Efficacy of the FDA selection criteria for radiographic assessment of the periodontium.

The diagnosis of periodontitis is generally made on the basis of a clinical examination supported by radiographic evidence of bone loss. Recent guidelines promulgated by the US Food and Drug Administration recommend that periapical radiographs be ordered on the basis of clinical signs and symptoms indicating the probable presence of disease. This study evaluated the effectiveness of the FDA Guidelines for ordering radiographs for new adult dental patients as related to assessment of the periodontal condition of the patient. We examined 490 patients and determined the periapicals needed to supplement the posterior bitewings based upon the patient's clinical findings. We measured the reduction in the number of radiographs ordered as well as the extent of missed alveolar and furcation bone loss resulting from the use of the selected set of radiographs compared with a complete set. Four hundred thirty-three subjects had at least one clinical sign of periodontitis present in their mouths, and 264 demonstrated radiographic evidence of alveolar bone loss. Of the 460 subjects on whom periodontal probing was conducted, two-thirds demonstrated periodontal probing depths in excess of 3 mm; almost half showed evidence of bleeding upon probing. Individuals with clinical signs of periodontitis had, on average, 10 periapicals ordered--more than twice the number as those with no sign of periodontitis. Of the 2,415 teeth with radiographic findings of proximal or furcal bone loss, 152 sites of bone loss (6%) were missed when the selected set of films plus the posterior bitewings was used.

Coaggregation between bacterial species.

Bacterial coaggregation, or interbacterial adherence, is one mechanism involved in the development of bacterial biofilms that are found on surfaces in nature. Assays used to measure coaggregation rely on the interaction of bacterial cells in suspension or attachment of one species to a second species that has been fixed to a solid substrate. Both semiquantitative and quantitative assays are described. These methods have also been used to determine the nature of the adherence and molecules involved in mediating the interaction, to characterize potential inhibitors, to isolate the bacterial adhesins and receptors, and to isolate adherence-deficient mutant strains. Each of the assay systems offers different advantages, with significant variations in sensitivity. Selection of a particular assay system should depend on the goals of the study to be performed.

Cloning of the YenI restriction endonuclease and methyltransferase from Yersinia enterocolitica serotype O8 and construction of a transformable R-M+ mutant.

Two different clonal groups of pathogenic Yersinia enterocolitica strains, American and non-American, have been recognized. These are distinguished by a number of criteria, including their virulence in a murine model of infection. However, genetic analysis of virulence in American strains has been hampered due to the severe restriction of transformed or electroporated DNA. Thus, we cloned the yenIMR locus from the American serotype strain 8081c, which encodes YenI, an isoschizomer of PstI. This clone encodes both the restriction endonuclease and methyltransferase. The location of the genes on the clone was determined and this information was used to construct a small deletion (400 bp) that results in an R-M+ phenotype. This mutation was recombined onto the Y. enterocolitica chromosome to give an R-M+ mutant which showed at least a 1000-fold increase in electroporation frequency compared to the wild-type strain. Southern analysis using a probe derived from yenIMR indicated that American serotype strains have this locus whereas non-American serotype strains do not.

Localization of the Fusobacterium nucleatum T18 adhesin activity mediating coaggregation with Porphyromonas gingivalis T22.

Adherence of pathogenic bacteria is often an essential first step in the infectious process. The ability of bacteria to adhere to one another, or to coaggregate, may be an important factor in their ability to colonize and function as pathogens in the periodontal pocket. Previously, a strong and specific coaggregation was demonstrated between two putative periodontal pathogens, Fusobacterium nucleatum and Porphyromonas gingivalis. The interaction appeared to be mediated by a protein adhesin on the F. nucleatum cells and a carbohydrate receptor on the P. gingivalis cells. In this investigation, we have localized the adhesin activity of F. nucleatum T18 to the outer membrane on the basis of the ability of F. nucleatum T18 vesicles to coaggregate with whole cells of P. gingivalis T22 and the ability of the outer membrane fraction of F. nucleatum T18 to inhibit coaggregation between whole cells of F. nucleatum T18 and P. gingivalis T22. Proteolytic pretreatment of the F. nucleatum T18 outer membrane fraction resulted in a loss of coaggregation inhibition, confirming the proteinaceous nature of the adhesin. The F. nucleatum T18 outer membrane fraction was found to be enriched for several proteins, including a 42-kDa major outer membrane protein which appeared to be exposed on the bacterial cell surface. Fab fragments prepared from antiserum raised to the 42-kDa outer membrane protein were found to partially but specifically block coaggregation. These data support the conclusion that the 42-kDa major outer membrane protein of F. nucleatum T18 plays a role in mediating coaggregation with P. gingivalis T22.

