Prevalence of Candida dubliniensis isolates in a yeast stock collection

Similarities and Differences among Species Closely Related to Candida albicans: C. tropicalis, C. dubliniensis, and C. auris

Although Candida species are widespread commensals of the microflora of healthy individuals, they are also among the most important human fungal pathogens that under certain conditions can cause diseases (candidiases) of varying severity ranging from mild superficial infections of the mucous membranes to life-threatening systemic infections. So far, the vast majority of research aimed at understanding the molecular basis of pathogenesis has been focused on the most common species—Candida albicans. Meanwhile, other closely related species belonging to the CTG clade, namely, Candida tropicalis and Candida dubliniensis, are becoming more important in clinical practice, as well as a relatively newly identified species, Candida auris. Despite the close relationship of these microorganisms, it seems that in the course of evolution, they have developed distinct biochemical, metabolic, and physiological adaptations, which they use to fit to commensal niches and achieve full virulence. Therefore, in this review, we describe the current knowledge on C. tropicalis, C. dubliniensis, and C. auris virulence factors, the formation of a mixed species biofilm and mutual communication, the environmental stress response and related changes in fungal cell metabolism, and the effect of pathogens on host defense response and susceptibility to antifungal agents used, highlighting differences with respect to C. albicans. Special attention is paid to common diagnostic problems resulting from similarities between these species and the emergence of drug resistance mechanisms. Understanding the different strategies to achieve virulence, used by important opportunistic pathogens of the genus Candida, is essential for proper diagnosis and treatment.

Candida dubliniensis fungemia in a patient with severe COVID-19: A case report

Candida dubliniensis phenotypically mimics Candida albicans in its microbiological features; thus, its clinical characteristics have yet to be fully elucidated. Here we report the case of a 68-year-old Japanese man who developed C. dubliniensis fungemia during treatment for severe coronavirus disease 2019 (COVID-19). The patient was intubated and received a combination of immunosuppressants, including high-dose methylprednisolone and two doses of tocilizumab, as well as remdesivir, intravenous heparin, and ceftriaxone. A blood culture on admission day 11 revealed Candida species, which was confirmed as C. dubliniensis by mass spectrometry. An additional sequencing analysis of the 26S rDNA and ITS regions confirmed that the organism was 100% identical to the reference strain of C. dubliniensis (ATCC MYA-646). Considering the simultaneous isolation of C. dubliniensis from a sputum sample, the lower respiratory tract could be an entry point for candidemia. Although treatment with micafungin successfully eradicated the C. dubliniensis fungemia, the patient died of COVID-19 progression. In this case, aggressive immunosuppressive therapy could have caused the C. dubliniensis fungemia. Due to insufficient clinical reports on C. dubliniensis infection based on definitive diagnosis, the whole picture of the cryptic organism is still unknown. Further accumulation of clinical and microbiological data of the pathogen is needed to elucidate their clinical significance.

New and Promising Chemotherapeutics for Emerging Infections Involving Drug-resistant Non-albicans Candida Species

Fungal infections are a veritable public health problem worldwide. The increasing number of patient populations at risk (e.g. transplanted individuals, cancer patients, and HIV-infected people), as well as the use of antifungal agents for prophylaxis in medicine, have favored the emergence of previously rare or newly identified fungal species. Indeed, novel antifungal resistance patterns have been observed, including environmental sources and the emergence of simultaneous resistance to different antifungal classes, especially in Candida spp., which are known for the multidrug-resistance (MDR) profile. In order to circumvent this alarming scenario, the international researchers' community is engaged in discovering new, potent, and promising compounds to be used in a near future to treat resistant fungal infections in hospital settings on a global scale. In this context, many compounds with antifungal action from both natural and synthetic sources are currently under clinical development, including those that target either ergosterol or β(1,3)-D-glucan, presenting clear evidence of pharmacologic/pharmacokinetic advantages over currently available drugs against these two well-known fungal target structures. Among these are the tetrazoles VT-1129, VT-1161, and VT-1598, the echinocandin CD101, and the glucan synthase inhibitor SCY-078. In this review, we compiled the most recent antifungal compounds that are currently in clinical trials of development and described the potential outcomes against emerging and rare Candida species, with a focus on C. auris, C. dubliniensis, C. glabrata, C. guilliermondii, C. haemulonii, and C. rugosa. In addition to possibly overcoming the limitations of currently available antifungals, new investigational chemical agents that can enhance the classic antifungal activity, thereby reversing previously resistant phenotypes, were also highlighted. While novel and increasingly MDR non-albicans Candida species continue to emerge worldwide, novel strategies for rapid identification and treatment are needed to combat these life-threatening opportunistic fungal infections.

Candida dubliniensis: A novel cause of fungal keratitis

A 45-year-old female with history of contact lens wear presented with a persistent corneal ulcer that was unresponsive to topical moxifloxacin. The patient's exam was concerning for fungal keratitis. Cultures were obtained, and the patient was started on fortified amphotericin B drops and oral voriconazole. The cultures identified Candida dubliniensis as the causative organism. The patient's exam worsened despite treatment, and the decision was made for surgery. At the time of surgery, her cornea was found to have unexpectedly perforated. She underwent cryotherapy; tectonic penetrating keratoplasty; anterior chamber tap; intracameral voriconazole, amphotericin B, and cefuroxime; and a partial conjunctival flap. Pathology from the cornea showed GMS and PAS stains positive for fungal forms. C. dubliniensis is a yeast closely related to Candida albicans that was first described in 1995 as a cause of oral candidiasis in patients with AIDS. There are a few published cases of endophthalmitis due to C. dubliniensis in the ophthalmology literature, but to our knowledge, no cases of fungal keratitis due to this organism have been reported. C. dubliniensis is a novel cause of fungal keratitis that can be difficult to identify and treat but is felt to be less virulent than C. albicans and generally susceptible to available anti-fungal therapies.

