A fluorescence assay to determine the viable biomass of microcosm dental plaque biofilms

Evading the host response: Staphylococcus "hiding" in cortical bone canalicular system causes increased bacterial burden

Extremity reconstruction surgery is increasingly performed rather than amputation for patients with large-segment pathologic bone loss. Debate persists as to the optimal void filler for this "limb salvage" surgery, whether metal or allograft bone. Clinicians focus on optimizing important functional gains for patients, and the risk of devastating implant infection has been thought to be similar regardless of implant material. Recent insights into infection pathophysiology are challenging this equipoise, however, with both basic science data suggesting a novel mechanism of infection of Staphylococcus aureus (the most common infecting agent) into the host lacunar-canaliculi network, and also clinical data revealing a higher rate of infection of allograft over metal. The current translational study was therefore developed to bridge the gap between these insights in a longitudinal murine model of infection of allograft bone and metal. Real-time Staphylococci infection characteristics were quantified in cortical bone vs metal, and both microarchitecture of host implant and presence of host immune response were assessed. An orders-of-magnitude higher bacterial burden was established in cortical allograft bone over both metal and cancellous bone. The establishment of immune-evading microabscesses was confirmed in both cortical allograft haversian canal and the submicron canaliculi network in an additional model of mouse femur bone infection. These study results reveal a mechanism by which Staphylococci evasion of host immunity is possible, contributing to elevated risks of infection in cortical bone. The presence of this local infection reservoir imparts massive clinical implications that may alter the current paradigm of osteomyelitis and bulk allograft infection treatment.

Photonic Therapy in Periodontal Diseases an Overview with Appraisal of the Literature and Reasoned Treatment Recommendations

Recent reviews and meta-analyses of the literature over the past quarter-century have failed to provide enough evidence to prove or disprove the actual utility of photonic therapy in periodontitis, alone or adjunctive to conventional approaches. This apparent paradox has been explained by the many physical, molecular, biological, anatomical, and technical variables of photonic treatments, which can differ in light-emitting devices (laser or LED), wavelengths, irradiation power and modes, clinical objectives, follow-up times, disease grading, and assessment methods. This multi-faceted, controversial scenario has led practitioners to underestimate the actual potential of photonic therapy in periodontal diseases. In this critical appraisal of the literature, we have briefly summarized the main photonic therapies and instruments used in Periodontology, highlighting their main characteristics and limitations. Then, we have tried to identify and discuss the key methodological issues which can have an impact on the outcome of photonic therapies. Our main goal was to identify the best parameters, settings, and methodologies to perform effective periodontal photonic treatments and to extrapolate some recommendations for clinical use. Should these recommendations find a consensus among periodontologists and be adopted in future clinical studies, they will hopefully contribute to dissipate the present confusion and uncertainty on this complex matter.

Antibacterial quaternary ammonium compounds in dental materials: A systematic review

OBJECTIVE

Quaternary ammonium compounds (QACs) represent one of the most effective classes of disinfectant agents in dental materials and resin nanocomposites. This reviews aims to give a wide overview on the research in the field of antibacterial QACs in dental materials and nanocomposites.

METHOD

An introduction to dental materials components as well as the microorganisms and methods of evaluation for the antimicrobial assays are presented. Then, the properties and synthesis route of QACs, as monomer and filler, are shown. Finally, antimicrobial monomers and fillers, specifically those contain quaternary ammonium salts (QASs), in dental materials are reviewed.

RESULTS

QACs have been used as monomer and micro/nanofiller in restorative dentistry. They possess one or more methacrylate functional groups to participate in polymerization reactions. QACs with multiple methacrylate groups can also be used as crosslinking agents. Furthermore, QACs with chain length from ∼12 to 16 have higher antimicrobial activity in cured dental resins. In general, increasing the chain length leads to a threshold value (critical point) and then it causes decrease in the antimicrobial activity.

SIGNIFICANCE

The current state of the art of dental materials and resin nanocomposites includes a wide variety of antimicrobial materials. Among them, QACs presents low cytotoxicity and excellent long-term antimicrobial activity without leaching out over time.

