Bactericidal Effect of Triple Antibiotic Paste against Enterococcus faecalis in Dentinal Tubules: An Ex Vivo Study.

OBJECTIVE: The aim of this study was to investigate the bactericidal effect of various concentrations of triple antibiotic paste (TAP) against Enterococcus faecalis (E. faecalis) in dentinal tubules using a bacterial culture assay and confocal laser scanning microscope (CLSM). METHODS: Ninety human teeth were contaminated with E. faecalis (ATCC 29212) and randomly allocated into 5 groups; the negative control (without TAP), 1 mg/ml, 5 mg/ml, 7.5 mg/ml and 10 mg/ml TAP (n=18). After a 3-week TAP treatment, samples were collected from the root canal space, root dentin at 100-µm and 200-µm depth. The collected samples were subjected to a bacterial culture assay (n=10). Eight roots from each group underwent CLSM analysis to determine the live/dead bacterial cells. RESULTS: The bacterial culture assay results indicated that the negative control samples were all culturable. The number of culture-positive samples decreased after TAP treatment at 1, 5, 7.5 and 10 mg/ml, with 2, 2, 1 and 0 culturable samples, respectively. However, there was no significant difference among the TAP treatments. Surprisingly, the CLSM analysis demonstrated live bacteria in the dentinal tubules in all samples. The negative control had 52.36%+-3.24 live bacteria. TAP treatment at 10 mg/ml had the lowest percentage of live bacterial cells (40.58%+-5.40), followed by 7.5 mg/ml (44.14%+-6.03), 5 mg/ml (46.31%+-5.32) and 1 mg/ml (52.55%+-8.82). The percentage of live cells in the 10 mg/ml, 7.5 mg/ml and 5 mg/ml TAP groups were significantly lower than the 1 mg/ml TAP and negative control groups. CONCLUSION: TAP treatment significantly decreased the percentage of viable E. faecalis cells in the dentinal tubules and its bactericidal effect was dose-dependent.

Effect of brushing on surface roughness, fluoride release, and biofilm formation with different tooth-colored materials.

BACKGROUND/PURPOSE: Tooth brushing, material mechanical ageing procedure, is the most effective way in removing biofilm. The purpose of this study was to investigate the surface roughness, fluoride-release, and S. mutans biofilm formation on various tooth-colored restorative materials before and after brushing. MATERIALS AND METHODS: Discs of materials, a nanocomposite (Filtek Z350XT; CO), a giomer (Beautifil II; GIOMER), a resin-modified glass-ionomer material (Fuji II LC; RMGI), and a conventional glass-ionomer material (Fuji IX GP Extra; GI), were prepared, polished with abrasive discs (SofLex), and divided into brushed and not brushed groups. The surface roughness of specimens was observed using a contact profilometer, fluoride-release was measured using a fluoride-specific ion electrode, and S. mutans biofilm formation, biovolume and live/dead cells, was observed under a confocal laser scanning microscope. RESULTS: Higher roughness was observed on GI and RMGI than on CO and GIOMER. Brushing had no effect on the roughness. The fluoride-release of GI and RMGI was higher than that of GIOMER. The fluoride-release decreased after brushing in all materials. The biovolume of S. mutans was not significantly different between GIOMER, RMGI and GI, while CO showed the highest. Brushing resulted in a higher biovolume for all materials, except CO, which showed no change. After brushing, all the tested materials demonstrated identical biovolumes. There were no significant differences in live/dead cells among all groups. CONCLUSION: Brushing demonstrated a negative effect on the fluoride-release and biovolume of S. mutans biofilms for all tested materials except nanocomposites.

Buffering capacity and antibacterial properties among bioactive glass-containing orthodontic adhesives.

This study was to evaluate the acid-buffering capacity and antibacterial properties of orthodontic adhesives containing bioactive glasses (BAGs) (45S5, 45S5F, S53P4), Hydroxyapatite, beta-tricalcium phosphate, and Canasite. Fillers comprising 15 wt% bioactive glasses, HAp, ß-TCP, and Canasite incorporated with 55 wt% silanated glass were added to a mixture of UDMA/TEGDMA. Acid-buffering capacity was tested by exposing disc-shaped samples of each adhesive to medium of bacteria-produced acids, and pH changes were recorded at 24 and 48 h. Antibacterial properties were assessed by indirect testing by exposing polymerized adhesive samples to a medium and direct testing by immersing the specimens in solutions containing S. mutans and S. sanguinis. A significant buffering capacity was shown by the 45S5, 45S5F and S53P4 BAG adhesives. The antibacterial properties were not significant in all experimental adhesives. Therefore, the experimental orthodontic adhesives containing BAGs demonstrated a significant buffering capacity but did not show significant antibacterial properties against S. mutans and S. sanguinis.

