Aim
To evaluate the effect of transport media and storage temperatures on the survival of two root canal isolates, Prevotella oralis and Fusobacterium nucleatum over time.
Methodology
A standardised inoculum of each bacterium was prepared and transferred via sterile paper points into triplicate 1 mL volumes of transport media (Phosphate buffer saline[PBS]; Viability medium Göteberg [VMG III]; Reduced transport fluid [RTF]; RTF plus 20% glycerol; Commercial Dental Transport Medium [DTM] and Skimmed milk plus 20% glycerol) The samples were placed at room temperature (22 °C), 4 °C and -20 °C and the number of colony forming units (cfu) determined at 0 (base line), 1, 4 and 24 h after inoculation. The percentage of cells surviving in each storage medium at each time period was calculated using the number of viable cfu at 0 h as the baseline.
Results
All the tested media were capable of maintaining bacterial viability for up to 1 h regardless of the temperature. Storage at 4 °C in RTF after 4 h gave the best bacterial survival rate among the transport media used. Median percentage survival rates were 82% for P. oralis to 92% for F. nucleatum. In order to store samples for longer than 4 h before microbiological processing then storage at -20 °C, in skimmed milk medium was the most effective medium in assisting bacterial recovery with 75% and 82% survival for F. nucleatum and P. oralis, respectively while PBS was the least effective (0–3% survival).
Conclusion
Due to the loss of bacterial viability during sample storage and transport, samples should ideally be processed within the first hour after collection. However, if this is not possible, the results from this study suggest samples should either be: (i) placed in RTF and stored at 4 °C for no more than 4 h; or (ii) for overnight storage, samples should be placed in skimmed milk medium plus 20% glycerol at -20 °C.
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