The Preservation of Bacteria and Fungi on anhydrous Silica Gel: an Assessment of Survival over Four years

The preservation method of Perkins (1962) using suspensions in skim-milk was used to preserve 33 bacteria and 22 fungi on anhydrous silica gel. During storage at room temperature, 64% of the bacteria and 77% of the fungi survived 1 year or more. Storage at 4° often increased the survival period c. 2- to 3-fold: 73% of the bacteria and all 12 of the fungi tested at 4° survived > 1 year. At the last testing, 60% of the bacteria and 36% of the fungi were still viable after storage at 4° for periods between 3 and 4 years. The Gram positive bacilli tended to survive the silica gel preservation process better than most Gram negative bacilli. Some factors influencing survival after preservation on silica gel are discussed; the results support the use of a closed storage tube.