Colonization and Persistence of Labeled and "Foreign" Strains of Aggregatibacter actinomycetemcomitans Inoculated into the Mouths of Rhesus Monkeys

Aggregatibacter actinomycetemcomitans (Aa) is a pathobiont and part of a consortium of bacteria that can lead to periodontitis in humans. Our aim was to develop a model for oral inoculation of labeled Aa into a suitable host in order to study Aa traits and ecological factors that either enhance or repress its persistence. Primate species were screened for Aa to select a host for colonization studies. Macaca mulatta (Rhesus/Rh) was selected. Rh Aa strains were isolated, subjected to sequencing and functional analysis for comparison to human strains. "Best" methods for microbial decontamination prior to inoculation were assessed. Three groups were studied; Group 1 (N=5) was inoculated with Aa Spectinomycin resistant (SpecR) Rh strain 4.35, Group 2 (N=5) inoculated with Aa SpecR human strain IDH 781, and Group 3 (N=5) the un-inoculated control. Repeated feeding with pancakes spiked with SpecRAa followed high dose oral inoculation. Cheek, tongue, and plaque samples collected at baseline 1, 2, 3, and 4 weeks after inoculation were plated on agar; 1) selective for Aa, 2) enriched for total counts, and 3) containing 50 µg/ml of Spec. Aa was identified by colonial morphology and DNA analysis. Rh and human Aa had > 93-98 % genome identity. Rh Aa attached to tissues better than IDH 781 in vitro (p < 0.05). SpecR IDH 781 was not recovered from any tissue at any time; whereas, RhSpecR 4.35 was detected in plaque, but never tongue or cheek, in all monkeys at all times (> 1 × 10⁵ colonies/ml; p < 0.001). In conclusion, the primate model provides a useful platform for studying integration of Aa strains into a reduced but established oral habitat. Primate derived SpecRAa was consistently detected in plaque at all collection periods; however, human derived Aa was never detected. The model demonstrated both microbial as well as tissue specificity.

Macrophage inflammatory protein-1α shows predictive value as a risk marker for subjects and sites vulnerable to bone loss in a longitudinal model of aggressive periodontitis

Improved diagnostics remains a fundamental goal of biomedical research. This study was designed to assess cytokine biomarkers that could predict bone loss (BL) in localized aggressive periodontitis. 2,058 adolescents were screened. Two groups of 50 periodontally healthy adolescents were enrolled in the longitudinal study. One group had Aggregatibacter actinomycetemcomitans (Aa), the putative pathogen, while the matched cohort did not. Cytokine levels were assessed in saliva and gingival crevicular fluid (GCF). Participants were sampled, examined, and radiographed every 6 months for 2-3 years. Disease was defined as radiographic evidence of BL. Saliva and GCF was collected at each visit, frozen, and then tested retrospectively after detection of BL. Sixteen subjects with Aa developed BL. Saliva from Aa-positive and Aa-negative healthy subjects was compared to subjects who developed BL. GCF was collected from 16 subjects with BL and from another 38 subjects who remained healthy. GCF from BL sites in the 16 subjects was compared to healthy sites in these same subjects and to healthy sites in subjects who remained healthy. Results showed that cytokines in saliva associated with acute inflammation were elevated in subjects who developed BL (i.e., MIP-1α MIP-1β IL-α, IL-1β and IL-8; p<0.01). MIP-1α was elevated 13-fold, 6 months prior to BL. When MIP-1α levels were set at 40 pg/ml, 98% of healthy sites were below that level (Specificity); whereas, 93% of sites with BL were higher (Sensitivity), with comparable Predictive Values of 98%; p<0.0001; 95% C.I. = 42.5-52.7). MIP-1α consistently showed elevated levels as a biomarker for BL in both saliva and GCF, 6 months prior to BL. MIP-1α continues to demonstrate its strong candidacy as a diagnostic biomarker for both subject and site vulnerability to BL.

Lactoferrin knockout mice demonstrates greater susceptibility to Aggregatibacter actinomycetemcomitans-induced periodontal disease

BACKGROUND

Among the innate defense mechanisms in the oral cavity, lactoferrin (LF) is a vital antimicrobial that can modify the host response against periodontopathogens. Aggregatibacter actinomycetemcomitans is the main periodontopathogen of localized aggressive periodontitis. The aim of this study is to evaluate the role of LF during A. actinomycetemcomitans-induced periodontitis.

METHODS

Differences in the expression levels of cytokines, chemokines, chemokine receptors, and bone loss markers between wild-type (WT) and LF knockout mice (LFKO(-/-)) were evaluated by real time-PCR. Serum IgG and LF levels were quantified by ELISA. Alveolar bone loss among the groups was estimated by measuring the distance from cemento-enamel junction (CEJ) to the alveolar bone crest (ABC) at 20 molar sites.

RESULTS

Oral infection with A. actinomycetemcomitans increased LF levels in periodontal tissue (P = 0.01) and saliva (P = 0.0004) of wild-type infected (WTI) mice compared to wild-type control mice. Pro-inflammatory cytokines such as interferon-γ, tumor necrosis factor-α, interleukin (IL)-1β, IL-6, and IL-12 were increased in the infected LF knockout (LFKO(-/-)I) mice compared to the WTI mice, whereas the anti-inflammatory cytokines IL-4 and IL-10 were decreased. Chemokines and chemokine receptors showed different expression patterns between WTI and LFKO(-/-)I mice. The LFKO(-/-)I mice developed increased bone loss (P = 0.002), in conjunction with increased expression of receptor activator of nuclear factor-κB ligand and decrease in osteoprotegerin, compared to WTI mice.

CONCLUSIONS

These results demonstrate that the infected LFKO(-/-) mice were more susceptible to A. actinomycetemcomitans-induced alveolar bone loss, with different patterns of immune responses compared to those of WTI mice.

Can salivary activity predict periodontal breakdown in A. actinomycetemcomitans infected adolescents?

OBJECTIVE

While Aggregatibacter actinomycetemcomitans (Aa) is highly associated with localised aggressive periodontitis (LAP) many Aa-carriers do not develop LAP. This study was designed to determine whether specific salivary factors could distinguish between subjects who have Aa initially and remain healthy (H/AA) as compared to those who develop LAP (LAP/AA).

DESIGN

H/AA subjects and healthy controls with no Aa (H) were enrolled in a longitudinal cohort study to investigate initiation of bone loss (LAP) over 3 years. After detection of LAP, stored saliva from 10 H, 10 H/AA, and 10 LAP/AA subjects was thawed, processed, and tested for (1) lactoferrin (Lf) concentration and iron levels; (2) agglutination of Aa; (3) killing of Gram-positive bacteria.

RESULTS

LAP/AA saliva levels of Lf iron were low prior to and after bone loss (3.6+1.7ngFe/μg) (LAP/AA vs. H and H/AA p≤0.01). Saliva from H/AA subjects caused Aa to agglutinate significantly more than H or LAP/AA saliva (p≤0.01). LAP/AA saliva killed Streptococcus mutans, Streptococcus sanguis and Lactobacillus in vitro by >83%. Saliva from H individuals killed these bacteria by <3.3% (LAP/AA vs. H; p≤0.01). H/AA killing was intermediate.

CONCLUSION

LAP/AA saliva showed: low levels of Lf iron, minimal Aa agglutinating activity, and high killing activity against Gram-positive bacteria. Aa-positive healthy saliva (H/AA) showed: higher levels of Lf iron, maximal Aa agglutinating activity, and moderate killing of Gram-positive bacteria. A salivary activity profile can distinguish between subjects who are Aa-positive and remain healthy from those who develop LAP.

