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Journal of Clinical Microbiology, November 2001, p. 3889-3894, Vol. 39, No. 11
Laboratorio di Micologia Medica, Istituto di
Igiene e Medicina Preventiva, Università degli Studi, IRCCS
Ospedale Maggiore, 20122 Milan, Italy,1 and
Department of Microbiology, University of Texas Health
Science Center at San Antonio, San Antonio, Texas
78229-39002
Received 8 May 2001/Returned for modification 18 June 2001/Accepted 12 August 2001
The basidiomycetous yeast Cryptococcus neoformans is
an important human fungal pathogen. Two varieties, C.
neoformans var. neoformans and C.
neoformans var. gattii, have been identified. Both are heterothallic with two mating types, MATa and
MAT
0095-1137/01/$04.00+0 DOI: 10.1128/JCM.39.11.3889-3894.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Origin of Cryptococcus neoformans var.
neoformans Diploid Strains
. Some rare isolates are self-fertile and are
considered occasional diploid or aneuploid strains. In the present
study, 133 isolates, mostly from Italian patients, were investigated to
detect the presence of diploid strains in the Igiene Università
Milano culture collection. All of the diploid isolates were further
investigated by different methods to elucidate their origins.
Forty-nine diploid strains were identified by flow cytometry. PCR
fingerprinting using the (GACA)4 primer showed that the
diploid state was associated with two specific genotypes identified as
VN3 and VN4. Determination of mating type on V8 juice medium confirmed
that the majority of the strains were sterile. PCR and dot blotting
using the two pheromone genes (MFa and
MF
) as probes identified 36 of the 49 diploid
isolates as MATa/
. The results of pheromone gene
sequencing showed that two allelic MF
genes exist and
are distinct for serotypes A and D. In contrast, the MFa
gene sequence was conserved in both serotype alleles. Amplification of
serotype-specific STE20 alleles demonstrated that the
diploid strains contained one mating locus inherited from a serotype A
parent and one inherited from a serotype D parent. The present results
suggest that diploid isolates may be common among the C.
neoformans population and that in Italy and other European
countries serotype A and D populations are not genetically isolated but
are able to recombine by sexual reproduction.
*
Corresponding author. Mailing address: Laboratorio di
Micologia Medica, Istituto di Igiene e Medicina Preventiva,
Università degli Studi di Milano, Via Sforza 35, 20122 Milan,
Italy. Phone: 39 02 55188373. Fax: 39 02 55191561. E-mail:
marianna.viviani{at}unimi.it.
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