A novel microplate-based spectrophotometric method for the quantitative assessment of freshwater bacterial coaggregation kinetics.

Coaggregation, the specific recognition and adhesion of genetically distinct bacteria, is proposed to contribute to the development of freshwater biofilms. This work aimed to develop a microplate-based system to measure and model the kinetics of freshwater bacterial coaggregation. Blastomonas natatoria 2.1 and Micrococcus luteus 2.13 were evaluated for coaggregation ability using 24-well microplates containing novel dome shaped wells (DSWs) and standard flat-bottom wells. Results were compared to a tube-based visual aggregation assay. The DSWs facilitated the reproducible detection of coaggregation via spectrophotometry and the estimation of coaggregation kinetics using a linked mathematical model. Quantitative analysis using DSWs was more sensitive than the visual tube aggregation assay and subject to substantially less variation than flat-bottom wells. Collectively these results demonstrate the utility of the DSW-based method and improve upon the current toolkit for studying freshwater bacterial coaggregation.

The effect of inoculum source and fluid shear force on the development of in vitro oral multispecies biofilms.

AIMS: Saliva has been previously used as an inoculum for in vitro oral biofilm studies. However, the microbial community profile of saliva is markedly different from hard- and soft-tissue-associated oral biofilms. Here, we investigated the changes in the biofilm architecture and microbial diversity of in vitro oral biofilms developed from saliva, tongue or plaque-derived inocula under different salivary shear forces. METHODS AND RESULTS: Four inoculum types (saliva, bacteria harvested from the tongue, toothbrush and curette-harvested plaque) were collected and pooled. Biofilms (n ≥ 15) were grown for 20 h in cell-free human saliva flowing at three different shear forces. Stained biofilms were imaged using a confocal laser scanning microscope. Biomass, thickness and roughness were determined by image analysis and bacterial community composition analysed using Ion Torrent. All developed biofilms showed a significant reduction in observed diversity compared with their respective original inoculum. Shear force altered biofilm architecture of saliva and curette-collected plaque and community composition of saliva, tongue and curette-harvested plaque. CONCLUSIONS: Different intraoral inocula served as precursors of in vitro oral polymicrobial biofilms which can be influenced by shear. SIGNIFICANCE AND IMPACT OF THE STUDY: Inoculum selection and shear force are key factors to consider when developing multispecies biofilms within in vitro models.

Effects of vitamin D2 or D3 supplementation on glycaemic control and cardiometabolic risk among people at risk of type 2 diabetes: results of a randomized double-blind placebo-controlled trial.

AIMS: To investigate the effect of short-term vitamin D supplementation on cardiometabolic outcomes among individuals with an elevated risk of diabetes. METHODS: In a double-blind placebo-controlled randomized trial, 340 adults who had an elevated risk of type 2 diabetes (non-diabetic hyperglycaemia or positive diabetes risk score) were randomized to either placebo, 100,000 IU vitamin D2 (ergocalciferol) or 100,000 IU vitamin D3 (cholecalciferol), orally administered monthly for 4 months. The primary outcome was change in glycated haemoglobin (HbA1c) between baseline and 4 months, adjusted for baseline. Secondary outcomes included: blood pressure; lipid levels; apolipoprotein levels; C-reactive protein levels; pulse wave velocity (PWV); anthropometric measures; and safety of the supplementation. RESULTS: The mean [standard deviation (s.d.)] 25-hydroxyvitamin D [25(OH)D]2 concentration increased from 5.2 (4.1) to 53.9 (18.5) nmol/l in the D2 group, and the mean (s.d.) 25(OH)D3 concentration increased from 45.8 (22.6) to 83.8 (22.7) nmol/l in the D3 group. There was no effect of vitamin D supplementation on HbA1c: D2 versus placebo: -0.05% [95% confidence interval (CI) -0.11, 0.02] or -0.51 mmol/mol (95% CI -1.16, 0.14; p = 0.13); D3 versus placebo: 0.02% (95% CI -0.04, 0.08) or 0.19 mmol/mol (95% CI -0.46, 0.83; p = 0.57). There were no clinically meaningful effects on secondary outcomes, except PWV [D2 versus placebo: -0.68 m/s (95% CI -1.31, -0.05); D3 versus placebo -0.73 m/s (95% CI -1.42, -0.03)]. No important safety issues were identified. CONCLUSIONS: Short-term supplementation with vitamin D2 or D3 had no effect on HbA1c. The modest reduction in PWV with both D2 and D3 relative to placebo suggests that vitamin D supplementation has a beneficial effect on arterial stiffness.

Biomedical applications of nisin.