Physicochemical and osteogenic properties of chairside processed tooth derived bone substitute and bone graft materials.

To analyze physicochemical such as surface structures, the crystallinity, chemical composition, calcium phosphate dissolution and osteogenic properties of tooth derived bone substitute (TDBS) processed chair-side and other grafting materials. The number of anaerobic and facultative anaerobic bacteria in the supernatant of processed TDBS was determined. Human osteoblasts were co-cultured with TDBS or allograft in transwell system to examine cell migration. BMP2 released from TDBS was measured by ELISA. TDBS had high crystallinity similar to BoneCeramic while it had a broad pattern to ramus bone, OraGRAFT, and Bio-Oss. TDBS contained carbon, calcium, oxygen, phosphate, sodium and magnesium elements like others. Calcium/phosphorus dissolution of TDBS show closely related to those of mandibular ramus bone and OraGRAFT. In addition, microbial decontamination of TDBS by the chemical processing revealed a hundred percent efficacy. The osteoconductive and osteoinductive properties demonstrated in the TDBS processed chairside suggested the potential of an alternative for bone grafting material.

In vitro evaluation of local antibiotic delivery via fibrin hydrogel.

BACKGROUND/PURPOSE: Fibrin hydrogel is commonly used as hemostatic agent and scaffold but it is questionable for carrying antibiotics. Thus, this study aimed to investigate whether the fibrin hydrogel can be used to deliver the optimal concentration of ciprofloxacin against oral pathogen. MATERIALS AND METHODS: The optimal concentration of ciprofloxacin was investigated from broth microdilution technique against three common oral bacteria. Ten times the bactericidal concentration of ciprofloxacin loaded to 0.4% fibrin hydrogel was observed by using a confocal laser scanning microscope and then was left in tris-buffer saline solution (TBS) for 0, 1, 12, 24, 72 and 168 h in parallel with the control group of ciprofloxacin loaded to 0.5% alginate hydrogel and ciprofloxacin solution. Spectrophotometer was used to analyze the accumulated drug release from the collected TBS, of which the measurement method was calibrated. The efficacy of the released ciprofloxacin was tested using an agar well diffusion assay. The inhibition zone of the released ciprofloxacin from fibrin hydrogel was statistically compared with 150 and 1500 µg/ml ciprofloxacin solution, while non-loaded fibrin hydrogel served as the control. RESULTS: The results revealed that minimum inhibitory concentration was 1-2 µg/ml and minimum bactericidal concentration was 4-15 µg/ml. The fibrin hydrogel gradually released ciprofloxacin until 168 h while the alginate hydrogel immediately liberated all the loaded ciprofloxacin within an hour. The agar well diffusion significantly showed greater clear zone in fibrin hydrogel loaded ciprofloxacin compared to non-loaded fibrin hydrogel but not with ciprofloxacin in TBS. CONCLUSION: The results suggested that fibrin hydrogel can be used for local ciprofloxacin delivery without interfering the efficacy of ciprofloxacin.

Bacterial leakage and marginal adaptation of various bioceramics as apical plug in open apex model.

AIM: The aim of the present study was to investigate bacterial leakage and marginal adaptation of bioceramic apical plugs. METHODS: Extracted human mandibular premolars were prepared to simulate open apex using No. 4 Peeso reamer in retrograde direction. In total, 150 specimens were divided into 10 groups by obturation with five bioceramics in two thicknesses. Groups 1, 3, 5, 7, and 9 were obturated with ProRootMTA, Biodentine, TotalFill BC RRM paste, TotalFill BC RRM putty, and RetroMTA at 3 mm, and groups 2, 4, 6, 8, and 10 were obturated with the same materials at 4 mm. Ten specimens in each group were evaluated for bacterial leakage of Enterococcus faecalis for 75 days. Five specimens from each group were sectioned to investigate the gap area under scanning electron microscope. RESULTS: The 3- and 4-mm Biodentine and TotalFill BC RRM putty groups and the 4-mm ProRootMTA group exhibited less bacterial leakage and lower mean percentage of gap area than those of the other groups. TotalFill BC RRM paste showed the highest leakage for both the 3- and 4-mm groups. CONCLUSION: The 3- and 4-mm Biodentine and TotalFill BC RRM putty groups and the 4-mm ProRootMTA group exhibited the best sealing ability and marginal adaptation of apical plugs.

