A. Howard Fieldsteel

Freeze-drying is an effective method for preserving infectious type C retroviruses

Conventional freeze-drying techniques using a sucrose stabilizer and gelatin can be employed to preserve the infectivity of retroviruses. Lyophilized virus retains its infectivity even at room temperature for more than one year. A lyophilized virus preparation of Friend leukemia virus kept at 4 degrees C for more than 20 years was found to contain high titers of infectious pathogenic virus. This technique offers an easy economic means for shipping type C viruses and for preserving them for long periods of time in the laboratory without the need for cold storage.

Role of serum in survival ofTreponema pallidum in tissue culture

SummaryDuring attempts to cultivateTreponema pallidum, it was determined that length of time for survival of virulent treponemes was highly dependent on the quality of the fetal bovine serum (FBS) used as a protein supplement in the culture medium. Eighteen lots of commercial FBS were tested for their ability to maintain survival ofT. pallidum in cultures of cottontail rabbit epithelial (SflEp) cells. All were capable of supporting growth of these cells. However, in tests on five of the lots, attachment of treponemes to the SflEp cells was either extremely poor or the 50% survival time (ST50) was less than 5 days. With two of these lots, no treponemes survived for 5 days. By contrast, in tests with 11 of the FBS lots, the ST50 of the treponemes was 12 days or greater; however, there was a great variation in the number of treponemes that attached. Selection of lots of FBS for ultimate experimental use was based on their influence both to extend length of time for survival of treponemes and to increase the number of treponemes that attached to the SflEp cells during that period.

Cultivation of pathogenic treponema in tissue cultures of SflEp cells.

SummaryRecently, the successful in vitro cultivation of the Nichols strain ofTreponema pallidum was achieved. Afterward, attempts were made to cultivate three other strains ofT. pallidum and two strains ofT. pertenue. The cultivation of the KKJ, Mexico A, and Bosnia A strains ofT. pallidum was somewhat successful; the average increases were 10.8, 9.1, and 7.5-fold, respectively. The range of growth for each of these strains varied dramatically from experiment to experiment. The KKJ strain varied from 14.4 to 8.0-fold; the Mexico A strain from 12.8 to 5.4-fold; and the Bosnia A strain from 11.3 to 3.6-fold. However, the attempts to cultivate the Gauthier and the FB strains ofT. pertenue were unsuccessful. The average increases were 1.7 and 1.9-fold, respectively. Although the maximum growth observed was about threefold with either of these strains ofT. pertenue, over 50% of the treponemes remained motile for 10 d. These results suggest that although each of these strains ofT. pallidum andT. pertenue has been shown to be genetically identical, they are very diverse biologically even among strains of the same species.

Biological characteristics and viral susceptibility of a stable dog kidney cell line

SummaryA cell line derived in 1956 from normal dog kidney is described. The cells are epithelial, contact-inhibited, and can be maintained in the same culture vessels for periods of more than 2.5 yr. Karyologically, the cells are hypodiploid with a modal number of 72 as opposed to the diploid number of 78. The karyotype indicates male origin of the cells and clonal derivation of extant cultures due to the presence of two marker chormosomes in all metaphases observed. At the 159th passage the dog kidney (DK) cells did not produce tumors in athymic rats. At least 13 viruses of various types produced transmissible cytopathogenic effects in the DK cells, including all of the human influenza viruses investigated.