Inhibitory effect of chromogenic culture media on the growth of Rhodotorula: relevance to the diagnosis of Rhodotorula spp. infections.

With the increasing incidence and diverse etiologies of fungal infections, chromogenic yeast culture media are increasingly used for routine diagnosis. Rhodotorula species, which are characterized by the production of carotenoid pigments, are considered as emerging opportunistic pathogens. We recently diagnosed two fungemia due to Rhodotorula spp. and noticed that in both cases, the yeast failed to grow in subculture on the chromogenic yeast culture medium. This study was thus undertaken to investigate more thoroughly the ability (or inability) of Rhodotorula species to grow on different commercially available chromogenic media for yeast. Eighteen Rhodotorula spp. were checked for their ability to grow on four chromogenic yeast culture media: CHROMagar Candida (BD), Candi 4 Select (Biorad), Brilliance Candida (Oxoid), and Candida ID 2 (BioMerieux). All the Rhodotorula spp. strains grew on Brilliance and Candida ID 2, while only six isolates grew on Candi 4, and seven on CHROMagar. Two chromogenic yeast culture media showed a significant inhibitory effect on the growth of Rhodotorula species. As all Rhodotorula species are resistant to echinocandins and fluconazole, it is essential to isolate and identify these yeast quickly to initiate appropriate amphotericin B antifungal treatment as early as possible. The choice of media for routine use should take into account the ability of different media to allow all emerging fungal pathogens to grow.

Retrospective assessment of ß-D-(1,3)-glucan for presumptive diagnosis of fungal infections.

ß-D-(1,3)-glucan (BG) is a component of the cell walls of many fungal organisms. Our aims were to investigate the feasibility of the BG assay and its contribution to early diagnosis of different types of invasive fungal infections (IFI) commonly diagnosed in a tertiary care centre. The BG serum levels of 28 patients diagnosed with six IFI [13 probable invasive aspergillosis (IA), 2 proven IA, 2 zygomycosis, 3 fusariosis, 3 cryptococcosis, 3 candidaemia and 2 pneumocystosis] were retrospectively evaluated. The kinetic variations in BG serum levels from the 15 patients diagnosed with IA were compared with those of the galactomannan antigen (GM). In 5/15 cases of IA, BG was positive earlier than GM (time lapse from 4 to 30 days), in 8/15 cases, BG was positive at the same time as GM and, in 2/15 cases, BG was positive after GM. For the five other fungal diseases, BG was highly positive at the period of diagnosis except for the two cases of zygomycosis and one of the three cases of fusariosis. This study, which reflects the common activity of a tertiary care centre, confirms that BG detection could be of interest for IFI screening in patients with haematological malignancies.