Rapid identification of oral isolates of Aggregatibacter actinomycetemcomitans obtained from humans and primates by an ultrafast super convection based polymerase chain reaction

Aggregatibacter actinomycetemcomitans is a Gram negative oral bacterium associated with localized aggressive periodontitis (LAP). Detection of A. actinomycetemcomitans in clinical samples is routinely done by PCR. Our aim was to develop a rapid and reliable PCR method that can be used as a chair-side tool to detect A. actinomycetemcomitans in clinical samples. Sensitivity and specificity assessment was performed on buccal and plaque samples obtained from 40 adolescents enrolled in an ongoing LAP study by comparing 20 A. actinomycetemcomitans-positive subjects and 20 who were negative. In a second study, A. actinomycetemcomitans presence was tested in oral samples from eighty-six primates that included rhesus monkeys, chimpanzees, marmosets, tamarins and baboons. All samples were processed for detection of A. actinomycetemcomitans by means of culture, conventional PCR (cPCR) and rapid PCR (rPCR) using a Super Convection based AmpXpress thermal cycler (AlphaHelix, Sweden). For human samples, culture, cPCR and rPCR showed perfect agreement. Using this method A. actinomycetemcomitans was detected in 27 of 32 rhesus monkeys, 4 of 8 chimpanzees and 1 of 34 marmosets. Rapidity of AmpXpress thermal cycler, combined with Ready-To-Go PCR beads (GE Life sciences), a quick DNA extraction kit (Epicentre Biotechnologies, Madison, Wisconsin, USA) and a bufferless fast agarose gel system, made it possible to obtain results on A. actinomycetemcomitans detection within 35 min. We conclude that AmpXpress fast PCR can be conveniently used as a chair-side tool for rapid detection of A. actinomycetemcomitans in clinical samples.

Mapping the epithelial-cell-binding domain of the Aggregatibacter actinomycetemcomitans autotransporter adhesin Aae

The Gram-negative periodontopathogen Aggregatibacter actinomycetemcomitans (Aa) binds selectively to buccal epithelial cells (BECs) of human and Old World primates by means of the outer-membrane autotransporter protein Aae. We speculated that the exposed N-terminal portion of the passenger domain of Aae would mediate binding to BECs. By using a series of plasmids that express full-length or truncated Aae proteins in Escherichia coli, we found that the BEC-binding domain of Aae was located in the N-terminal surface-exposed region of the protein, specifically in the region spanning amino acids 201–284 just upstream of the repeat region within the passenger domain. Peptides corresponding to amino acids 201–221, 222–238 and 201–240 were synthesized and tested for their ability to reduce Aae-mediated binding to BECs based on results obtained with truncated Aae proteins expressed in E. coli. BEC-binding of E. coli expressing Aae was reduced by as much as 50 % by pre-treatment of BECs with a 40-mer peptide (201–240; P40). Aae was also shown to mediate binding to cultured human epithelial keratinocytes (TW2.6), OBA9 and TERT, and endothelial (HUVEC) cells. Pre-treatment of epithelial cells with P40 resulted in a dose-dependent reduction in binding and reduced the binding of both full-length and truncated Aae proteins expressed in E. coli, as well as Aae expressed in Aa. Fluorescently labelled P40 peptides reacted in a dose-dependent manner with BEC receptors. We propose that these proof-of-principle experiments demonstrate that peptides can be designed to interfere with Aa binding mediated by host-cell receptors specific for Aae adhesins.

Macrophage inflammatory protein-1alpha: a salivary biomarker of bone loss in a longitudinal cohort study of children at risk for aggressive periodontal disease?

BACKGROUND

Periodontitis develops in a time-dependent manner. Cross-sectional studies document one moment in time but fail to capture the progressive nature of disease. Radiographic measures of bone loss are relatively insensitive but are reliable markers of irreversible disease. Longitudinal studies are needed to identify biomarkers that can precede radiographic evidence of bone loss and, thus, mark the period prior to clinical evidence of irreversible disease. A longitudinal study of students susceptible to localized aggressive periodontitis (LAgP) was conducted to evaluate chemokines/cytokines found in saliva derived from periodontally healthy children who subsequently developed alveolar bone loss.

METHODS

Students were screened, sampled for Aggregatibacter actinomycetemcomitans (previously Actinobacillus actinomycetemcomitans [Aa]), and divided into a cohort of Aa+ and Aa- students. Ninety-six periodontally healthy Aa+ and Aa- students were recalled every 6 to 9 months following screening. Examinations, saliva collections, and radiographs were performed. After seven students developed bone loss, the levels of 21 cytokines were assessed and matched to saliva from seven Aa+ and seven Aa- students who remained healthy for > or =1 year. Subsequently, saliva from an additional 27 students who remained healthy was analyzed.

RESULTS

Nineteen cytokines were not detected or were detected at low levels. Macrophage inflammatory protein (MIP)-1alpha was elevated 50-fold in seven Aa+ students who developed disease 6 to 9 months prior to radiographic detection of bone loss compared to levels in 21 Aa+ and 20 Aa- students who remained healthy (P <0.001). Interleukin (IL)-1beta was also elevated (P = 0.01). MIP-1alpha had a specificity of 96.8% and a sensitivity of 100%, whereas IL-1beta showed 90.3% specificity and 85.7% sensitivity relative to bone loss. MIP-1alpha levels were also related to increasing probing depth and the number of pockets >6 mm.

CONCLUSION

The superior sensitivity and specificity of MIP-1alpha, which correlated well with probing depths and the onset of bone loss, suggested that it could be used as an early biomarker for LAgP.

An improved cost-effective, reproducible method for evaluation of bone loss in a rodent model

AIM

This study was designed to investigate the utility of two "new" definitions for assessment of bone loss in a rodent model of periodontitis.

MATERIAL AND METHODS

Eighteen rats were divided into three groups. Group 1 was infected by Aggregatibacter actinomycetemcomitans (Aa), group 2 was infected with an Aa leukotoxin knock-out, and group 3 received no Aa (controls). Microbial sampling and antibody titres were determined. Initially, two examiners measured the distance from the cemento-enamel-junction to alveolar bone crest using the three following methods; (1) total area of bone loss by radiograph, (2) linear bone loss by radiograph, (3) a direct visual measurement (DVM) of horizontal bone loss. Two "new" definitions were adopted; (1) any site in infected animals showing bone loss >2 standard deviations above the mean seen at that site in control animals was recorded as bone loss, (2) any animal with two or more sites in any quadrant affected by bone loss was considered as diseased.

RESULTS

Using the "new" definitions both evaluators independently found that infected animals had significantly more disease than controls (DVM system; p<0.05).

CONCLUSIONS

The DVM method provides a simple, cost effective, and reproducible method for studying periodontal disease in rodents.

Activity of an antimicrobial peptide mimetic against planktonic and biofilm cultures of oral pathogens

Antimicrobial peptides (AMPs) are naturally occurring, broad-spectrum antimicrobial agents that have recently been examined for their utility as therapeutic antibiotics. Unfortunately, they are expensive to produce and are often sensitive to protease digestion. To address this problem, we have examined the activity of a peptide mimetic whose design was based on the structure of magainin, exhibiting its amphiphilic structure. We demonstrate that this compound, meta-phenylene ethynylene (mPE), exhibits antimicrobial activity at nanomolar concentrations against a variety of bacterial and Candida species found in oral infections. Since Streptococcus mutans, an etiological agent of dental caries, colonizes the tooth surface and forms a biofilm, we quantified the activity of this compound against S. mutans growing under conditions that favor biofilm formation. Our results indicate that mPE can prevent the formation of a biofilm at nanomolar concentrations. Incubation with 5 nM mPE prevents further growth of the biofilm, and 100 nM mPE reduces viable bacteria in the biofilm by 3 logs. Structure-function analyses suggest that mPE inhibits the bioactivity of lipopolysaccharide and binds DNA at equimolar ratios, suggesting that it may act both as a membrane-active molecule, similar to magainin, and as an intracellular antibiotic, similar to other AMPs. We conclude that mPE and similar molecules display great potential for development as therapeutic antimicrobials.

Effect of an essential oil-containing antimicrobial mouthrinse on specific plaque bacteria in vivo

AIM

This study was conducted to investigate the effect of rinsing with an essential oil-containing mouthrinse on levels of specific supra and subgingival bacteria in subjects with gingivitis.

