Bespoke cationic nano-objects via RAFT aqueous dispersion polymerisation

Cationic diblock copolymer spheres, worms and vesicles are synthesised via polymerisation-induced self-assembly; worms form soft, thermoresponsive anti-bacterial gels at 20 °C.

Decontamination of orthodontic bands following size determination and cleaning

OBJECTIVE

To measure the effectiveness of ultrasonic cleaning for decontaminating orthodontic molar bands following size determination using a quantitative antibody capture assay technique.

DESIGN

A prospective, cross-sectional, clinical and laboratory investigation.

SETTING

The Orthodontic Department of the Charles Clifford Dental Hospital and the Microbiology Laboratory of the School of Clinical Dentistry, Sheffield.

PARTICIPANTS

Thirty-two patients about to start orthodontic treatment with fixed orthodontic appliances.

METHODS

Four first molar bands were tried in the mouth and then removed. They were randomly assigned either for no decontamination (control) or to be decontaminated in an ultrasonic cleaning bath for 15 minutes (experimental). The bands were placed in a predetermined volume of phosphate-buffered saline (PBS) and assayed by enzyme-linked immunosorbent assay (ELISA) for albumin, to detect the presence of blood and amylase, to detect the presence of saliva.

RESULTS

Fifty per cent of decontaminated molar bands showed detectable amounts of amylase, albumin or both. The quantity of detectable amylase was significantly reduced on the cleaned compared with uncleaned bands (P = 0.036); however, the reduction in the quantity of albumin was not statistically significant (P = 0.074).

CONCLUSIONS

Ultrasonic cleaning for 15 minutes reduces, but does not always eliminate, salivary proteins (amylase) from tried-in bands. It is less effective at removing serum protein (albumin). There is a need, therefore, to investigate effective means of cleaning organic material from orthodontic bands if they are to be adequately sterilized and reused.

Gingipain-dependent degradation of mammalian target of rapamycin pathway proteins by the periodontal pathogen Porphyromonas gingivalis during invasion

Porphyromonas gingivalis and Tannerella forsythia are gram-negative pathogens strongly associated with periodontitis. Their abilities to interact, invade and persist within host cells are considered crucial to their pathogenicity, but the mechanisms by which they subvert host defences are not well understood. In this study, we set out to investigate whether P. gingivalis and T. forsythia directly target key signalling molecules that may modulate the host cell phenotype to favour invasion and persistence. Our data identify, for the first time, that P. gingivalis, but not T. forsythia, reduces levels of intracellular mammalian target of rapamycin (mTOR) in oral epithelial cells following invasion over a 4-h time course, via the action of gingipains. The ability of cytochalasin D to abrogate P. gingivalis-mediated mTOR degradation suggests that this effect is dependent upon cellular invasion. We also show that levels of several other proteins in the mTOR signalling pathway are modulated by gingipains, either directly or as a consequence of mTOR degradation including p-4E-BP1. Taken together, our data suggest that P. gingivalis manipulates the mTOR pathway, providing evidence for a potentially novel mechanism by which P. gingivalis mediates its effects on host cell responses to infection.

Glycoprotein Ibα and FcγRIIa play key roles in platelet activation by the colonizing bacterium, Streptococcus oralis

BACKGROUND

Infective endocarditis (IE) is characterized by thrombus formation on a cardiac valve. The oral bacterium, Streptococcus oralis, is recognized for its ability to colonize damaged heart valves and is frequently isolated from patients with IE. Platelet interaction with S. oralis leads to the development of a thrombotic vegetation on heart valves, which results in valvular incompetence and congestive heart failure.

OBJECTIVE

To investigate the mechanism through which platelets become activated upon binding S. oralis.

PATIENTS AND METHODS

Platelet interactions with immobilized bacteria under shear conditions were assessed using a parallel flow chamber. S. oralis-inducible platelet reactivity was determined using light transmission aggregometry. Dense granule secretion was measured by luminometry using a luciferin/luciferase assay.

