Highly expressed genes in a rough-colony-forming phenotype of Aggregatibacter actinomycetemcomitans: implication of a mip-like gene for the invasion of host tissue.

Aggregatibacter actinomycetemcomitans, a potent pathogen of periodontitis, typically grows as a rough and adherent colony on primary isolated cultures. The colony transforms into a smooth phenotype during repeated subculture. In this study, we aimed to identify highly expressed genes in the rough-colony-forming phenotype for isolation of host-induced genes. Using a cDNA-subtractive hybridization technique, three genes, homologous to a macrophage infectivity potentiator gene (mip), peroxiredoxin gene (prx) and outer membrane protein gene (ompA), were identified. The expression levels of these genes in the rough-colony-forming phenotype were 4-10-fold higher as compared with the smooth-colony-forming phenotype. Attention was focused on the mip-like gene, and a recombinant protein and a deficient mutant were constructed. The recombinant protein reacted with sera from patients with periodontitis, suggesting the production of the Mip-like protein in periodontal lesions. Viable quantitative invasion assay demonstrated that the viable cell counts of the wild-type strain that invaded HeLa cells were more than fourfold as compared with the mip-deficient mutant. The expression of the mip-like gene, prx-like gene and ompA-like gene may be enhanced in the host, and the mip-like gene may play an important role in the infection of A. actinomycetemcomitans, especially in its invasion of the epithelium.

Quantitative real-time PCR using TaqMan and SYBR Green for Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis, Prevotella intermedia, tetQ gene and total bacteria.

Accurate quantification of bacterial species in dental plaque is needed for microbiological diagnosis of periodontal diseases. The present study was designed to assess the sensitivity, specificity and quantitativity of the real-time PCR using the GeneAmp Sequence Detection System with two fluorescence chemistries. TaqMan probe with reporter and quencher dye, and SYBR Green dye were used for sources of the fluorescence. Primers and probes were designed for Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis, Prevotella intermedia and total bacteria based on the nucleotide sequences of the respective 16S ribosomal RNA genes. Since spread of antibiotic resistance genes is one of the crucial problems in periodontal therapy, quantitative detection of tetQ gene, which confers resistance to tetracycline, was included in the examination. The detection of P. gingivalis, P. intermedia and A. actinomycetemcomitans was linear over a range of 10-10(7) cells (10-10(7) copies for tetQ gene), while the quantitative range for total bacteria was 10(2)-10(7) cells. Species-specific amplifications were observed for the three periodontal bacteria, and there was no significant difference between the TaqMan and SYBR Green chemistry in their specificity, quantitativity and sensitivity. The SYBR Green assay, which was simpler than TaqMan assay in its manipulations, was applied to the clinical plaque samples. The plaque samples were obtained from eight patients (eight periodontal pockets) before and 1 week after the local drug delivery of minocycline. Although the number of P. gingivalis, P. intermedia and A. actinomycetemcomitans markedly decreased after the antibiotic therapy in most cases, higher copy numbers of the tetQ gene were detectable. The real-time PCR demonstrated sufficient sensitivity, specificity and quantitativity to be a powerful tool for microbiological examination in periodontal disease, and the quantitative monitoring of antibiotic resistance gene accompanied with the antibiotic therapy should be included in the examination.