Comparison of standard phenotypic assays with a PCR method to discriminate Candida albicans and C. dubliniensis

Phenotypic and genotypic detection of Candida albicans and Candida dubliniensis strains isolated from oral mucosa of AIDS pediatric patients

The aim of this study was to assess a collection of yeasts to verify the presence of Candida dubliniensis among strains isolated from the oral mucosa of AIDS pediatric patients which were initially characterized as Candida albicans by the traditional phenotypic method, as well as to evaluate the main phenotypic methods used in the discrimination between the two species and confirm the identification through genotypic techniques, i.e., DNA sequencing. Twenty-nine samples of C. albicans isolated from this population and kept in a fungi collection were evaluated and re-characterized. In order to differentiate the two species, phenotypic tests (Thermotolerance tests, Chromogenic medium, Staib agar, Tobacco agar, Hypertonic medium) were performed and genotypic techniques using DNA sequencing were employed for confirmation of isolated species. Susceptibility and specificity were calculated for each test. No phenotypic test alone was sufficient to provide definitive identification of C. dubliniensis or C. albicans, as opposed to results of molecular tests. After amplification and sequencing of specific regions of the 29 studied strains, 93.1% of the isolates were identified as C. albicans and 6.9% as C. dubliniensis. The Staib agar assay showed a higher susceptibility (96.3%) in comparison with other phenotypic techniques. Therefore, genotypic methods are indispensable for the conclusive identification and differentiation between these species.

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.

Effects of eating disorders on oral fungal diversity

BACKGROUND

The eating disorders anorexia and bulimia nervosa can cause several systemic and oral alterations related to poor nutrition and induced vomiting; however, the oral microflora of these patients is poorly studied.

OBJECTIVE

The aim of this study was to evaluate fungal microflora in the oral cavity of these patients by culture-dependent and culture-independent methods.

STUDY DESIGN

Oral rinse samples were cultured to assess the prevalence of Candida species, and the isolates were identified by API system. Microorganism counts were compared by the Mann-Whitney test (5%). Ribotyping, a type of molecular analysis, was performed by sequencing the D1/D2 regions of 28S rRNA.

RESULTS

Our results demonstrated that the eating disorder group showed higher oral Candida spp. prevalence with culture-dependent methods and higher species diversity with culture-independent methods.

CONCLUSIONS

Eating disorders can lead to an increased oral Candida carriage. Culture-independent identification found greater fungal diversity than culture-dependent methods.

A simple and reliable PCR-restriction fragment length polymorphism assay to identify Candida albicans and its closely related Candida dubliniensis

Candida dubliniensis is an emerging pathogen capable of causing superficial as well as systemic infections. Due to its close similarity to C. albcians, conventional methods based on phenotypic traits are not always reliable in identification of C. dubliniensis. In this study, we developed a PCR-restriction fragment length polymorphism (RFLP) assay to identify and discriminate between the two closely related species. The D1/D2 region of 28S rDNA was amplified by PCR and enzymatically digested by ApaI and BsiEI respectively. PCR products of both species were digested into two fragments by ApaI, but those of other yeast species were undigested. BsiEI cut the PCR products of C. albicans into two fragments but not those of C. dubliniensis. Thus two species were differentiated. We evaluated 10 reference strains representing 10 yeast species, among which C. albicans and C. dubliniensis were successfully identified. A total of 56 phenotypically characterized clinical isolates (42 C. albicans isolates and 14 C. dubliniensis isolates) were also investigated for intra-species variability. All tested isolates produced identical RFLP patterns to their respective reference strains except one initially misidentified isolate. Our method offers a simple, rapid and reliable molecular method for the identification of C. albicans and C. dubliniensis.

