicans and Candida dubliniensis identifies SFL2, a C. albicans gene required for virulence in a reconstituted epithelial infection model

Candida albicans and Candida dubliniensis are closely related species displaying differences in virulence and genome content, therefore providing potential opportunities to identify novel C. albicans virulence genes. C. albicans gene arrays were used for comparative analysis of global gene expression in the two species in reconstituted human oral epithelium (RHE). C. albicans (SC5314) showed upregulation of hypha-specific and virulence genes within 30 min postinoculation, coinciding with rapid induction of filamentation and increased RHE damage. C. dubliniensis (CD36) showed no detectable upregulation of hypha-specific genes, grew as yeast, and caused limited RHE damage. Several genes absent or highly divergent in C. dubliniensis were upregulated in C. albicans. One such gene, SFL2 (orf19.3969), encoding a putative heat shock factor, was deleted in C. albicans. DeltaDeltasfl2 cells failed to filament under a range of hypha-inducing conditions and exhibited greatly reduced RHE damage, reversed by reintroduction of SFL2 into the DeltaDeltasfl2 strain. Moreover, SFL2 overexpression in C. albicans triggered hyphal morphogenesis. Although SFL2 deletion had no apparent effect on host survival in the murine model of systemic infection, DeltaDeltasfl2 strain-infected kidney tissues contained only yeast cells. These results suggest a role for SFL2 in morphogenesis and an indirect role in C. albicans pathogenesis in epithelial tissues.

Paradoxical growth of Candida dubliniensis does not preclude in vivo response to echinocandin therapy

Candida dubliniensis commonly shows paradoxical or trailing growth effects in vitro in the presence of echinocandins. We tested the in vitro activities of anidulafungin, caspofungin, and micafungin against clinical isolates of C. dubliniensis and evaluated the efficacy of these drugs in two murine models of systemic infection. The three echinocandins were similarly effective in the treatment of experimental disseminated infections with C. dubliniensis strains showing or not showing abnormal growth in vitro.

[Candida dubliniensis: Identification methods and epidemiologic implication]

Candida dubliniensis was recently described (1995) associated with oral candidiasis in HIV-positive patients. This organism is very closely related to the pathogenic human yeast, Candida albicans, and share a great number of phenotypic and genotypic characters. This great similarity limits the discrimination between these two species. Several phenotypic and molecular methods were developed. The phenotypic methods are simply used in routine discrimination between these two species and depend on the growth at high temperature, sugar assimilation, growth on special mediums and chlamydospore production…; but these methods are insensitive in discrimination between these two species. The molecular biology methods are highly reliable and able to confirm rapidly the identification of this species. In this article, we will review the various studies run out concerning the methods deployed for the identification of C. dubliniensis as well as the epidemiological implication of this new pathogen.