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Brazilian Journal of Microbiology

Print version ISSN 1517-8382On-line version ISSN 1678-4405

Braz. J. Microbiol. vol.37 no.3 São Paulo July/Sept. 2006

http://dx.doi.org/10.1590/S1517-83822006000300004 

MEDICAL MICROBIOLOGY

 

Performance of the Albicans ID2Ò chromogenic medium for rapid identification of Candida albicans

 

Performance do meio cromogênico Albicans ID2Ò para a rápida identificação de Candida albicans

 

 

Patricio Godoy-MartínezI; Ana C. Azevedo; Viviane ReisI; Thelma AlvesI; Leila P. AlmeidaI; Arnaldo L. ColomboI,*

ILaboratório Especial de Micologia, Disciplina de Infectologia, Universidade Federal de São Paulo, São Paulo, SP, Brasil

 

 


ABSTRACT

The aim of our study was to evaluate the accuracy of the chromogenic media Albicans ID2Ò (bioMérieux, France) for the identification of Candida albicans among 330 yeast strains. All C. albicans (100) and C. dubliniensis (20) strains exhibited blue color when cultured on Albicans ID2Ò. However, the blue color was also exhibited by cultures of C. rugosa (30/30) and C. tropicalis (3/50) isolates.

Key words: Candida albicans, chromogenic medium, Albicans ID2Ò media


RESUMO

O objetivo do nosso estudo foi avaliar a eficácia do meio cromogênico Albicans ID2Ò (bioMérieux, France) na identificação de Candida albicans entre 330 amostras de leveduras. As cepas de C. albicans (100) e C. dubliniensis (20) exibiram coloração azul quando semeadas em Albicans ID2Ò. Contudo, a coloração azul também foi verificada em culturas de C. rugosa (30/30) e C. tropicalis (3/50).

Palavras-chave: Candida albicans, meio cromogênico, meio Albicans ID2Ò


 

 

During the past decade, there has been increasing recognition of emerging fungal pathogens. The cause of the emergence of different new fungal pathogens is not completely understood. The changing spectrum of invasive mycoses is probably secondary to a combination of factors including the substantial improvements in the management of malignant diseases, advances in critical care and organ transplantation, the increasing number of patients undergoing invasive medical procedures and the selective pressure of antimicrobial drug use (9,19).

Although Candida albicans still accounts for most of the species isolated from yeast-infected patients, other Candida species such as C. glabrata, C. tropicalis, C. parapsilosis and C. krusei are emerging as opportunistic pathogens (13,15). Of interest, invasive infection due to non- albicans species may be refractory to therapy with conventional antifungal agents (1).

Traditionally, rapid identification of C. albicans depends on the germ tube test, which can identify C. albicans strains in 2h since the fungus produces germ tubes during growth at 37ºC in serum. However, up to 5% of the C. albicans isolates have been reported as germ tube negative, and non-albicans isolates may produce some structures which can be misinterpreted as germ tubes (12,17).

Otherwise, this method is time consuming and requires manipulation of human or animal serum. Alternative methods for quick C. albicans identification include the use of chromogenic media, as well as simple and rapid biochemical tests for detection of specific enzymes (2,11). Albicans ID2Ò chromogenic medium (bioMérieux, Marcy l'Etoile, France) has been developed and marketed for the identification of C. albicans (blue colonies). This assay is based on a chromogenic indolyl glucosaminide substrate, which is hydrolyzed by C. albicans to give a turquoise or blue color (4,12). The purpose of this study was to evaluate the accuracy of Albicans ID2Ò plates to identify C. albicans strains among yeasts different species with clinical relevance.

A total of 330 yeast isolates obtained from the fungal culture collection of the Laboratório Especial de Micologia, UNIFESP-EPM, was used to assess the accuracy of Albicans ID2Ò in the identification of C. albicans strains. All isolates were obtained from clinical material and included the following strains: C. albicans (100), C.dubliniensis (20), C. tropicalis (50), C. glabrata (30), C. rugosa (30), C.parapsilosis (20), C. krusei (20), C. lusitaniae (20), C. guilliermondii (20), Cryptococcus neoformans (10), Trichosporon spp. (10). The isolates were identified by standard methods, except for C. dubliniensis strains that were identified by molecular methods RAPD (random amplified polymorphic DNA analysis).