Opportunistic microorganisms in patients undergoing antibiotic therapy for pulmonary tuberculosis

Antimicrobial therapy may cause changes in the resident oral microbiota, with the increase of opportunistic pathogens. The aim of this study was to compare the prevalence of Candida, Staphylococcus, Pseudomonas and Enterobacteriaceae in the oral cavity of fifty patients undergoing antibiotic therapy for pulmonary tuberculosis and systemically healthy controls. Oral rinsing and subgingival samples were obtained, plated in Sabouraud dextrose agar with chloramphenicol, mannitol agar and MacConkey agar, and incubated for 48 h at 37°C. Candida spp. and coagulase-positive staphylococci were identified by phenotypic tests, C. dubliniensis, by multiplex PCR, and coagulase-negative staphylococci, Enterobacteriaceae and Pseudomonas spp., by the API systems. The number of Candida spp. was significantly higher in tuberculosis patients, and C. albicans was the most prevalent specie. No significant differences in the prevalence of other microorganisms were observed. In conclusion, the antimicrobial therapy for pulmonary tuberculosis induced significant increase only in the amounts of Candida spp.

Oral Candida albicans isolates from HIV-positive individuals have similar in vitro biofilm-forming ability and pathogenicity as invasive Candida isolates

Background

Candida can cause mucocutaneous and/or systemic infections in hospitalized and immunosuppressed patients. Most individuals are colonized by Candida spp. as part of the oral flora and the intestinal tract. We compared oral and systemic isolates for the capacity to form biofilm in an in vitro biofilm model and pathogenicity in the Galleria mellonella infection model. The oral Candida strains were isolated from the HIV patients and included species of C. albicans, C. glabrata, C. tropicalis, C. parapsilosis, C. krusei, C. norvegensis, and C. dubliniensis. The systemic strains were isolated from patients with invasive candidiasis and included species of C. albicans, C. glabrata, C. tropicalis, C. parapsilosis, C. lusitaniae, and C. kefyr. For each of the acquired strains, biofilm formation was evaluated on standardized samples of silicone pads and acrylic resin. We assessed the pathogenicity of the strains by infecting G. mellonella animals with Candida strains and observing survival.

Results

The biofilm formation and pathogenicity in Galleria was similar between oral and systemic isolates. The quantity of biofilm formed and the virulence in G. mellonella were different for each of the species studied. On silicone pads, C. albicans and C. dubliniensis produced more biofilm (1.12 to 6.61 mg) than the other species (0.25 to 3.66 mg). However, all Candida species produced a similar biofilm on acrylic resin, material used in dental prostheses. C. albicans, C. dubliniensis, C. tropicalis, and C. parapsilosis were the most virulent species in G. mellonella with 100% of mortality, followed by C. lusitaniae (87%), C. novergensis (37%), C. krusei (25%), C. glabrata (20%), and C. kefyr (12%).

Conclusions

We found that on silicone pads as well as in the Galleria model, biofilm formation and virulence depends on the Candida species. Importantly, for C. albicans the pathogenicity of oral Candida isolates was similar to systemic Candida isolates, suggesting that Candida isolates have similar biofilm-forming ability and virulence regardless of the infection site from which it was isolated.

Presence of Candida spp. in the oral cavity of heart transplantation patients

Candida spp. can lead to infections or even fungal sepsis particularly among immunocompromized individuals.

Research on Candida dubliniensis in a Brazilian yeast collection obtained from cardiac transplant, tuberculosis, and HIV-positive patients, and evaluation of phenotypic tests using agar screening methods

