Update on citric acid use in endodontic treatment: a systematic review.

This systematic review aims to analyse the available evidence concerning the use of citric acid (CA) in endodontics treatment and to assess its results in terms of different considerations: effect on smear layer removal, influence on sealer bond strength, activation effect by means of sonic or ultrasonic devices, effects on dentine surface, antibacterial activity, and effectiveness boost for regenerative procedures, releasing growth factors from dentin. To evaluate the results of CA as a final irrigant and compare them to other chelating agents. This review followed the PRISMA checklist. An electronic search was conducted in MEDLINE (OVID), Scopus (Elsevier) and the Web of Science (Thomson Reuters) databases. Risk of bias of included studies was evaluated using the modified CONSORT checklist and the PRIRATE checklist 2020 guidelines. 39 studies fulfilled the eligibility criteria to be included in this review: 27 in vitro studies using extracted human teeth, 10 in vitro studies using human dentin disks, and 2 RCT. Citric acid has proven to be effective in smear layer removal, showing better results in coronal and middle root thirds, improving its effect when combined with manual dynamic activation. There is no agreement regarding citric acid effect on sealer adhesion and adaptation to root canal walls due to heterogeneity within studies. Citric acid irrigation can decrease dentine microhardness and cause decalcification and erosion, especially when used before NaOCl. Citric acid has proven to be beneficial in regenerative endodontic procedures due to higher TGF-ß1 release.Trial registration: Prospero database CRD42021267055.

Inflammatory biomarkers in dentinal fluid as an approach to molecular diagnostics in pulpitis.

AIM: To explore a set of inflammatory biomarkers obtained from dentinal fluid (DF) from patients with symptomatic irreversible pulpitis (IP), reversible pulpitis (RP) and normal pulp (NP). METHODOLOGY: A cross-sectional exploratory study was performed, recruiting 64 patients on the basis of their respective pulp condition. DF samples were obtained from all patients (23, from IP patients; 20, from RP patients; and 21, from NP patients). Quantification of biomarkers was performed using a Luminex® MAGPIX platform system and multiplex assay kits. The Kruskal-Wallis test was used for comparisons with regard to pulp state. A simple logistic regression model and the odds ratio (OR) with a 95% level of confidence (P = 0.05) were used to evaluate associations between biomarker levels and pulpal diagnosis. The performance discrimination of the biomarkers was evaluated through the construction of a receiver operating characteristic (ROC) curve by calculating the area under the curve (AUC) for IP versus RP after logistic regression modelling. Youden criteria were used to establish cut-off points for biomarkers alone with AUC > 70 and P-value < 0.05, or estimated probabilities from the multivariable logistic model. RESULTS: The biomarkers that had significantly higher values in participants with IP versus RP were IL-1α, VEGF-α and FGF acid (P < 0.05). FGF acid (OR: 12.62; P = 0.0085; CI 95% 1.91-83.29) and VEGF-α (OR: 2.61; P = 0.0252; CI 95% 1.13-6.03) were associated with pulp diagnoses of IP versus RP. The AUC-ROC curve for FGF acid was 0.79. The model containing FGF acid, IL-1α, IL-6 and TIMP-1 had an AUC-ROC of 0.92 for IP versus RP with a significant difference from the FGF acid ROC curve (P = 0.0231). CONCLUSIONS: Dentinal fluid could be used to assay pulpal mediators in the molecular diagnosis of pulpitis. Despite the limitation of the clinical diagnostics used in the present study, it was possible to detect a difference between irreversible symptomatic pulpitis and reversible pulpitis associated with the following combined biomarkers: FGF acid + IL-6 + IL-1α, +TIMP-1.

Photodynamic therapy in endodontics.

