Vital microorganisms in early supragingival dental plaque and in stimulated human saliva

LFchimera: a synthetic mimic of the two antimicrobial domains of bovine lactoferrin

Saliva is essential for the maintenance of oral health. When salivary flow is impaired, the risk of various oral diseases such as caries and candidiasis increases drastically. Under healthy conditions, saliva provides effective protection against microbial colonization by the collaborative action of numerous host-defense molecules. This review describes how saliva has been the guideline for the design and characterization of a heterodimeric antimicrobial construct called LFchimera. This construct mimics the helical parts of two antimicrobial domains in the crystal structure of bovine lactoferrin. It shows high antimicrobial activity against a broad spectrum of Gram-positive and Gram-negative bacteria, fungi, and parasites including biowarfare agents such as Bacillus anthracis, Burkholderia pseudomallei, and Yersinia pestis. Further, sublethal concentrations of LFchimera inhibited biofilm formation, the invasiveness of HeLa cells by Yersinia spp., and prevented haemolysis of enteropathogenic Escherichia coli, demonstrating the versatility of these peptides.

Antibacterial Activity of Commercial Dentine Bonding Systems against E. faecalis-Flow Cytometry Study

Literature presents inconsistent results on the antibacterial activity of dentine bonding systems (DBS). Antibacterial activity of adhesive systems depends on several factors, including composition and acidity. Flow cytometry is a novel detection method to measure multiple characteristics of a single cell: total cell number, structural (size, shape), and functional parameters (viability, cell cycle). The LIVE/DEAD^® BacLight™ bacterial viability assay was used to evaluate an antibacterial activity of DBS by assessing physical membrane disruption of bacteria mediated by DBS. Ten commercial DBSs: four total-etching (TE), four self-etching (SE) and two selective enamel etching (SEE) were tested. Both total-etching DBS ExciTE F and OptiBond Solo Plus showed comparatively low antibacterial activity against E. faecalis. The lowest activity of all tested TE systems showed Te-Econom Bond. Among SE DBS, G-ænial Bond (92.24% dead cells) followed by Clearfil S3 Bond Plus (88.02%) and Panavia F 2.0 ED Primer II (86.67%) showed the highest antibacterial activity against E. faecalis, which was comparable to isopropranol (positive control). In the present study, self-etching DBS exhibited higher antimicrobial activity than tested total-etching adhesives against E. faecalis.

Quantification and qualification of bacteria trapped in chewed gum

Chewing of gum contributes to the maintenance of oral health. Many oral diseases, including caries and periodontal disease, are caused by bacteria. However, it is unknown whether chewing of gum can remove bacteria from the oral cavity. Here, we hypothesize that chewing of gum can trap bacteria and remove them from the oral cavity. To test this hypothesis, we developed two methods to quantify numbers of bacteria trapped in chewed gum. In the first method, known numbers of bacteria were finger-chewed into gum and chewed gums were molded to standard dimensions, sonicated and plated to determine numbers of colony-forming-units incorporated, yielding calibration curves of colony-forming-units retrieved versus finger-chewed in. In a second method, calibration curves were created by finger-chewing known numbers of bacteria into gum and subsequently dissolving the gum in a mixture of chloroform and tris-ethylenediaminetetraacetic-acid (TE)-buffer. The TE-buffer was analyzed using quantitative Polymerase-Chain-Reaction (qPCR), yielding calibration curves of total numbers of bacteria versus finger-chewed in. Next, five volunteers were requested to chew gum up to 10 min after which numbers of colony-forming-units and total numbers of bacteria trapped in chewed gum were determined using the above methods. The qPCR method, involving both dead and live bacteria yielded higher numbers of retrieved bacteria than plating, involving only viable bacteria. Numbers of trapped bacteria were maximal during initial chewing after which a slow decrease over time up to 10 min was observed. Around 10(8) bacteria were detected per gum piece depending on the method and gum considered. The number of species trapped in chewed gum increased with chewing time. Trapped bacteria were clearly visualized in chewed gum using scanning-electron-microscopy. Summarizing, using novel methods to quantify and qualify oral bacteria trapped in chewed gum, the hypothesis is confirmed that chewing of gum can trap and remove bacteria from the oral cavity.