RESULTS

Using shear rates that mimic physiological conditions, we demonstrated that S. oralis was able to support platelet adhesion under venous (50-200 s(-1) ) and arterial shear conditions (800 s(-1) ). Platelets rolled along immobilized S. oralis through an interaction with GPIbα. Following rolling, platelet microaggregate formation was observed on immobilized S. oralis. Aggregate formation was dependent on S. oralis binding IgG, which cross-links to platelet FcγRIIa. This interaction led to phosphorylation of the ITAM domain on FcγRIIa, resulting in dense granule secretion, amplification through the ADP receptor and activation of RAP1, culminating in platelet microaggregate formation.

CONCLUSIONS

These results suggest a model of interaction between S. oralis and platelets that leads to the formation of a stable septic vegetation on damaged heart valves.

Identification of bistable populations of Porphyromonas gingivalis that differ in epithelial cell invasion

Bistable populations of bacteria give rise to two or more subtypes that exhibit different phenotypes. We have explored whether the periodontal pathogen Porphyromonas gingivalis exhibits bistable invasive phenotypes. Using a modified cell invasion assay, we show for the first time that there are two distinct subtypes within a population of P. gingivalis strains NCTC 11834 and W50 that display differences in their ability to invade oral epithelial cells. The highly invasive subtype invades cells at 10-30-fold higher levels than the poorly invasive subtype and remains highly invasive for approximately 12-16 generations. Analysis of the gingipain activity of these subtypes revealed that the highly invasive type had reduced cell-associated arginine-specific protease activity. The role of Arg-gingipain activity in invasion was verified by enhancement of invasion by rgpAB mutations and by inclusion of an Arg-gingipain inhibitor in invasion assays using wild-type bacteria. In addition, a population of ΔrgpAB bacteria did not contain a hyperinvasive subtype. Screening of the protease activity of wild-type populations of both strains identified high and low protease subtypes which also showed a corresponding reduction or enhancement, respectively, of invasive capabilities. Microarray analysis of these bistable populations revealed a putative signature set of genes that includes oxidative stress resistance and iron transport genes, and which might be critical to invasion of or survival within epithelial cells.

Antibacterial coatings for medical devices based on glass polyalkenoate cement chemistry

A biofilm is an accumulation of micro-organisms and their extracellular products forming a structured community on a surface. Biofilm formation on medical devices has severe health consequences as bacteria growing in this lifestyle are tolerant to both host defense mechanisms and antibiotic therapies. However, silver and zinc ions inhibit the attachment and proliferation of immature biofilms. The objective of this study is to evaluate whether it is possible to produce silver and zinc-containing glass polyalkenoate cement (GPC) coatings for medical devices that have antibacterial activity and which may therefore inhibit biofilm formation on a material surface. Two silver and zinc-containing GPC coatings (A and B) were synthesised and coated onto Ti6Al4V discs. Their handling properties were characterised and atomic absorption spectrometery was employed to determine zinc and silver ion release with coating maturation up to 30 days. The antibacterial properties of the coatings were also evaluated against Staphylococcus aureus and a clinical isolate of Pseudomonas aeruginosa using an agar diffusion assay method. The majority of the zinc and silver ions were released within the first 24 h; both coatings exhibited antibacterial effect against the two bacterial strains, but the effect was more intense for B which contained more silver and less zinc than A. Both coatings produced clear zones of inhibition with each of the two organisms tested. In this assay, Ps. aeruginosa was more sensitive than S. aureus. The diameters of these zones were reduced after the coating had been immersed in water for varying periods due to the resultant effect on ion release.

Characterization of minimal bacteriocin operon from Prevotella nigrescens ATCC 25261

AIMS

To characterize a minimal bacteriocin operon of Prevotella nigrescens ATCC 25261.

METHODS AND RESULTS

A genomic DNA library of Pr. nigrescens ATCC 25261 was constructed and screened for bacteriocin production by an agar overlay assay. Sequence analysis of the bacteriocin-producing recombinant plasmid, pGP2, has shown that the insert DNA consists of 4868 base pairs, termed nig locus. There is a cluster of four genes within the nig locus, respectively designated nigA, B, C and D. Deleting 160 nucleotides at the 3'-end of nigAB resulted in loss of bacteriocin production, indicating that nigAB may belong to a bacteriocin operon. nigA is thought to be the bacteriocin gene, while nigB may encode an immunity protein. Escherichia coli containing pGP2 expressed the bacteriocin, which is similar in size, antimicrobial activity, and biochemical properties to that purified from Pr. nigrescens ATCC 25261.