MATERIAL AND METHODS

Fifteen subjects meeting entry criteria completed this randomized, controlled, double-blind, crossover study. Subjects were required to have >or=1000 target organisms per millilitre in pooled samples from two subgingival sites. Following sampling of supra and subgingival plaque, subjects began twice-daily rinsing for 14 days with either an essential oil-containing mouthrinse (Cool Mint Listerine Antiseptic) or a negative control. Supra and subgingival plaque was again sampled on day 15, and the procedure repeated after a 1-week washout period with subjects using the alternate rinse.

RESULTS

Compared with the negative control, the essential oil mouthrinse produced significant reductions in supragingival plaque levels of Veillonella sp., Capnocytophaga sp., Fusobacterium nucleatum, and total anaerobes ranging from 52.3 to 88.5% (p<0.001 except for Veillonella, p=0.002); respective reductions in subgingival plaque ranged from 54.1 to 69.1% (p<0.001).

CONCLUSIONS

Rinsing with the essential oil mouthrinse can have an impact on the subgingival plaque flora. This study provides additional evidence indicating that reduction in supragingival plaque can reduce levels of subgingival plaque.

A second Aggregatibacter actinomycetemcomitans autotransporter adhesin exhibits specificity for buccal epithelial cells in humans and Old World primates

Previous work showed that the Aggregatibacter actinomycetemcomitans adhesin Aae demonstrated species specificity and tissue tropism to buccal epithelial cells (BECs) derived from humans and Old World primates, but a second, lower-affinity adhesin was noted. This study was designed to determine if Omp100 (also known as ApiA), a surface-expressed A. actinomycetemcomitans adhesin, is that second adhesin and if so to investigate its tissue tropism and species specificity. A targeted mutagenesis protocol was used to construct an isogenic apiA mutant and an aae apiA double mutant with wild-type A. actinomycetemcomitans. In addition, Escherichia coli strain DH5alpha was used to express apiA to further assess binding parameters. Results indicated that the apiA mutant strain showed significantly less binding to BECs than its parent strain (P < or = 0.05). Further, binding mediated by ApiA was specific to BECs from humans and Old World primates, as seen in both wild-type A. actinomycetemcomitans and E. coli expressing ApiA (P < or = 0.05). Pretreatment of wild-type A. actinomycetemcomitans cells with anti-ApiA antiserum reduced binding in a dose-dependent manner. The aae apiA double mutant completely abrogated A. actinomycetemcomitans binding to both human and Old World primate BECs. Taken together, these studies indicate that ApiA and Aae, in concert, modulate binding of A. actinomycetemcomitans to human BECs. Since the BEC is a prominent reservoir for A. actinomycetemcomitans, identification of this second adhesin could lead to important therapeutic strategies.

Saliva from subjects harboring Actinobacillus actinomycetemcomitans kills Streptococcus mutans in vitro

BACKGROUND

Previous research indicated that patients with localized aggressive periodontitis (LAgP) had minimal proximal decay. We speculated that differences in these two proximal dental diseases (LAgP and proximal decay) in LAgP could be due to the effect of saliva on the growth of key microorganisms related to these two infections. Carbon dioxide (CO(2)) is required for growth of Actinobacillus actinomycetemcomitans (Aa), the reputed cause of LAgP. Bicarbonate, a source of CO(2), buffers acid production by Streptococcus mutans (Sm), a key organism associated with caries. The purpose of this study was to determine whether the saliva of LAgP patients and subjects with Aa had higher levels of bicarbonate, or an elevated pH, and/or reduced survival of Sm.

METHODS

Eleven Aa-positive subjects (seven with LAgP) were matched with 11 Aa-negative controls. A total of 5 ml saliva obtained from each subject was tested for CO(2) levels, pH, and effects on survival of Aa and Sm. Saliva from 22 additional subjects was used for confirmatory data.

RESULTS

CO(2) levels in the test group (Aa-positive subjects) and controls (Aa-negatives) were similar. No clinically relevant differences were found in salivary pH. However, saliva from the test group killed Sm by more than two logs (P <0.05). No effect was seen on Aa. The saliva from the Aa-negative group killed Aa by two logs (P <0.05). No effect was seen on Sm.

CONCLUSION

Aa-positive subjects had a salivary factor that significantly reduced survival of Sm, which may help to explain the fact that this group typically has minimal proximal decay.

The antimicrobial effect of a triclosan/copolymer dentifrice on oral microorganisms in vivo

BACKGROUND

The authors compared the in vivo antimicrobial effects on microorganisms from dental plaque, saliva and the tongue in subjects who used a triclosan/copolymer dentifrice and a fluoride dentifrice (control).

METHODS

The authors assigned 15 subjects randomly to the control dentifrice or the triclosan/copolymer dentifrice for twice-daily use for one week. They collected samples of plaque, saliva and tongue scrapings six and 12 hours after the final brushing. They analyzed colony-forming units of Veillonella species, Fusobacteria species, total cultivable anaerobes and hydrogen sulfide (H(2)S)-producing bacteria. A one-week washout followed. The authors repeated the protocol with the second dentifrice.

RESULTS

The results showed no differences at baseline. Significant reductions (88 to 96 percent) in oral anaerobic bacteria were observed in the triclosan/copolymer group six and 12 hours after brushing compared with the control group (P = .001). Fusobacteria decreased by 77 to 92 percent and Veillonella decreased by 84 to 89 percent six and 12 hours after brushing in the triclosan/copolymer group versus the control group. The triclosan/copolymer group also demonstrated a significant decrease in H(2)S-producing bacteria six and 12 hours after brushing (74 to 85 percent) (P = .001).

CONCLUSIONS

Brushing with the triclosan/copolymer dentifrice resulted in significant reductions in microorganisms from the three sites compared with the control dentifrice.

CLINICAL IMPLICATIONS

The triclosan/copolymer dentifrice produced sustained effects on oral bacteria for 12 hours.

The Actinobacillus actinomycetemcomitans autotransporter adhesin Aae exhibits specificity for buccal epithelial cells from humans and old world primates

Cells of the gram-negative periodontopathogen Actinobacillus actinomycetemcomitans express a surface-exposed, outer membrane autotransporter protein, designated Aae, which has been implicated in epithelial cell binding. We constructed a mutant strain of A. actinomycetemcomitans that contained a transposon insertion in the Aae structural gene (aae) and tested the mutant to determine its ability to bind to buccal epithelial cells (BECs) isolated from healthy volunteers. Significantly fewer mutant cells than wild-type cells bound to BECs. A broad-host-range plasmid that contained an intact aae gene driven by a heterologous tac promoter restored the ability of the mutant strain to bind to BECs at wild-type levels. This plasmid also conferred upon Escherichia coli the ability to express the Aae protein on its surface and to bind to human BECs. Aae-expressing E. coli also bound to BECs isolated from six Old World primates but not to BECs isolated from four New World primates or nine other nonprimate mammals, as well as to human gingival epithelial cells but not to human pharyngeal, palatal, tongue, bronchial, or cervical epithelial cells. Our findings indicate that Aae mediates binding of A. actinomycetemcomitans to BECs from humans and Old World primates and that this process may contribute to the host range specificity and tissue tropism exhibited by this bacterium.

In vivo antimicrobial effectiveness of an essential oil-containing mouth rinse 12 h after a single use and 14 days' use

OBJECTIVES

Two studies were conducted to determine the antimicrobial effect of rinsing with an essential oil-containing mouth rinse 12 h after a single rinse and 12 h after 2 weeks of twice daily rinsing, during the daytime and overnight.