In situ chlorhexidine substantivity on saliva and plaque-like biofilm: influence of circadian rhythm

BACKGROUND

The aim of the present study is to assess in situ substantivity of a single mouthrinse with 0.2% chlorhexidine (CHX) on saliva and on undisturbed de novo plaque-like biofilm (PL-biofilm), differentiating between two times of application: 1) CHX mouthrinse in the morning; and 2) CHX mouthrinse at night.

METHODS

The study participants were 10 healthy volunteers who wore an individualized splint with glass disks for 48 hours to boost the growth of PL-biofilm. Saliva samples were collected, and two disks were removed from each volunteer's splint at 8, 10, and 12 hours after performing a mouthrinse with 0.2% CHX at 7:00 am (M-0.2% CHX-diurnal) and 1:00 am (M-0.2% CHX-nocturnal). The saliva and plaque samples were analyzed by epifluorescence and confocal laser scanning microscopy, respectively, using a green fluorescent nucleic acid stain/propidium iodide staining.

RESULTS

With M-0.2% CHX-diurnal, the frequency of vital bacteria in saliva was significantly higher than in the PL-biofilm at 8, 10, and 12 hours after mouthrinse. After M-0.2% CHX-nocturnal, the frequency of vital bacteria in saliva was significantly lower than in the PL-biofilm at 8 hours and higher than in the PL-biofilm at 12 hours after mouthrinse.

CONCLUSION

These results support the more active physiologic dynamics of the salivary flora and the possible reservoir function associated with the structure of undisturbed de novo PL-biofilm.

Evaluation of chlorhexidine substantivity on salivary flora by epifluorescence microscopy

OBJECTIVE

To evaluate the in vivo antimicrobial activity of chlorhexidine (CHX) in saliva 7 h after its application using an epifluorescence microscopy technique.

SUBJECTS AND METHODS

Fifteen volunteers performed a single mouthrinse with sterile water (SM-water) and with 0.2% CHX (SM-0.2% CHX). Saliva samples were taken at 30 s and 1, 3, 5 and 7 h after each application. The bacterial suspension was mixed with the SYTO 9/propidium iodide staining and observed using an Olympus BX51 microscope. The mean percentage of viable bacteria was calculated for each sample.

RESULTS

In comparison with baseline values, the frequency of viable bacteria decreased significantly at 30 s after the SM-0.2% CHX (P < 0.001) and presented significant antibacterial activity up to 7 h after the mouthrinse (P < 0.001). In comparison with SM-water, the prevalence of viable bacteria was significantly lower at 30 s after the SM-0.2% CHX (P < 0.001) and showed a significant antibacterial effect up to 7 h after the mouthrinse (P < 0.001).

CONCLUSIONS

Epifluorescence microscopy permits evaluating the antimicrobial activity of CHX on the salivary flora in real-time. Fluorescence assays could be particularly useful to analyse simultaneously the effect of antimicrobials that alter the cytoplasmic membrane integrity on different oral ecosystems.

In vitro effect of Chinese herb extracts on caries-related bacteria and glucan

The purpose of this study was to evaluate the inhibitory effects of herb extracts on caries-related bacteria and glucan of dental plaque in vitro. Bacterial sensitivity tests were done using broth dilution, and the phenol sulphate method was used to assess glucan inhibition. The results showed that tannic acid could inhibit bacterial growth more effectively than other herb extracts. Eugenol showed a 46.87 +/- 12.74 and 36.67 +/- 6.30% inhibitory effect on insoluble and soluble glucan synthesis, respectively. Cnidium, barbaloin, caryophyllin, and piperine had > 40.0% inhibitory effect on soluble glucan synthesis. Both insoluble and soluble glucan synthesis of S. sobrinus were inhibited by eugenol and piperine. Eugenol and piperine were efficacious in inhibiting glucan synthesis making them desirable agents for oral care products.

Digestive tract microbiota in healthy volunteers

PURPOSE

The aim of this study was to standardize the methods of sample collection of mucus from the digestive tract and to determine the microbiota in healthy volunteers from Brazil, collecting samples from the mouth, esophagus, stomach, duodenum, jejunum, ileum, colon, and rectum.

