Effect of oral specimens on qPCR. Samples of serially diluted S. sobrinus chromosomal DNA and S. sobrinus chromosomal DNA spiked with DNA from S. sobrinus-free oral specimens were analyzed by S. sobrinus-specific qPCR. Spike experiments with (A) saliva and (B) dental plaque. Saliva (+), S. sobrinus DNA with DNA from S. sobrinus-free saliva. Saliva (−), S. sobrinus DNA only. Plaque (+), S. sobrinus DNA with DNA from S. sobrinus-free dental plaque. Plaque (−), S. sobrinus DNA only. All experiments were performed independently three times. Means ± S.D. are shown.