MATERIALS AND METHODS

These studies utilized a randomized, double-blind, controlled crossover design. Following baseline sampling of bacteria from supragingival plaque and the dorsum of the tongue, subjects began twice-daily rinsing with either an essential oil mouth rinse containing 0.09% zinc chloride (Tartar Control Listerine Antiseptic) or a negative control rinse. Bacterial sampling was repeated 12 h after the first rinse, and again 12 h after the final rinse 14 days later. The sampling schedule was adjusted according to whether the study was investigating daytime or overnight activity. Samples were plated on Schaedlers medium (total anaerobes), Schaedlers Nalidixic/Vancomycin medium (Gram-negative anaerobes), and OOPS medium (volatile sulphur compound (VSC)-producing organisms). Inter-group log10 transformed colony-forming units/ml counts from samples of supragingival plaque and tongue swabs on each of the three media were compared by analysis of covariance.

RESULTS

The mean bacterial counts in subjects using the essential oil mouth rinse were significantly lower (p< or =0.005) than mean counts in subjects using the control rinse in all the comparisons, i.e., tongue and supragingival plaque samples on each of three media at two sampling periods in the daytime and overnight study, respectively. Mean bacterial count percent reductions for plaque samples ranged from 56.3 to 95.3; percent reductions for tongue samples ranged from 61.1 to 96.1. There was a trend to higher reductions after 14 days' rinsing than after the initial rinse.

CONCLUSION

Rinsing with the essential oil mouth rinse can have long-lasting effects in reducing anaerobic bacteria overall as well as Gram-negative anaerobes and VSC-producing bacteria. The significant reductions in numbers of these bacteria produced by the essential oil mouth rinse, both in plaque and on the dorsum of the tongue, can play a key role in explaining the essential oil mouth rinse's effectiveness in reducing supragingival plaque and gingivitis as well as its effectiveness in controlling intrinsic oral malodor over prolonged periods.

Antimicrobial effects of a new therapeutic liquid dentifrice formulation on oral bacteria including odorigenic species

The control of oral malodor is well-recognized in efforts to improve oral health. Antimicrobial formulations can mitigate oral malodor, however, procedures to assess effects on oral bacteria including those implicated in halitosis are unavailable. This investigation examined the antimicrobial effects of a new liquid triclosan/copolymer dentifrice (test) formulation that demonstrated significant inhibition of oral malodor in previous organoleptic clinical studies. Procedures compared antimicrobial effects of the test and control formulations on a range of oral micro-organisms including members implicated in halitosis, substantive antimicrobial effects of formulations with hydroxyapatite as a surrogate for human teeth and ex vivo effects on oral bacteria from human volunteers. With Actinomyces viscosus, as a model system, the test formulation demonstrated a dose-dependent effect. At these concentrations the test formulation provided significant antimicrobial effects on 13 strains of oral bacteria including those implicated in bad breath at selected posttreatment time points. Treatment of hydroxyapatite by the test dentifrice resulted in a significant and substantive antimicrobial effect vs. controls. Oral bacteria from subjects treated ex vivo with the test dentifrice resulted in significant reductions in cultivable oral bacteria and odorigenic bacteria producing hydrogen sulfide. In summary, microbiological methods adapted to study odorigenic bacteria demonstrate the significant antimicrobial effects of the test (triclosan/copolymer) dentifrice with laboratory and clinical strains of oral bacteria implicated in bad breath.

One of two human lactoferrin variants exhibits increased antibacterial and transcriptional activation activities and is associated with localized juvenile periodontitis

The iron-binding protein lactoferrin is a ubiquitous and abundant constituent of human exocrine secretions. Lactoferrin inhibits bacterial growth by sequestering essential iron and also exhibits non-iron-dependent antibacterial, antifungal, antiviral, antitumor, anti-inflammatory, and immunoregulatory activities. All of these non-iron-dependent activities are mediated by the highly charged N terminus of lactoferrin. In this study we characterized a Lys/Arg polymorphism at position 29 in the N-terminal region of human lactoferrin that results from a single nucleotide polymorphism in exon 1 of the human lactoferrin gene. We expressed cDNAs encoding both lactoferrin variants in insect cells and purified the two proteins by ion exchange chromatography. The two lactoferrin variants exhibited nearly identical iron-binding and iron-releasing activities and equivalent bactericidal activities against a strain of the gram-negative bacterium Actinobacillus actinomycetemcomitans. When tested against the gram-positive species Streptococcus mutans and Streptococcus mitis, however, lactoferrin containing Lys at position 29 exhibited significantly greater bactericidal activity than did lactoferrin containing Arg. In addition, the Lys-containing lactoferrin stimulated bovine tracheal epithelial cells to synthesize much higher levels of tracheal antimicrobial peptide mRNA than did the Arg-containing variant. A genotyping assay that distinguished between the two alleles based on a polymorphic EarI restriction site showed that the Lys and Arg alleles had frequencies of 24% and 76%, respectively, among 17 healthy human subjects, and 72% and 28%, respectively, among nine patients with localized juvenile periodontitis. Our findings suggest that these two lactoferrin variants are functionally different and that these differences may contribute to the pathogenesis of localized juvenile periodontitis.

The effects of a new therapeutic triclosan/copolymer/sodium-fluoride dentifrice on oral bacteria, including odorigenic species

This investigation examined the in vitro and ex vivo antimicrobial effects of a new dentifrice, Colgate Total Advanced Fresh, formulated with triclosan/copolymer/sodium fluoride, on oral bacteria, including those odorigenic bacteria implicated in bad breath. The effects of Colgate Total Advanced Fresh were compared to commercially available fluoride dentifrices that served as controls. Three experimental approaches were undertaken for these studies. In the first approach, the dentifrice formulations were tested in vitro against 13 species of oral bacteria implicated in bad breath. The second approach examined the antimicrobial activity derived from dentifrice that was adsorbed to and released from hydroxyapatite disks. In this approach, dentifrice-treated hydroxyapatite disks were immersed in a suspension of bacteria, and reduction in bacterial viability from the release of bioactive agents from hydroxyapatite was determined. The third approach examined the effect of treating bacteria immediately after their removal from the oral cavity of 11 adult human volunteers. This ex vivo study examined the viability of cultivable oral bacteria after dentifrice treatment for 2 minutes. Antimicrobial effects were determined by plating Colgate Total Advanced Fresh and control-dentifrice-treated samples on enriched media (for all cultivable oral bacteria) and indicator media (for hydrogen-sulfide-producing organisms), respectively. Results indicated that the antimicrobial effects of Colgate Total Advanced Fresh were significantly greater than either of the other dentifrices for all 13 oral odorigenic bacterial strains tested in vitro (P < or = 0.05). In the second approach, Colgate Total Advanced Fresh-treated hydroxyapatite disks were significantly more active in reducing bacterial growth than the other dentifrices tested (P < or = 0.05). Finally, ex vivo treatment of oral bacteria with Colgate Total Advanced Fresh demonstrated a 90.9% reduction of all oral cultivable bacteria and a 91.5% reduction of oral bacteria producing hydrogen sulfide compared with the control dentifrice. In conclusion, these results, taken together with the significant reductions in clinical malodor scores by Colgate Total Advanced Fresh demonstrated in organoleptic studies, strongly suggest that this dentifrice kills the bacteria that are implicated in the cause of bad breath.

Tight-adherence genes of Actinobacillus actinomycetemcomitans are required for virulence in a rat model

Actinobacillus actinomycetemcomitans is a Gram-negative coccobacillus that has been associated with localized aggressive periodontitis and infections of the heart, brain, and urinary tract. Wild-type clinical isolates have the remarkable ability to adhere tenaciously and nonspecifically to solid surfaces such as glass, plastic, and hydroxyapatite. Adherence by A. actinomycetemcomitans is mediated by the tight-adherence (tad) gene locus, which consists of 14 genes (flp-1-flp-2-tadV-rcpCAB-tadZABCDEFG). All but 2 of the genes have been shown to be required for the secretion and assembly of long, bundled Flp1 fibrils. To test whether the tad locus is required for colonization and disease, we developed a rat model for periodontal disease. To mimic the natural route of infection, Sprague-Dawley rats were inoculated orally by adding bacteria directly to their food for 8 days. After inoculation with wild-type or mutant strains defective in adherence (flp-1 and tadA), the rats were assessed for colonization of the oral cavity and pathogenesis. Wild-type A. actinomycetemcomitans was able to colonize and persist for at least 12 weeks in the oral cavity, elicit a humoral immune response, and cause significant bone loss in rats. In contrast, rats fed flp-1 or tadA mutant strains showed no bone loss and their immune responses were indistinguishable from those of the uninoculated controls. These results demonstrate the critical importance of the tad locus in the colonization and pathogenesis of A. actinomycetemcomitans.