METHODS

Microbiota of selected healthy volunteers from the oral cavity (n=10), the esophagus (n=10), the upper digestive tract (n=20), and the lower digestive tract (n=24) were evaluated through distinct collection methods. Collection methods took into account the different sites, using basic scraping and swabbing techniques, stimulated saliva from the oral cavity, irrigation-aspiration with sterile catheters especially designed for the esophagus, a probe especially designed for upper digestive tract, and a special catheter for the lower digestive tract.

RESULTS

(i) Mixed microbiota were identified in the oral cavity, predominantly Gram-positive aerobic and anaerobic cocci; (ii) transitional flora mainly in the esophagus; (iii) Veillonella sp, Lactobacillus sp, and Clostridium sp in the stomach and duodenum; (iv) in the jejunum and upper ileum, we observed Bacteroides sp, Proteus sp, and Staphylococcus sp, in addition to Veillonella sp; (v) in the colon, the presence of "nonpathogenic" anaerobic bacteria Veillonella sp (average 10(5) UFC) indicates the existence of a low oxidation-reduction potential environment, which suggests the possibility of adoption of these bacteria as biological markers of total digestive tract health.

CONCLUSIONS

The collection methods were efficient in obtaining adequate samples from each segment of the total digestive tract to reveal the normal microbiota. These procedures are safe and easily reproducible for microbiological studies.

Streptococcal diversity in oral biofilms with respect to salivary function

OBJECTIVE

In a previous study, we screened 149 subjects and established four groups high or low for salivary killing of oral bacteria, and for aggregation and live and dead adherence of oral bacteria (as a combined factor). Caries scores were significantly lower in both High Aggregation-Adherence groups. In this study we looked at the effects of those differences in salivary function on the quantity and diversity of oral biofilm streptococci.

DESIGN

Subjects from those four groups were recalled for collection of overnight oral biofilm from buccal upper central incisors, lingual lower central incisors, buccal upper and lower first molars, and lingual upper and lower first molars. At each site, groups were compared for total biofilm (by DNA concentration), total streptococci (by quantitative PCR), and streptococcal diversity (by Streptococcus-specific denaturing gradient gel electrophoresis).

RESULTS

Total biofilm DNA and total streptococci were correlated. Both were highest on buccal molar surfaces and lowest on lingual lower central incisors, and both were significantly lower in the High Aggregation-Adherence groups (particularly at the buccal molar site). Fifty distinct bands were observed in denaturing gradient gels. There was great diversity within and between sites. Three major bands were present in almost every person at every site. Densities for two of those bands were significantly lower in both High Aggregation-Adherence groups. Other less-prevalent bands also showed the same pattern.

CONCLUSION

These findings are consistent with our caries results in suggesting that differences in salivary function can influence the quantity and composition of streptococci in oral biofilms.

Simultaneous measurement of the viability, aggregation, and live and dead adherence of Streptococcus crista, Streptococcus mutans and Actinobacillus actinomycetemcomitans in human saliva in relation to indices of caries, dental plaque and periodontal disease

Salivary proteins have multiple functions and many share similar functions, which may be why it has been difficult to relate variations in their concentrations to oral health and ecology. An alternative is to focus on variations in the major functions of saliva. An hydroxyapatite-coated microplate model has been developed that simultaneously measures saliva-promoted bacterial viability, bacterial aggregation, and live and dead bacterial adherence, while simulating oral temperature and shearing forces from swallowing. That model was applied to resting whole and stimulated parotid saliva from 149 individuals, using representative strains of Streptococcus crista, S. mutans, and Actinobacillus actinomycetemcomitans. Two major factors were defined by multivariate analysis (this was successful only for whole-saliva). One factor was correlated with aggregation, live adherence and dead adherence for all three strains; the other was correlated with total viability of all three strains. Participants were grouped <25th percentile and >75th percentile for each factor. Those groups were compared for clinical indices of oral health. Caries scores were significantly lower in those with high scores for aggregation-adherence, regardless of whether total viability scores were low or high. Live bacteria always predominated on surfaces when live and dead adherence scores were expressed as ratios. However, participants with high scores for aggregation-adherence showed significantly more dead adherent bacteria than those with low scores (these ratios were uncorrelated with total viability). This finding may indicate that extreme differences in the ability to kill bacteria on surfaces can influence caries risk.

