Identification of Porphyromonas gingivalis strains by heteroduplex analysis and detection of multiple strains

Heteroduplex analysis has been used extensively to identify allelic variati on among mammalian genes. It provides a rapid and reliable method for deter mining and cataloging minor differences between two closely related DNA seq uences. We have adapted this technique to distinguish among strains or clon al types of Porphyromonas gingivalis. The ribosomal intergenic spacer regio n (ISR) was amplified directly from a subgingival plaque sample by PCR with species-specific primers, avoiding the need for culturing the bacteria, Th e PCR products were then directly compared by heteroduplex analysis with kn own strains of P, gingivalis for identification, We identified 22 distinct but closely related heteroduplex types of P, gingivalis in 1,183 clinical s amples. Multiple strains were found in 34% of the samples in which P, gingi valis was detected. Heteroduplex types were identified from these multistra in samples without separating them by culturing or molecular cloning. PCR w ith species-specific primers and heteroduplex analysis makes it possible to reliably and sensitively detect and identify strains of P, gingivalis in l arge numbers of samples.