Silica Desiccant Packets for Storage and Transport of Streptococcus pneumoniae and Other Clinically Relevant Species

Abstract

Bacterial isolates are often transported between laboratories for research and diagnostic purposes. Silica desiccant packets (SDPs), which are inexpensive and do not require freezing, were evaluated for storage and recovery of bacterial isolates. Conditions such as inoculum size, swab type and temperature of storage were investigated using ten Streptococcus pneumoniae isolates. The optimized protocol was then tested using 49 additional S. pneumoniae isolates representing 40 serogroups. Overall, S. pneumoniae growth was considered satisfactory (>100 colony forming units) for 98/109 (89.9%) and 20/20 (100%) swabs after 14 days at room temperature or 28 days at 4° C, respectively. Storage in SDPs did not impact on the ability of S. pneumoniae isolates to be subsequently serotyped. When the survival of nine other clinically relevant bacterial species was tested, seven were viable after 28 days at room temperature, the exceptions being Neisseria gonorrhoeae and Haemophilus influenzae. SDPs are suitable for transport and short-term storage of bacterial species including S. pneumoniae.

Evaluation of Two Supplemented Culture Media for Long-Term, Room-Temperature Preservation ofStreptococcus pneumoniaeStrains

“…Siberry et al, in 2001, found that strains preserved in glycerol-chocolate broth, skimmed milk, rabbit blood, and sheep blood at 4°C became nonviable by the fourth month [ 4 ]. In our case, after 4 months of storage, TH-HYC and TH-SYC agar types were able to maintain a satisfactory number of CFU and pneumococci recovered from storage produced the required growth to perform phenotypic techniques such as serotyping (≥2+ of growth or ≥100 CFU) [ 15 ].…”

“…Data was further used to perform survival-time curves. Finally, the number of viable CFU was defined as satisfactory (≥2+ or ≥100 CFU) or unsatisfactory (≤1+ growth or <100 CFU) based on the number of colonies from a plate required for techniques such as serotyping, using the criteria described by Pell et al, in 2013 [ 15 ].…”