Photodynamic therapy (PDT) is a treatment modality that was initiated in 1900; however, it was not until the last decade that PDT regained attention for its several favourable features during the treatment of microbial infections in endodontics. Recently, several papers advocated its use for root canal treatment. The concept of photodynamic inactivation requires microbial exposure to either exogenous or endogenous photosensitizer molecules, followed by visible light energy, typically wavelengths in the red/near-infrared region that cause the excitation of the photosensitizers resulting in the production of singlet oxygen and other reactive oxygen species that react with intracellular components and consequently produce cell inactivation and death. Recently, PDT has been suggested as a promising effective adjunct to standard antimicrobial intracanal cleaning and shaping for the treatment of periapical lesions. Current publications tested PDT in terms of bacterial load reduction in vivo, in vitro and ex vivo, showing promising results. The purpose of this article was to review the existing literature on PDT in the endodontic field regarding its mechanism of action, photosensitizers and light sources, limitations and clinical procedures. Although positive results have been demonstrated in vitro, there are considerably fewer in vivo investigations. In conclusion, more in vivo studies are needed on the use of antimicrobial PDT in root canal treatment.

Effectiveness of complementary irrigation routines in debriding pulp tissue from root canals instrumented with a single reciprocating file.

AIM: To compare histologically the debridement efficacy of four irrigation techniques in root canals instrumented with a reciprocating single file. METHODOLOGY: From recently extracted premolars with vital pulp, 68 were selected and classified as having round canals (mesiodistal diameter similar to buccolingual) or oval-shaped canals (mesiodistal diameter 2.5 times larger than buccolingual) (n = 32, each) by means of bidirectional radiographs. Four additional uninstrumented samples served as histological controls. The root canals of the specimens were accessed and then instrumented with Reciproc R25® and further assigned to one of four experimental groups according to the complementary irrigation technique: Group I, conventional syringe; Group II, passive ultrasonic irrigation; Group III, manual dynamic activation (MDA); and Group IV, EndoActivator® . Roots were then demineralized and the apical 3 mm was multi-sliced and processed for histologic examination. The percentage of residual pulp tissue was calculated at each cross section. Kruskal-Wallis and Mann-Whitney tests were used to evaluate the effects of irrigation technique, root canal shape and level of cross section on the percentage of residual pulp tissue (P < 0.05). RESULTS: Irrigation technique and root canal shape significantly influenced the percentage of residual pulp tissue (P < 0.05) of canals instrumented with the R25 instrument. Percentage of residual pulp tissue was significantly less using ultrasonic irrigation (P < 0.05), but there was no difference between other irrigation techniques (P > 0.05). Round canals retained significantly less percentage of residual pulp tissue compared to oval-shaped canals (P = 0.001). At 3 mm, there was less pulp tissue compared to levels 2 and 1 mm (P < 0.05). CONCLUSIONS: In canals instrumented with R25 files, ultrasonic irrigation was more effective in removing pulp tissue in the apical level, especially for the debridement of oval-shaped canals.

Short-term treatment outcome of pulpotomies in primary molars using mineral trioxide aggregate and Biodentine: a randomized clinical trial.

INTRODUCTION: An ideal pulpotomy agent for primary molars has been sought for many years. Recently, new materials that allow regeneration of residual pulp tissue have been developed. In this study, we compared the preliminary clinical results obtained using Biodentine and mineral trioxide aggregate (MTA) as pulp-dressing agents in pulpotomies of primary molars. METHODS: A randomized clinical study was performed in children aged 4-9 years with at least one primary tooth with decay or caries requiring pulp treatment. A total of 90 primary molars requiring pulpotomy were randomly allocated to the MTA or Biodentine group, and 84 pulpotomies were performed. Clinical and radiographic evaluations were undertaken 6 and 12 months after treatment. All teeth were restored with a reinforced zinc oxide-eugenol base and stainless steel crowns. Statistical analysis using Fisher's exact test was performed to determine the significant differences between the groups. RESULTS: A total of four clinical failures were observed; all involved gingival inflammation. The clinical success rate in the MTA Group after 12 months was 92 % (36/39), whereas the Biodentine Group obtained 97 % (38/39) (p = 0.346). All radiographic failures were observed at the 12-month follow-up evaluation. One molar from MTA Group showed internal resorption obtaining a radiographic success rate of 97 % (38/39). Two molars from the Biodentine Group showed radiographic failure (1 internal resorption and 1 periradicular radiolucency) obtaining a radiographic success rate of 95 % (37/39). CONCLUSIONS: Biodentine showed similar clinical results as MTA with comparable success rates when used for pulpotomies of primary molars. However, longer follow-up studies are required to confirm our findings. CLINICAL RELEVANCE: This article demonstrates the effectiveness of Biodentine as a primary teeth pulpotomy material, performing similar results as MTA at 12-months evaluation.

