Porphyromonas gingivalis is a major pathogen in destructive periodontal disease in humans. Detection and quantification of this microorganism are relevant for diagnosis and treatment planning. The prevalence and quantity of P. gingivalis in subgingival plaque samples of periodontitis patients were determined by anaerobic culture and real-time PCR amplification of the 16S small-subunit rRNA gene. The PCR was performed with primers and a fluorescently labeled probe specific for the P. gingivalis 16S rRNA gene. By the real-time PCR assay, as few as 1 CFU of P. gingivalis could be detected. Subgingival plaque samples from 259 adult patients with severe periodontitis were analyzed. P. gingivalis was detected in 111 (43%) of the 259 subgingival plaque samples by culture and in 138 (53%) samples by PCR. The sensitivity, specificity, and positive and negative predictive values of the real-time PCR were 100, 94, 94, and 100%, respectively. We conclude that real-time PCR confirms the results of quantitative culture of P. gingivalis and offers significant advantages with respect to the rapidity and sensitivity of detection of P. gingivalis in subgingival plaque samples.The microflora colonizing the oral cavities of humans consists of numerous bacterial species (15,25). Most of these species are innocuous, but colonization of the subgingival plaque by certain species can lead to periodontal disease (6,25,26,36). Periodontitis is a chronic, multifactorial inflammatory disease that leads to destruction of the tissues supporting the teeth, and it is a major cause of tooth loss (3). Periodontitis occurs in humans as well as in several animal species (30).Periodontitis lesions are associated with a complex subgingival microflora which consists mainly of gram-negative bacterial species (37), of which the dark-pigmented organism Porphyromonas gingivalis is considered a major pathogen (2,6,20). P. gingivalis is a strict anaerobic, oral microorganism that is involved in periodontitis, endodontic infections, and odontogenic abscesses in humans (34). P. gingivalis is infrequently isolated from individuals with healthy periodontia (4,5,33). Anaerobic culture is most commonly used to detect and quantify major components of the subgingival plaque and to determine the in vitro antimicrobial susceptibilities of oral pathogens. Culture, however, has several drawbacks: it is timeconsuming and laborious and has a low level of sensitivity. This is due to the extremely slow growth or very specific growth requirements of some oral pathogens. Several alternative methods have been developed for the detection of P. gingivalis, such as immunoassays (9), DNA probe assays (9, 22, 23), and PCR assays (2, 10, 17, 21).Recently, real-time PCR has been shown to be a sensitive and rapid method for the detection and quantification of individual microbial species (7,10,11,16). Most real-time PCR tests are based on the detection of bacterial small-subunit 16S rRNA sequences (7). This subunit of DNA is present in multiple copies in all bacterial species and con...

Periodontitis is a multi-factorial chronic inflammatory and destructive disease of the tooth-supporting tissues. Quantitative anaerobic culture techniques have been used for microbial diagnosis of the different forms of the disease. The aim of this study was to compare real-time PCR with quantitative anaerobic culture for detection and quantification of 5 prominent periodontal pathogens. Real-time PCR assays with the 16s rRNA genes of Actinobacillus actinomycetemcomitans, Prevotella intermedia, Tannerella forsythensis, Peptostreptococcus micros and Fusobacterium spp. were developed. The PCR was validated on pure cultures of various bacterial strains. Subsequently, subgingival plaque samples from 259 adult patients with periodontitis were analyzed with quantitative anaerobic culture and real-time PCR. A standard curve for DNA quantification was created for each primer-probe set based on colony-forming units equivalents. All bacterial species were correctly identified. The lower limits of detection by PCR varied between 1-50 colony-forming units equivalents depending on the species. No cross-reactivities with heterologous DNA of other bacterial species were observed. Real-time PCR results showed a high degree of agreement with anaerobic culture results. Real-time PCR is a reliable alternative for diagnostic quantitative anaerobic culture of subgingival plaque samples.

Capsular polysaccharides of gram-negative bacteria play an important role in maintaining the structural integrity of the cell in hostile environments and, because of their diversity within a given species, can act as useful taxonomic aids. In order to characterize the genetic locus for capsule biosynthesis in the oral gramnegative bacterium Porphyromonas gingivalis, we analyzed the genome of P. gingivalis W83 which revealed two candidate loci at PG0106-PG0120 and PG1135-PG1142 with sufficient coding capacity and appropriate gene functions based on comparisons with capsule-coding loci in other bacteria. Insertion and deletion mutants were prepared at PG0106-PG0120 in P. gingivalis W50-a K1 serotype. Deletion of PG0109-PG0118 and PG0116-PG0120 both yielded mutants which no longer reacted with antisera to K1 serotypes. Restriction fragment length polymorphism analysis of the locus in strains representing all six K-antigen serotypes and K ؊ strains demonstrated significant variation between serotypes and limited conservation within serotypes. In contrast, PG1135-PG1142 was highly conserved in this collection of strains. Sequence analysis of the capsule locus in strain 381 (K ؊ strain) demonstrated synteny with the W83 locus but also significant differences including replacement of PG0109-PG0110 with three unique open reading frames, deletion of PG0112-PG0114, and an internal termination codon within PG0106, each of which could contribute to the absence of capsule expression in this strain. Analysis of the Arg-gingipains in the capsule mutants of strain W50 revealed no significant changes to the glycan modifications of these enzymes, which indicates that the glycosylation apparatus in P. gingivalis is independent of the capsule biosynthetic machinery.