The efficiency of topical anesthetics as antimicrobial agents: A review of use in dentistry.

Topical anesthetics are commonly used in oral & maxillofacial surgery to control pain in the oral cavity mucosa before local anesthetic injection. These anesthetic agents come in many forms, developed for different usages, to minimize adverse reactions, and for optimal anesthetic efficiency. Earlier studies have revealed that these agents may also limit the growth of microorganisms in the area of anesthetic application. Many topical anesthetic agents show different levels of antimicrobial activity against various bacterial strains and Candida. The dosage of local anesthetic agent used in some clinical preparations is too low to show a significant effect on microbial activity. Efficiency of antimicrobial activity depends on the local anesthetic agent's properties of diffusion within the bloodstream and binding efficiency with cytoplasmic membrane, which is followed by disruption of the bacterial cell membrane. The antimicrobial properties of these agents may extend their usage in patients to both control pain and infection. To develop the topical local anesthetic optimal usage and antimicrobial effect, a collaborating antiseptic agent may be used to benefit the local anesthetic. However, more research is required regarding minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of topical local anesthetic agents with drug interaction between anesthetics and antiseptic agents.

Bacterial leakage and micro-computed tomography evaluation in round-shaped canals obturated with bioceramic cone and sealer using matched single cone technique.

OBJECTIVES: To evaluate sealing ability of root canals obturated with bioceramic-impregnated gutta percha cone (BCC) or gutta percha (GP), with bioceramic sealer (BCS) or AH Plus (AH; Dentsply-Maillefer), in roundly-prepared canals using matched single-cone technique, based on bacterial leakage test, and to analyze obturation quality using micro-computed tomography (CT) analysis. MATERIALS AND METHODS: Ninety-two distobuccal roots of maxillary molars were prepared using nickel-titanium files to apical size 40/0.06. The roots were divided into 4 groups (n = 20) that were obturated with a master cone and sealer: GP/AH, BCC/AH, GP/BCS, and BCC/BCS. Bacterial leakage model using Enterococcus faecalis was used to evaluate sealing ability for 60-day period. Obturated samples from each group (n = 4) were analyzed using micro-CT. RESULTS: All groups showed bacterial leakage at 20%-45% of samples with mean leakage times of 42-52 days. There were no significant differences in bacterial leakage among the groups. Micro-CT showed minimal gaps and voids in all groups at less than 1%. CONCLUSIONS: In roundly-prepared canals, the single cone obturation with BCC/BCS was comparable to GP/AH for bacterial leakage at 60 days.

Induction of inducible nitric oxide synthase (iNOS) in Porphyromonas gingivalis LPS-treated mouse macrophage cell line (RAW264.7) requires Toll-like receptor 9.

OBJECTIVE: The aim of this study is to investigate the involvement of TLR9 in the regulation of iNOS expression and nitric oxide (NO) production in Porphyromonas gingivalis LPS-treated mouse macrophages. METHODS: Mouse macrophage cell line (RAW264.7) was transfected with siRNAs against TLR9 and then stimulated with P. gingivalis LPS. At indicated time points, the activated cells were lysed. Gene and protein expression of iNOS were determined by RT-PCR and immunoblotting, respectively. The level of nitric oxide (NO) production in the supernatant of the activated cells was determined by Griess reaction assay. RESULTS AND CONCLUSION: Depletion of TLR9 in mouse macrophages demonstrated the markedly decreased iNOS gene and protein expression by P. gingivalis LPS compared to those of the wild-type or control siRNA transfected cells. In consistent with these results, the level of NO secretion was also significantly diminished in TLR9-depleted cells after challenged with P. gingivalis LPS. These results indicate that TLR9 involves in the regulation of the iNOS expression and the NO secretion in P. gingivalis LPS-treated macrophages.

Hypochlorite solution for root canal irrigation that lacks a chlorinated odor.