Comparison of duplex PCR and phenotypic analysis in differentiating Candida dubliniensis from Candida albicans from oral samples

Candida dubliniensis shares a wide range of phenotypic characteristics with Candida albicans including a common trait called germ tube positivity. Hence, laboratory differentiation of these two species is cumbersome. Duplex PCR analyses for C. albicans and C. dubliniensis was performed directly on DNA extracted from a total of 122 germ tube positive isolates derived from 100 concentrated oral rinse samples from a random cohort of diabetics attending a clinic in Sri Lanka. These results were confirmed by DNA sequencing of internal transcribed spacer (ITS) region of rDNA of the yeasts. Performance efficacy of duplex PCR was then compared with phenotypic identification using a standard battery of phenotypic tests. Of the 122 germ tube positive isolates three were identified by duplex PCR as C. dubliniensis and the remainder as C. albicans. On the contrary, when the standard phenotypic tests, sugar assimilation and chlamydospore formation, were used to differentiate the two species 13 germ tube positive isolates were erroneously identified as C. dubliniensis. Duplex PCR was found to be rapid, sensitive and more specific than phenotypic identification methods in discriminating C. dubliniensis from C. albicans. This is also the first report on the oral carriage of C. dubliniensis in a Sri Lankan population.

Exoenzyme activity and possibility identification of Candida dubliniensis among Candida albicans species isolated from vaginal candidiasis

OBJECTIVES

Vulvovaginal candidiasis (VVC) or vaginal candidiasis is a common fungal infection of the genitals causing inflammation, irritation, itching, and vaginal discharge. Common yeast infections are caused by the yeast species C. albicans. However, there are other species of Candida such as C. dubliniensis which are considered as the causative agents of this infection. Hydrolytic enzymes such as proteinase and coagulase are known as virulence factors. The aim of this study was the molecular confirmation and differentiation of C. dubliniensis among C. albicans strains isolated from women with vulvovaginal candidiasis by PCR-Restriction Fragment Length Polymorphism (PCR-RFLP) and the evaluation of proteinase and coagulase activities.

METHODS

A total of 100 C. albicans strains isolated from women with vulvovaginal candidiasis referred to Shiraz medical clinics were enrolled in the study. All the isolates were primarily identified by conventional methods. PCR-RFLP method was used for the confirmation and identification of C. albicans and C. dubliniensis. Moreover, in vitro proteinase and coagulase activities of these isolates were evaluated using bovine serum albumin media and classical rabbit plasma tube test.

RESULTS

As a result, PCR-RFLP identified 100% of the isolates as C. albicans, and no C. dubliniensis could be identified in this study. 84% of the isolates showed proteinase activity, whereas coagulase activity was only detected in 5% of the isolates.

CONCLUSIONS

This study reveals that C. dubliniensis plays no role in vaginal candidiasis in Iranian patients. Proteinase production could be an essential virulence factor in C. albicans pathogenicity, but coagulase activity has less potential in this matter.

Dissecting Candida albicans Infection from the Perspective of C. albicans Virulence and Omics Approaches on Host-Pathogen Interaction: A Review

Candida bloodstream infections remain the most frequent life-threatening fungal disease, with Candida albicans accounting for 70% to 80% of the Candida isolates recovered from infected patients. In nature, Candida species are part of the normal commensal flora in mammalian hosts. However, they can transform into pathogens once the host immune system is weakened or breached. More recently, mortality attributed to Candida infections has continued to increase due to both inherent and acquired drug resistance in Candida, the inefficacy of the available antifungal drugs, tedious diagnostic procedures, and a rising number of immunocompromised patients. Adoption of animal models, viz. minihosts, mice, and zebrafish, has brought us closer to unraveling the pathogenesis and complexity of Candida infection in human hosts, leading towards the discovery of biomarkers and identification of potential therapeutic agents. In addition, the advancement of omics technologies offers a holistic view of the Candida-host interaction in a non-targeted and non-biased manner. Hence, in this review, we seek to summarize past and present milestone findings on C. albicans virulence, adoption of animal models in the study of C. albicans infection, and the application of omics technologies in the study of Candida–host interaction. A profound understanding of the interaction between host defense and pathogenesis is imperative for better design of novel immunotherapeutic strategies in future.

Candida dubliniensis and Candida albicans differentiation by colony morphotype in Sabouraud-triphenyltetrazolium agar

BACKGROUND

Candida dubliniensis is a germ tube and chlamydoconidia producing Candida species that may be misidentified as Candida albicans. Molecular-based methods are the most reliable techniques for C. albicans and C. dubliniensis differentiation. However, accurate, quick and inexpensive phenotypic tests are needed to be used in low-complexity mycology laboratories.

AIMS

To evaluate colony morphotypes on Sabouraud-triphenyltetrazolium agar as a tool for C. dubliniensis and C. albicans differentiation.

METHODS

The morphology of 126 C. albicans and C. dubliniensis strains was evaluated and compared with their identification by molecular methods.

RESULTS

The method showed 100% sensitivity and specificity when color and the presence or absence of large white mycelial halo was evaluated.

CONCLUSIONS

Colony morphotype on Sabouraud-triphenyltetrazolium agar should be considered as a new tool to differentiate C. dubliniensis and C. albicans.