An evaluation of the periapical status of teeth with necrotic pulps using periapical radiography and cone-beam computed tomography.

AIM: To evaluate the presence or absence of periapical (PA) radiolucencies on individual roots of teeth with necrotic pulps, as assessed with digital PA radiographs and cone-beam computed tomography (CBCT). METHODOLOGY: Digital PA radiographs and CBCT scans were taken from 161 endodontically untreated teeth (from 155 patients) diagnosed with non-vital pulps (pulp necrosis with normal PA tissue, symptomatic apical periodontitis, asymptomatic apical periodontitis, acute apical abscess and chronic apical abscess). Images were assessed by two calibrated endodontists to analyse the radiographic PA status of the teeth. A consensus was reached in the event of any disagreement. The data were analysed using a McNemar's test, and significance was set at P ≤ 0.05. RESULTS: Three hundred and forty paired images of roots were assessed with both digital PA radiographs and CBCT images. Fifteen additional roots were identified with CBCT. PA radiolucencies were present in 132 (38.8%) roots when assessed with PA radiographs, and in 196 (57.6%) roots when assessed with CBCT. This difference was statistically significant (P < 0.05). In teeth diagnosed with pulp necrosis, symptomatic apical periodontitis or acute apical abscess, CBCT images revealed a statistically larger number of PA radiolucencies than did PA radiographs (P < 0.05). No statistical differences were observed between PA radiographs and CBCT in teeth classified with asymptomatic apical periodontitis (P = 0.31) or chronic apical abscess (P = 1). CONCLUSIONS: Unlike PA radiographs, CBCT revealed a higher prevalence of PA radiolucencies when endodontically untreated teeth with non-vital pulps were examined.

In vivo evaluation of the iPex and Root ZX electronic apex locators using various irrigants.

AIM: To evaluate in vivo the performance of the iPex and Root ZX electronic apex locators (EALs) in the presence of several irrigant solutions: 2.5% sodium hypochlorite (NaOCl) and 2% chlorhexidine (CHX). METHODOLOGY: Thirty-two single-rooted human teeth that were scheduled for extraction were selected. Teeth with metallic restorations, fractures, root resorption, pulp necrosis or open apices were not included The working length (WL) was determined electronically for the root canals with the iPex and Root ZX EALs in the presence of two different irrigant solutions, 2.5% NaOCl and 2% CHX. After the teeth had been extracted, a size 10 K-file was used to determine the reference working length (RWL), which was established at 0.5 mm short of the major foramen. In each case, the RWL was subtracted from the electronic measurements. Positive values indicated electronic measurements that exceeded the RWL (long measurements), whereas negative values indicated measurements that were short of the RWL. The values obtained with the different irrigants and EALs were compared using the paired t-test. Significance was set at P < 0.05. RESULTS: The accuracy of the iPex nor Root ZX EAL was not affected by 2.5% NaOCl or 2% CHX (P > 0.05). However, significant differences were observed between the readings of the iPex and Root ZX, irrespective of whether 2.5% NaOCl or 2% CHX was used as the irrigant (P < 0.05). The iPex was less accurate than the Root ZX in determining the RWL. CONCLUSIONS: The accuracy of neither the iPex nor Root ZX EAL was affected by the irrigant used. However, the iPex was less accurate than the Root ZX in determining the RWL both for 2.5% NaOCl and for 2% CHX.