Bactericidal effect of delmopinol on attached and planktonic Streptococcus sanguinis cells

The aim of this investigation was to determine the antibacterial effect of varying concentrations of delmopinol-HCl on attached as well as on planktonic Streptooccus sanguinis cells in vitro. In addition, a possible antiadhesive effect on attached micro-organisms was to be investigated. S. sanguinis cells were allowed to attach to glass surfaces. These as well as planktonic cells were exposed to delmopinol-HCI in concentrations ranging from 0.2% to 0.00005% for 2 min. The percentage of vital bacteria was calculated by means of a fluorescence staining method. Total counts of attached bacteria were performed to determine any possible detaching effect by the delmopinol-HCl. The CFU were determined for the planktonic bacteria. Attached as well as planktonic bacteria showed a marked decrease in vitality following exposure to 0.2% delmopinol-HCl. After exposure to 0.05% this was only the case with the attached microorganisms. The total number of attached bacteria was not reduced by the delmopinol treatment. During initial dental biofilm formation, delmopinol-HCl causes a bactericidal effect when applied in concentrations of 0.05% and higher.

Conofocal microscopy study of undisturbed and chlorhexidine-treated dental biofilm

Culturing of dispersed plaque samples and vitality staining of plaque smears are the most commonly used methods for evaluating the effects of antimicrobials on dental plaque. The visualization of the antimicrobial action on oral biofilm present on the substrate surface (in situ) would add valuable information to the existing knowledge about the treatment effects. This study aimed at combining the advantage of confocal laser scanning microscopy (CLSM) to visualize plaque non-destructively with a vitality staining technique to assess the immediate bactericidal effect of chlorhexidine (CHX) on biofilm. Three 200-microm-wide grooves were cut into bovine dentin discs for plaque accumulation. The discs were worn by six subjects for 6, 24, and 48 hrs, then broken into halves, one of which received a one-minute extraoral 0.2% CHX treatment, while the other served as control. Both halves were stained for vital fluorescence measurements and visualized by CLSM. Plaque vitality (in %) was quantified by image analysis in three plaque layers-outer, middle, and inner. The CHX effect was significant in six-hour samples (p < 0.001) and only in the outer layer of the 48-hour plaque (p < 0.001), demonstrating a resistant nature of dental biofilm to a single CHX treatment. With the present approach, we have shown that it is possible to visualize and quantitate the antimicrobial treatment effect on biofilm still present on the substrate on which it was grown.

Saliva and dental plaque

Dental plaque is being redefined as oral biofilm. Diverse overlapping microbial consortia are present on all oral tissues. Biofilms are structured, displaying features like channels and projections. Constituent species switch back and forth between sessile and planktonic phases. Saliva is the medium for planktonic suspension. Several major functions can be defined for saliva in relation to oral biofilm. It serves as a medium for transporting planktonic bacteria within and between mouths. Bacteria in transit may be vulnerable to negative selection. Salivary agglutinins may prevent reattachment to surfaces. Killing by antimicrobial proteins may lead to attachment of dead cells. Salivary proteins form conditioning films on all oral surfaces. This contributes to positive selection for microbial adherence. Saliva carries chemical messengers which allow live adherent cells to sense a critical density of conspecifics. Growth begins, and thick biofilms may become resistant to antimicrobial substances. Salivary macromolecules may be catabolized, but salivary flow also may clear dietary substrates. Salivary proteins act in ways that benefit both host and microbe. All have multiple functions, and many do the same job. They form heterotypic complexes, which may exist in large micelle-like structures. These issues make it useful to compare subjects whose saliva functions differently. We have developed a simultaneous assay for aggregation, killing, live adherence, and dead adherence of oral species. Screening of 149 subjects has defined high killing/low adherence, low killing/high adherence, high killing/high adherence, and low killing/low adherence groups. These will be evaluated for differences in their flora.

Transmission electron microscope study of bacterial morphotypes on the anterior dorsal surface of human tongues

The human tongue has been the subject of many cytological and histological studies. When a literature search disclosed no reports of the ultrastructure of the morphotypes of bacteria residing on the tongue's surface, a transmission electron microscope study of ultrathin sections of bacteria obtained by scraping eight human tongues was undertaken. The scrapings from the anterior dorsal tongue surfaces, processed conventionally for electron microscope study, revealed 33-35 different bacterial morphotypes. Several of the morphotypes were unique to a tongue. Morphotype differences were also related to donor characteristics such as smoking, tongue site, location in centrifuge pellet, diet, and medications. The predominant morphotypes were Gram-positive cocci. These preliminary findings suggest that the microbiota of the human tongue and variations in that microbiota, related to physical condition, lifestyle, medications, and dietary preferences, merit more attention from anatomists.

