Digital PCR outperforms quantitative real-time PCR for the detection and quantification of major periodontal pathobionts.

Abstract

Background: This study comparatively evaluated the analytical and diagnostic performance of a multiplex digital polymerase-chain reaction (dPCR) assay and a quantitative real-time PCR (qPCR) for the simultaneous detection and quantification of periodontal pathobionts: Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans, and Fusobacterium nucleatum.

Materials and methods: Subgingival plaque samples from 20 periodontitis patients and 20 periodontally healthy controls were analyzed. Several analytical parameters of the dPCR assay, optimized using DNA standards, were assessed versus qPCR: dynamic range linearity, precision, accuracy, prevalence, sensitivity, specificity, and concordance. The statistical analyses included Mann-Whitney U test, Wilcoxon test, McNemar's test, and Bland-Altman plots.

Results: dPCR showed high linearity (R² > 0.99) and lower intra-assay variability (median CV%: 4.5%) than qPCR (p = 0.020), with comparable accuracy and agreement. dPCR demonstrated superior sensitivity, detecting lower bacterial loads, particularly for P. gingivalis and A. actinomycetemcomitans. The Bland-Altman plots highlighted good agreement at medium/high loads but discrepancies at low concentrations (< 3 log₁₀Geq/mL), resulting in qPCR false negatives and a 5-fold underestimation of the prevalence of A. actinomycetemcomitans in periodontitis patients. High concordance between the assays was observed for F. nucleatum across both study groups.

Conclusions: dPCR outperformed qPCR for quantifying periodontal pathobionts and had superior sensitivity and precision, making it particularly effective in detecting low-level bacterial loads.