CONCLUSION

nig Locus is a chromosomal fragment of Pr. nigrescens ATCC 25261, consisting of 4868 base pairs, and has been proved to be important for bacteriocin production.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report of the successful cloning and expression of the bacteriocin from Pr. nigrescens ATCC 25261 into E. coli. This will facilitate the construction of bacteriocin analogues and permit investigation of their structure/function relationships.

Characterization of a bacteriocin produced by Prevotella nigrescens ATCC 25261

AIMS

To characterize the antimicrobial activity produced by Prevotella nigrescens ATCC 25261, and to evaluate its safety on cultured gingival fibroblasts.

METHODS AND RESULTS

An antimicrobial activity was obtained from purifying the culture supernatant of Pr. nigrescens ATCC 25261. Purification of the active compound was achieved with ammonium sulphate precipitation followed by anion-exchange and gel filtration chromatography. As revealed by SDS-PAGE, the active fraction was relatively homogeneous, showing a protein with an approximate molecular weight of 41 kDa. The antimicrobial compound, named nigrescin, exhibited a bactericidal mode of action against Porphyromonas gingivalis, Prevotella intermedia, Tannerella forsythensis, and Actinomyces spp. Nigrescin was stable in a pH range between 6.5 and 9.5, at 100 degrees C for 10 min, and resistant to lyophilization. But its activity was lost after proteinase K treatment. Despite at very high concentrations beyond the minimum inhibitory concentration (MIC), nigrescin was not toxic to the gingival fibroblasts.

CONCLUSION

Nigrescin is a novel bacteriocin produced by Pr. nigrescens ATCC 25261. It exhibits antimicrobial activity against species that are implicated in periodontal diseases. The absence of toxicity on the gingival fibroblasts suggests the possibility in using of nigrescin for an application in periodontal treatment.

SIGNIFICANCE AND IMPACT OF THE STUDY

Novel evidence on nigrescin would make Pr. nigrescens ATCC 25261 attractive in biotechnological applications as an antimicrobial agent in clinical dentistry.

Inhibitory effect of garlic extract on oral bacteria

Garlic (Allium sativum) has long been known to have antibacterial, antifungal and antiviral properties but there are few data on its effects against oral bacterial species particularly putative periodontal pathogens or their enzymes. Filter sterilised, aqueous extract of garlic was tested for ability to inhibit the growth of a range of oral species and to inhibit the trypsin-like and total protease activity Porphyromonas gingivalis. The garlic extract (57.1% (w/v), containing 220 microg/ml allicin) inhibited the growth and killed most of the organisms tested. In general, the minimal inhibitory and minimum bactericidal concentrations for the Gram-negative strains (garlic MIC range 35.7-1.1 mg/ml; allicin mean MIC 4.1 microg/ml; mean MBC 7.9 microg/ml) were lower than those for the Gram-positive strains tested (garlic MIC range 142.7-35.7 mg/ml; allicin mean MIC 27.5 microg/ml; mean MBC 91.9 microg/ml). Also, of the organisms tested, the putative periodontal pathogens had among the lowest MICs (17.8-1.1 mg/ml garlic) and MBCs (35.7-1.1 mg/ml garlic). Time-kill curves for Streptococcus mutans and P. ginigvalis, showed that killing of the latter started almost immediately, whereas there was a delay before S. mutans was killed. The garlic extract also inhibited the trypsin-like and total protease activity of P. gingivalis by 92.7% and 94.88%, respectively. These data indicate that garlic extract inhibits the growth of oral pathogens and certain proteases and so may have therapeutic value, particularly for periodontitis.

