Viability and morphological alterations of Paracoccidioides brasiliensis strains preserved under mineral oil for long periods of time.

We evaluated the survival and the morphological alteration of 70 strains of Paracoccidioides brasiliensis maintained in the Fungal Culture Collection of Institute Oswaldo Cruz and initially preserved by successive subculturing and later under mineral oil at room temperature from 1923 to 1992. Of the 70 strains preserved under mineral oil, 18 (26%) continued to be viable. The mycelia of the 18 viable strains and the mycelia of four representatives of the non-viable strains presented transitional micromorphology under mineral oil. Macroscopy and microscopy of the first subcultures of five of the seven strains, taken as random samples from the 18 viable strains and plated onto peptone-yeast extract-glucose agar, glucose-glycine-yeast extract agar and brain-heart infusion agar media at room temperature, revealed that all samples appeared to be in a transition phase (Y<-->M). These five strains were unable to grow and complete thermal dimorphism at a temperature of 37 degrees C. Only two strains were able to complete the entire dimorphic process. The period of preservation of these strains under oil was relatively short, i.e. 9 and 10 years. The results demonstrate that less widely spaced subculturing and more appropriate culture and environmental conditions are needed to preserve P. brasiliensis strains under oil.