Molecular probe for typing strains of Candida albicans

Genotyping of Candida albicans isolated from animals using 25S ribosomal DNA and ALT repeats polymorphism in repetitive sequence

Background and Purpose:

Candida albicans is the most prevalent Candida species isolated from animals. Candidiasis can be systemic in animals or may affect a single organ, such as the mouth, urinary tract, and skin. The aim of the present study was to determine the genetic diversity of C. albicans isolated from different animals and investigate the presence of a relationship between host specificity and genetic typing of C. albicans.

Materials and Methods:

For the purpose of the study, DNA extraction was performed on 27 clinical isolates of C. albicans obtained from animals. Subsequently, they were subjected to 25S ribosomal DNA amplification and ALT repeats in repetitive sequences (RPSs). The minimum inhibitory concentrations of fluconazole, ketoconazole, clotrimazole, nystatin, amphotericin B, and caspofungin were determined using the microdilution method based on the Clinical and Laboratory Standards Institute M27-S4 standard.

Results:

Out of 27 C. albicans strains, 11, 6, 5, and 5 cases were recognized as genotypes A (40.8%), E (22.2%), B (18.5%), and C (18.5%), respectively, through amplification using AS-I, which revealed 17 different types of C. albicans. By combining the two typing methods, 27 C. albicans strains were finally divided into 22 genotypes.

Conclusion:

Different genotypes showed genetic diversity among the C. albicans strains isolated from animal sources. The results revealed no special genotype relationship according to the host, anatomical source of isolation, and antifungal susceptibility.

Prevalence of fluconazole-resistant strains of Candida albicans in otherwise healthy outpatients

BACKGROUND

In contrast to the immunosuppressed patient population, the prevalence of fluconazole-resistant strains of Candida albicans among healthy individuals has not been extensively studied.

METHODS

Candida species were cultured form 50 healthy outpatients with clinical signs of oral candidiasis. Following one week of the recommended fluconazole regimen, post-treatment cultures were obtained. Both pre- and post-treatment yeasts were identified and in vitro susceptibility testing was performed using the NCCLS M-27A method. Strains were further differentiated using established cDNA probes.

RESULTS

Forty-four patients (88%) had positive C.albicans cultures prior to treatment. Antifungal susceptibility testing of these strains demonstrated no in vitro resistance to fluconazole. At post-treatment evaluation, eight patients (18%) had persistent signs of infection and 10 patients (23%) had positive Candida sp. cultures despite no clinical signs of infection. DNA analysis confirmed that the same C. albicans strain was present both in the pre-treatment and the post-treatment cultures.

CONCLUSIONS

Our results showed that the presence of fluconazole-resistant strains of C.albicans does not appear to be prevalent among healthy outpatients furthermore, in vitro antifungal susceptibility testing does not always predict successful therapy in these patients.

Typing of Candida albicans and Candida parapsilosis: species-related limitations of electrophoretic karyotyping and restriction endonuclease analysis of genomic DNA

Species-related discrimination limits of electrophoretic karyotyping (EK) and restriction endonuclease analysis of genomic DNA (REAG), using pulse-field gel electrophoresis, in typing Candida albicans (CA) and Candida parapsilosis (CP) were compared. Eleven CA and 12 CP isolates from individual neonates and three CA and three CP control isolates were used. For CA, EK and REAG with sfiI displayed seven and six banding-patterns, respectively. One karyotype and two SfiI banding-patterns were observed among the control-isolates. Combining EK/REAG (SfiI) demonstrated nine composites and three distinct control-composites. For CP, EK displayed nine karyotypes, REAG (SfiI) demonstrated four banding-patterns, and REAG (BssHII) yielded six banding-patterns. EK and REAG/SfiI failed to distinguish any CP-controls whereas REAG/BssHII distinguished 2/3 CP-controls. Combining EK/REAG (SfiI) showed 10 composites indistinguishable from CP-controls whereas EK/REAG (BssHII) demonstrated 11 composites and three distinct control-composites. These results illustrate that singly, EK and REAG have significant limitation in typing Candida species though EK is more precise. Combining both methods yields better results but the appropriate restriction endonuclease may vary by strains or species. These findings underscore the importance of combining multiple typing methods, testing several control isolates, and correlating the results with careful epidemiological assessment.

Microsatellite polymorphism in the promoter sequence of the elongation factor 3 gene of Candida albicans as the basis for a typing system

The polymorphism of a TTC/TTTC microsatellite in the promoter sequence of the elongation factor 3 gene of Candida albicans was investigated by PCR. One primer was fluorescein labeled, and PCR signals were read with an automatic sequencer. Twenty-nine reference strains and 31 independent clinical isolates were studied. Eleven different alleles were identified, giving 16 different profiles among the 60 strains tested, with a discriminatory power of 0.88. This marker is stable upon subculture, and reproducibility was achieved by automated procedures. When several microsatellite markers are available, many isolates can be rapidly and reproducibly tested for epidemiological questions, such as the prevalence of a given strain in a hospital setting and transmission between patients.