Mandibular first molars with disto-lingual roots: review and clinical management.

The purpose of this review was (i) to conduct a literature review on the prevalence and morphologic classification of mandibular first molars with disto-lingual (DL) roots, and (ii) to discuss the clinical approach to diagnosis and root canal treatment of these teeth. A search was carried out on electronic (MEDLINE, PubMed and Cochrane) and hand databases, which covered all publications from 1970 to December 2011. Two reviewers independently assessed the studies and recorded type of study, origin and sample sizes, number of teeth with three roots and type of root canal configuration. Forty-five studies were identified with a total of 19,056 mandibular first molar teeth. The frequency of DL roots was 14.4% and was associated with certain ethnic populations. The most common canal configuration of mesial and distal roots was Vertucci types IV and I, respectively. No significant differences were observed in the prevalence of DL roots according to gender. Variable results related to side were observed as well as a trend in bilateral occurrence. The root length of the DL roots was in general shorter than that of the disto-buccal roots (DB). Most DL roots had a greater angle of curvature and a smaller radius of curvature in a bucco-lingual orientation. The best methods to identify DL roots are a 25° mesial parallax periapical radiograph or cone-beam computed tomography (CBCT). A trapezoidal shape access cavity is desirable to locate the orifice of the DL canal. Clinicians should be aware of the variable furcation levels during coronal pre-flaring or post-space preparation to avoid furcal/strip perforations and a weakening of DL roots.

Centring ability and apical transportation after overinstrumentation with ProTaper Universal and ProFile Vortex instruments.

AIM: To evaluate morphological changes to the major foramen after overinstrumentation with ProTaper Universal and ProFile Vortex Ni-Ti rotary instruments. METHODOLOGY: Twenty-eight mesiobuccal canals of maxillary and mandibular first molars were divided into two groups of 14 canals each. The root canals were prepared with ProTaper Universal or ProFile Vortex instruments. ProTaper and Vortex instruments were used until the file tip protruded 1 mm beyond the working length (0.5 mm beyond the major foramen). The major foramen was photographed before and after overinstrumentation with each file of the two systems used. The images were superimposed and evaluated using Adobe Photoshop. The parameters evaluated were canal transportation, centring ability and shape of the major foramen. Transportation and centring ability were calculated in two directions: the direction of maximum curvature (MC) and a direction vertical to the maximum curvature (VC). Measurements of canal transportation and centring ability were analysed by anova followed by post hoc least significance difference (LSD) multiple comparisons. RESULTS: No significant differences were observed amongst the different instruments with respect to centring ability in either direction (P > 0.05). The F3 ProTaper Universal instrument was associated with a higher mean values for transportation in the direction of MC (P < 0.05) than the S1, S2 and F1 ProTaper Universal instruments and the size 15, 0.06 taper, size 20, 0.06 taper, and size 25, 0.06 taper ProFile Vortex instruments. The size 30, 0.06 taper ProFile Vortex instrument had a larger mean value for transportation in the direction of MC (P < 0.05) than the S1 ProTaper Universal and size 15, 0.06 taper ProFile Vortex instruments. The S1, S2, F1, F2 and F3 ProTaper Universal files and the size 15, 0.06 taper, size 20, 0.06 taper, size 25, 0.06 taper, and size 30, 0.06 taper ProFile Vortex files produced an oval foramen in 71%, 71%, 85%, 85%, 71%, 71%, 85%, 85% and 89% of the cases, respectively. CONCLUSIONS: In most samples, the ProTaper Universal and ProFile Vortex files produced transportation of the major foramen and created an oval-shaped major foramen after overinstrumentation.

Managing severe curvature of radix entomolaris: three-dimensional analysis with cone beam computed tomography.