An in vitro study into the effect of a limited range of denture cleaners on surface roughness and removal of Candida albicans from conventional heat-cured acrylic resin denture base material

This study evaluated the abrasiveness of four denture cleaners on the surface of denture base material and assessed their ability to remove Candida albicans. Acrylic resin discs 20 mm diameter and 2 mm thick were identically produced and polished. Four cleaners were evaluated: conventional toothpaste; toothpaste with stain remover; denture cleaning paste and an immersion type cleaner, and water were used as control. These were used at dilutions of 1:1, 1:2 and 1:3 with water. An electric toothbrush was used, and the discs cleaned to simulate 1 years' cleaning. The surface roughness of the discs were then measured, before and after cleaning, using a stylus profilometer, then inoculated with 1.2 x 10(6)C. albicans cells. The effectiveness of the denture cleaners to remove C. albicans cells was assessed following a single cleaning event. The immersion cleaner was significantly less abrasive than paste cleaners (P < 0.05). There were no significant differences between any dilutions for any cleaner used (P > 0.05). Immersion and paste cleaners removed almost all recoverable C. albicans from the discs, as cleaning with water alone was less effective (P < 0.05). An immersion type cleaner was found to be the most suitable cleaner because of its low abrasivity and effective removal of organic debris.

Activation of human matrix metalloproteinase 2 by gingival crevicular fluid and Porphyromonas gingivalis

AIM

To assess the potential of gingival crevicular fluid (GCF) from adult periodontitis patients and Porphyromonas gingivalis proteases to activate matrix metalloproteinase 2 (MMP-2) in vitro.

MATERIAL AND METHODS

GCF samples were collected from each of 15 adult periodontitis patients, from a clinically healthy site, a deep (>6 mm) bleeding site, and a deep nonbleeding site. The GCF samples were examined for general proteolytic activity, gelatinolytic activity and ability to activate pro-MMP-2 by zymography. Ultrasonic extracts of a range of clinical isolates of P. gingivalis cells and purified arg- and lys-gingipains were also assessed for their ability to activate pro-MMP-2.

RESULTS

GCF from deep nonbleeding sites showed higher general proteolytic activity than samples from deep bleeding and healthy sites but this did not reach statistical significance. Pefabloc, a general serine protease inhibitor, inhibited the majority (92%) of the proteolytic activity. GCF samples contained neutrophil MMP-9 in its latent form in 93% of the samples, and in its activated form in 40% of the samples. In contrast, MMP-2 was present in only trace amounts in 9% of the samples. When latent MMP-2 was added to these GCF samples, it was converted to the activated form (59 kDa) in 68% of the samples. Lower molecular weight (55 and 45 kDa) activated forms also appeared in 53% of the samples, particularly those from deep sites. Activation to the 55 and 45 kDa forms was inhibited by MSAAPket (a neutrophil elastase inhibitor), whereas Pefabloc completely inhibited the activation of latent MMP-2. All ultrasonic extracts of P. gingivalis activated latent MMP-2 in a concentration- and time-dependent manner. Also, latent MMP-2 was activated by purified arg-gingipain but less efficiently by lys-gingipain.

CONCLUSION

These findings suggest that P. gingivalis arg-gingipain and neutrophil elastase present in GCF can activate latent MMP-2, which may contribute in vivo to local periodontal tissue destruction.

Molecular fingerprinting of Porphyromonas gingivalis by PCR of repetitive extragenic palindromic (REP) sequences and comparison with other fingerprinting methods

Knowledge of the genetic structure of populations of potentially pathogenic bacteria is important in understanding the epidemiology of diseases. Porphyromonas gingivalis is thought to be an important aetiological agent in periodontal diseases and several methods have been used for typing strains of this species. Here, PCR with primers to repetitive extragenic palindromic sequences (REP-PCR) was compared with three other widely used molecular fingerprinting techniques -- restriction endonuclease analysis (REA), ribotyping and PCR with arbitrary primers (AP-PCR) -- to type P. gingivalis isolates from healthy and diseased periodontal sites. The data obtained with all four methods were in broad agreement and, with one exception, each subject harboured a single unique genotype of P. gingivalis. REP-PCR of P. gingivalis resulted in the production of 5-10 amplicons, which gave unique electrophoretic patterns in each individual (10 REP-PCR types in 10 patients) and similar results were obtained with AP-PCR. Two isolates from one subject appeared identical by REP-PCR and AP-PCR, but could be differentiated by ribotyping, although there was only minor polymorphism. Thus, ribotyping and REA were the most discriminating methods; however, these are time-consuming and expensive relative to the PCR-based techniques. REP-PCR has the advantage that the same pair of primers is used for all species, whereas AP-PCR needs to be optimised by screening a range of primers. These results show that REP-PCR is a useful and rapid technique for typing P. gingivalis.