Biofilms in Endodontics-Current Status and Future Directions

Microbiota are found in highly organized and complex entities, known as biofilms, the characteristics of which are fundamentally different from microbes in planktonic suspensions. Root canal infections are biofilm mediated. The complexity and variability of the root canal system, together with the multi-species nature of biofilms, make disinfection of this system extremely challenging. Microbial persistence appears to be the most important factor for failure of root canal treatment and this could further have an impact on pain and quality of life. Biofilm removal is accomplished by a chemo-mechanical process, using specific instruments and disinfecting chemicals in the form of irrigants and/or intracanal medicaments. Endodontic research has focused on the characterization of root canal biofilms and the clinical methods to disrupt the biofilms in addition to achieving microbial killing. In this narrative review, we discuss the role of microbial biofilms in endodontics and review the literature on the role of root canal disinfectants and disinfectant-activating methods on biofilm removal.

In vitro study of Streptococcus mutans adhesion on composite resin coated with three surface sealants

OBJECTIVES

Although the coating of surface sealants to dental composite resin may potentially reduce bacterial adhesion, there seems to be little information regarding this issue. This preliminary in vitro study investigated the adhesion of Streptococcus mutans (S. mutans) on the dental composite resins coated with three commercial surface sealants.

MATERIALS AND METHODS

Composite resin (Filtek Z250) discs (8 mm in diameter, 1 mm in thickness) were fabricated in a mold covered with a Mylar strip (control). In group PoGo, the surfaces were polished with PoGo. In groups PS, OG, and FP, the surfaces polished with PoGo were coated with the corresponding surface sealants (PermaSeal, PS; OptiGuard, OG; Fortify Plus, FP). The surfaces of the materials and S. mutans cells were characterized by various methods. S. mutans adhesion to the surfaces was quantitatively evaluated using flow cytometry (n = 9).

RESULTS

Group OG achieved the lowest water contact angle among all groups tested (p < 0.001). The cell surface of S. mutans tested showed hydrophobic characteristics. Group PoGo exhibited the greatest bacterial adhesion among all groups tested (p < 0.001). The sealant-coated groups showed statistically similar (groups PS and FP, p > 0.05) or significantly lower (group OG, p < 0.001) bacterial adhesion when compared with the control group.

CONCLUSIONS

The application of the surface sealants significantly reduced S. mutans adhesion to the composite resin polished with the PoGo.

Delayed Propionibacterium acnes surgical site infections occur only in the presence of an implant

Whether Propionibacterium acnes (P. acnes) causes surgical-site infections (SSI) after orthopedic surgery is controversial. We previously reported that we frequently find P. acnes in intraoperative specimens, yet none of the patients have clinically apparent infections. Here, we tracked P. acnes for 6 months in a mouse osteomyelitis model. We inoculated P. acnes with an implant into the mouse femur in the implant group; the control group was treated with the bacteria but no implant. We then observed over a 6-month period using optical imaging system. During the first 2 weeks, bacterial signals were detected in the femur in the both groups. The bacterial signal completely disappeared in the control group within 28 days. Interestingly, in the implant group, bacterial signals were still present 6 months after inoculation. Histological and scanning electron-microscope analyses confirmed that P. acnes was absent from the control group 6 months after inoculation, but in the implant group, the bacteria had survived in a biofilm around the implant. PCR analysis also identified P. acnes in the purulent effusion from the infected femurs in the implant group. To our knowledge, this is the first report showing that P. acnes causes SSI only in the presence of an implant.