Characterization of coaggregation between Bacteroides gingivalis T22 and Fusobacterium nucleatum T18.

Bacterial adherence is a key factor in the colonization of the oral ecosystem, yet little is known about the mechanisms by which the pathogen Bacteroides gingivalis adheres in the periodontal environment. We examined the ability of strains of B. gingivalis to coaggregate with selected microorganisms isolated from the subgingival microbiota of the cynomolgus monkey. A strong interaction was demonstrated between strains of B. gingivalis and Fusobacterium nucleatum, whereas less pronounced or no interaction was observed with other oral isolates. Electron microscopic examination of coaggregates revealed large masses of bacteria, in which the fusiform F. nucleatum T18 and coccobacillary B. gingivalis T22 cells formed a woven pattern. To investigate this interaction and the nature of the bacterial cell surface molecules involved, we used a microcoaggregation assay. Galactose and galactose-related sugars blocked coaggregation, in contrast with the lack of effect of glucose or glucose-related sugars. The ability of F. nucleatum T18 cells to coaggregate was diminished by pretreatment with pronase. Pretreatment of B. gingivalis T22 cells with pronase resulted in an inhibition of coaggregation, whereas pretreatment with sodium metaperiodate completely abolished coaggregation. These data suggest that the coaggregation between B. gingivalis T22 and F. nucleatum T18 represents a carbohydrate-lectin interaction, mediated by a galactose-containing carbohydrate on B. gingivalis T22 and a protein on F. nucleatum T18.

Characterization of selected gram-negative oral microorganisms by SDS-PAGE.

SDS-PAGE analysis of bacterial cell proteins was used to examine a diverse group of oral microorganisms. Most of the species examined, including physiologically similar microorganisms, produced distinct protein patterns which are characterized by the distribution of their major protein bands. The SDS-PAGE system described provides a rapid, simple and standardized identification technique to be used in consort with routine taxonomic procedures.

Penicillin resistance in the subgingival microbiota associated with adult periodontitis.

In this investigation, the penicillin-resistant and beta-lactamase-producing subgingival microbiota associated with adult periodontitis was identified, and the impact of a recent exposure to penicillin on the recovery of resistant organisms from this microbiota was assessed. Subjects with adult periodontitis were examined clinically and microbiologically. Twenty-one subjects had a documented history of penicillin therapy within the previous 6 months whereas an additional 21 subjects had no history of antibiotic use within 1 year. Subgingival plaque samples were cultured anaerobically on nonselective and penicillin-containing elective media. MICs and beta-lactamase production were determined for the isolates from the elective medium. The penicillin-resistant microbiota consisted primarily of gram-negative organisms, including Bacteroides, Veillonella, Haemophilus, Eikenella, and Capnocytophaga species. The prevalence (P less than 0.05) and proportions (P less than 0.005) of both penicillin-resistant pigmented Bacteroides and Veillonella species were significantly greater in subjects with recent penicillin exposure. Of the penicillin-resistant genera identified, beta-lactamase production was detected in species of pigmented Bacteroides, Capnocytophaga, and Streptococcus. The prevalence of beta-lactamase-producing Bacteroides species was significantly greater in subjects with recent penicillin exposure (P less than 0.05). Of the antibiotics examined, no single agent was uniformly effective against all of the penicillin-resistant strains, but metronidazole and clindamycin were active against all of the penicillin-resistant pigmented Bacteroides strains.