Prospective evaluation of the chromogenic medium CandiSelect 4 for differentiation and presumptive identification of non-Candida albicans Candida species

Rapid Detection of Candida tropicalis in Clinical Samples From Different Sources Using RPA-LFS

Candida tropicalis is one of the few Candida species besides Candida albicans that is able to produce true hyphae. At present, the commonly used clinical methods for the identification of this organism are traditional fungal culture, CTB staining, and color development. Polymerase chain reaction (PCR) and real-time quantitative PCR (qPCR) are also used to identify this fungus. Since the course of C. tropicalis infection progresses rapidly, there is an urgent need for rapid, sensitive, real-time field assays to meet the needs of clinical diagnosis. Recombinase polymerase amplification (RPA) combined with lateral flow strip (LFS) can rapidly amplify and visualize target genes within 20 min, and by pre-processing samples from different sources, the entire process can be controlled within 30 min. In this study, RPA-LFS was used to amplify the internal transcribed spacer-2 (ITS2) gene of C. tropicalis, and primer-probe design was optimized by introducing base mismatches to obtain a specific and sensitive primer-probe combination for clinical sample detection. LFS assay for 37 common clinical pathogens was performed, sensitivity and specificity of the detection system was determined, reaction temperature and time were optimized, and 191 actual clinical samples collected from different sources were tested to evaluate the detection performance of the established RPA-LFS system to provide a reliable molecular diagnostic method for the detection of C. tropicalis, the results show that the RPA-LFS system can specifically detect C. tropicalis without cross-reacting with other fungi or bacterial, with a sensitivity of 9.94 CFU/µL, without interference from genomic DNA of other species, at an optimal reaction temperature of 39°C, and the whole reaction process can be controlled within 20 min, and to meet the clinical need for rapid, sensitive, real-time, and portable field testing.

Current Aspects in the Biology, Pathogeny, and Treatment of Candida krusei, a Neglected Fungal Pathogen

Fungal infections represent a constant and growing menace to human health, because of the emergence of new species as causative agents of diseases and the increment of antifungal drug resistance. Candidiasis is one of the most common fungal infections in humans and is associated with a high mortality rate when the fungi infect deep-seated organs. Candida krusei belongs to the group of candidiasis etiological agents, and although it is not isolated as frequently as other Candida species, the infections caused by this organism are of special relevance in the clinical setting because of its intrinsic resistance to fluconazole. Here, we offer a thorough revision of the current literature dealing with this organism and the caused disease, focusing on its biological aspects, the host-fungus interaction, the diagnosis, and the infection treatment. Of particular relevance, we provide the most recent genomic information, including the gene prediction of some putative virulence factors, like proteases, adhesins, regulators of biofilm formation and dimorphism. Moreover, C. krusei veterinary aspects and the exploration of natural products with anti-C. krusei activity are also included.

Comparison of four commercially available chromogenic media to identify Candida albicans and other medically relevant Candida species

BACKGROUND

The number of invasive Candida infections has significantly increased in recent decades. For the successful treatment of fungal infections, rapid identification at the species level, particularly in polyfungal infections, is a key factor. In this study, four commercially available chromogenic media, CandiSelect™ 4 (CS4), chromID™ Candida Agar (CCA), BBL™ CHROMagar™ Candida Medium (BBL) and Brilliance™ Candida Agar (BCA) were evaluated for Candida identification.

MATERIAL/METHODS

Overall, 181 bronchial secretion samples from intensive care patients were analysed prospectively. In addition, 18 primarily sterile materials, previously tested positive for Candida, were investigated retrospectively. All samples were cultured as recommended by the manufacturer and visually inspected after 24 and 48 hours by three independent investigators. As a control, colonies were identified by MALDI-TOF MS. Specificity and sensitivity were determined for C albicans identification prospectively.