Deposition and retention of vital and dead Streptococcus sanguinis cells on glass surfaces in a flow-chamber system

The proportion of vital as compared with dead Streptococcus sanguinis cells attached to glass surfaces was monitored and related to varying proportions of planktonic vital as compared with dead Strep. sanguinis cells. In a flow chamber with six parallel-mounted glass plates, Strep. sanguinis was suspended in pretreated sterile human saliva. Deposition of Strep. sanguinis took place, with a proportion of vital sanguinis streptococci in saliva (%VSs) of 90%, 45% or 22.5%. After exposure times of 30, 60, 90, 120 and 240 min, adherent microorganisms were labelled with two fluorescence stains to differentiate between vital and dead bacteria. Proportions of vital attached streptococci (%VSa) were determined microscopically. Dead bacteria were detected on all glass plates. The %VSa at 30 min and 60 min was significantly lower than the baseline %VSs. During the course of a single run the %VSa frequently increased after either 30, 60 or 90 min without exceeding the %VSs at 4 h. %VSs was the only variable exerting a significant effect on %VSa at 30 and 60 min. It is suggested that during the initial events of microbial attachment the dead rather than vital Strep. sanguinis cells attach preferably to solid surfaces.

An approach to differentiate between antibacterial and antiadhesive effects of mouthrinses in vivo

An experimental set-up allowing differentiation in vivo between antibacterial and antiadhesive properties of mouthrinses is described. The percentage of vital bacteria (= microbial vitality) and the bacterial counts were microscopically evaluated in saliva and in supragingival dental plaque both collected simultaneously at various times during de novo plaque formation. In a cross-over design, 12 healthy participants refrained from all oral hygiene for four separate periods of 2 x 4 h and 2 x 72 h after having rinsed with either an amine fluoride/stannous fluoride solution (Meridol) or 0.9% NaCl (placebo). Stimulated whole saliva was collected before and after the rinse. Together with whole-saliva samples, representative 4, 24 and 72-h-old plaque samples were separately taken from defined vestibular tooth surfaces that had been either exposed to the mouthrinse (unprotected sites) or temporarily covered with inert plastic films (protected sites) during rinsing. The pooled plaque and saliva were stained with fluorescent dyes to differentiate vital from dead micro-organisms which permitted the estimation of the percentages of vital bacteria. The total bacterial counts were quantified under the darkfield microscope. The Wilcoxon test was used for selected pairwise comparisons (alpha = 0.05). The percentage of vital bacteria in saliva fell significantly from 80-95% to about 50-60% as a result of the antibacterial activity of the test solution. These baseline values and those found in the presence of 4 and 24-h-old plaque were frequently lower than those recorded after the placebo rinse. In comparison to the placebo, microbial vitality was significantly reduced in early supragingival plaque formed on unprotected sites after applying the test solution. The similar total bacterial counts in 4-h-old plaque recorded after the use of the test solution on the unprotected and the protected areas did not point to an antiadhesive effect of the agent. It is concluded that this new experimental set-up allows decoding of the mode of action of a mouthrinse.

A pilot study of confocal laser scanning microscopy for the assessment of undisturbed dental plaque vitality and topography

Confocal microscopy and vital fluorescence techniques were combined for the first time to investigate ex vivo human dental plaque. The vital fluorescence technique used discriminates vital from dead cells, while confocal laser scanning microscopy allows the optical sectioning of undisturbed biofilms leaving the samples intact during analysis. The concomitant use of both methods made an examination of the three-dimensional architecture of dental plaque possible. The topography of plaque biofilms that were allowed to accumulate in situ on glass and enamel was recorded. The distribution of plaque microflora vitality as well as its accumulation varied according to plaque age. A plaque thickness of up to 8, 35 and 45 microm was estimated ex vivo on enamel after 1, 2 and 3 days, respectively. Young and sparse plaque biofilms consisted mainly of dead material. Vital bacteria were observed on top of this dead layers.