Nisin is a bacteriocin produced by a group of Gram-positive bacteria that belongs to Lactococcus and Streptococcus species. Nisin is classified as a Type A (I) lantibiotic that is synthesized from mRNA and the translated peptide contains several unusual amino acids due to post-translational modifications. Over the past few decades, nisin has been used widely as a food biopreservative. Since then, many natural and genetically modified variants of nisin have been identified and studied for their unique antimicrobial properties. Nisin is FDA approved and generally regarded as a safe peptide with recognized potential for clinical use. Over the past two decades the application of nisin has been extended to biomedical fields. Studies have reported that nisin can prevent the growth of drug-resistant bacterial strains, such as methicillin-resistant Staphylococcus aureus, Streptococcus pneumoniae, Enterococci and Clostridium difficile. Nisin has now been shown to have antimicrobial activity against both Gram-positive and Gram-negative disease-associated pathogens. Nisin has been reported to have anti-biofilm properties and can work synergistically in combination with conventional therapeutic drugs. In addition, like host-defence peptides, nisin may activate the adaptive immune response and have an immunomodulatory role. Increasing evidence indicates that nisin can influence the growth of tumours and exhibit selective cytotoxicity towards cancer cells. Collectively, the application of nisin has advanced beyond its role as a food biopreservative. Thus, this review will describe and compare studies on nisin and provide insight into its future biomedical applications.

Evaluation of the ability of Acinetobacter baumannii to form biofilms on six different biomedical relevant surfaces.

UNLABELLED: The human opportunistic pathogen, Acinetobacter baumannii, has the propensity to form biofilms and frequently cause medical device-related infections in hospitals. However, the physio-chemical properties of medical surfaces, in addition to bacterial surface properties, will affect colonization and biofilm development. The objective of this study was to compare the ability of A. baumannii to form biofilms on six different materials common to the hospital environment: glass, porcelain, stainless steel, rubber, polycarbonate plastic and polypropylene plastic. Biofilms were developed on material coupons in a CDC biofilm reactor. Biofilms were visualized and quantified using fluorescent staining and imaged using confocal laser scanning microscopy (CLSM) and by direct viable cell counts. Image analysis of CLSM stacks indicated that the mean biomass values for biofilms grown on glass, rubber, porcelain, polypropylene, stainless steel and polycarbonate were 0·04, 0·26, 0·62, 1·00, 2·08 and 2·70 µm(3) /µm(2) respectively. Polycarbonate developed statistically more biofilm mass than glass, rubber, porcelain and polypropylene. Viable cell counts data were in agreement with the CLSM-derived data. In conclusion, polycarbonate was the most accommodating surface for A. baumannii ATCC 17978 to form biofilms while glass was least favourable. Alternatives to polycarbonate for use in medical and dental devices may need to be considered. SIGNIFICANCE AND IMPACT OF THE STUDY: In the hospital environment, Acinetobacter baumannii is one of the most persistent and difficult to control opportunistic pathogens. The persistence of A. baumannii is due, in part, to its ability to colonize surfaces and form biofilms. This study demonstrates that A. baumannii can form biofilms on a variety of different surfaces and develops substantial biofilms on polycarbonate - a thermoplastic material that is often used in the construction of medical devices. The findings highlight the need to further study the in vitro compatibility of medical materials that could be colonized by A. baumannii and allow it to persist in hospital settings.

High-throughput quantitative method for assessing coaggregation among oral bacterial species.

UNLABELLED: This paper describes a high-throughput method that relies upon a microplate reader to score coaggregation 60 min postmixing, and use of a high-speed real-time imaging technology to describe the rate of coaggregation over time. The results of visual, microplate, and FlowCam(™) aggregation scores for oral bacteria Streptococcus gordonii, Streptococcus oralis, and Actinomyces oris, whose ability to coaggregate are well characterized, are compared. Following mixing of all possible pairs, the top fraction of the supernatant was added to a microplate to quantify cell-density. Pairs were also passed through a flow cell within a FlowCam(™) to quantify the rate of coaggregation of each pair. Results from both the microplate and FlowCam(™) approaches correlated with corresponding visual coaggregation scores and microscopic observations. The microplate-based assay enables high-throughput screening, whereas the FlowCam(™) -based assay validates and quantifies the extent that autoaggregation and coaggregation occur. Together these assays open the door for future in-depth studies of autoaggregation and coaggregation among large panels of test strains. SIGNIFICANCE AND IMPACT OF THE STUDY: Coaggregation between bacterial species is integral to multi-species biofilm development. Difficulties in rapidly and reproducibly identifying and quantifying coaggregation have limited mechanistic studies. This paper demonstrates two complementary quantitative methods to screen for coaggregation. The first approach uses a microplate-based high-throughput approach and the other uses a FlowCam(™) device. The microplate-based approach enables rapid detection of coaggregation between candidate coaggregating pairs of strains simultaneously while controlling for variation between replicates. The FlowCam(™) approach allows for in-depth analysis of the rates of coaggregation and size of aggregates formed.