Prevalence of Candida albicans-closely related yeasts, Candida africana and Candida dubliniensis, in vulvovaginal candidiasis

Isolates of Candida africana and C. dubliniensis were recovered from patients with vulvovaginal candidiasis (VVC). The isolates were initially identified as C. albicans through use of the API Candida System. We retrospectively reexamined 1014 vaginal isolates presumptively determined to be C. albicans at the Department of Obstetrics and Gynecology of Peking University Shenzhen Hospital from 1 January 2003 through 31 December 2012. Our objective was to determine, via detection of the HWP1 gene, if any of the isolates were C. africana or C. dubliniensis. One and a half percent of these isolates (15/1014) were found to be C. africana, whereas C. dubliniensis was not detected. The 15 C. africana isolates were susceptible to nystatin, fluconazole, itraconazole, miconazole, and clotrimazole. Candida africana could not be recovered from clinical vaginal specimens from the 15 patients at follow-up on days 7-14 and days 30-35 when treated with different antifungal agents. We conclude that C. africana, but not C. dubliniensis, was present in the vaginal samples of patients with VVC. The C. africana isolates were susceptible to the tested antifungal agents. VVC caused by C. africana appears to respond well to current therapies.

The usefulness of DNA sequencing after extraction by Whatman FTA filter matrix technology and phenotypic tests for differentiation of Candida albicans and Candida dubliniensis

Since C. dubliniensis is similar to C. albicans phenotypically, it can be misidentified as C. albicans. We aimed to investigate the prevalence of C. dubliniensis among isolates previously identified as C. albicans in our stocks and to compare the phenotypic methods and DNA sequencing of D1/D2 region on the ribosomal large subunit (rLSU) gene. A total of 850 isolates included in this study. Phenotypic identification was performed based on germ tube formation, chlamydospore production, colony colors on chromogenic agar, inability of growth at 45 °C and growth on hypertonic Sabouraud dextrose agar. Eighty isolates compatible with C. dubliniensis by at least one phenotypic test were included in the sequence analysis. Nested PCR amplification of D1/D2 region of the rLSU gene was performed after the fungal DNA extraction by Whatman FTA filter paper technology. The sequencing analysis of PCR products carried out by an automated capillary gel electrophoresis device. The rate of C. dubliniensis was 2.35 % (n = 20) among isolates previously described as C. albicans. Consequently, none of the phenotypic tests provided satisfactory performance alone in our study, and molecular methods required special equipment and high cost. Thus, at least two phenotypic methods can be used for identification of C. dubliniensis, and molecular methods can be used for confirmation.

Issues in identifying germ tube positive yeasts by conventional methods

Candida speciation is vital for epidemiology and management of candidiasis. Nonmolecular conventional methods often fail to identify closely related germ tube positive yeasts from clinical specimens. The present study was conducted to identify these yeasts and to highlight issues in conventional versus molecular methods of identification. A total of 98 germ tube positive yeasts from high vaginal swabs were studied over a 12-month period. Isolates were examined with various methods including growth at 42 °C and 45 °C on Sabouraud dextrose agar (SDA), color development on CHROMagar Candida medium, chlamydospore production on corn meal agar at 25 °C, carbohydrate assimilation using ID 32C system, and polymerase chain reaction using a single pair of primers targeting the hyphal wall protein 1 (Hwp1) gene. Of all the isolates studied, 97 were molecularly confirmed as C. albicans and one isolate was identified as C. dubliniensis. No C. africana was detected in this study. The molecular method used in our study was an accurate and useful tool for discriminating C. albicans, C. dubliniensis, and C. africana. The conventional methods, however, were less accurate and riddled with many issues that will be discussed in further details.

Candida dubliniensis endophthalmitis: five cases over 15 years

Background

Recent studies have shown that the recently identified organism Candida dubliniensis is less pathogenic than the more common Candida albicans. Due to its rare nature, C. dubliniensis has been previously reported as the causative organism in endophthalmitis in only three cases. We undertook a multicenter, retrospective, consecutive case series to describe the clinical features and outcomes of patients with culture-proven C. dubliniensis endophthalmitis. Medical records were reviewed for all patients with C. dubliniensis endophthalmitis on vitreous/aqueous cultures from June 1998 to June 2013 from all public hospitals throughout Queensland, Australia.

Results

Six eyes from five patients were identified - four males and one female aged from 21 to 55 years (mean 37 years). Four patients were intravenous drug users and four patients had hepatitis C. All five patients were treated with systemic antifungal therapy and intravitreal antifungal injections, and all required vitrectomy. Two eyes developed retinal detachment over the course of the endophthalmitis. Five eyes had visual outcomes of 20/60 or better, and one eye had a poor outcome with final visual acuity of hand movements only. There was no associated mortality, and no infected eyes required enucleation or evisceration.

Conclusions

C. dubliniensis endophthalmitis is a rare condition which occurs mainly in intravenous drug users and can occur in both HIV-positive and HIV-negative patients. Unlike C. albicans endophthalmitis, C. dubliniensis endophthalmitis has reasonable visual outcomes and does not appear to be associated with high mortality.

Advantages of using matrix-assisted laser desorption ionization-time of flight mass spectrometry as a rapid diagnostic tool for identification of yeasts and mycobacteria in the clinical microbiological laboratory

