Evaluation of Microsporum canis in different methods of storage.

The main objective of this investigation was to evaluate different methods of storage for Microsporum canis based on materials and equipment that are readily available in developing countries. We tested 32 strains of M. canis at - 20 degrees C in potato dextrose agar (PDA) in its plain condition, or amended with 10% dimethyl sulfoxide or with 10% glycerol. In addition, we tested 25 degrees C storage of isolates in plain saline (0.9% NaCl) and in saline covered with a mineral-oil layer. After 9 months of storage, none of the M. canis strains frozen in PDA supplemented with glycerol survived, while only 16 and 6%, respectively, of the isolates in plain and DMSO medium lost viability. Nine month's storage in saline with or without mineral oil increased the amount of pleomorphic development of sterile hyphae; this phenomenon occurred at a significantly higher level than was seen in isolates stored at -20 degrees C. The physiological characteristics of M. canis were not affected by the different storage tests. The results suggest that, in order to ensure optimal viability, purity and pristine isolate condition, each M. canis isolate maintained should be held in at least two methods of storage, namely, PDA at -20 degrees C and saline with a mineral-oil layer at 25 degrees C.