Testing a dual-fluorescence assay to monitor the viability of filamentous cyanobacteria

Filamentous cyanobacteria are currently being engineered to produce long-chain organic compounds, including 3rd generation biofuels. Because of their filamentous morphology, standard methods to quantify viability (e.g., plate counts) are not possible. This study investigated a dual-fluorescence assay based upon the LIVE/DEAD® BacLight™ Bacterial Viability Kit to quantify the percent viability of filamentous cyanobacteria using a microplate reader in a high throughput 96-well plate format. The manufacturer's protocol calls for an optical density normalization step to equalize the numbers of viable and non-viable cells used to generate calibration curves. Unfortunately, the isopropanol treatment used to generate non-viable cells released a blue pigment that altered absorbance readings of the non-viable cell solution, resulting in an inaccurate calibration curve. Thus we omitted this optical density normalization step, and carefully divided cell cultures into two equal fractions before the isopropanol treatment. While the resulting calibration curves had relatively high correlation coefficients, their use in various experiments resulted in viability estimates ranging from below 0% to far above 100%. We traced this to the apparent inaccuracy of the propidium iodide (PI) dye that was to stain only non-viable cells. Through further analysis via microplate reader, as well as confocal and wide-field epi-fluorescence microscopy, we observed non-specific binding of PI in viable filamentous cyanobacteria. While PI will not work for filamentous cyanobacteria, it is possible that other fluorochrome dyes could be used to selectively stain non-viable cells. This will be essential in future studies for screening mutants and optimizing photobioreactor system performance for filamentous cyanobacteria.

Confusion over live/dead stainings for the detection of vital microorganisms in oral biofilms--which stain is suitable?

BACKGROUND

There is confusion over the definition of the term "viability state(s)" of microorganisms. "Viability staining" or "vital staining techniques" are used to distinguish live from dead bacteria. These stainings, first established on planctonic bacteria, may have serious shortcomings when applied to multispecies biofilms. Results of staining techniques should be compared with appropriate microbiological data.

DISCUSSION

Many terms describe "vitality states" of microorganisms, however, several of them are misleading. Authors define "viable" as "capable to grow". Accordingly, staining methods are substitutes, since no staining can prove viability.The reliability of a commercial "viability" staining assay (Molecular Probes) is discussed based on the corresponding product information sheet: (I) Staining principle; (II) Concentrations of bacteria; (III) Calculation of live/dead proportions in vitro. Results of the "viability" kit are dependent on the stains' concentration and on their relation to the number of bacteria in the test. Generally this staining system is not suitable for multispecies biofilms, thus incorrect statements have been published by users of this technique.To compare the results of the staining with bacterial parameters appropriate techniques should be selected. The assessment of Colony Forming Units is insufficient, rather the calculation of Plating Efficiency is necessary. Vital fluorescence staining with Fluorescein Diacetate and Ethidium Bromide seems to be the best proven and suitable method in biofilm research.Regarding the mutagenicity of staining components users should be aware that not only Ethidium Bromide might be harmful, but also a variety of other substances of which the toxicity and mutagenicity is not reported.

SUMMARY

- The nomenclature regarding "viability" and "vitality" should be used carefully.- The manual of the commercial "viability" kit itself points out that the kit is not suitable for natural multispecies biofilm research, as supported by an array of literature.- Results obtained with various stains are influenced by the relationship between bacterial counts and the amount of stain used in the test. Corresponding vitality data are prone to artificial shifting.- As microbiological parameter the Plating Efficiency should be used for comparison.- Ethidium Bromide is mutagenic. Researchers should be aware that alternative staining compounds may also be or even are mutagenic.

Investigation of microbial biofilm structure by laser scanning microscopy

Microbial bioaggregates and biofilms are hydrated three-dimensional structures of cells and extracellular polymeric substances (EPS). Microbial communities associated with interfaces and the samples thereof may come from natural, technical, and medical habitats. For imaging such complex microbial communities confocal laser scanning microscopy (CLSM) is the method of choice. CLSM allows flexible mounting and noninvasive three-dimensional sectioning of hydrated, living, as well as fixed samples. For this purpose a broad range of objective lenses is available having different working distance and resolution. By means of CLSM the signals detected may originate from reflection, autofluorescence, reporter genes/fluorescence proteins, fluorochromes binding to specific targets, or other probes conjugated with fluorochromes. Recorded datasets can be used not only for visualization but also for semiquantitative analysis. As a result CLSM represents a very useful tool for imaging of microbiological samples in combination with other analytical techniques.

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.

