Differentiation of clinical isolates of Actinobacillus actinomycetemcomitans using an insertion sequence, ISAa1

Use of insertion sequence element IS1126 in a genotyping and transmission study of Porphyromonas gingivalis

Porphyromonas gingivalis is strongly associated with periodontal diseases and is regarded as one of the risk factors for periodontitis. Insertion sequence element IS1126-based PCR was used to investigate the genetic heterogeneity of P. gingivalis from periodontitis patients and to examine the frequency of the parent-child and spouse-spouse transmission. Two sets of IS1126-specific primers were used for the PCR. The inward primer set (PI1 and PI2), which amplifies the IS1126 fragment of approximately 690 bp, was used to identify P. gingivalis. The outward primer set (PI1RC and PI2RC), which is reverse complementary to PI1 and PI2, respectively, and amplifies the gene fragments between the adjacent IS1126 elements was used to characterize the genotypes of the P. gingivalis strains. PCR of P. gingivalis with PI1RC and PI2RC resulted in the production of two to seven amplicons, which showed a unique electrophoretic pattern in each strain (4 laboratory strains and 37 clinical isolates cultured from 12 patients with aggressive periodontitis). The usefulness of the method for transmission study was confirmed by detecting identical genotypes between the isolates and the plaque samples from which the isolates were cultured and between the plaque samples from different tooth sites in the same patient. Thirty probands with periodontal diseases and their thirty immediate family members were included in the transmission study. In 11 of 14 parent-child pairs (78.6%), P. gingivalis revealed an identical or similar band pattern, whereas 5 of 16 spouse pairs (31.25%) had this similarity. These results show that IS1126-based PCR for genotyping P. gingivalis has a highly discriminating potential with reproducible data and is a simple and reliable method for a transmission study.

Phylogenetic associations of ISAa1 and IS150-like insertion sequences in Actinobacillus actinomycetemcomitans

The distribution and number of two insertion sequences (ISs), ISAa1 and an IS150-like element, in the genomes of a collection of Actinobacillus actinomycetemcomitans strains previously subjected to population genetic analysis were determined to obtain information about their stability and biological significance. The hybridization patterns revealed that these IS elements are widespread in the genome of A. actinomycetemcomitans strains and that their occurrence agrees with the overall population structure of the species. While the patterns of ISAa1 showed significant evolutionary stability, the IS150-like element showed evidence of intra-genomic variability even within members of the previously identified high-toxicity JP2 clone. Searching of the available genome sequence of strain HK1651 of the JP2 clone (www.genome.ou.edu/act.html) revealed close proximity of the IS elements to housekeeping genes, but no evidence of structural disruption of genes or integrations that may be presumed to influence pathogenic potential.