Lactoferrin iron levels are reduced in saliva of patients with localized aggressive periodontitis

BACKGROUND

Actinobacillus actinomycetemcomitans (Aa) is associated with localized aggressive periodontal disease in juveniles (LAgP). Lactoferrin (LF) is an iron-binding salivary protein that has been shown to kill Aa in its iron-free form (apo) and reduce binding to host cells in its iron-saturated form (halo). However, recent in vitro studies show that LF does not kill clinical isolates of Aa, and LF with reduced levels of bound iron does not interfere with its attachment. These findings suggest that colonization of Aa may occur more readily in an environment containing LF with low iron levels. The purpose of this study was to examine the relationship of LF iron levels in saliva of LAgP patients as compared to their age-, gender-, and race-matched controls.

METHODS

Whole and parotid saliva was collected from LAgP patients and matched controls. Micrograms of LF/mg of protein as well as nanograms of iron/micrograms of LF were determined. Iron binding was determined in parotid saliva by addition of nonlabeled and 59Fe labeled iron.

RESULTS

LAgP patients' whole saliva had higher LF levels than controls, but their LF contained less iron (P < or =0.005). No iron was found in LF from parotid saliva in either group. When iron was added to parotid saliva, the LAgP saliva bound 20 to 30 times less iron than controls (P< or =0.001). Finally, LF was identified as the major iron-binding protein in parotid saliva by 59Fe autoradiography and Western blotting.

CONCLUSIONS

This study shows that the level of bound iron in LF is significantly reduced in LAgP patients compared to controls. These data suggest that LF from LAgP patients has a reduced capacity to bind iron and that LF iron levels may play an important role in Aa-induced LAgP.

Lactoferrin iron levels affect attachment of Actinobacillus actinomycetemcomitans to buccal epithelial cells

BACKGROUND

Prior reports have suggested that the iron-binding protein lactoferrin (LF) may either kill Actinobacillus actinomycetemcomitans (Aa) or interfere with its binding to host cells. Other studies have indicated that the degree of iron saturation of LF might play a role in these interactions. However, these studies utilized strains that had lost critical attachment characteristics found in well-preserved clinical isolates of Aa. The purpose of this work was to study the effect of LF iron levels on survival and attachment of well-preserved clinical isolates of Aa.

METHODS

LF containing 0%, 30%, and 100% iron saturation was tested for its ability to kill clinical isolates of Aa and to inhibit their binding to buccal epithelial cells (BECs).

RESULTS

Neither iron-free LF (apo-LF) nor iron-saturated LF killed Aa clinical isolates. Increasing the iron saturation of LF resulted in an increased inhibition of Aa binding to BECs (P < or =0.005). This effect was consistent for the 3 clinical isolates tested. Pretreatment of Aa with iron-saturated LF reduced binding to BECs by 58%, 61.8%, and 64.2%, respectively, for each of the 3 clinical strains tested (P < or =0.005). Pretreatment of Aa strains with apo-LF, iron alone, or bovine serum albumin had no effect on binding. Pretreatment of BECs with LF (either apo-LF or iron-containing LF) had no influence on Aa binding.

CONCLUSIONS

These results indicate that reduction in binding of Aa to epithelial cells is maximized by pretreatment of Aa cells with iron-saturated lactoferrin. These in vitro results suggest that patients with lactoferrin containing lowered levels of iron would be more susceptible to Aa colonization.

Population structure and genetic diversity of Actinobacillus actinomycetemcomitans strains isolated from localized juvenile periodontitis patients

The phylogeny of 20 Actinobacillus actinomycetemcomitans strains isolated from patients with localized juvenile periodontitis (LJP) was investigated by using partial sequence analysis of 16S rRNA genes, arbitrarily primed PCR (AP-PCR), and four additional PCR assays that amplified polymorphic regions in the leukotoxin (lkt), cytolethal distending toxin (cdt), major fimbrial subunit (flp-1), and serotype-specific O polysaccharide gene clusters. Our analysis also included four strains isolated from healthy subjects and nine reference strains. We found that A. actinomycetemcomitans strains comprised three major phylogenetic lineages. One lineage consisted of serotype b strains, a second lineage consisted of serotype c strains, and a third lineage consisted of serotype a, d, e, and f strains. 16S rRNA sequences within each lineage were highly conserved (<1% base substitutions), whereas sequences between lineages were exceptionally divergent (1.9 to 5.0% substitutions). Two strains exhibited 16S rRNA sequences that were even more distantly related to those of the three major lineages (2.7 to 6.7% substitutions), indicating that additional minor lineages or variants exist. The distribution of 16S rRNA sequences and lkt, cdt, flp-1, and AP-PCR genotypes was consistent with a clonal population structure, with little evidence of assortative recombination between strains of different serotypes. Strains from all three major lineages were recovered from LJP patients, suggesting that phylogenetically diverse strains of A. actinomycetemcomitans carry pathogenic potential.

Colonization and persistence of rough and smooth colony variants of Actinobacillus actinomycetemcomitans in the mouths of rats

Fresh isolates of Actinobacillus actinomycetemcomitans (Aa) bind avidly to surfaces in vitro, but existing in vivo studies of the adherence of Aa are limited. This study had two goals: (1) to compare the oral colonization of two isogenic strains of Aa-CU1010, a clinical isolate that expresses the adherent phenotype, and CU1012, a minimally adherent laboratory variant-and (2) to check for phenotypic reversion of these strains in a clinical setting. Rifampicin-resistant strains, developed for tracking in Sprague-Dawley rats, were tested in vitro to determine their stability and binding. In study 1, after antibiotic suppression, six rats (group I) received CU1010 in their feed. The eight rats in group II received CU1012 in their feed and four were supplemented by oral swabbing and four by gastric gavage. Group III consisted of three sham-inoculated controls. All rats were inoculated for 4 days. Microbiological data were collected at 1, 4 and 8 weeks after inoculation. Supporting data were supplied by antibody titres and clinical measures of alveolar bone loss. Study 2 consisted of six rats in each of three groups as above, but tagged strains of Aa were delivered by food alone. At all time-points in both studies, Aa was absent before inoculation and controls had no Aa or antibody to Aa. In study 1, all six rats in group I yielded positive cultures for Aa at 8 weeks. In group II, five of eight had positive cultures for Aa at 1 week, two of eight at 4 weeks and none had Aa at 8 weeks (P < or =0.001). All six rats in group I had serum anti-Aa titres compared to group II, where titres were seen in four of eight rats (P < or =0.015). In vitro data paralleled those found in vivo. No phenotypic reversion of either strain was seen in vivo. In study 2, four of six rats in group I showed Aa and had titres to Aa, while no other animals showed Aa at any time. The model provides convincing evidence that, unlike laboratory variants, clinical isolates colonize, persist and integrate into an already established, albeit reduced, econiche.

