Comparison of different culture media and storage temperatures for the long-term preservation of Streptococcus pneumoniae in the tropics.
OBJECTIVE
The preservation of Streptococcus pneumoniae by standard freezing methods for subsequent tests--such as serotyping and antibiotic susceptibility--is not possible or is difficult in many developing countries because of the high cost of equipment, inadequate equipment maintenance, and irregular power supply. We evaluated alternative low-cost methods, by comparing different culture media and storage temperatures.


METHODS
Clinical isolates of five capsular types (1, 5, 7, 19, and 23) of S. pneumoniae were preserved in rabbit blood, sheep blood, skimmed milk, or glycerol-chocolate broth, and stored at -20 degrees C or -70 degrees C. The cultures were also preserved by lyophilization or sand desiccation, followed by storage at room temperature and 4 degrees C. The viability of the preserved cultures was determined by making serial colony counts on day 0 and after 1 week, 4 weeks, 4 months and 16 months. The viability of cultures preserved by sand desiccation and storage at 4 degrees C was also determined every 6 months for up to 68 months.


RESULTS
Irrespective of the media used, cultures maintained at -20 degrees C became nonviable by the fourth month, while those maintained at -70 degrees C were still viable at 16 months. Cultures preserved by lyophilization or sand desiccation lost their viability by the fourth month when maintained at local room temperature (30-42 degrees C), but remained viable when stored at 4 degrees C for up to 68 months.


CONCLUSIONS
Our results confirm that freezing at -70 degrees C, or lyophilization and storage at 4 degrees C are the ideal methods for the preservation of S. pneumoniae. In laboratories where lyophilization is not feasible, sand desiccation and storage at 4 degrees C offers an alternative low-cost method for the long-term preservation of S. pneumoniae.
Siberry
G
G
Department of Paediatrics, Johns Hopkins Medical Institutions, 600 N Wolfe Street, Baltimore, MD 21287, USA. gsiberry@worldnet.attn.net
Brahmadathan
K N
KN
Pandian
R
R
Lalitha
M K
MK
Steinhoff
M C
MC
John
T J
TJ
D018929:Cell Culture Techniques / Q000379:methods*; D003362:Cost-Benefit Analysis; D015925:Cryopreservation / Q000379:methods; D003470:Culture Media; D006801:Humans; D007194:India; D011309:Preservation, Biological / Q000191:economics / Q000379:methods*; D013048:Specimen Handling / Q000191:economics / Q000379:methods*; D013296:Streptococcus pneumoniae; D014329:Tropical Climate
D003470:Culture Media