AIM: To present a case of a mandibular first molar with an additional distolingual root [radix entomolaris (RE)] and to discuss the use of cone beam computed tomography (CBCT) for its identification and management during root canal treatment. SUMMARY: A 52-year-old Caucasian woman was referred for root canal treatment of the right mandibular first molar (tooth 46). After clinical and radiographic examination, a symptomatic irreversible pulpitis was diagnosed. Three periapical radiographs with different horizontal angulations revealed the presence of an additional distolingual root. This extra root, termed RE, has an incidence of <5% in the Caucasian population. A CBCT examination was also taken, which revealed a severe root canal curvature, especially in the middle third, of this supernumerary root. CBCT provided more accurate information in terms of RE inclination and root canal curvature before commencing root canal treatment. The conventional access opening was modified into a more trapezoidal cavity, and five root canals were found. All canals were instrumented with new nickel-titanium (NiTi) files to reduce the risk of fractured instruments. After preparation, the root canals were filled using thermoplastified techniques. The 1-year follow-up periapical radiographs and CBCT images revealed a continuous periodontal space with no signs of apical periodontitis. KEY LEARNING POINTS: • Cone beam computed tomography imaging is useful in identifying the root canal system and the surrounding structures. • An accurate detection of supernumerary roots, such as RE, can avoid complications during and after root canal treatment. • The analysis of root canal curvature is important because instrument fracture has been linked to angle and radius of curvature. • The use of new instruments can reduce the incidence of instrument fracture.

Comparison of active versus passive audiovisual distraction tools on children's behaviour, anxiety and pain in paediatric dentistry: a randomised crossover clinical trial.

AIM: To determine the effect of active distraction when playing PlayStation® video games, compared to passive distraction when watching a cartoon with audiovisual eyeglasses, on parental perception of patients' anxiety, and children's anxiety, pain, behaviour and heart rate during restorative procedures in paediatric dentistry. MATERIALS AND METHODS: Study design: Randomised crossover clinical trial. There were 34 patients in the cartoon film group (passive distraction) and 34 in the Playstation® video game group (active distraction), aged 6-8 years, who required a minimum of 2 visits for restorative treatment. Rimax® iVision 5.0 eyeglasses were used in both groups. Parental perception of patients' anxiety (Modified Corah Dental Anxiety Scale), and children's anxiety (Venham Picture Test), pain (Wong-Baker Faces Scale), behaviour (Frankl Scale) and heart rate were evaluated at each of the treatment visits. Preference for and satisfaction with the audiovisual product were also assessed. RESULTS: There were significant differences in self-reported pain between control (P=0.016) and experimental (P=0.013) visits in both groups, with lower values in the Playstation® video game group. No significant differences were found (P>0.05) in the other variables evaluated with the use of active distraction. A significant increase in heart rate was recorded at each treatment visit (P=0.0001) when the anaesthetic was injected. All the patients wanted to continue watching or playing their chosen cartoon or Playstation® video game during subsequent visits. CONCLUSION: The use of PlayStation® video games for active audiovisual distraction, compared with passive distraction with a cartoon, improved self-reported pain but did not reduce parents' perception of patients' anxiety, pain, global behaviour, or heart rate. Both distraction methods were accepted by paediatric patients.

Long-term evaluation of primary teeth molar pulpotomies with Biodentine and MTA: a CONSORT randomized clinical trial.

BACKGROUND: Calcium silicate-based materials have become widely used in recent years due to their positive effect on pulp cells, which stimulate tertiary dentin formation. AIM: The aim of the present study was to evaluate and compare clinically and radiographically the performance of MTA and Biodentine as pulp-dressing materials following pulpotomy in primary molars at 24-month follow-up. DESIGN: Molars from patients aged 4-9 years scheduled for pulpotomy were treated with either MTA or Biodentine followed by a stainless-steel crown. These molars were clinically and radiographically followed up at 6, 12, 18, and 24 months. Statistical analysis was performed to detect differences between the two groups. RESULTS: A total of 84 pulpotomies were performed obtaining a total success rate of 99.4 and 97.2% for Biodentine and MTA, respectively, at 24 months, showing no statistically significant differences between the two groups. CONCLUSION: 24-month follow-up showed that Biodentine and MTA have similar effectiveness.