The aim of this study was to research Candida dubliniensis among isolates present in a Brazilian yeast collection and to evaluate the main phenotypic methods for discrimination between C. albicans and C. dubliniensis from oral cavity. A total of 200 isolates, presumptively identified as C. albicans or C. dubliniensis obtained from heart transplant patients under immunosuppressive therapy, tuberculosis patients under antibiotic therapy, HIV-positive patients under antiretroviral therapy, and healthy subjects, were analyzed using the following phenotypic tests: formation and structural arrangement of chlamydospores on corn meal agar, casein agar, tobacco agar, and sunflower seed agar; growth at 45 °C; and germ tube formation. All strains were analyzed by polymerase chain reaction (PCR). In a preliminary screen for C. dubliniensis, 48 of the 200 isolates on corn meal agar, 30 of the 200 on casein agar, 16 of the 200 on tobacco agar, and 15 of the 200 on sunflower seed agar produced chlamydoconidia; 27 of the 200 isolates showed no or poor growth at 45 °C. All isolates were positive for germ tube formation. These isolates were considered suggestive of C. dubliniensis. All of them were subjected to PCR analysis using C. dubliniensis-specific primers. C. dubliniensis isolates were not found. C. dubliniensis isolates were not recovered in this study done with immunocompromised patients. Sunflower seed agar was the medium with the smallest number of isolates of C. albicans suggestive of C. dubliniensis. None of the phenotypic methods was 100% effective for discrimination between C. albicans and C. dubliniensis.

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.

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.

Prevalence and antifungal resistance profile of Candida spp. oral isolates from patients with type 1 and 2 diabetes mellitus

OBJECTIVE

The goal of the study was to measure the prevalence of Candida spp. in the oral cavity of patients with diabetes types 1 and 2 when compared to healthy individuals and to study antifungal resistance profile of the isolates.

DESIGN

There were 162 subjects in the study: diabetes type 1 (n=39); control group 1 (n=50): healthy individuals matched in gender, age, and oral conditions to diabetes type 1 patients; diabetes type 2 (n=37); control group 2 (n=36) who were matched to each patient of the diabetes type 2 group. Stimulated saliva was collected and isolates were identified with phenotypic tests. The presence of C. dubliniensis was determined by multiplex PCR.

RESULTS

There were no statistically significant differences in Candida spp. frequency between the diabetes 1 group and its control (p=0.443) nor between the diabetes 2 group and its control (p=0.429). C. albicans was the most frequently isolated yeast in all groups. In the diabetes groups, C. stellatoidea, C. parapsilosis, C. tropicalis, C. lipolytica, C. glabrata, and C. krusei were also identified. Additionally, in control groups, C. kefyr was also detected. None of the isolates were resistant to amphotericin B and flucytosine. A low percentage of the isolates were resistant to ketoconazole.

CONCLUSIONS

No differences were detected in colonization of Candida spp. oral isolates from type 1 and type 2 diabetes when compared to matched controls. The antifungal resistance of Candida spp. isolates for ketoconazole from type 1 diabetes patients was significantly higher than that of its matched control.

Comparison of phenotypic methods for the identification of Candida dubliniensis

BACKGROUND/PURPOSE

Mixed infections caused by different Candida species are the rule rather than the exception. The discrimination between the two closely related species Candida albicans and Candida dubliniensis is not trivial. Therefore, there is a need for fast, reliable, and inexpensive methods with high specificity for the identification and differentiation of these two Candida species, which are frequently detected in the oral cavities of patients with a human immunodeficiency virus infection.

METHODS

We applied several phenotypic identification methods (growth on Rice-agar, Bird-seed agar, CHROMagar Candida, API ID 32C; growth at 42 degrees C and 45 degrees C) and compared them with genotyping by arbitrarily primed-polymerase chain reaction.

RESULTS

A sensitivity of 44% for the identification of C. dubliniensis was achieved for growth on Rice-agar, 97% for discrimination on Bird-seed agar, 95% with the assimilation profile index API ID 32C, and 97% when grown at 45 degrees C. We found two API codes not described for C. dubliniensis so far. Additionally, 88% of our C. dubliniensis isolates assimilated palatinose, in contrast to the 1% described in the API reference manual.

CONCLUSION

According to our results, cultivation of Candida isolates on Bird-seed agar after screening on CHROMagar Candida is a very sensitive, simple, and cost-effective method for discriminating C. dubliniensis from C. albicans in routine practice.

