Candida dublinensis: New Species and Old Strains

abstracts & commentary

Synopsis: Far from being a new species, Candida dublinensis was first isolated from oral samples obtained as far back as 1973 but was originally identified as Candida albicans. The species can be recognized by its unusual green color on CHROMagar and failure to grow at 45°C.

Sources: Odds FC, et al. Prevalence of Candida dublinensis isolates in a yeast stock collection. J Clin Microbiol 1998; 36:2869-2873; Kirkpatrick WR, et al. Detection of Candida dublinensis in oropharyngeal samples from human immunodeficiency virus-protected patients in North America by primary CHROMagar Candida screening and susceptibility testing of isolates. J Clin Microbiol 1998;36:3007-3012.

A sample of 2589 yeasts originally identified as Candida albicans were reexamined by Odds and colleagues by culturing them on the differential medium CHROMagar testing for the presence of the enzyme beta-glucosidase and hybridization with the C. albicans specific oligonucelotide sequence Ca3. An abnormal color of green was produced on the CHROMagar by 502 (19.4%) of which 93 (18.5%) failed to elaborate beta-glucosidase. Fifty-three of these strains failed to hybridize with Ca3 and, hence, were reidentified as Candida dublinensis. Forty-four (83%) of these yeasts originated from oral samples, eight from faces, and one each from sputum, the vagina, and an undisclosed site. Far from being recent isolates, C. dublinensis was being deposited from 1973 onward unbeknown to everyone. In 1986, there had already been six isolates from IV drug users deposited as well as 15 strains from oral surveillance cultures taken from patients treated for hematological malignancies in the same hospital. From 1988 on, 19 C. dublinensis isolated from the oropharynxes of patients with AIDS had been deposited. In the study by Kirkpatrick and associates, the oral rinses of 63 patients with HIV infection were screened prospectively using CHROMagar and C. dublinensis was detected in 23 cases. These isolates were then contrasted with 28 C. albicans isolated from the samples with the results shown in the Table.

Table
C. dublinensis vs. C. albicans in oral cultures
Test
C. dublinensis (n = 23)
C. albicans (n = 28)
Germ tube production
100%
100%
Abundant chlamydospores
70%
4%
Correctly identified by API 20C
 0%
89%
Ability to use xylose
0%
100%
Growth at 42°C 
4%
100%
Growth at 45°C
0%
64%
Good hybridization with Ca3 probe
0%
100%
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Comment by J. Peter Donnelly, PhD

No real difference in susceptibility to amphotericin B or the azole antifungal agents was noted. It is too early to claim any particular virulence for C. dublinensis but these studies serve to remind us that oral samples frequently yield more than one species of Candida. Armed only with CHROMagar and a hotter than normal incubator, it is possible to distinguish C. dublinensis from its cousin C. albicans and other Candida species so there is no longer any excuse for reporting yeasts as C. albicans, and Candida species not albicans when dealing with HIV-infected and other immunocompromised patients.