Yeast and mycobacteria can cause infections in immunocompromised patients and normal hosts. The rapid identification of these organisms can significantly improve patient care. There has been an increasing number of studies on using matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) for rapid yeast and mycobacterial identifications. However, studies on direct comparisons between the Bruker Biotyper and bioMérieux Vitek MS systems for the identification of yeast and mycobacteria have been limited. This study compared the performance of the two systems in their identification of 98 yeast and 102 mycobacteria isolates. Among the 98 yeast isolates, both systems generated species-level identifications in >70% of the specimens, of which Candida albicans was the most commonly cultured species. At a genus-level identification, the Biotyper system identified more isolates than the Vitek MS system for Candida (75/78 [96.2%]versus 68/78 [87.2%], respectively; P = 0.0426) and non-Candida yeasts (18/20 [90.0%]versus 7/20 [35.0%], respectively; P = 0.0008). For mycobacterial identification, the Biotyper system generated reliable identifications for 89 (87.3%) and 64 (62.8%) clinical isolates at the genus and species levels, respectively, from solid culture media, whereas the Vitek MS system did not generate any reliable identification. The MS method differentiated 12/21 clinical species, despite the fact that no differentiation between Mycobacterium abscessus and Mycobacterium chelonae was found by using 16S rRNA gene sequencing. In summary, the MALDI-TOF MS method provides short turnaround times and a standardized working protocol for the identification of yeast and mycobacteria. Our study demonstrates that MALDI-TOF MS is suitable as a first-line test for the identification of yeast and mycobacteria in clinical laboratories.

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.

The first Korean case of candidemia due to Candida dubliniensis

Candidemia due to uncommon Candida spp. appears to be increasing in incidence. C. dubliniensis has been increasingly recovered from individuals not infected with HIV. Identification of C. dubliniensis can be problematic in routine clinical practice due to its phenotypic resemblance to C. albicans. We report the first case of C. dubliniensis candidemia in Korea, which occurred in a 64-yr-old woman who presented with partial seizure, drowsiness, and recurrent fever. Germ-tube positive yeast that was isolated from blood and central venous catheter tip cultures formed smooth, white colonies on sheep blood agar and Sabouraud agar plates, indicative of Candida spp. C. dubliniensis was identified using the Vitek 2 system (bioMerieux, USA), latex agglutination, chromogenic agar, and multiplex PCR. The blood isolate was susceptible to flucytosine, fluconazole, voriconazole, and amphotericin B. After removal of the central venous catheter and initiation of fluconazole treatment, the patient's condition gradually improved, and she was cleared for discharge from our hospital. Both clinicians and microbiologists should be aware of predisposing factors to C. dubliniensis candidemia in order to promote early diagnosis and appropriate treatment.

Molecular identification of Pichia guilliermondii, Debaryomyces hansenii and Candida palmioleophila

Traditional phenotypic methods and commercial kits based on carbohydrate assimilation patterns are unable to consistently distinguish among isolates of Pichia guilliermondii, Debaryomyces hansenii and Candida palmioleophila. As result, these species are often misidentified. In this work, we established a reliable method for the identification/differentiation of these species. Our assay was validated by DNA sequencing of the polymorphic region used in a real-time PCR assay driven by species-specific probes targeted to the fungal ITS 1 region. This assay provides a new tool for pathogen identification and for epidemiological, drug resistance and virulence studies of these organisms.

First isolation of Candida dubliniensis from oral cavities of dermatological patients in Nanjing, China

Candida dubliniensis is an emerging pathogen capable of causing both superficial and systemic infections. Although C. dubliniensis and C. albicans are phenotypically similar, the two species differ in terms of epidemiology and the ability to rapidly develop resistance to fluconazole. C. dubliniensis is primarily associated with oral candidiasis of human immunodeficiency virus (HIV)-infected individuals. In this study, we describe the first recovery of C. dubliniensis from oral cavities of non-HIV-infected patients with dermatological diseases in Nanjing, China. The isolates were phenotypically characterized as C. dubliniensis by their production of brown rough colonies and chlamydospores on tobacco agar and their inability to grow on hypertonic Sabouraud dextrose agar or to assimilate xylose or α-methyl-D-glycoside. The species identification was subsequently confirmed by amplification and sequencing of the internal transcribed spacer region (ITS). Three C. dubliniensis isolates out of 128 (2.3%) presumptive C. albicans/C. dubliniensis ones were finally identified. Further sequence analysis separated the three isolates into two of the four reported ITS genotypes. Antifungal susceptibility testing showed that they were susceptible to fluconazole, itraconazole, voriconazole, micafungin, and amphotericin B. This study adds to the accumulating evidence that C. dubliniensis is widely distributed in non-HIV-infected populations worldwide.

Application of hypertonic Sabouraud glucose agar for differentiation of Candida dubliniensis from Candida albicans

An evaluation of hypertonic Sabouraud glucose agar (SGA) with 6.5% NaCl for phenotypic differentiation of Candida dubliniensis from Candida albicans is reported. Identity of the test fungi (C. albicans, 84; C. dubliniensis, 18) was based on their typical phenotypic characteristics and confirmed by a diagnostic polymerase chain reaction that targets the novel C. dubliniensis group I intron in the large ribosomal subunit. At 96 h of incubation at 28 °C, all of the 84 C. albicans isolates showed growth on hypertonic SGA contrary to the consistently negative results with the 20 C. dubliniensis isolates. In strong contrast, chlamydospore formation on Staib agar yielded 10 (11.9%) false-positive results and 74 (88%) of the test C. albicans isolates showed false-negative results at 45 °C. We conclude that hypertonic SGA with 6.5% NaCl can be recommended for wider application as a reliable and inexpensive medium for routine differentiation of C. dubliniensis from C. albicans.

Cdr2p contributes to fluconazole resistance in Candida dubliniensis clinical isolates

The development of resistance to azole antifungals used in the treatment of fungal infections can be a serious medical problem. Here, we investigate the molecular mechanisms associated with reduced susceptibility to fluconazole in clinical isolates of Candida dubliniensis , showing evidence of the trailing growth phenomenon. The changes in membrane sterol composition were studied in the presence of subinhibitory fluconazole concentrations. Despite lanosterol and eburicol accumulating as the most prevalent sterols after fluconazole treatment, these ergosterol precursors still support growth of Candida isolates. The overexpression of ABC transporters was demonstrated by immunoblotting employing specific antibodies against Cdr1p and Cdr2p. The presence of a full-length 170 kDa protein Cdr1p was detected in two isolates, while a truncated form of Cdr1p with the molecular mass of 85 kDa was observed in isolate 966/3(2). Notably, Cdr2p was detected in this isolate, and the expression of this transporter was modulated by subinhibitory concentrations of fluconazole. These results suggest that C. dubliniensis can display the trailing growth phenomenon, and such isolates express similar molecular mechanisms like that of fluconazole-resistant isolates and can therefore be associated with recurrent infections.