Identification of Candida spp. by phenotypic tests and PCR

The correct identification of Candida species is of great importance, as it presents prognostic and therapeutical significance, allowing an early and appropriate antifungical therapy. The purpose of this study was to identify isolates of Candida spp. from oral mucosa of 38 patients with oral candidosis evaluated in 2004 by phenotypic methods and PCR, discriminating C. albicans from the other Candida species. The tests used for phenotypic analysis were germ-tube and chlamydoconidia production, culture in CHROMAgar™ Candida, carbohydrate assimilation test, growth at 45ºC and culture in Tween 80 agar. Genotypic confirmation was performed by PCR. Phenotypic tests showed that 63.2% strains formed germ-tubes, 73.7% produced chlamydoconidia, and 63.2% showed green colonies in chromogenic medium, presumptively indicating C. albicans or C. dubliniensis. The carbohydrate assimilation test confirmed these results. A total of 21% strains were identified as C. krusei and 13.2% were indicative of C. tropicalis. Of these later strains, three produced chlamydoconidia. The association of other phenotypic tests with culture in Tween 80 agar identified 95.8% of strains as C. albicans and 4.2% as C. dubliniensis. All 24 strains indicative of C. albicans and C. dubliniensis were confirmed by PCR as C. albicans.

Secretion of E,E-farnesol and biofilm formation in eight different Candida species

Production of E,E-farnesol (FOH) and biofilm formation were studied under various conditions in 56 strains of eight Candida spp. FOH production differed significantly not only between Candida spp. but within Candida albicans strains as well. FOH concentrations and biofilm formation were the highest for C. albicans.

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.

[An update on Candida dubliniensis]

Eleven years ago, Irish authors, using molecular biology, demonstrated the existence of Candida dubliniensis, a new species of Candida close to Candida albicans. Initially isolated from AIDS patients with oral candidiasis, this species was detected, even in immunocompetent patients. Recently, with new, easy to implement identification tests (latex, immunochromatography), numerous epidemiological studies were undertaken. In most studies, C. dubliniensis was most often identified in the oral cavity. In the absence of HIV infection, the proportion C. dubliniensis/C. albicans ranged from 1 to 5% but it increased to 15-20% in case of HIV infection. It should be stressed that, from an experimental point of view, the acquisition of a secondary resistance to fluconazole is more quickly obtained with C. dubliniensis that with C. albicans, this resistance remains exceptionally observed in clinical observations.

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.

Candida dubliniensis: ten years on

Candida dubliniensis was first described as a novel species in 1995. This organism is very closely related to the important human yeast pathogen, Candida albicans. However, despite the very close phylogenetic relationship between C. albicans and C. dubliniensis and the fact that they share a large number of phenotypic traits, epidemiological and virulence model data indicate that the former is a far more successful pathogen. In order to investigate the molecular basis of the lower virulence of C. dubliniensis recent comparative genomic hybridisation studies have revealed the absence and divergence of specific genes implicated in candidal virulence. Data from the C. dubliniensis genome sequencing project will allow a complete comparison between the genomes of the two species to be performed and thus enhance our understanding of candidal virulence and how virulence has evolved in Candida species.

Phenotypic identification ofCandida albicansby growth on chocolate agar

In this study, we describe a simple method for the identification of Candida albicans in clinical samples. A total of 383 clinical isolates of Candida species were streaked onto chocolate agar and incubated for 48 h at 37 degrees C in the presence of an atmosphere of 6% CO2. All 208 of the C. albicans isolates tested, developed an easy to identify filamentous colony morphology. Of 175 other Candida species tested, 172 (98.3%) were distinguishable from C. albicans by their smooth colony morphology. Three isolates (1.7%) exhibited weak filamentation after prolonged incubation. Although not a routine medium in medical mycology a significant advantage of using chocolate agar lies in its use in clinical bacteriology laboratories for the isolation of fastidious bacteria. Implementation of the proposed method is applicable across a range of specimen types, thus allowing the direct identification of C. albicans in clinical samples. This simple method may allow a quicker entry into directed treatment.