1989 Volume 35 Pages 82-89
Frozen-stored and thawed suspensions of cells of fungus test strains kept at -80℃ were directly used as inocula for primary antimicrobial tests of pharmaceutical and cosmetic products. The test strains were Candida albicans NHL 4019, Hansenula anomala C-1 and H-1, and Aspergillus niger NHL 5088. The yeast cells and the fungal spores were suspended in phosphate buffered saline containing 0.05% Tween 80 (PBS), 10% glycerol and 5% dimethyl sulfoxide (DMSO) solutions. They were frozen at the cooling rates of -0.2, -1 and -5℃ per minute to -40℃, and then were directly preserved at -80℃ in a deep freezer. The survival values of the frozen inocula ranged from 19% to over 100% of the initial viable counts during 3 months through all the cooling conditions. The other survival values of the antimicrobial test of a model cream with p-hydroxybenzoate benzoate ester with the frozen inocula were fairly coincident with the results of the tests with unfrozen inocula at all the cooling conditions in the case of H. anomala C-1, H-1, and A. niger NHL 5088. The frozen inocula of C. albicans NHL 4019 suspended in PBS and DMSO as cryoprotectant were more sensitive to the model cream than unfrozen inocula. This discrepancy may be ascribed to some injury of the cells by the cooling conditions.
