Comparison of phospholipase and proteinase activity in Candida albicans and C. dubliniensis

Intracellular phospholipase activity has previously been detected in Candida albicans. A plate method is described which allows rapid detection and measurement of the extracellular activity in a number of clinical isolates. The ratio of colony diameter to diameter of the dense white zone of precipitation around phospholipase positive colonies, (Pz value), correlates with hydrolysis of [14C]phosphatidylcholine by concentrated culture filtrates of selected test isolates. A large variation in phospholipase activity is found between different isolates of C. albicans, however the Pz value is constant for any one isolate regardless of the site from which it is recovered in the patient. Fifty five % of fresh blood isolates are positive and these are also the most potent phospholipase producers. Fifth % of wound isolates and 30% of urine isolates are also positive. A larger sample group must be studied, however, before it can be determined whether these differences are highly significant.

Atypical oral Candida isolates were recovered from 60 HIV-infected and three HIV-negative individuals. These organisms were germ-tube-positive and produced abundant chlamydospores which were frequently arranged in triplets or in contiguous pairs. They belonged to C. albicans serotype A and had atypical carbohydrate assimilation profiles. Fingerprinting the genomic DNA of a selection of these organisms with the C. albicans-specific probe 27A and five separate oligonucleotides, homologous to eukaryotic microsatellite repeat sequences, demonstrated that they had a very distinct genomic organization compared to C. albicans and C. stellatoidea. This was further established by random amplified polymorphic DNA (RAPD) and karyotype analysis. Comparison of 500 bp of the V3 variable region of the large ribosomal subunit genes from nine atypical isolates and the corresponding sequences determined from C. albicans, C. stellatoidea, C. tropicalis, C. parapsilosis, C. glabrata, C. kefyr and C. krusei showed that they atypical organisms formed a homogeneous cluster (100% similarity) that was significantly different from the other Candida species analysed, but was most closely related to C. albicans and C. stellatoidea. These genetic data combined with the phenotypic characteristics of these atypical organisms strongly suggest that they constitute a novel species within the genus Candida for which the name Candida dubliniensis is proposed.