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JOURNAL OF CLINICAL MICROBIOLOGY, OCt. 1984, P. 813-814 0095-1137/84/100813-02$02.00/0

Vol. 20, No. 4

Copyright © 1984, American Society for Microbiology

Taxonomic and Nomenclatural Evaluation of the Genera Candida and Torulopsis M. R. McGINNIS,l* L. AJELLO,2 E. S. BENEKE,3 E. DROUHET,4 N. L. GOODMAN,5 C. J. HALDE,6 L. D. HALEY,7 J. KANE,8 G. A. LAND,9 A. A. PADHYE,2 D. H. PINCUS,10 M. G. RINALDI, A. L. ROGERS,3 I. F. SALKIN,12 W. A. SCHELL,"3 AND I. WEITZMAN'4 Department of Microbiology and Immunology, University of North Carolina at Chapel Hill,1 and Clinical Microbiology and Immunology Laboratories, North Carolina Memorial Hospital, 13 Chapel Hill, North Carolina 27514; Division of Mycotic Diseases, Center for Infectious Diseases,2 and Mycology Training Section, Division of Laboratory Training and Consultation, Laboratory Program Office,7 Centers for Disease Control, Atlanta, Georgia 30333; Department of Botany and Plant Pathology, Michigan State University, East Lansing, Michigan 488243; Unite de Mycologie, Institut Pasteur, Paris, France4; Department of Pathology, University of Kentuicky Medical College, Lexington, Kentucky 405365; Department of Microbiology, University of California Medical Center, San Francisco, California 941436; Laboratory Service Branch, Ontario Ministry of Health, Toronto, Ontario M5W IR5, Canada8; Department of Microbiology, Methodist Central Hospital, Dallas, Texas 752229; Analytab Produicts, Division of Sherwood Medical, Plainview, New York 1180310; Department of Microbiology, Montana State University, Bozeman, Montana 597171 1; Center for Laboratories and Research, New York State Department of Health, Albany, New York 1220112; and Bureau of Laboratories, The City of New York Department of Health, New York, New York 1001614 Received 8 June 1984/Accepted 28 June 1984

It is concluded that the validly published recently proposed merger of these two yeast

genera genera

Candida and Torulopsis is rejected.

taxonomically distinct. The

dohyphae absent, rudimentary, or well developed." Since yeast genera classified in the class Blastomycetes are distinguished primarily by morphology, the proposed amended description of Yarrow and Meyer could also permit the inclusion of species currently classified in such genera as Cryptococcus Kutzing emend. Phaff et Spencer, 1969 and Rhodotorula Harrison, 1927. Thus, the proposals by Yarrow and Meyer have raised both taxonomic and nomenclatural issues which need to be clarified. In our experience, members of the genus Torulopsis are clearly recognizable, in part, by the presence of budding yeast cells and the absence of pseudohyphae. This is the concept of the genus which has been used consistently since 1894. Although budding cells of Torulopsis may occasionally remain attached to each other to form rudimentary pseudohyphae, this is different from what occurs in Candida species, which produce well-developed pseudohyphae. Since no taxonomic system can always unequivocally differentiate all taxa, yeast isolates may occasionally be difficult to classify as species of either Candida or Torulopsis. It must be remembered that these form genera were established to contain asporgenous yeasts that share common morphological and physiological characteristics. We feel that the genera Candida and Torulopsis are taxonomically distinct and useful for clinical microbiologists. Nomenclaturally, the treatment of the genus Torulopsis Berlese by Yarrow and Meyer (5) as a nomen dubium is erroneous because such a designation is used only to denote a name that has an uncertain taxonomic application. The original description of the genus and the consistent manner in which the generic concept has been used clearly indicate that this designation does not apply to the genus Torulopsis. Even though a preserved nomenclatural type apparently does not exist for T. rosea, the name was validly published. A nomenclatural type was not required until after 1 January 1958 (4). Furthermore, under the provisions of the ICBN (4), a nomenclatural type must be permanently preserved and