Candida albicans or Candida dubliniensis?

Candida albicans is increasing as an opportunistic pathogen causing candidemia and candidiasis worldwide. In addition, other non-albicans Candida species are now also associated with pertinent infections. These include the closely related C. dubliniensis, which shares many phenotypic similarities with C. albicans. These similarities pose problems in the identification of isolates and have previously led to misidentification of these species. As a result, several identification techniques based on phenotypic and genotypic characteristics have been developed to differentiate between these Candida species. This review will focus on the similarities and differences between these two Candida species highlighting different identification methods and their advantages and disadvantages.

Candida dubliniensis screening using the germ tube test in clinical yeast isolates and prevalence of C. dubliniensis in Korea

The aim of this study was to screen for C. dubliniensis using the germ tube test with human pooled serum (HPS) in clinical isolates and investigate the prevalence of C. dubliniensis in Korea. Among 1,854 yeast strains isolated, 1,404 strains of C. albicans (on the basis of positive results of the germ tube test) and 192 germ tube-negative yeast strains were examined. All 1,596 clinical isolates were examined using the germ tube test with HPS, the differential temperature, and NaCl tolerance test. Only 81 isolates that did not grow at 45 degrees C nor on Sabouraud 6.5% NaCl broth were selected and tested using the VITEK 2 ID-YST system and the multiplex-PCR assay for the study. The two strains, C. dubliniensis ATCC MYA-646 and KCTC 17427 failed to produce germ tubes in HPS but produced them in fresh rabbit serum (FRS) and fetal bovine serum (FBS). No C. dubliniensis was found in this study population. The results of this study suggest that the germ tube test with HPS in combination with FRS or FBS can be used for discriminating between C. albicans and C. dubliniensis strains and that the prevalence of C. dubliniensis appears to be extremely low in Korea.

Candida africana and its closest relatives

Candida africana is a recently described opportunistic yeast pathogen that has been linked to vaginal candidiasis. This yeast was first described, in 1995, as atypical chlamydospore-negative Candida albicans strain, and subsequently proposed as a new Candida species on the basis of morphological, biochemical and physiological characteristics clearly different from those of typical C. albicans isolates. Phylogenetic studies based on the comparison of ribosomal DNA sequences demonstrated that C. africana and C. albicans isolates are too closely related to draw any conclusions regarding the status of a new species. Therefore, on the basis of these studies, some authors considered C. africana as a biovar of C. albicans even if genetic differences may be found if additional regions of genomic DNA are sequenced. The taxonomic situation of C. africana and its phylogenetic relationship with other Candida species is still controversial and remains, at present, a matter of debate. Our goal is to review the current knowledge about C. africana and highlight the development of rapid and accurate tests for its discrimination from C. albicans, Candida dubliniensis and Candida stellatoidea. Furthermore, through the analysis of literature data, we have found that C. africana has a worldwide distribution and a considerable number of features making its study particularly interesting.

Experimental systemic virulence of oral Candida dubliniensis isolates in comparison with Candida albicans, Candida tropicalis and Candida krusei

There are no previous studies on the comparative virulence of Candida dubliniensis with other non-albicans species. The aim of this study was to compare the virulence and infection kinetics of C. dubliniensis and other species. Candida albicans, C. dubliniensis, Candida tropicalis and Candida krusei (reference strains) were inoculated intravenously in mice. For infection kinetics evaluation, a group of five animals were sacrificed after 6 h, 3, 7, 14 and 21 days. Microbiological evaluations (liver, spleen, kidneys, lungs and brain) and histopathological examination of the kidney were performed. The results of virulence evaluation were analysed using Kaplan-Meier survival analysis (5%). Candida dubliniensis-inoculated mice survived for longer periods compared with those with C. albicans (P = 0.005). No differences were detected in relation to C. tropicalis (P = 0.326) and C. krusei (P = 0.317). Most of the organs were persistently colonised by C. albicans and C. dubliniensis even by day 21. Tendency of C. krusei clearance was observed in all organs. Fungal masses and renal lesions were observed after inoculation of C. albicans, C. dubliniensis and C. tropicalis. Within the limits of the study, data on survival rate and dissemination capacity suggest that C. dubliniensis is less virulent than C. albicans.

The Relationship between Tobacco Smoking and Oral Colonization with Candida Species

Aim

The aim of this study was to assess and compare the quantitative and qualitative oral colonization of Candida species between a group of healthy tobacco smokers and a comparable group of nonsmokers, and to investigate a possible correlation between oral candidal colonization and the quantity or duration of the smoking habit.

Methods and Materials

Fifty smokers and 50 nonsmokers were included in the study. Candida species were isolated using the concentrated oral rinse (COR) technique and identified using the germ tube test and API 20 C AUX yeast identification system.

Results

Overall candidal transmission was 84 percent. Candida species were isolated from 42 (84 percent) of the smokers and 37 (74 percent) of the nonsmokers (p>0.05). The mean CFU/ml were 333 (SD=358) and 268 (SD=332), respectively (p>0.05).

Conclusion

Tobacco smoking did not appear to increase oral colonization with Candida species in healthy subjects.

