Intra- and inter-individual comparison of Porphyromonas gingivalis genotypes

Genetic analysis of 31 clinical strains of Porphyromonas gingivalis isolated from nine subjects, 2-6 strains per subject, was performed by Southern hybridization. Chromosomal DNA was extracted by the method of Moncla et al. [1] and digested to completion with restriction endonucleases PstI, ClaI and BglI. The DNA fragments were separated electrophoretically on agarose gels, transferred to nylon membranes and hybridized to the non-radioactively labelled plasmid pKK 3535 which contains the rmB ribosomal RNA operon of the Escherichia coli chromosome. Of the three enzymes, BglI was the most suitable for the genetic analysis of P. gingivalis. With this enzyme, the intra-individual strains were shown to be identical in eight of the nine subjects, whereas inter-individual strains were different.