Isolation of Cryptococcus adeliensis from Clinical Samples and the Environment in Germany

Rimek and colleagues (1) recently published an account of the first case of meningitis caused by Cryptococcus adeliensis in a German patient with acute myeloid leukemia. C. adeliensis was previously described as a new cryptococcal species isolated from algae in Antarctica (2).

In the context of an excursion aimed at getting some information about the occurrence of different genotypes of C. neoformans in Germany, bird droppings from various German areas were cultured on Sabouraud glucose agar and Guizotia abyssinica agar. Yeast colonies suspected to belong to the genus Cryptococcus were isolated and characterized by studying urease hydrolyzation on Christensen's urea medium and assimilation of carbohydrates (ID 32C; bioMérieux, Marcy l'Étoile, France) and by sequence analysis of the internal transcribed spacer (ITS) region and the D1/D2 domain in the 28S rRNA gene (2).

Surprisingly, we isolated C. adeliensis in two out of nine samples: one isolate (RKI 147I/04) from pigeon droppings taken from an urban recreation area (Tegel Lake in Berlin) and one (RKI 173III/04) from a pigeon breeding facility near Hanover, Germany.

C. adeliensis can be misidentified as C. albidus due to the high variability of phenotypic markers of the latter. Therefore, we reexamined six isolates from our strain collection originally identified as C. albidus. Three of the six strains turned out to be in fact C. adeliensis: (i) strain RKI 779/76, isolated from pigeon droppings (Berlin), (ii) RKI 311/77, originally obtained from a lung biopsy of a male adult suffering from progressive lung disease, and (iii) RKI 456/93, obtained from the oral cavity of an 8-year-old human immunodeficiency virus-infected girl. Both patients lived in Berlin. Since the clinical isolates were found in mixed cultures with other fungi, their clinical significance is not clear.

C. adeliensis isolates grew in cream-colored and smooth colonies (1, 2). Colonies of RKI 779/76 and RKI 456/93 were markedly mucoid, resembling Cryptococcus gattii. All isolates were able to grow at 30°C but not at 35°C and failed to assimilate lactate. Biocoding for the carbohydrate assimilation test (ID32C) resulted in 4473 3441, 4473 7643, or 4473 3443, each of which should indicate an “excellent identification of C. albidus.” In contrast to the type strain, the isolates were not able to tolerate 0.01% cycloheximide. This has already been noticed before for isolate CBS 9061 (1). Also in contrast to the results seen with CBS 8351^T, the C. adeliensis isolates from Europe were not able to tolerate 10% NaCl.

Sequence analysis of the five C. adeliensis isolates studied revealed a 100% identity within the D1/D2 domain already deposited in the GenBank (AF137603) and the ITS1-5.8S rRNA gene-ITS2 region (AF145328) of CBS 8351^T except for the isolate RKI 147I/04. The latter demonstrates a single nucleotide exchange (T instead of C) at position 450 in the ITS region (AY733079).

The isolation of C. adeliensis from clinical as well as environmental specimens in Germany might indicate a wider distribution of the species in Germany and possibly in other Western European countries. Their intolerance for 10% NaCl might give a hint that the continental strains are not as well adapted to salt water as the type strain originally obtained from algae in Antarctica. Sequence analysis for clinical isolates of the C. albidus clade is mandatory to identify C. adeliensis (3) and to elucidate its role as an opportunistic pathogen in man.

The described C. adeliensis isolates have been deposited in our culture collection.