Clinical Significance

The effects of smoking on oral tissues and the mechanisms by which Candida proliferate intra-orally as a result of cigarette smoking warrant additional study.

Citation

Darwazeh AM, Al-Dwairi ZN, Al-Zwairi AA. The Relationship between Tobacco Smoking and Oral Colonization with Candida Species. J Contemp Dent Pract [Internet]. 2010 May; 11(3):017-024. Available from: http://www.thejcdp. com/journal/view/volume11-issue3-al_dwairi

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.

Prevalence of Candida dubliniensis among cancer patients in Kuwait: a 5-year retrospective study

Despite close genetic and phenotypic relationship of Candida dubliniensis with Candida albicans, its role in human disease is mostly restricted to oral colonisation, particularly among HIV-infected patients. The prevalence of C. dubliniensis in association with other disease conditions has been infrequently reported. In this study, we present data on the prevalence of C. dubliniensis among yeast species isolated from cancer patients over a 5-year period. A total of 1445 yeast isolates recovered from respiratory specimens, blood, urine and oral swabs were analysed. Candida dubliniensis isolates were provisionally identified by phenotypic methods and their identity was further confirmed by species-specific amplification and/or sequencing of internally transcribed spacer region of rDNA. Antifungal susceptibility for fluconazole was determined by Etest. The number of isolates identified as C. dubliniensis, C. albicans and other yeast species were 71 (4.9%), 862 (59.6%) and 512 (35%) respectively. All the C. dubliniensis isolates originated from respiratory (5.9%) or oral (3.2%) specimens with an overall prevalence of 4.9%, and were found to be susceptible to fluconazole. The isolation of C. dubliniensis from respiratory or oral specimens and not from blood or urine specimens suggests that this species has preference to colonise these sites of human body.

Zero prevalence of parasites associated with oral lesions of HIV infected and AIDS patients in South Western Uganda

BACKGROUND

Despite paucity of information regarding oral lesions with parasitic etiology, parasitic diseases continue to be problematic among impoverished and immunocompromised individuals in developing countries.

OBJECTIVE

To determine the prevalence of parasites in the oral lesions of Ugandan HIV infected and AIDS patients, in South Western Uganda.

METHODS

Adult HIV/AIDS positive patients attending The AIDS Support Organization Clinics in South Western Uganda with oral lesions were recruited for this study. Standard parasitological methods (direct microscopy, saline and iodine wet preparations, Giemsa-Romanosky staining of smears and culture) were adopted in analysis of randomly collected six hundred and five samples (469 from females; 136 from males) for parasites.

RESULTS

No ova, cyst, trophoziotes, lava or segment of parasites were seen in the oral lesions identified among the studied population.

CONCLUSION

Parasites were absent and therefore may not be implicated as etiologic microbial agents of observed oral lesions associated with HIV infected and AIDS patients living in South Western Uganda.

[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.

Molecular epidemiology of Candida albicans and its closely related yeasts Candida dubliniensis and Candida africana

We performed a molecular study to determine the occurrence of Candida albicans, Candida africana, and Candida dubliniensis in different clinical samples. The study provides new insights into the epidemiology of candidiasis in hospitalized patients in three hospitals in southern Italy. It also reports the first detailed epidemiological data concerning the occurrence of C. africana in clinical samples.

Differentiation of Candida dubliniensis from Candida albicans on rosemary extract agar and oregano extract agar

Candida dubliniensis is a recently described pathogenic species which shares many phenotypic features with Candida albicans and therefore, may be misidentified in microbiological laboratories. Because molecular methods can be onerous and unfeasible in routine mycological laboratories with restricted budgets such as those in developing countries, phenotypic techniques have been encouraged in the development of differential media for the presumptive identification of these species. We examined the colony morphology and chlamydospore production of 30 C. dubliniensis isolates and 100 C. albicans isolates on two new proposed media: rosemary (Rosmarinus officinalis) extract agar (REA) and oregano (Origanum vulgare) extract agar (OEA). These substrates are traditionally used as spices and medicinal herbs. In both of these media, all C. dubliniensis isolates (100%) showed rough colonies with peripheral hyphal fringes and abundant chlamydospores after 24 to 48 hr of incubation at 25 degrees C. In contrast, under the same conditions, all isolates of C. albicans (100%) showed smooth colonies without hyphal fringes or chlamydospores. In conclusion, REA and OEA offer a simple, rapid, and inexpensive screening media for the differentiation of C. albicans and C. dubliniensis.

Prevalence and phenotypic evaluation of Candida dubliniensis in pregnant women with vulvovaginal candidosis in a university hospital in Ankara

Candida dubliniensis is very similar to Candida albicans in terms of genotypic and phenotypic characteristics. As the hormonal milieu of the vagina during pregnancy, characterised by a lack of maternal cell-mediated immunity, enhances Candida colonisation and serves as a risk factor for symptomatic expression, investigation into the isolation of C. dubliniensis in vaginal discharges of pregnant women with vulvovaginal candidosis was made. A total of 77 Candida isolates obtained from 60 patients positive for vulvovaginal candidosis collected from 218 pregnant women were investigated for C. dubliniensis subsistence. In total 41 Candida species phenotypically identified as C. albicans on the basis of a positive germ tube test and carbohydrate assimilation tests were screened for the presence of C. dubliniensis. Phenotypic tests for differentiation of C. dubliniensis from C. albicans, such as growth at 42 and 45 degrees C on Sabouraud dextrose agar, appearance on CHROMagar and colony morphology on Cornmeal-Tween-80 agar and Staib agar were carried out. Only one strain (2.43%) was phenotypically identified as C. dubliniensis. According to our study, a combination of at least five phenotypic methods is necessary for an exact diagnosis of C. dubliniensis. Large-scale studies of pregnant women are required to discover the aetiological importance of this yeast.