[Survey on innovation in the teaching of Geriatrics at the Spanish Medical Schools]. / Encuesta sobre innovación en la docencia de Geriatría en las Facultades de Medicina españolas.

OBJECTIVE: To identify the innovations in teaching of Geriatrics at the Spanish Medical Schools. METHODOLOGY: Interviews with those responsible for Geriatrics teaching at the Spanish Medical Schools through a short online survey. Existing Geriatrics curricula and responsible professors were identified by reviewing the curricula of the different Medical Schools. RESULTS: 35 of the 42 Medical Schools incorporated teaching in Geriatrics in 2019 with an answer rate of 94.3%. Regarding Geriatrics training it stand out classic methods (master classes, clinical rotations, and theoretical seminars), followed by innovation of teaching programs (clinical simulation and use of new technologies). While OSCE and portfolio stand out among the innovative evaluation tools of Geriatrics teaching. Of the 33 Medical Schools with Geriatrics teaching surveyed, 60.6% of them included the use of at least one innovative teaching or evaluation methodology. CONCLUSIONS: Although the classical model predominates as a teaching methodology in Geriatrics, different innovations are also used in the undergraduate teaching in Spain. It is necessary to continue working in this area that may help a better level of skills in Geriatrics for our students.

Efficacy of three different rotary files to remove gutta-percha and Resilon from root canals.

AIM: To evaluate the efficacy of ProTaper Retreatment files, Mtwo Retreatment files and Twisted Files for removal of gutta-percha and Resilon in straight root canals. METHODOLOGY: Ninety single root canals were instrumented and randomly allocated into 6 groups of 15 specimens each with regards to the filling material and instruments used. Group 1: gutta-percha/ProTaper; Group 2: Resilon/ProTaper; Group 3: gutta-percha/Mtwo; Group 4: Resilon/Mtwo; Group 5: gutta-percha/Twisted Files; Group 6: Resilon/Twisted Files. For all roots, the following data were recorded: procedural errors, duration of retreatment, canal wall cleanliness through optical microscope and cone beam computed tomography (CBCT). Data were statistically analysed, and the level of significance was set at P=0.05. RESULTS: No system completely removed the root filling material from root canal walls. No significant differences were observed between the rotary systems in terms of the area of filling material left within the canals (P>0.05). There were statistically significant differences between the filling materials: Resilon/Real Seal had less residual material than gutta-percha/AH plus (CBCT: P=0.01; microscope: P=0.018). Mtwo Retreatment files were more rapid when removing filling material than ProTaper Retreatment files (P=0.19) and Twisted Files (P=0.04). CONCLUSIONS: No system removed the root filling materials entirely. Mtwo Retreatment files required less time to remove root filling material than the other instruments. Resilon was removed significantly better from the canal walls than gutta-percha, irrespective of the rotary instruments used.

Supernumerary fourth molar and dental pathologies in a Chalcolithic individual from the El Mirador Cave site (Sierra de Atapuerca, Burgos, Spain).

