P. gingivalis rDNA spacer region PCR product amplified from a plaque sample duplexed with DNA from five different known strains of P. gingivalis and analyzed by polyacrylamide gel electrophoresis. The first lane contains DNA size markers: phage lambda digested with the restriction enzymes EcoRI and HindIII. The second lane contains ISR DNA from the clinical sample, A62, by itself. The remaining five lanes contain the A62 PCR product duplexed with DNA from P. gingivalis ATCC 53978 (W50), 23A4, A7A1, ATCC 33277, and ATCC 49417, respectively.