Fluconazole and itraconazole susceptibilities of Candida spp. isolated from oropharyngeal specimens and blood cultures of paediatric haematology/oncology patients

This study examined the in vitro susceptibilities to fluconazole and itraconazole of isolates of Candida spp. from surveillance oropharyngeal specimens and blood cultures from paediatric patients with malignancy. The species distribution of 100 isolates from oropharyngeal specimens was C. albicans 86%, C. glabrata 7%, C. lusitaniae 4%, C. parapsilosis 2% and C. tropicalis 1%. From a total of nine isolates from blood cultures the species distribution was C. albicans 33.3%, C. parapsilosis 33.3 % and C. guilliermondii 33.3%. Only three of the oropharyngeal isolates were resistant to fluconazole (MIC > or = 64 mg l(-1)) and only two were resistant to itraconazole (MIC > or = 1 mg l(-1)). None of the blood culture isolates was resistant to either agent. At this centre, C. albicans is the predominant species from oropharyngeal specimens, but non-albicans Candida species predominate in blood cultures. Although resistance to fluconazole and itraconazole is rare at present, continued surveillance is warranted to monitor trends in species distribution and antifungal susceptibility.

Candida albicans strain maintenance, replacement, and microvariation demonstrated by multilocus sequence typing

We typed 165 Candida albicans isolates from 44 different sources by multilocus sequence typing (MLST) and ABC typing of rRNA genes and determined their homozygosity or heterozygosity at the mating-type-like locus (MTL). The isolates represented pairs or larger sets from individual sources, which allowed the determination of strain diversity within patients. A comparison of replicate sequence data determined a reproducibility threshold for regarding isolates as MLST indistinguishable. For 36 isolate sets, MLST and ABC typing showed indistinguishable or highly related strain types among isolates from different sites or from the same site at different times from each patient. This observation included 11 sets with at least one isolate from a blood culture and a nonsterile site from the same patient. For one patient, strain replacement was evidenced in the form of two sets of isolates from different hospital admissions where the strain types within each set were nearly identical but where the two sets differed both by MLST and ABC typing. MLST therefore confirms the existing view of C. albicans strain carriage. Microvariation, evidenced as small differences between MLST types, resulted in most instances from a loss of heterozygosity at one or more of the sequenced loci. Among isolate sets that showed major strain type differences, some isolates could be excluded as likely examples of handling errors during storage. However, for a minority of isolates, intermittent differences in ABC type for tightly clustered MLST types and intermittent appearances of MTL homozygosity lead us to propose that some C. albicans isolates, or all isolates under yet-to-be-determined conditions, maintain a high level of genetic diversity by mechanisms such as recombination, gene conversion, or chromosomal ploidy change.

Evaluation of 5 new media containing extracts of seeds applied to Candida dubliniensis screening

Candida dubliniensis is a recently described pathogenic species that shares many phenotypic features with Candida albicans and so may be misidentified in microbiologic laboratories. The aim of this study is to find a useful and cost-effective method suitable for screening C. dubliniensis before proceeding to further identification. We examined the colony morphology and chlamydospore production of 26 C. dubliniensis isolates and 100 C. albicans isolates on the following 5 proposed media: sesame seed agar (SSA), rapeseed agar, canary grass seed agar, millet seed agar, and linseed agar (LA). The best results were obtained with SSA and LA because all 26 C. dubliniensis isolates showed rough colonies with peripheral hyphal fringes and abundant chlamydospores after 24 to 48 h of incubation at 25 degrees C. All C. albicans isolates (100%) showed smooth colonies without hyphal fringes or chlamydospores. These 2 media consist of new and simple tools for presumptive differentiation of C. dubliniensis from C. albicans.

Molecular fingerprinting methods for the discrimination between C. albicans and C. dubliniensis

Opportunistic fungal pathogens are becoming increasingly important causes of both community-acquired and nosocomial infections. The most important fungal pathogens are yeast species belonging to the genus Candida. These species show differences in levels of resistance to antifungal agents and mortality. Consequently, it is important to correctly identify the causative organism to the species level. Identification of Candida dubliniensis in particular remains problematic because of the high degree of phenotypic similarity between this species and Candida albicans. However, as the differences between both are most pronounced at the genetic level, several studies have been conducted in order to provide a specific and rapid identification fingerprinting molecular test. In most candidal infectious, no single DNA fingerprinting technique has evolved as a dominant method, and each method has its advantages, disadvantages and limitations. Moreover, the current challenge of these techniques is to compile standardized patterns in a database for interlaboratory use and future reference. This review provides an overview of most common molecular fingerprinting techniques currently available for discrimination of C. albicans and C. dubliniensis.

Molecular identification of Candida dubliniensis isolated from oral lesions of HIV-positive and HIV-negative patients in São Paulo, Brazil

Candida dubliniensis is a new, recently described species of yeast. This emerging oral pathogen shares many phenotypic and biochemical characteristics with C. albicans, making it hard to differentiate between them, although they are genotypically distinct. In this study, PCR (Polymerase Chain Reaction) was used to investigate the presence of C. dubliniensis in samples in a culture collection, which had been isolated from HIV-positive and HIV-negative patients with oral erythematous candidiasis. From a total of 37 samples previously identified as C. albicans by the classical method, two samples of C. dubliniensis (5.4%) were found through the use of PCR. This study underscores the presence of C. dubliniensis, whose geographical and epidemiological distribution should be more fully investigated.