Structural and genetic analyses of O polysaccharide from Actinobacillus actinomycetemcomitans serotype f

The oral bacterium Actinobacillus actinomycetemcomitans is implicated as a causative agent of localized juvenile periodontitis (LJP). A. actinomycetemcomitans is classified into five serotypes (a to e) corresponding to five structurally and antigenically distinct O polysaccharide (O-PS) components of their respective lipopolysaccharide molecules. Serotype b has been reported to be the dominant serotype isolated from LJP patients. We determined the lipopolysaccharide O-PS structure from A. actinomycetemcomitans CU1000, a strain isolated from a 13-year-old African-American female with LJP which had previously been classified as serotype b. The O-PS of strain CU1000 consisted of a trisaccharide repeating unit composed of L-rhamnose and 2-acetamido-2-deoxy-D-galactose (molar ratio, 2:1) with the structure -->2)-alpha-L-Rhap-(1-3)-2-O-(beta-D-GalpNAc)-alpha-L-Rhap-(1-->* O-PS from strain CU1000 was structurally and antigenically distinct from the O-PS molecules of the five known A. actinomycetemcomitans serotypes. Strain CU1000 was mutagenized with transposon IS903phikan, and three mutants that were deficient in O-PS synthesis were isolated. All three transposon insertions mapped to a single 1-kb region on the chromosome. The DNA sequence of a 13.1-kb region surrounding these transposon insertions contained a cluster of 14 open reading frames that was homologous to gene clusters responsible for the synthesis of A. actinomycetemcomitans serotype b, c, and e O-PS antigens. The CU1000 gene cluster contained two genes that were not present in serotype-specific O-PS antigen clusters of the other five known A. actinomycetemcomitans serotypes. These data indicate that strain CU1000 should be assigned to a new A. actinomycetemcomitans serotype, designated serotype f. A PCR assay using serotype-specific PCR primers showed that 3 out of 20 LJP patients surveyed (15%) harbored A. actinomycetemcomitans strains carrying the serotype f gene cluster. The finding of an A. actinomycetemcomitans serotype showing serological cross-reactivity with anti-serotype b-specific antiserum suggests that a reevaluation of strains previously classified as serotype b may be warranted.

Comparative antimicrobial activities of antiseptic mouthrinses against isogenic planktonic and biofilm forms of Actinobacillus actinomycetemcomitans

BACKGROUND

Bacteria contained in biofilms have been shown to have a decreased susceptibility to antimicrobial agents compared to those in planktonic form. Thus, in vitro biofilm models have been developed for screening oral antimicrobial formulations in an effort to produce findings more predictive of clinical activity. This study compared the antimicrobial activity of three mouthrinse formulations when tested against isogenic strains of Actinobacillus actinomycetemcomitans (Aa), one of which was a clinical isolate which forms tenacious biofilms in vitro and the other of which was a spontaneous variant which always grows planktonically.

METHOD

Biofilm-forming Aa strains CU1000 and NJ4300, obtained as clinical isolates, and their respective spontaneous planktonic variants, CU1060 and NJ4350, were grown under standard laboratory conditions and exposed for 15 s to either a negative control (phosphate buffered saline [PBS]), an essential-oil containing mouthrinse (Listerine Antiseptic [LA]), an amine fluoride/stannous fluoride-containing mouthrinse (Meridol [M]), or a triclosan and PVM/MA copolymer-containing mouthrinse (Plax [P]). The cells were then washed, serially diluted, plated, and incubated for enumeration of viable bacteria. Colony-forming units (CFU)/ml were log10 transformed and the mouthrinse groups were compared to the PBS group using analysis of variance.

RESULTS

All 3 mouthrinses produced statisically significant 99.99% reductions (p< or =0.0001) in both planktonic strains compared to the PBS control. Effects on the biofilm forms of the organisms were more variable. Exposure to LA produced statistically significant (p< or =0.0001) reductions in strains CU1000 and NJ4300 of 98.20% and 96.47%, respectively, compared to PBS. M and P produced much smaller reductions which were not statistically significant.

CONCLUSIONS

The results of this study, in which antimicrobial mouthrinses were tested against biofilm-forming and planktonic strains of the same organism, provide a clear demonstration of the resistance to antimicrobial agents conferred by biofilm formation and provide additional support for employing tests using biofilms to more accurately assess the relative activities of antiplaque agents in vitro.

A model for clinical evaluation of anti-microbial effects of agents on plaque colonization

PURPOSE

To evaluate a new improved method of microbial analysis in a cross-over clinical study by investigating the efficacy of a single application of an essential oil-containing (EOC) dentifrice as compared to its vehicle control (VC) over a 6-hr period.

MATERIALS AND METHODS

Acrylic stents with retention areas for 7, 3 mm x 3 mm hydroxyapatite (HA) squares were fabricated for 12 subjects. 30 min following stent placement, one HA square was removed and sampled for viable microflora. After stent replacement, subjects were assigned either the EOC dentifrice or its VC and brushed under supervision for 1 min. Stents remained in place for the next 6 hrs. A HA square was removed at hourly intervals for 6 hrs following brushing. The microflora was analyzed for total anaerobes on Schaedler's media, for total gram-negative anaerobes on Schaedler-NV selective media, and for total Fusobacterium species on CVE selective media. Plates were incubated anaerobically at 37 degrees C for 2-5 days. Colony forming units were calculated. For each time point, pairwise t-tests were performed using the adjusted means and the pooled error term from the analysis of variance (ANOVA).

RESULTS

Treatment with the EOC dentifrice resulted in a statistically reduced plaque growth. Differences were seen as reductions in: (1) total gram-negative anaerobes seen from 1-6 hrs (P < or = 0.011), (2) total anaerobic bacteria which achieved significance at 3 hrs and continued through 6 hrs (P < or = 0.005), and (3) Fusobacterium species as seen from 4-6 hrs (P < or = 0.002).

Proximal caries in juvenile periodontitis patients

BACKGROUND

Caries is recognized as the prevalent proximal dental disease in adolescents, while proximal bone loss is minimal to non-existent in this population. Adolescents demonstrating an inverse disease pattern, i.e., minimal caries and active periodontitis, could provide powerful clues with regard to both diseases. However, data are inconsistent. This study was designed to clarify this relationship by comparing proximal caries prevalence in a juvenile periodontitis (JP) group to a matched non-periodontally diseased control group.

METHODS

Two groups (cases [JPs] and control patients [CPs]) were matched for age, sex, and race and evaluated for decayed, missing, filled teeth and surfaces (DMFS) by radiographic analysis. Statistical analysis was performed by ANOVA and Student t test. The study consisted of four phases. Phase I was based on data from a previous study that failed to include race in the analysis. Thus, the original 23 JP patients (mostly African-Americans from New York City) were rematched for race as well as sex and age with CPs from Newark, NJ. The effect of water fluoridation (found in NYC) was evaluated in Phase II by matching the 23 original CPs (mostly Caucasian from NYC) with 23 CPs from NJ. Since differences were seen, we rematched our original JPs from NYC with a new set of race-matched CPs from NYC (Phase III). Finally, 13 JP patients from the University of Medicine and Dentistry of New Jersey (UMDNJ) were matched with CPs from NJ (Phase IV).

RESULTS

Phase I and III indicated that JP patients had significantly less proximal caries than their matched CPs (P < or =0.05). Phase II confirmed the role of fluoride in caries reduction. Phase IV (NJ sample) supported our previous data and suggested that JP patients had less proximal caries than CPs (P < or =0.05).

CONCLUSIONS

JP patients had significantly less proximal caries than their matched CPs when groups were balanced and radiographic evaluations were performed. In-depth studies of JP patients could provide important clues about both caries and periodontal disease etiology and pathogenesis.

Effect of an essential oil-containing antiseptic mouthrinse on plaque and salivary Streptococcus mutans levels

BACKGROUND

Clinical studies in which antimicrobial mouthrinses were shown to have significant antiplaque activity most frequently have used gingivitis as the clinically relevant endpoint. However, there is evidence to suggest that mouthrinses containing active agents effective against Streptococcus mutans, such as chlorhexidine, may also have a role in inhibiting dental caries. This clinical study was conducted to determine the effect of 2x-daily rinsing with an essential oil-containing antiseptic mouthrinse (Listerine Antiseptic) on levels of recoverable S. mutans and total streptococci in supragingival interproximal plaque and in saliva. Additionally, a follow-up in vitro study is reported which determined whether a differential susceptibility to the antiseptic mouthrinse exists among different strains of streptococci.

METHOD

Following baseline saliva and plaque sampling for quantification of recoverable S. mutans and total streptococci, 29 qualifying subjects were randomly assigned either the essential oil mouthrinse or a sterile water control. They rinsed with 20 ml for 30s 2 x daily for 11 days and once on the 12th day, in addition to their usual oral hygiene procedures. On day 12, saliva and plaque samples were again collected and microbiological quantification performed. The procedures were repeated with the alternate rinse after a 1-week washout period.

