Effect of storage conditions on the extraction of PCR-quality genomic DNA from saliva.
Saliva is a potentially useful source of genomic DNA for genetic studies since it can be collected in a painless and non-invasive manner. We sought to determine whether different storage conditions of saliva samples impact our ability to extract genomic DNA that is of sufficient quality for use in the polymerase chain reaction (PCR). Saliva was collected from healthy volunteers and 2-ml aliquots subjected to different storage conditions: S1--washing of saliva using phosphate-buffered saline (PBS) and extraction of DNA on the same day of collection; S2--washing and centrifugation to yield a pellet, which was stored at-70 degrees C for 1 week prior to DNA extraction; S3--storage of whole saliva at 4 degrees C for 7 days, followed by washing and extraction of DNA; S4--storage at 4 degrees C for 7 days, followed by washing and pellet formation. The pellet was stored at -70 degrees C for 1 month before extraction of the DNA; S5--storage at-70 degrees C for 1 month, followed by washing and extraction of DNA. DNA yield and purity was determined by spectrophotometry at 260 and 280 nm. Twenty nanograms of genomic DNA was used for the polymerase chain reaction, and the resulting PCR band was captured by digital photography and quantified. The amounts of DNA extracted from 2 ml of saliva varied widely under the different storage conditions, while purity of the DNA extraction, based on OD(260/280) ratios, was good and comparable. PCR resulted in the presence of a single specific product of the correct size from all samples regardless of saliva storage conditions. Quantification of PCR bands showed significant differences between the various storage conditions (P<0.05). Compared to S1 samples, PCR bands from conditions S2 and S3 were not as strong, while those amplified from S4 and S5 samples were the weakest. Post-hoc analyses showed that the means for conditions S4 and S5 were significantly different from S1-S3. Qualitatively similar results were obtained when the PCR experiment was repeated. Saliva can act as a useful source of genomic DNA, even when stored under less than optimal conditions.