Detection of Candida dubliniensis in Venezuela

Over the past decades there has been a significant increase in fungal infections caused by Candida species, and continues to be common in immunocompromised individuals infected with the human immunodeficiency virus (HIV). Although Candida albicans remains the fungal species most frequently isolated as an opportunistic oral pathogen, other non-albicans are often identified in this cohort of patients, including C. dubliniensis. This yeast is closely related to and shares many phenotypic characteristics with C. albicans. Colonies of these two species appear morphologically identical when not grown on special media. The shared phenotypic characteristics of C. dubliniensis and C. albicans suggest that many C. dubliniensis isolates may have been misidentified as C. albicans in the past. The present studies aim is to recover and identify C. dubliniensis, and presumptive clinical C. albicans, from the oral cavities of HIV-seropositive individuals, comparing conventional media to obtain a simple, low-cost and reliable identification system for C. dubliniensis. A total of 16 isolates (3,98%) had been obtained from 402 HIV infected individuals with recurrent oropharyngitis and were identified as C. dubliniensis. Out of these C. dubliniensis isolates 19% were resistant, with MICs above 64 microg/ml to fluconazole. This constitutes, to the authors knowledge the first recovery of this organism in Venezuela.

A rapid screening test to distinguish between Candida albicans and Candida dubliniensis using NMR spectroscopy

Nuclear magnetic resonance (NMR) spectroscopy combined with a statistical classification strategy (SCS) successfully distinguished between Candida albicans and Candida dubliniensis. 96% of the isolates from an independent test set were identified correctly. This proves that this rapid approach is a valuable method for the identification and chemotaxonomic characterisation of closely related taxa. Most discriminatory regions were correlated with metabolite profiles, indicating biochemical differences between the two species.

Population structure and properties of Candida albicans, as determined by multilocus sequence typing

We submitted a panel of 416 isolates of Candida albicans from separate sources to multilocus sequence typing (MLST). The data generated determined a population structure in which four major clades of closely related isolates were delineated, together with eight minor clades comprising five or more isolates. By Fisher's exact test, a statistically significant association was found between particular clades and the anatomical source, geographical source, ABC genotype, decade of isolation, and homozygosity versus heterozygosity at the mating type-like locus (MTL) of the isolates in the clade. However, these associations may have been influenced by confounding variables, since in a univariate analysis of variance, only the clade associations with ABC type and anatomical source emerged as statistically significant, providing the first indication of possible differences between C. albicans strain type clades and their propensity to infect or colonize different anatomical locations. There were no significant differences between clades with respect to distributions of isolates resistant to fluconazole, itraconazole, or flucytosine. However, the majority of flucytosine-resistant isolates belonged to clade 1, and these isolates, but not flucytosine-resistant isolates in other clades, bore a unique mutation in the FUR1 gene that probably accounts for their resistance. A significantly higher proportion of isolates resistant to fluconazole, itraconazole, and flucytosine were homozygous at the MTL, suggesting that antifungal pressure may trigger a common mechanism that leads both to resistance and to MTL homozygosity. The utility of MLST for determining clade assignments of clinical isolates will form the basis for strain selection for future research into C. albicans virulence.

Supplementation of CHROMagar Candida medium with Pal's medium for rapid identification of Candida dubliniensis

CHROMagar Candida medium is used for the isolation and identification of Candida species, but it does not differentiate Candida albicans from Candida dubliniensis. This differentiation can be achieved by using Pal's agar, which cannot be used in primary isolation. We have combined both media to obtain a new medium that can be used for the isolation and identification of C. dubliniensis in primary cultures.

Azole susceptibility and resistance in Candida dubliniensis

Candida dubliniensis is a recently described species of pathogenic yeast that shares many phenotypic features with Candida albicans. It is primarily associated with oral colonization and infection in HIV-infected individuals. Isolates of C. dubliniensis are generally susceptible to commonly used azole antifungal agents; however, resistance has been observed in clinical isolates and can be induced by in vitro exposure. Molecular mechanisms of azole resistance in C. dubliniensis include increased drug efflux, modifications of the target enzyme and alterations in the ergosterol biosynthetic pathway.

Incubation at room temperature may be an independent factor that induces chlamydospore production in Candida dubliniensis

Production of chlamydospores is one of the phenotypic features used to differentiate Candida albicans and Candida dubliniensis. C. albicans produces few chlamydospores on only cornmeal/rice-Tween agar at room temperature, whereas C. dubliniensis produces abundant chlamydospores at this temperature both on cornmeal agar and some other commonly used media. We tried to determine whether the room temperature is the main factor that induces chlamydospore production of C. dubliniensis, regardless of the medium used. For this purpose, 100 C. albicans and 24 C. dubliniensis isolates were tested for chlamydospore production at room temperature and at 37 degrees C on some routinely used media, including eosin-methylene blue agar (EMB), nutrient agar (NA), nutrient broth (NB), and also on an investigational medium, phenol red agar (PR). At 37 degrees C, none of the isolates produced chlamydospores on any of the tested media. At 26 degrees C, all C. dubliniensis isolates produced abundant chlamydospores and pseudohyphae after 24-48 h on all tested media. At this incubation temperature, all C. albicans isolates failed to produce chlamydospores and pseudohyphae on EMB, NA, and NB, whereas 2 of the C. albicans isolates produced a few chlamydospores on PR. We also observed that all C. dubliniensis isolates tested on EMB and PR produced rough colonies with a hyphal fringe around the colonies, whereas none of the C. albicans isolates showed this property. In conclusion, incubation at 26 degrees C may play the key role for production of abundant chlamydospores and pseudohyphae by C. dubliniensis. Comprehensive molecular studies are needed to clarify the genetic basis of this observation. Using EMB and PR may be an inexpensive, a time-saving, and a simple way of presumptive identification of C. dubliniensis based on chlamydospore formation and colony morphology.