RESULTS

The essential oil mouthrinse produced respective reductions of 69.9% and 75.4% in total recoverable streptococci and in S. mutans in plaque, and corresponding reductions of 50.8% and 39.2% in saliva. The in vitro study revealed that streptococci from the mutans group were more susceptible to the bactericidal activity of the essential oil mouthrinse than streptococci from the mitis group.

CONCLUSIONS

As antimicrobial mouthrinses are most frequently recommended to patients whose mechanical oral hygiene procedures are not adequate for the control of supragingival plaque and gingivitis, this study provides an additional rationale for the inclusion of the essential-oil mouthrinse as an adjunct to daily oral hygiene procedures.

Tenacious adhesion of Actinobacillus actinomycetemcomitans strain CU1000 to salivary-coated hydroxyapatite

Adherence of Actinobacillus actinomycetemcomitans to hard-tissue surfaces was evaluated by comparing a phenotypically stable, well-maintained clinical isolate (strain CU1000) to Streptococcus gordonii G9B, an extensively studied oral-colonizing bacterium. Standard innocula of radiolabelled bacteria were added to saliva-coated hydroxyapatite (SHA) and the ratio of bound to unbound cells counted. Several other clinical isolates as well as laboratory strain Y4 were studied. In other experiments, cell detachment from SHA was compared in static and shaking vessels to calculate controlled desorption of cells over time. A sonic-displacement assay was used to measure avidity of binding to HA and SHA. To better define the attachment properties of CU1000, bacteria were treated with a variety of agents including detergents, salts and enzymes before or after incubation with SHA. Results indicated that CU1000 bound better than G9B (a minimum of 10-fold greater; p < or = 0.05) and did not desorb from SHA, while G9B desorbed to equilibrium in 4 h. Furthermore, Langmuir isotherm calculations indicated that, unlike G9B, CU1000 did not follow second-order adsorption kinetics and thus did not achieve saturation. In addition, of the agents tested only periodate reduced attachment and resulted in detachment of CU1000 from surfaces. These experiments suggest that clinical isolates of A. actinomycetemcomitans possess unique binding properties that promote adsorption to and impede desorption from SHA. The characteristics described for the actinobacillus in this study have been previously underestimated, appear to be mediated by glycoconjugates, and may resemble attachment described for several biofilm-forming, non-oral pathogens.

Phenotypic variation in Actinobacillus actinomycetemcomitans during laboratory growth: implications for virulence

This study examined alteration of specific virulence traits associated with phenotypic changes seen when a low-passage disease-associated and well maintained parent strain of Actinobacillus actinomycetemcomitans was compared to a laboratory-grown spontaneous variant/mutant. Clinical isolates of A. actinomycetemcomitans recovered from periodontitis patients typically grow as rough, adherent colonies on primary culture but undergo transformation to smooth, non-adherent colonies following repeated passage in vitro. The relationship of these phenotypic changes to the virulence of the organism or to the processes that underlie this transformation are not understood. A fresh clinical isolate, designated strain CU1000, was obtained from the first molar site of a patient with classical signs of localized juvenile periodontitis and used as the parent strain to study virulence-related phenotypes. Following several passages of CU1000 on selective agar, a spontaneous variant that demonstrated smooth, opaque, non-adherent colonies was isolated and designated strain CU1060. This study compared the properties of these two strains with respect to colony morphology, autoaggregation, surface appendages, adherence to saliva-coated hydroxyapatite (SHA), LPS chemotype and activity, induction of fibroblast proteinase activity and antigenic properties. CU1000 demonstrated rough, raised, star-positive colonies which upon electron microscopic examination revealed the presence of large, flexible, bundled fibrils. In addition, CU1000 showed adherence to SHA, several unique protein antigens and elevated endotoxin and fibroblast proteinase activity. CU1060, on the other hand, showed minimal adherence to SHA and fewer reactive proteins compared to the fresh clinical isolates. This strain formed smooth, opaque colonies on agar, showed minimal fibril formation and limited endotoxin and fibroblast-proteinase-inducing activity. These findings demonstrate that clinical isolates of A. actinomycetemcomitans undergo significant virulence-reducing phenotypic alterations during in vitro passage and support the need to study this organism in its clinical form.

Efficacy of a triclosan/NaF dentifrice in the control of plaque and gingivitis and concurrent oral microflora monitoring

PURPOSE

To compare the effect of a dentifrice containing 0.3% triclosan and 1100 ppm fluoride and a control dentifrice containing 1100 ppm fluoride on plaque, gingiva and the oral microflora in a long-term study simulating clinical usage.

MATERIALS AND METHODS

159 subjects entered the clinical study and 80 were randomly selected to participate in the microbiological evaluation. 71 subjects completed the detailed evaluation of the oral microflora after 6 months use. Plaque was collected at baseline, 3 months, and 6 months, and examined by darkfield microscopy, Gram stain, immunofluorescence, and selective and non-selective media. Changes in antimicrobial susceptibilities were determined for the first 6-month period and for 6 months post-therapy for 68 subjects who completed the entire study. Susceptibilities of whole plaque samples and MIC values for two pre-designated common plaque organisms, A. viscosus and V. parvula were performed.

RESULTS

Multivariate ANOVA and non-parametric analyses revealed no statistical differences for any factor tested. No detrimental shifts were found in either; (1) the compositional make up of the normal flora, (2) the periodontopathic or cariogenic flora, or (3) the opportunistic flora in either group of dentifrice users. Both treatments resulted in decreases in Gram positive cocci over time. There was a reduction in spirochetes in the triclosan/fluoride group as compared to the control group. No overgrowth in opportunists, periodontal pathogens, or cariogenic flora was found in either group. No increase in the proportion of the whole plaque flora resistant to triclosan was found nor was an increase in the MIC values of either A. viscosus or V. parvula in either group. Overall, there appeared to be a general decrease in plaque bacteria in both groups over the course of the experiment.

Assessing pre-procedural subgingival irrigation and rinsing with an antiseptic mouthrinse to reduce bacteremia

In this controlled clinical study, the authors examined the effect of subgingival irrigation and rinsing with an antiseptic mouthrinse before ultrasonic scaling of a quadrant containing inflamed gingivae. The results showed that pre-procedural subgingival irrigation and rinsing can significantly reduce the level of bacteremia associated with ultrasonic scaling. These results support the American Heart Association's recommendation of adjunctive subgingival irrigation prior to invasive procedures in patients at risk of developing bacterial endocarditis.

Effects of sublethal exposure to an antiseptic mouthrinse on representative plaque bacteria

Although the mechanism responsible for the clinical antiplaque efficacy of oral antiseptics is generally considered to be primarily one of bactericidal activity, it has been suggested that oral antiseptics may have additional effects on bacteria exposed to sublethal levels. Studies reported herein, investigated the effects of sublethal levels of an essential oil-containing antiseptic mouthrinse (Listerine Antiseptic, Warner-Lambert Co., Morris Plains, NJ) on selected activities of representative plaque microorganisms using in vitro models. These studies demonstrated that sublethal exposure to the tested oral antiseptic can have significant effects in reducing intergeneric coaggregation, increasing bacterial generation time, and extracting endotoxin from Gram-negative bacteria. These in vitro activities can be correlated with features of plaque formation and pathogenicity seen in vivo; however, additional studies will be necessary to confirm that these mechanisms are, in fact, operative clinically.