Rapid clinical bacteriology and its future impact

Clinical microbiology has always been a slowly evolving and conservative science. The sub-field of bacteriology has been and still is dominated for over a century by culture-based technologies. The integration of serological and molecular methodologies during the seventies and eighties of the previous century took place relatively slowly and in a cumbersome fashion. When nucleic acid amplification technologies became available in the early nineties, the predicted "revolution" was again slow but in the end a real paradigm shift did take place. Several of the culture-based technologies were successfully replaced by tests aimed at nucleic acid detection. More recently a second revolution occurred. Mass spectrometry was introduced and broadly accepted as a new diagnostic gold standard for microbial species identification. Apparently, the diagnostic landscape is changing, albeit slowly, and the combination of newly identified infectious etiologies and the availability of innovative technologies has now opened new avenues for modernizing clinical microbiology. However, the improvement of microbial antibiotic susceptibility testing is still lagging behind. In this review we aim to sketch the most recent developments in laboratory-based clinical bacteriology and to provide an overview of emerging novel diagnostic approaches.

Combined photoablative and photodynamic diode laser therapy as an adjunct to non-surgical periodontal treatment: a randomized split-mouth clinical trial

AIM

Comparing the efficacy of photoablative and photodynamic diode laser in adjunct to scaling -root planing (SRP) and SRP alone for the treatment of chronic periodontitis.

MATERIALS AND METHODS

Twenty-six patients were studied. Maxillary left or right quadrants were randomly assigned to sham-laser treatment + SRP or laser + SRP. This consisted of photoablative intra/extra-pocket de-epithelization with diode laser (λ = 810 nm), followed by single SRP and multiple photodynamic treatments (once weekly, 4-10 applications, mean ± SD: 3.7 ± 2.4) using diode laser (λ = 635 nm) and 0.3% methylene blue as photosensitizer. The patients were monitored at days 0 and 365 by clinical assessment (probing depth, PD; clinical attachment level, CAL; bleeding on probing, BOP) and at days 0, 15, 30, 45, 60, 75, 90, 365 by cytofluorescence analysis of gingival exfoliative samples taken in proximity of the teeth to be treated (polymorphonuclear leukocytes, PMN; red blood cells, RBC; damaged epithelial cells, DEC; bacteria).

RESULTS

At day 365, compared with the control quadrants, the laser + SRP therapy yielded a significant (p < 0.001) reduction in PD (-1.9 mm), CAL (-1.7 mm) and BOP (-33.2% bleeding sites), as well as in bacterial contamination - especially spirochetes - and PMN and RBC shedding in the gingival samples (p < 0.001).

CONCLUSIONS

Diode laser treatment (photoablation followed by multiple photodynamic cycles) adjunctive to conventional SRP improves healing in chronic periodontitis patients.

Control of methicillin-resistant Staphylococcus aureus in planktonic form and biofilms: a biocidal efficacy study of nonthermal dielectric-barrier discharge plasma

BACKGROUND

Bacterial contamination of surfaces with methicillin-resistant Staphylococcus aureus (MRSA) is a serious problem in the hospital environment and is responsible for significant nosocomial infections. The pathogenic contaminants form biofilms, which are difficult to treat with routine biocides. Thus, a continuous search for novel disinfection methods is essential for effective infection control measures. This demonstration of a novel technique for the control of virulent pathogens in planktonic form as well as in established biofilms may provide a progressive alternative to standard methodology.

METHODS

We evaluated a novel technique of normal atmospheric nonthermal plasma known as floating-electrode dielectric-barrier discharge (FE-DBD) plasma against a control of planktonic and biofilm forms of Escherichia coli, S aureus, multidrug-resistant methicillin-resistant S aureus (MRSA) -95 (clinical isolate), -USA300, and -USA400, using widely accepted techniques such as colony count assay, LIVE/DEAD BacLight Bacterial Viability assay, and XTT (2,3-Bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide) assay.

