Molecular subtyping of clinical isolates of Candida albicans and identification of Candida dubliniensis Malaysia

Molecular Identification and Antifungal Susceptibility Patterns of Candida Species Isolated from Candidemia Patients in Yasuj, Southwestern Iran

Background: Candidemia is the most common systemic infection in hospitalized patients causing high mortality. Hence, the diagnosis of this infection in the early stage with appropriate antifungal therapy is paramount. Objectives: The study aimed at molecular identification of Candida species isolated from candidemia patients and evaluation of the in vitro antifungal susceptibility patterns of these strains to fluconazole, amphotericin B, and caspofungin. Methods: In the present study, 800 hospitalized patients who were suspected to have candidemia were sampled. Candida species were isolated and identified based on morphological characteristics and PCR-sequencing of the ITS1-5.8S-ITS2 region. Antifungal susceptibility tests for fluconazole, amphotericin B, and caspofungin were performed according to the Clinical and Laboratory Standards Institute protocol M27-A3. Also, clinical data were recorded from the patients' records. Results: Twenty-seven patients among the sample of hospitalized patients were found to have candidemia. A total of 33.3% of candidemia patients were treated with amphotericin B, in which case the mortality rate was 14.8%. The majority of patients (59%) were from the neonatal intensive care unit, and premature birth was the most common underlying condition. Candida albicans (n = 18; 66.6%) was the most common species isolated from blood cultures, followed by C. parapsilosis (n = 7; 25.9%), C. pelliculosa (n = 1; 3.7%), and C. tropicalis (n = 1; 3.7%). Only one C. albicans isolate resistant to fluconazole (minimum inhibitory concentration = 32 µg/mL). Conclusions: Generally, C. albicans has been the most frequent causative agent of candidemia. Resistance to antifungal drugs among candidemia agents was rare. Also, the identification of Candida isolates at the species level with in vitro antifungal susceptibility tests helps manage candidemia patients better and decrease the mortality rate among them.

Growth inhibition of Candida species by Wickerhamomyces anomalus mycocin and a lactone compound of Aureobasidium pullulans

Background

The increasing resistance of Candida yeasts towards antifungal compounds and the limited choice of therapeutic drugs have spurred great interest amongst the scientific community to search for alternative anti-Candida compounds. Mycocins and fungal metabolites have been reported to have the potential for treatment of fungal infections. In this study, the growth inhibition of Candida species by a mycocin produced by Wickerhamomyces anomalus and a lactone compound from Aureobasidium pullulans were investigated.

Methods

Mycocin was purified from the culture supernatant of an environmental isolate of W. anomalus using Sephadex G-75 gel filtration column chromatography. The mycocin preparation was subjected to SDS-PAGE analysis followed by MALDI TOF/TOF mass spectrometry analysis. The thermal and temperature stability of the mycocin were determined. The glucanase activity of the mycocin was investigated by substrate staining of the mycocin with 4-methyl-umbelliferyl-ß-D-glucoside (MUG). Gas chromatography mass spectrometry (GCMS) analysis was used to identify anti-Candida metabolite in the culture supernatant of an environmental isolate of Aureobasidium pullulans. The inhibitory effects of the anti-Candida compound against planktonic and biofilm cultures of various Candida species were determined using broth microdilution and biofilm quantitation methods.

Results

A mycocin active against Candida mesorugosa but not C. albicans, C. parapsilosis and C. krusei was isolated from the culture supernatant of W. anomalus in this study. The mycocin, identified as exo-ß-1,3 glucanase by MALDI TOF/TOF mass spectrometry, was stable at pH 3–6 and temperature ranging from 4-37°C. The glucanase activity of the mycocin was confirmed by substrate staining with MUG. 5-hydroxy-2-decenoic acid lactone (HDCL) was identified from the culture supernatant of A. pullulans. Using a commercial source of HDCL, the planktonic and biofilm MICs of HDCL against various Candida species were determined in this study.

Conclusions

W. anomalus mycocin demonstrated a narrow spectrum of activity targeting only against C. mesorugosa, while HDCL demonstrated a broad spectrum of inhibitory action against multiple Candida species. The growth inhibition of W. anomalus mycocin and the lactone compound from A. pullulans against Candida yeasts should be further explored for therapeutic potentials against candidiasis.

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.

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: an appraisal of its clinical significance as a bloodstream pathogen

A nine-year prospective study (2002–2010) on the prevalence of Candida dubliniensis among Candida bloodstream isolates is presented. The germ tube positive isolates were provisionally identified as C. dubliniensis by presence of fringed and rough colonies on sunflower seed agar. Subsequently, their identity was confirmed by Vitek2 Yeast identification system and/or by amplification and sequencing of the ITS region of rDNA. In all, 368 isolates were identified as C. dubliniensis; 67.1% came from respiratory specimens, 11.7% from oral swabs, 9.2% from urine, 3.8% from blood, 2.7% from vaginal swabs and 5.4% from other sources. All C. dubliniensis isolates tested by Etest were susceptible to voriconazole and amphotericin B. Resistance to fluconazole (≥8 µg/ml) was observed in 2.5% of C. dubliniensis isolates, 7 of which occurred between 2008–2010. Of note was the diagnosis of C. dubliniensis candidemia in 14 patients, 11 of them occurring between 2008–2010. None of the bloodstream isolate was resistant to fluconazole, while a solitary isolate showed increased MIC to 5-flucytosine (>32 µg/ml) and belonged to genotype 4. A review of literature since 1999 revealed 28 additional cases of C. dubliniensis candidemia, and 167 isolates identified from blood cultures since 1982. In conclusion, this study highlights a greater role of C. dubliniensis in bloodstream infections than hitherto recognized.

Mechanisms of antifungal drug resistance in Candida dubliniensis

Candida dubliniensis was first described in 1995 and is the most closely related species to the predominant human fungal pathogen Candida albicans. C. dubliniensis is significantly less prevalent and less pathogenic than C. albicans and is primarily associated with infections in HIV-infected individuals and other immunocompromised cohorts. The population structure of C. dubliniensis consists of three well-defined major clades and is significantly less diverse than C. albicans. The majority of C. dubliniensis isolates are susceptible to antifungal drugs commonly used to treat Candida infections. To date only two major patterns of antifungal drug resistance have been identified and the molecular mechanisms of these are very similar to the resistance mechanisms that have been described previously in C. albicans. However, significant differences are evident in the predominant antifungal drug mechanisms employed by C. dubliniensis, differences that reflect its more clonal nature, its lower prevalence and characteristics of its genome, the complete sequence of which has only recently been determined.

Molecular analysis of Candida albicans isolates from clinical specimens

The aim of this study was to genotype Candida albicans strains isolated from various clinical specimens by using CA-INT-R and CA-INT-L primer pairs designed to span the region that includes the site of the transposable group-1 intron in the 25S rRNA gene. A total of 194 C. albicans isolates (28 invasive and 166 noninvasive) were genotyped. The frequencies of genotypes A, B, C and D were found as 51.0, 29.4, 19.1 and 0.5%, respectively. Statistically significant difference was determined between frequency of genotype distribution between invasive and noninvasive isolates (P < 0.001). Genotype C was more prevalent among invasive isolates while genotype A was in noninvasive ones. Furthermore, six different subtypes were determined among genotype A C. albicans isolates by restriction endonuclease analysis using a previously constructed differentiation scheme consisting of HaeIII and MspI digestions. This study demonstrated the genetic diversity of clinical isolates of C. albicans in our hospital.

[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.