OBJECTIVES: This is an in vitro study to develop a formulation of a hypochlorite solution for root canal irrigation that lacks a chlorinated odor. The antibacterial effect, tissue dissolution efficacy, and the cytotoxicity of the solution were assessed in cell culture and were compared with those of commercial sodium hypochlorite (NaOCl) solutions. MATERIALS AND METHODS: Trichloroisocyanuric acid (TCA) was used as the source of hypochlorite ions in solution. All required properties of the NaOCl irrigant were evaluated and compared with those of original 2.5% NaOCl solutions currently in use. RESULTS: Our results revealed that a TCA 3.5% + 1/6 Buffer-1 solution passed the short-term stability test. Moreover, no odor of chlorine gas was detected by three independent observers. The hypochlorite ion content and pH were stable over an incubation period of 4 weeks. The new solution did not differ from commercial products in terms of the dissolution property on bovine pulpal tissue (P > 0.05). Moreover, the antibacterial effect of this solution on Enterococcus faecalis did not differ from that of the commercial products (P > 0.05). In addition, our biocompatibility analysis demonstrated no difference among the tested solutions (P > 0.05). CONCLUSIONS: According to the results of all properties tested, TCA 3.5% + 1/6 Buffer-1 could be considered an option for NaOCl irrigation with the benefit of no detectable chlorine odor.

EFFECTS OF SHORT-TERM USE OF XYLITOL CHEWING GUM AND MOLTITOL ORAL SPRAY ON SALIVARY STREPTOCOCCUS MUTANS AND ORAL PLAQUE.

The purpose of this study was to investigate the short-term effects of xylitol chewing gum and maltitol spray on the concentration of salivary mutans streptococci (MS) and on the plaque index. Eighty-one second, third and fourth year dental and dental assistant students with a salivary MS concentration > 103 CFU/ml cultured on mitis salivarius bacitracin (MSB) agar were included in the study. The age range of subjects was 18-23 years. The participants were divided into 3 groups: control, xylitol chewing gum and maltitol spray groups. Each subject brushed their teeth with fluoridated toothpaste (1,000 ppm). Each subject in the xylitol chewing gum group was told to chew 2 pieces, 6 times a day (total xylitol dose=7.3 g/day) for 4 weeks. Each subject in the maltitol spray group was told to spray one puff twice daily (morning and evening) for 4 weeks. A dental examination and saliva samples to determine the salivary MS concentration were collected at baseline and at 2 and 4 weeks after experiment initiation. The nonparametric Mann­Whitney U test was used to analyze differences among groups. The mean ages in the control, xylitol chewing gum and maltitol spray groups were 22±1, 20±1 and 20±1 years, respectively. The mean MS concentrations at the beginning of the study and after 2 weeks in the control, and xylitol chewing gum and moltitol oral spray groups were not significantly different from each other. There was a significantly lower MS concentration in the moltitol oral spray group than in the control group by 4 weeks (p=0.045) but no significant difference between the control group and the xylitol gum group by 4 weeks. There were no significant differences in the mean plaque index at baseline among the control group, the xylitol chewing gum group and the moltitol oral spray group. The plaque index was significantly lower in the xylitol chewing gum group than the control group (p=0.003) at 2 weeks but not 4 weeks. There was no significant difference in the mean plaque index between the control group and the moltitol oral spray group at any time. Using the maltitol spray significantly reduced the MS level in the saliva by 4 weeks use but using the xylitol gum did not. However, using the xylitol chewing gum did reduce the mean plaque by 2 weeks use but the effect did not last; by 4 weeks there was no difference from control. The moltitol spray provided no benefit over the control in reducing the mean plaque index.

Antimicrobial effect of topical local anesthetic spray on oral microflora.

BACKGROUND: To evaluate the antimicrobial activity of lidocaine (LD) topical anesthetic spray against oral microflora. METHODS: Antimicrobial effects of 10% LD spray were assessed against six bacterial cultures obtained from volunteers: Escherichia coli, Enterococcus faecalis, Staphylococcus aureus, Streptococcus salivarius, Streptococcus pyogenes, and Streptococcus sanguinis. The filter papers contained 50-µl LD, brain heart infusion (BHI) broth, or 0.2% chlorhexidine. Papers were placed on the cultured blood plates for 1-3 min. After the papers were removed, plates were incubated for 24 h. Bacterial growth on the contact areas was recorded as the antimicrobial score. The split mouth technique was use in for sample collection in clinical study. Filter papers soaked with either BHI broth or LD were placed on the right or left buccal mucosa for 1 min, and replaced with other papers to imprint biofilms onto the contact areas. Papers were placed on blood plates, incubated for 24 h, and antimicrobial scores were determined. Experiments were conducted for 2- and 3-min exposure times with a 1-day washout period. RESULTS: LD exhibited bactericidal effects against E. coli, S. sanguinis, and S. salivarius within 1 min but displayed no effect against S. aureus, E. faecalis, and S. pyogenes. The antimicrobial effect of LD on oral microflora depended upon exposure time, similar to the results obtained from the clinical study (P < 0.05). LD showed 60-95% biofilm reduction on buccal mucosa. CONCLUSIONS: Antimicrobial activity of 10% LD topical anesthetic spray was increased by exposure time. The 3 min application reduced oral microflora in the buccal mucosa.

