Preservation of Neisseria gonorrhoeae at -20°C

Abstract

To explore the feasibility of preserving Neisseria gonorrhoeae at -20°C, we studied its viability quantitatively and qualitatively for 12 and 18 months, respectively, in the following media: a gelatin-based medium used mainly to prepare dried gelatin discs (S. Yamai, Y. Obara, T. Nikkawa, Y. Shimoda, and Y. Miyamoto, Br. J. Vener. Dis. 55:90-93, 1979), a simplified version (LSPQ preservation medium), and Trypticase soy broth with 10% (vol/vol) glycerol, a medium commonly used for preservation at -70°C. The latter was studied for 4 months only. Four reference strains and two clinical isolates of N. gonorrhoeae were used. The storage temperature was rigorously preadjusted and monitored at -20 ± 1°C during the entire project. After 12 months of storage, all strains remained viable in both gelatin-based media, whereas a significant loss of viability was observed in Trypticase soy broth- 10% glycerol after only 4 months. After 18 months, five strains were still viable in both gelatin-based media and no significant difference was observed between antimicrobial susceptibility results and those of the original strains preserved at -70°C. On the basis of these results, we believe that LSPQ preservation medium represents a good alternative for the storage of N. gonorrhoeae at -20°C for at least a year. Furthermore, it is easy to prepare and use and can be stored at 4 to 8°C for a year prior to use.