The purity and viability of original yeast cultures were checked by plating on CHROMagar Candida (CHROMagar Microbiology Paris, France). C. albicans and C. dubliniensis isolates were screened by their ability to produce green colonies on CHROMagar Candida and chlamydoconidia on corn meal-Tween 80 agar (Difco laboratories, Detroit, USA). All positive chlamydoconidia isolates were submitted to growth test at 42ºC on Sabouraud dextrose agar. The isolates that did not grow at 42ºC were genotyped by randomly amplified polymorphic DNA (RAPD) analysis using the oligonucleotide primers CDU (5'GCG ATC CCC A3') and B14 (5'GAT CAA GTC C3') in order to confirm the identification of C. dubliniensis (18,14). Candida non-albicans isolates were identified on the basis of their micromorphology on corn meal-Tween 80 agar and biochemical tests using the commercial system ID 32C, bioMérieux Marcy l'Etoile, France (3).

Suspensions of all isolates were prepared in physiological saline (scale 3 McFarland), and 0.1 mL of each suspension was plated onto Albicans ID2Ò plates. The reading of the plates and interpretation of the results were conducted after 24h, 48h and 72h of incubation at 32ºC. In order to prevent prejudice in reading the results, the determination of the color and the size of colonies on Albicans ID2Ò agar plates was performed by two different readers. Identification of yeasts was carried out according to the manufacturer's instruction: smooth blue colonies were identified as Candida albicans and other types of colonies were considered non-albicans yeasts.

Sensitivity, specificity, positive predictive value and negative predictive value were calculated comparing the identification of C. albicans on Albicans ID2Ò and the preliminary identification by standard methods (5).

A total of 330 isolates were successfully cultured on Albicans ID2Ò. Table 1 presents the colony color exhibited by the tested isolates. The plates were incubated for 72h, but 24h and 48h partial results were also recorded.

 

 

After 24h of incubation at 32ºC, all 100 C. albicans strains exhibited growth on the chromogenic media and were identified by their blue pigmentation on the media (sensitivity 100%). There was no significant change in the reading pattern of the blue colonies after 48h and 72h of incubation. C. dubliniensis strains also gave smooth blue colonies but, unlike C. albicans strains, exhibited weak growth at 24h reading. Significant growth of C. dubliniensis was observed only after 48h of incubation. This is an original finding because previous publications did not attempt to evaluate the dynamics of colony growth between 24h and 72h of incubation (4,7).

Besides C. albicans and C. dubliniensis strains, isolates representative of other species also exhibited blue colonies on Albicans ID2Ò media after 48h of incubation, including 30 out of 30 C. rugosa (100%) strains, 3 out of 50 C. tropicalis (6%) and 5 out of 10 Trichosporon spp. (50%) strains.

Problems in the misidentification of pathogens by using the Candida ID2Ò media were also reported by other authors. Fricker-Hidalgo et al. (7) found that blue colonies were exhibited on Albicans ID2Ò cultures by 10 out of 10 C. dubliniensis strains (100%), 15 out of 29 C. tropicalis strains (51.7%), 22 out of 28 Trichosporon spp. strains (78.6%) and 2 out 5 C. rugosa (40%) strains. Cárdenes et al. (4) reported misidentification of yeast by using Candida ID2Ò, after testing C. tropicalis (2 out 69 or 2.8%), C. parapsilosis (3 out 76 or 3.9%) and C. glabrata (2 out 47 or 4%) strains. In our study, the identification of C. albicans using Candida ID2Ò presented specificity of 82% and predictive positive value of 72.4%, which are very similar to those obtained by Fricker-Hidalgo et al. (7).

Comparing the performance of Albicans IDÒ and Albicans ID2Ò in the identification of C. albicans strains (Table 2), both methods present some limitations in the identification of C. dubliniensis, C. rugosa, C. tropicalis, Trichosporon spp. and Cryptococcus spp.

In conclusion, Albicans ID2Ò chromogenic medium present some advantages in terms of the ease, rapidity and reliability for identification of C. albicans. However, this chromogenic medium has low specificity and low positive predictive value in the identification of C. albicans strains. Therefore, we do not recommend the use of Albicans ID2Ò as the only screening test for the identification of C. albicans from clinical specimens.

 

ACKNOWLEDGEMENTS

This study was partially supported by grants from the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) (479335/2003-6).

 

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Submitted: May 10, 2005; Returned to authors for corrections: January 18, 2006; Approved: March 26, 2006

 

 

* Corresponding author. Mailing address: Laboratório Especial de Micologia, Disciplina de Infectologia, Universidade Federal de São Paulo. Rua Napoleão de Barros, 740 - 7º andar. 04023-062, São Paulo, SP, Brasil. Fax: (+5511) 5083-0806 E-mail: colomboal@terra.com.br

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