EFFECTIVENESS OF AN ORAL HYGIENE EDUCATION PROGRAM COMBINED WITH FLUORIDE MOUTHRINSE AMONG VISUALLY IMPAIRED STUDENTS IN BANGKOK, THAILAND.

The objective of this study was to assess the effectiveness of oral hygiene education kits (OHE kits) and 0.05% sodium fluoride mouth rinse among visually impaired students (VIS) in Bangkok, Thailand. Seventy-five VIS aged 10-12 years were included in the study and examined for plaque index (PI), gingival index (GI) and mutans streptococci (MS) salivary levels at baseline and after intervention. The subjects were then randomly divided into three groups. Group 1 received OHE kits and 0.05% NaF mouth rinse and brushing instructions. Group 2 received only the OHE kits and brushing instructions. Group 3 (control) received only brushing instructions. PI, GI and MS levels, were reassessed 3 months after intervention. Pre- and post-intervention evaluation data were compared with the Wilcoxon match-pairs test (p < 0.05). The post-intervention results were significantly better in all 3 groups compared to the pre-intervention result (p < 0.01). Group 1 had the lowest PI and the PI was significantly lower than the other groups (p < 0.05). The GI was significantly lower in Group 1 than Group 3, Group 2 than Group 3 (p < 0.05). MS level was reduced significantly in group 1 and 2 compared to control (p < 0.001, p = 0.038, respectively). All groups showed the reduction of PI, GI, and MS levels. However, students who either received OHE kits with or without sodium fluoride mouthrinse showed significantly lower gingival index and lower number of MS than control group.

Variation of expression defects in cell surface 190-kDa protein antigen of Streptococcus mutans.

Streptococcus mutans, which consists of four serotypes, c, e, f, and k, possesses a 190-kDa cell surface protein antigen (PA) for initial tooth adhesion. We used Western blot analysis to determine PA expression in 750 S. mutans isolates from 150 subjects and found a significantly higher prevalence of the isolates with PA expression defects in serotypes f and k compared to serotypes c and e. Moreover, the defect patterns could be classified into three types; no PA expression on whole bacterial cells and in their supernatant samples (Type N1), PA expression mainly seen in supernatant samples (Type N2), and only low expression of PA in the samples of whole bacterial cells (Type W). The underlying reasons for the defects were mutations in the gene encoding PA as well as in the transcriptional processing of this gene for Type N1, defects in the sortase gene for Type N2, and low mRNA expression of PA for Type W. Since cellular hydrophobicity and phagocytosis susceptibility of the PA-defective isolates were significantly lower than those of the normal expression isolates, the potential implication of such defective isolates in systemic diseases involving bacteremia other than dental caries was suggested. Additionally, multilocus sequence typing was utilized to characterize S. mutans clones that represented a proportion of isolates with PA defects of 65-100%. Therefore, we described the molecular basis for variation defects in PA expression of S. mutans. Furthermore, we also emphasized the strong association between PA expression defects and serotypes f and k as well as the clonal relationships among these isolates.

Multilocus sequence typing analysis of Streptococcus mutans strains with the cnm gene encoding collagen-binding adhesin.

Streptococcus mutans is one of the oral pathogens associated with infective endocarditis (IE). With respect to bacterial binding ability to the extracellular matrix, the Cnm protein, a cell surface collagen-binding adhesin of S. mutans, is known as one of the possible virulence factors with regard to IE. In this study, we aimed to determine the distribution of the cnm gene, which encodes Cnm, in a large number of clinical isolates of S. mutans from Thai subjects. Then, the cnm-positive strains were classified using a multilocus sequence typing (MLST) scheme, which we constructed previously. In addition, the data were analysed together with our previous MLST data of cnm-positive strains from Japan and Finland in order to evaluate the clonal relationship among S. mutans strains harbouring the cnm gene. The cnm gene was detected in 12.4 % of all 750 Thai isolates, and serotype f showed the highest rate of detection (54.5 %). According to the MLST data, two clonal complex groups were revealed as the important clones related to cnm-positive S. mutans from various origins of isolation. Moreover, the collagen-binding properties of S. mutans strains with the cnm gene were significantly greater than those of strains without the gene, although four cnm-negative strains classified into two sequence types (STs), ST110 and ST136, showed extremely high collagen-binding rates suggesting the presence of additional genes involved with collagen binding in these STs. Taken together, these results provided information on both epidemiological as well as evolutional aspects of S. mutans possessing the cnm gene.