Several recent taxonomic and nomenclatural changes involving medically important fungi have resulted in confusion for clinical microbiologists. In particular, the recently proposed merger of the genera Candida Berkhout, 1923 nom. cons. and Torulopsis Berlese, 1894 by Yarrow and Meyer (5) has created a great deal of misunderstanding and controversy. To resolve this difficulty, we have examined the pertinent taxonomic works and evaluated the various proposals in light of the provisions of the International Code of Botanical Nomenclature (ICBN) (4). Our findings and conclusions regarding the proposed merger of these two genera are presented in this communication. In 1894, Berlese (1) isolated several yeasts from Sangiovese grapes and grape juice. He considered these isolates to be identical and to represent a previously undescribed genus and species. The yeast, which he named Torulopsis rosea, was morphologically indistinguishable from Saccharomyces ellipsoideus Reess, 1870, except for the development of a pink color on plaster cones. It is clear from the original diagnosis and description and from a figure of the genus Torulopsis in a subsequent study (2), that the genus was meant to accommodate elliptical asporogenous yeasts that possess the ability to ferment carbon sources but do not form pseudohyphae. In 1906, Saccardo (3) summarized the concept of the genus Torulopsis by stating that the yeast produces "small cells, constantly ellipsoidal or globose, not apiculate neither catenulate, hyaline to slightly colored. No mycelium. No endospores. Alcoholic fermentation." From this description, it is clear that the yeast did not form pseudohyphae, hyphae, or sexual spores. In 1978, Yarrow and Meyer (5) considered the genus Torulopsis Berlese to be a nomen dubium and transferred its species to the genus Candida. They also proposed that the description for Candida be modified, in part, to read "pseu*

are

Corresponding author. 813

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cannot be a living culture. Thus, arguments that the fungus cannot be recognized because a living type culture does not

exist are without merit. The genus Candida is a conserved name which was not specifically conserved against Torulopsis. These two genera are based on different yeasts that were validly published under the provisions of the ICBN (4). Therefore, if these two genera were merged for taxonomic reasons, Torulopsis would be the nomenclaturally correct name since it was proposed before Candida. The redesignation of taxa, such as Torulopsis glabrata and Torulopsis candida as Candida glabrata and Candida famata, respectively, is in direct conflict with the rules of botanical nomenclature. Furthermore, if the taxonomic proposals of Yarrow and Meyer (5) are accepted, it would require the reclassification of nearly all asporogenous yeasts into a single genus, which would also logically include the members of the genus Cryptococcus. Owing to the fact that Cryptococcus was originally proposed in 1833, 90 years before Candida, if their proposal were extended to its logical conclusion, it could be argued that all of these asporogenous yeasts should become Cryptococcus

J. CLIN. MICROBIOL.

NOTES

species.

The selection of the generic name Candida by Yarrow and Meyer (5) is also in conflict with Article 62.1 of the ICBN, which states that "an epithet or a legitimate name must not be rejected merely because it is inappropriate or disagreeable, or because another is preferable or better known, or because it has lost its original meaning...." Regardless of whether yeasts or molds are being studied, the ICBN (4)

must be followed to provide nomenclatural stability and consistency. Names cannot be arbitrarily favored, as in the case of Candida versus Torulopsis, because they are more popular. In summary, it is clearly evident that the genera Candida and Torulopsis are taxonomically distinct, being distinguished by the presence or absence of pseudohyphae, respectively. Both genera were validly published according to the provisions of the ICBN (4) and should be maintained as separate entities. If the taxonomic proposal of Yarrow and Meyer (5) were to be accepted, the correct generic designation of these species would be Torulopsis, not Candida. LITERATURE CITED 1. Berlese, A. N. 1894. I fungi diversi dai saccaromiceti e capaci di determinare la fermentaziene alcoolica. Gior. Vitic. Enol. 3:5255. 2. Berlese, A. 1897. Rapporti fra la vite ed I Saccaromiceti. Riv. Patalog. Veg. 5:211-237, 354-360. 3. Saccardo, P. A. 1906. Sylloge Fungorum Omnium Hucusque Cognitorum. 18:495. (In Latin.) 4. Voss, E. G., H. M. Burdet, W. G. Chaloner, V. Demoulin, P. Hiepko, J. McNeill, R. D. Meikle, D. H. Nicolson, R. C. Rollins, P. C. Silva, and W. Greuter. 1983. International code of botanical nomenclature. Bohn, Scheltema and Holkema, Utrecht, The Netherlands. 5. Yarrow, D., and S. A. Meyer. 1978. Proposal for amendment of the diagnosis of the genus Candida Berkhout nom. cons. Int. J. Syst. Bacteriol. 28:611-615.