RESULTS

CS4 and BCA showed the best overall consensus with the identification results reached by MALDI-TOF MS for Candida albicans and species. A clear differentiation between the species could be ascertained via easily identifiable, species-specific coloration in contrast to BBL and CCA. Sensitivity for C albicans (n = 73) identification varied between 32% (BCA) and 69% (CS4 and CCA) after 24 hours and 68% (BBL) and 82% (BCA) after 48 hours incubation, while specificity ranged between 62% (BBL) and 81% (CCA) after 24 hours and 82% (BBL) and 85% (CS4) after 48 hours.

CONCLUSION

CS4 and BCA are recommended for routine identification of Candida species in human samples.

Different detection capabilities by mycological media for Candida isolates from mono- or dual-species cultures

The aim of this study was to compare the Candida bromcresol green (BCG) medium with the chromogenic (CHROM) Brilliance Candida agar and Sabouraud dextrose agar (SDA) media in regard to their capability of detecting Candida isolates from mono- or dual-species cultures. We prepared Candida isolates' suspensions to obtain mono-species (n = 18) or dual-species (n = 153) culture plates per each medium, and three readers independently observed 513 plates at 24-h, 48-h and 72-h incubation time. We scored reading results as correct, over or under detection compared to the expected species number(s). BCG showed significantly higher correct-detection and lower under-detection rates for all Candida species when observed by at least one reader. At 24-h reading, 12 mono-species cultures had correct (or over) detections in all media, whereas 106, 60 and 78 dual-species cultures had correct (or over) detections in BCG, CHROM or SDA, respectively. BCG provides the basis for an accurate laboratory diagnosis of Candida infections.

An Update on Candida tropicalis Based on Basic and Clinical Approaches

Candida tropicalis has emerged as one of the most important Candida species. It has been widely considered the second most virulent Candida species, only preceded by C. albicans. Besides, this species has been recognized as a very strong biofilm producer, surpassing C. albicans in most of the studies. In addition, it produces a wide range of other virulence factors, including: adhesion to buccal epithelial and endothelial cells; the secretion of lytic enzymes, such as proteinases, phospholipases, and hemolysins, bud-to-hyphae transition (also called morphogenesis) and the phenomenon called phenotypic switching. This is a species very closely related to C. albicans and has been easily identified with both phenotypic and molecular methods. In addition, no cryptic sibling species were yet described in the literature, what is contradictory to some other medically important Candida species. C. tropicalis is a clinically relevant species and may be the second or third etiological agent of candidemia, specifically in Latin American countries and Asia. Antifungal resistance to the azoles, polyenes, and echinocandins has already been described. Apart from all these characteristics, C. tropicalis has been considered an osmotolerant microorganism and this ability to survive to high salt concentration may be important for fungal persistence in saline environments. This physiological characteristic makes this species suitable for use in biotechnology processes. Here we describe an update of C. tropicalis, focusing on all these previously mentioned subjects.

Comparative evaluation of six chromogenic media for presumptive yeast identification

AIMS

The present study was undertaken to evaluate the discrimination ability of six chromogenic media in presumptive yeast identification.

METHODS

We analysed 108 clinical isolates and reference strains belonging to eight different species: Candida albicans,Candida dubliniensis, Candida tropicalis, Candida krusei, Candida glabrata, Candida parapsilosis,Candida lusitaniae and Trichosporon mucoides.

RESULTS

C. albicans, C. tropicalis and C. krusei could be distinguished from one another in all the tested chromogenic media, as predicted by the manufacturers. In addition, C. albicans could be distinguished from C. dubliniensis on BBL CHROMagar Candida, Kima CHROMagar Candida and Brilliance Candida, and C. parapsilosis could be identified on CHROMATIC Candida agar, CHROMOGENIC Candida agar, and Brilliance Candida agar.

CONCLUSIONS

Brilliance Candida provided the widest discrimination ability, being able to discriminate five out of the seven Candida species tested. Interestingly, C. tropicalis and C. krusei could be already distinguished from each other after 24 hours of incubation.