Translocation of Porphyromonas gingivalis infected monocytes and associated cellular responses.

Porphyromonas gingivalis (P. gingivalis), an important periodontal pathogen in adult chronic periodontitis, has been reported to colocalize in human atheromatous lesions. We have studied the phagocytosis and survival of P. gingivalis in human monocytes, together with the cellular responses of infected human monocytes. Human monocytes were cocultured with P. gingivalis and the external bacteria were killed with metronidazole and gentamycin. Localization of P. gingivalis in cells was studied by transmission electron microscopy (TEM). The survival of P. gingivalis was determined by lysing the monocytes and plating on blood agar under anaerobic conditions. Interleukin-1 beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) were determined using specific enzyme-linked immunosorbent assays (ELISAs) kits. The transwell chamber system was used to investigate the chemotactic response of the infected cells. TEM showed that P. gingivalis organisms were localized within the autophagosome-like structure of monocytes. No significant difference on the survival of P. gingivalis at 0, 4 and 8 h after infection was found. IL-1beta and TNF-alpha were present in the cell culture media in response to bacterial challenge. The infected monocytes showed a normal chemotactic response to monocyte chemotactic protein-1 (MCP-1). The number of monocyte cells migrating through membrane in the presence and absence of P. gingivalis were 18.64 +/- 2.33 x 10(4) cells and 19.11 +/- 1.76 x 10(4) cells respectively. The number of viable P. gingivalis per monocyte following translocation in response to the chemotactic gradient was 5.83 +/- 1.45 x 10(-3) CFU/cell. The results indicate that P. gingivalis can stimulate cytokine production and survive in monocytes without affecting cell migration.

Modulation of gamma interferon-induced major histocompatibility complex class II gene expression by Porphyromonas gingivalis membrane vesicles.

Gamma interferon (IFN-gamma)-induced endothelial cells actively participate in initiating immune responses by interacting with CD4(+) T cells via class II major histocompatibility complex (MHC) surface glycoproteins. Previously, Porphyromonas gingivalis membrane vesicles were shown to selectively inhibit IFN-gamma-induced surface expression of HLA-DR molecules by human umbilical cord vascular endothelial cells. In this study, we demonstrated an absence of HLA-DR alpha mRNA from IFN-gamma-induced cells in the presence of P. gingivalis membrane vesicles by using reverse transcriptase-PCR and Southern blotting. Vesicles also prevented transcription of the gene encoding class II transactivator, a transactivator protein required for IFN-gamma-induced expression of MHC class II genes. In addition, the effects of vesicles on IFN-gamma signal transduction involving Jak and Stat proteins were characterized by using immunoprecipitation and Western blot analyses. Jak1 and Jak2 proteins could not be detected in endothelial cells treated with membrane vesicles. Consequently, IFN-gamma-induced phosphorylation of Jak1, Jak2, and Stat1 alpha proteins was prevented. The class II-inhibitory effect of the membrane vesicles could be eliminated by heating vesicles at 100 degrees C for 30 min or by treating them with a cysteine proteinase inhibitor. This indicates that the cysteine proteinases were most likely responsible for the absence of Jak proteins observed in vesicle-treated cells. The observed increased binding of radiolabeled IFN-gamma to vesicle-treated cells suggests that vesicles may also modulate the IFN-gamma interactions with the cell surface. However, no evidence was obtained demonstrating that vesicles affected the expression of IFN-gamma receptors. Thus, P. gingivalis membrane vesicles apparently inhibited IFN-gamma-induced MHC class II by disrupting the IFN-gamma signaling transduction pathway. Vesicle-inhibited class II expression also occurred in other IFN-gamma-inducible cells. This suggested that the ability of P. gingivalis membrane vesicles to modulate antigen presentation by key cells may be an important mechanism used by this particular bacterium to escape immunosurveillance, thereby favoring its colonization and invasion of host tissues.