Four cases of Candida albicans infections with isolates developing pink colonies on CHROMagar Candida plates

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.

Oral Candida carriage of patients attending a dental clinic in Braga, Portugal

BACKGROUND

The ability of the Candida species to colonize surfaces can be considered as a risk factor for oral infection.

AIMS

To establish oral Candida carriage in patients attending a dental clinic in Braga, Portugal.

METHODS

A total of 97 patients were analysed. Swab samples were collected and directly cultured onto CHROMagar Candida. Representative yeasts were identified by polymerase chain reaction.

RESULTS

From the samples analysed 54.6% (n=53) were Candida positive, and Candida albicans was the most frequently isolated species, accounting for 79% of all the species identified. Non-C. albicans Candida (NCAC) species recovered included Candida parapsilosis, Candida glabrata, Candida tropicalis, and Candida guilliermondii. There was a lack of association between the presence of C. albicans or NCAC species, and age, gender, or prostheses wearing in this population. In 17% of the cases (n=9), polymicrobial cultures, with two different Candida species, were identified.

CONCLUSIONS

This study shows a high Candida carriage rate among this population, thus pointing to the relevance of an accurate diagnostic approach in Candida species identification.

In vitro evaluation of putative virulence attributes of oral isolates of Candida spp. obtained from elderly healthy individuals

Identification of Candida isolates obtained from oral cavity of elderly healthy individuals revealed the predominance of non-albicans Candida species (88.9%) compared to Candida albicans (11%). CHROMagar Candida differential medium and PCR revealed the presence of Candida tropicalis (33.3%), Candida glabrata (27.8%), and Candida krusei (16.7%). We investigated the presence of virulence attributes in a total of 18 isolates, including acid protease and phospholipase production, hemolytic activity, and biofilm production. Extracellular protease was found in five isolates (27.8%) whereas extracellular phospholipase was found in three isolates (17%). All isolates showed hemolytic activity. About 56% of the isolates were weakly positive for biofilm formation (score +) whereas a minority (5.6%) of them showed strong biofilm formation (score 4+). Susceptibility in vitro of the isolates to fluconazole was carried out by microdilution method. Fluconazole showed a strong inhibition against most buccal isolates. The resistant isolates were 2 C. tropicalis, 2 C. glabrata, and 1 C. krusei.

Yeast identification--past, present, and future methods

The focus of this review is the evolution of biochemical phenotypic yeast identification methods with emphasis on conventional approaches, rapid screening tests, chromogenic agars, comprehensive commercial methods, and the eventual migration to genotypic methods. As systemic yeast infections can be devastating and resistance is common in certain species, accurate identification to the species level is paramount for successful therapy and appropriate patient care.

Evaluation of the new chromogenic medium Candida ID 2 for isolation and identification of Candida albicans and other medically important Candida species

The usefulness of Candida ID 2 (CAID2) reformulated medium (bioMérieux, France) has been compared with that of the former Candida ID (CAID; bioMérieux), Albicans ID 2 (ALB2; bioMérieux), and CHROMagar Candida (CAC; Chromagar, France) chromogenic media for the isolation and presumptive identification of clinically relevant yeasts. Three hundred forty-five stock strains from culture collections, and 103 fresh isolates from different clinical specimens were evaluated. CAID2 permitted differentiation based on colony color between Candida albicans (cobalt blue; sensitivity, 91.7%; specificity, 97.2%) and Candida dubliniensis (turquoise blue; sensitivity, 97.9%; specificity, 96.6%). Candida tropicalis gave distinguishable pink-bluish colonies in 97.4% of the strains in CAID2 (sensitivity, 97.4%; specificity, 100%); the same proportion was reached in CAC, where colonies were blue-gray (sensitivity, 97.4%; specificity, 98.7%). CAC and CAID2 showed 100% sensitivity values for the identification of Candida krusei. However, with CAID2, experience is required to differentiate the downy aspect of the white colonies of C. krusei from other white-colony-forming species. The new CAID2 medium is a good candidate to replace CAID and ALB2, and it compares well to CAC for culture and presumptive identification of clinically relevant Candida species. CAID2 showed better results than CAC in some aspects, such as quicker growth and color development of colonies from clinical specimens, detection of mixed cultures, and presumptive differentiation between C. albicans and C. dubliniensis.