Prevalence and distribution of bacteriophage phi Aa DNA in strains of Actinobacillus actinomycetemcomitans

phi Aa is a bacteriophage that was originally isolated by induction of a lysogenic strain of the oral bacterium Actinobacillus actinomycetemcomitans. Since the discovery of phage phi Aa, additional phages infecting several other strains of A. actinomycetemcomitans have been identified. To determine the prevalence of phi Aa or phi Aa-related temperate phages in this species, a phi Aa-specific DNA probe was prepared to screen for homologous sequences among 42 strains of A. actinomycetemcomitans. Fourteen (33%) of the 42 strains examined contained DNA sequences that hybridized with the phage phi Aa probe. A bacteriophage designated phi Aa33384 was isolated by induction from one of the strains (ATCC 33384) that contained a sequence that hybridized with the phi Aa probe. The phi Aa probe hybridized with the DNA extracted from bacteriophage phi Aa33384. The distribution of the phage phi Aa sequence among A. actinomycetemcomitans serotypes was 5/13 (38%) of the serotype a strains, 0/16 (0%) of the serotype b strains, and 9/13 (69%) of the serotype c strains. The results of this investigation suggest that the target sequence prepared from the phage phi Aa genome is fairly common in the A. actinomycetemcomitans chromosome, and that the sequence is distributed among the A. actinomycetemcomitans serotypes in a seemingly nonrandom manner.

Reduction of viable bacteria in dental aerosols by preprocedural rinsing with an antiseptic mouthrinse

Two double-blind controlled clinical studies were conducted to determine the efficacy of preprocedural rinsing with Cool Mint Listerine Antiseptic mouthrinse on the level of viable bacteria recovered from dental aerosols when generated immediately after and 40 minutes after rinsing. Eighteen healthy subjects participated in each study. In the first study, following a 24-hour no-oral-hygiene period, subjects received a 10-minute ultrasonic scaling of a randomly chosen half mouth, rinsed with either Cool Mint Listerine or a control, and received an ultrasonic scaling of the remaining half mouth. During each scaling period, aerosolized bacteria were collected on a sterile filter using a modified air-sampling device. The filters were overlaid on culture media, incubated aerobically, and colonies were counted. The second study followed the same basic design except that ultrasonic scaling was done for 5 minutes, and the post-rinsing sampling was performed following a 40-minute simulated dental treatment period. Rinsing with Cool Mint Listerine resulted in a 92.1% reduction in viable bacteria in aerosols generated immediately after rinsing and a 91.3% reduction in aerosols generated 40 minutes after rinsing. These reductions were significantly greater than control (P = 0.0001). These studies suggest that preprocedural rinsing with Cool Mint Listerine Antiseptic may potentially reduce the risk of cross contamination in the dental operatory.

Conjugal transfer of broad-host-range incompatibility group P and Q plasmids from Escherichia coli to Actinobacillus actinomycetemcomitans

The first example of conjugal transfer of DNA from Escherichia coli to the periodontal pathogen Actinobacillus actinomycetemcomitans is presented. Derivatives of the incompatibility group P (IncP) plasmid RK2 successfully transferred from an E. coli donor to an A. actinomycetemcomitans recipient. The resulting A. actinomycetemcomitans transconjugants transferred the plasmids back to E. coli recipients. The IncP transfer functions were also used in trans to mobilize the IncQ plasmid pBK1 from E. coli to A. actinomycetemcomitans. The IncP and IncQ plasmids both transferred into A. actinomycetemcomitans at high frequencies (0.3 to 0.5 transconjugants per donor) and showed no gross deletions, insertions, or rearrangements. Determinations of MICs of various antibiotics for the A. actinomycetemcomitans transconjugant strains demonstrated the expression of ampicillin, chloramphenicol, and kanamycin resistance determinants.

Reducing bacteria in dental aerosols: pre-procedural use of an antiseptic mouthrinse

This study, using a simulated office visit model, showed that the pre-procedural use of an antimicrobial mouthrinse produces a significant reduction in number of viable bacteria in a dental aerosol.

Characterization and physical mapping of the genome of bacteriophage phi Aa from Actinobacillus actinomycetemcomitans

The size, configuration and restriction map of Actinobacillus actinomycetemcomitans bacteriophage phi Aa DNA was determined by means of restriction endonuclease analysis. Digestion of the phi Aa DNA with restriction enzymes Hind III, Eco RI and Sal I produced 6, 5, and 4 fragments, respectively. Based upon the sum of the sizes of the restriction fragments of these enzymes, the DNA was estimated to be 47.2 kilobase pairs in length. A restriction map was constructed using Hind III and Sal I. Incubation with exonuclease Bal 31 for increasing lengths of time resulted in progressive hydrolysis of the DNA, as expected for a linear molecule. No sub-molar fragments or diffuse bands were observed in the agarose gels of the restriction endonuclease digests of the phi Aa DNA. Attempts at ligating the ends of the DNA were consistently unsuccessful. Therefore, we found no evidence for cohesive ends, a circular permutation of the genome or for headful packaging mechanism from a concatameric DNA precursor.

Endotoxin levels in periodontally healthy and diseased sites: correlation with levels of gram-negative bacteria

This study investigated the correlation between endotoxin levels and the percentage of Gram-negative bacteria in healthy sites and in periodontitis sites. Twelve healthy adults participated. Each subject provided 3 periodontitis sites with 5 to 8 mm probing depths that bled on gentle probing and 3 healthy sites with sulcus depths of 1 to 3 mm that did not bleed. Clinical examinations and sterile paper point sampling of all study sites were conducted on days 0, 7, and 14, and site-specific endotoxin levels and percentage of Gram-negative bacteria were determined. There were significant differences in both endotoxin levels and percentage Gram-negative bacteria between healthy and periodontitis sites across all 3 sampling periods, but no difference across sampling periods in the healthy sites and the periodontitis sites, respectively. Correlation coefficients revealed a high degree of correlation between site-specific endotoxin levels and percentage of Gram-negative organisms. Using a sample dilution of 1 x 10(4), endotoxin levels differentiated healthy from periodontitis sites with a specificity of approximately 91% and a sensitivity of approximately 90%.

Efficacy of preprocedural rinsing with an antiseptic in reducing viable bacteria in dental aerosols

This double-blind, controlled, cross-over, clinical study evaluated the effect of preprocedural rinsing with an antiseptic mouthrinse on the level of recoverable viable bacteria in an aerosol generated during a typical dental procedure. Eighteen subjects participated. Following 24 hours of abstention from all oral hygiene procedures, subjects received a 10-minute ultrasonic scaling of a randomly selected one-half of their mouth which served as the unrinsed control. They were then randomly assigned either antiseptic mouthwash or a control rinse and rinsed with 20 ml for 30 seconds, after which the remaining half mouth (experimental side) was scaled ultrasonically for 10 minutes. During each 10-minute scaling period aerosolized bacteria were collected on a sterile filter using a modified vacuum air-sampling device. Microbes captured on the sterile filter were quantitated by overlaying the filters onto trypticase soy agar, incubating the filters aerobically at 37 degrees C for 24 to 72 hours, and counting the resulting colony forming units (CFU). Preliminary experiments had confirmed that neither the collection method nor residual antiseptic mouthwash in the aerosol adversely affected the number of viable bacteria recovered from the filter. Rinsing with the antiseptic mouthwash produced a 94.1% reduction in recoverable CFUs compared to the non-rinsed control, while the control rinse produced a 33.9% reduction. The difference between the mouthwash and control was statistically significant (P < .001). This study indicates that preprocedural rinsing with an antiseptic mouthwash can significantly reduce the microbial content of aerosols generated during ultrasonic scaling and may have potential in-office use as part of an infection control regimen.

Bovine serum eliminates rapid nonspecific toxic reactions during bioassay of stored fish for Clostridium botulinum toxin

When stored fish or some fish products were tested for the presence of Clostridium botulinum toxin, nonspecific toxic reactions in mice often occurred, rendering the bioassay inconclusive. The nonspecific toxic reactions were mediated by the gram-negative microbiota, inherent to the fish, which were the source of lethal, heat-stable endotoxins. The treatment of assay samples with bovine serum eliminated nonspecific reactions through the interaction of constituent serum immunoglobulin M (IgM) with endotoxic material. Removal of IgM from bovine serum through treatment with protein A or concanavalin A resulted in a loss of protective activity.