We present a middle-aged Chalcolithic male with a supernumerary distomolar in the mandible. The prevalence of supernumerary teeth in present-day populations is low, ranging from 0.1% to 3.4%; most supernumerary teeth are documented in the anterior and molar regions of the maxilla in present populations. However, the prevalence of supernumerary molars in past populations is still unknown. Moreover, a complete pathological study has been done of this individual. Maxilla, mandible and teeth have been analyzed searching for dental pathologies. A cone-beam computed tomography (CBCT) analysis of mandibular and maxillary fragments was performed to check the evidence of hyperdontia. Dental wear and maxillary alveolar bone have been analyzed with environmental scanning electron microscope (ESEM) to improve the diagnosis of an abscess and evidence of tooth picking. This individual shows a left distomolar in the mandible without any evidence of other supernumerary teeth. The fourth molar is not associated with any congenital disease. However, this individual suffered severe dental wear and a variety of oral pathologies such as, dental decay, abscesses, pulpitis, periodontal disease, toothpicking marks in an upper molar, arthritis of the temporomandibular joint and malocclusion associated with high masticatory loads. To our knowledge, this individual from El Mirador Cave (Sierra de Atapuerca, Spain) shows the most ancient case of a fourth molar documented. The poor oral health of this individual corresponds to the general dental health of Chalcolithic populations.

Metabolism of Lactococcus lactis subsp. cremoris MG 1363 in acid stress conditions.

The metabolism of glucose by Lactococcus lactis subsp. cremoris MG 1363 remains homolactic whatever the pH of the culture medium. The growth rate decreased with the acidification of the medium until a limit pH value of 4.0 for which no growth was observed. In contrast, the specific rate of glucose consumption decreased only for very low pH values, i.e., below 4.5. The efficiency of biomass synthesis relative to the energy supply decreased when the medium pH diminished, as illustrated by Y(ATP) values. This observation was related to the increase in both components of the proton-motive force when the pH decreased. The growth stopped when the internal pH reached a limit value of 5.4 due to organic acid accumulation.

Protective effect caused by the exopolymer excreted by Pseudoalteromonas antarctica NF(3) on liposomes against the action of octyl glucoside.

The capacity of the glycoprotein (GP) excreted by Pseudoalteromonas antarctica NF(3), to protect phosphatidylcholine (PC) liposomes against the action of octyl glucoside (OG) was studied in detail. Increasing amounts of GP assembled with liposomes resulted for the same interaction step in a linear increase in the effective surfactant to PC molar ratios (Re) and in a linear fall in the surfactant partitioning between bilayer and the aqueous phase (partition coefficients K). Thus, the higher the proportion of GP assembled with liposomes the lower the surfactant ability to alter the permeability of vesicles and the lower its affinity with these bilayer structures. In addition, increasing GP proportions resulted in a progressive increase of the free surfactant concentration (S(W)) needed to produce the same alterations in liposomes. The fact that S(W) was always lower than the surfactant critical micelle concentration indicates that the interaction was mainly ruled by the action of surfactant monomers, regardless of the amount of assembled GP.

The succinate:menaquinone reductase of Bacillus cereus: characterization of the membrane-bound and purified enzyme.

Utilization of external succinate by Bacillus cereus and the properties of the purified succinate:menaquinone-7 reductase (SQR) were studied. Bacillus cereus cells showed a poor ability for the uptake of and respiratory utilization of exogenous succinate, thus suggesting that B. cereus lacks a specific succinate uptake system. Indeed, the genes coding for a succinate-fumarate transport system were missing from the genome database of B. cereus. Kinetic studies of membranes indicated that the reduction of menaquinone-7 is the rate-limiting step in succinate respiration. In accordance with its molecular characteristics, the purified SQR of B. cereus belongs to the type-B group of SQR enzymes, consisting of a 65-kDa flavoprotein (SdhA), a 29-kDa iron-sulphur protein (SdhB), and a 19-kDa subunit containing 2 b-type cytochromes (SdhC). In agreement with this, we could identify the 4 conserved histidines in the SdhC subunit predicted by the B. cereus genome database. Succinate reduced half of the cytochrome b content. Redox titrations of SQR-cytochrome b-557 detected 2 components with apparent midpoint potential values at pH 7.6 of 79 and -68 mV, respectively; the components were not spectrally distinguishable by their maximal absorption bands as those of Bacillus subtilis. The physiological properties and genome database analyses of B. cereus are consistent with the cereus group ancestor being an opportunistic pathogen.