RESULTS

Exposure of free living planktonic forms of E coli, S aureus, and MRSA were rapidly inactivated by DBD plasma. Approximately 10(7) bacterial cells were completely (100%) killed, whereas 10(8) and 10(9) were reduced by approximately 90% to 95% and 40% to 45%, respectively, in less than 60 seconds (7.8 J/cm(2)) and completely disinfected in < or =120 seconds. In established biofilms, the susceptibility of MRSA USA400 was comparable with USA300 but less susceptible than MRSA95 (clinical isolate), S aureus, and E coli (P < .05) to FE-DBD plasma, and plasma was able to kill MRSA more than 60% within 15 seconds (1.95 J/cm(2)). The killing responses were plasma exposure-time dependent, and cell density dependent. The plasma was able disinfect surfaces in a less than 120 seconds.

CONCLUSION

Application of DBD plasma can be a valuable decontamination technique for the removal of planktonic and biofilm-embedded bacteria such as MRSA -USA 300, -USA 400, methicillin-sensitive S aureus (MSSA), and E coli, the more common hospital contaminants. Of interest, E coli was more resistant than S aureus phenotypes.

Real-time microsensor measurement of local metabolic activities in ex vivo dental biofilms exposed to sucrose and treated with chlorhexidine

Dental biofilms are characterized by structural and functional heterogeneity. Due to bacterial metabolism, gradients develop and diverse ecological microniches exist. The aims of this study were (i) to determine the metabolic activity of microorganisms in naturally grown dental biofilms ex vivo by measuring dissolved oxygen (DO) and pH profiles with microelectrodes with high spatial resolution and (ii) to analyze the impact of an antimicrobial chlorhexidine (CHX) treatment on microbial physiology during stimulation by sucrose in real time. Biofilms were cultivated on standardized human enamel surfaces in vivo. DO and pH profiles were measured in a flow cell system in sterile human saliva, after sucrose addition (10%), again after alternative treatment of the sucrose exposed biofilms with CHX (0.2%) for 1 or 10 min or after being killed with paraformaldehyde (4%). Biofilm structure was visualized by vitality staining with confocal microscopy. With saliva as the sole nutrient source oxygen consumption was high within the superficial biofilm layers rendering deeper layers (>220 mum) anoxic. Sucrose addition induced the thickness of the anaerobic zone to increase with a concurrent decrease in pH (7.1 to 4.4). CHX exposure reduced metabolic activity and microbial viability at the biofilm surface and drove metabolic activity deeper into the biofilm. CHX treatment led to a reduced viability at the biofilm surface with minor influence on overall biofilm physiology after 1 min; even after 10 min there was measurable respiration and fermentation inside the biofilm. However, the local microenvironment was more aerated, less acidogenic, and presumably less pathogenic.

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.

Effects of a dental adhesive incorporating antibacterial monomer on the growth, adherence and membrane integrity of Streptococcus mutans

OBJECTIVES

This study was attempted to incorporate an antibacterial monomer, methacryloxylethyl cetyl dimethyl ammonium chloride (DMAE-CB), into a commercial dental adhesive and to evaluate the antibacterial activity of the DMAE-CB-incorporated adhesive after being cured against Streptococcus mutans.

METHODS

DMAE-CB was incorporated at 3% (w/v) into a clinically used dental adhesive, Single Bond 2. Single Bond 2 without DMAE-CB was served as a negative control; Clearfil Protect Bond, containing an intensively researched antibacterial monomer MDPB, was enrolled as a positive control. The effects of the cured adhesives and their eluents on the growth of S. mutans were determined by film contact test and absorbance measurement, respectively. The effects of the cured adhesives on the adherence and membrane integrity of S. mutans were investigated using confocal laser scanning microscopy (CLSM) in conjunction with fluorescent indicators.

RESULTS

Compared with negative control, the cured DMAE-CB-incorporated dental adhesive and positive control were found to exhibit inhibitory effect on the growth of S. mutans (P<0.05), whereas their eluents did not show detectable antibacterial activity. Moreover, the fluorescence analysis of CLSM images demonstrated that the cured DMAE-CB-incorporated adhesive and positive control could hamper the adherence of S. mutans and exert detrimental effect on bacterial membrane integrity (P<0.05).

CONCLUSIONS

The incorporation of DMAE-CB can render dental adhesive with contact antibacterial activity after polymerization via influencing the growth, adherence and membrane integrity of S. mutans.