Alternative identification test relying upon sexual reproductive abilities of Candida lusitaniae strains isolated from hospitalized patients.

The in vitro mating ability of Candida lusitaniae (teleomorph Clavispora lusitaniae) clinical isolates has been investigated. Studying the effects of culture conditions, we showed that ammonium ion depletion in the medium is a major trigger of the sexual cycle. Moreover, a solid support is required for mating, suggesting a role for adhesion factors in addition to the mating type gene recognition function. Monitoring of mating and meiosis efficiency with auxotrophic strains showed great variations in ascospore yields, which appeared to be strain and temperature dependent, with an optimal range of 18 to 28 degrees C. The morphogenetic events taking place from mating to ascospore release were studied by scanning and electron microscopy, and the ultrastructure of the conjugation canal, through which intercellular nuclear exchanges occur, was revealed. Labeling experiments with a lectin-fluorochrome system revealed that the nuclear transfer was predominantly polarized, thus allowing a distinction between the nucleus donor and the nucleus acceptor strains. The direction of the transfer depended on the strain combination used, rather than on the genotypes of the strains, and did not appear to be controlled by the mating type genes. Finally, we demonstrated that all of the 76 clinical isolates used in this study were able to reproduce sexually when mated with an opposite mating type strain, and we identified a 1:1 MATa/MATalpha ratio in the collection. These results support the idea that there is no anamorph state in C. lusitaniae. Accordingly, the mating type test, which is easy to use and can usually be completed within 48 h, is a reliable alternative identification system for C. lusitaniae.