Paediatric traumatic cardiac arrest: data from the Joint Theatre Trauma Registry.

BACKGROUND: Traumatic cardiac arrest (TCA) in children is associated with a low probability of survival and poor neurological outcome in survivors. Since 2003, over 600 seriously injured local national children have been treated at deployed UK military medical treatment facilities during the Iraq and Afghanistan conflicts. A number of these were in cardiac arrest after sustaining traumatic injuries. This study defined outcomes from paediatric TCA in this cohort. METHODS: A retrospective database review was undertaken using the UK Joint Theatre Trauma Registry. This includes UK military, coalition military, civilians and local security forces personnel who prompted trauma team activation. All children in this series were local nationals. Patients aged less than 18 years who presented between January 2003 and April 2014, and who underwent cardiopulmonary resuscitation, were included. RESULTS: 27 children with TCA were included. Four children survived to discharge from the medical treatment facility (14.8%), though limited data are available regarding the long-term neurological outcome in these patients. CONCLUSIONS: This study demonstrates that the outcomes for paediatric TCA in our military field hospitals were similar to other paediatric civilian and adult military studies, despite patients being injured by severe blast injuries. Further work is needed to define the optimal management of paediatric TCA.

Branching ratios for the reactions of OH with ethanol amines used in carbon capture and the potential impact on carcinogen formation in the emission plume from a carbon capture plant.

The OH initiated gas-phase chemistry of several amines that are potential candidates for use in post-combustion carbon capture (PCCC) plants have been studied by laser flash photolysis with OH monitored by laser induced fluorescence. The rate coefficients for the reaction of OH with N-methylethanolamine (MMEA) and N,N-dimethylethanolamine (DMEA) have been measured as a function of temperature (∼300-500 K): k(OH+MMEA) = (8.51 ± 0.65) × 10(-11)(T/298)(-(0.79±0.22), k(OH+DMEA) = (6.85 ± 0.25) × 10(-11)(T/298)(-(0.44±0.12). The results for DMEA lie between previous values. This is the first kinetic study of the OH + MMEA reaction. At low pressures in the presence of oxygen, OH is recycled in the DMEA reaction as has been observed for other tertiary amines. Branching ratios for OH abstraction with MEA, DMEA and MMEA are dominated by abstraction from the αCH2 group. Abstraction from N-H is determined to be 0.38 ± 0.06 for MEA and 0.52 ± 0.06 for MMEA at 298 K. The impact of these studies has been assessed by using a modified chemical box model to calculate downwind concentrations of nitramines and nitrosamine formed in the photo-oxidation of MEA. Under clear sky conditions, the simulations suggest that current safe guidelines for nitramines may be significantly exceeded with predicted MEA emission rates.

Theoretical study of the reactions of Criegee intermediates with ozone, alkylhydroperoxides, and carbon monoxide.

The reaction of Criegee intermediates (CI) with ozone, O3, has been re-examined with higher levels of theory, following earlier reports that O3 could be a relevant sink of CI. The updated rate coefficients indicate that the reaction is somewhat slower than originally anticipated, and is not expected to play a role in the troposphere. In experimental (laboratory) conditions, the CI + O3 reaction can be important. The reaction of CI with ROOH intermediates is found to proceed through a pre-reactive complex, and the insertion process allows for the formation of oligomers in agreement with recent experimental observations. The CI + ROOH reaction also allows for the formation of ether oxides, which don't react with H2O but can oxidize SO2. Under tropospheric conditions, the ether oxides are expected to re-dissociate to the CI + ROOH complex, and ultimately follow the insertion reaction forming a longer-chain hydroperoxide. The CI + ROOH reaction is not expected to play a significant role in the atmosphere. The reaction of CI with CO molecules was studied at very high levels of theory, but no energetically viable route was found, leading to very low rate coefficients. These results are compared against an extensive literature overview of experimental data.

S-aryl-L-cysteine sulphoxides and related organosulphur compounds alter oral biofilm development and AI-2-based cell-cell communication.

AIMS: To design and synthesize a library of structurally related, small molecules related to homologues of compounds produced by the plant Petiveria alliacea and determine their ability to interfere with AI-2 cell-cell communication and biofilm formation by oral bacteria. Many human diseases are associated with persistent bacterial biofilms. Oral biofilms (dental plaque) are problematic as they are often associated with tooth decay, periodontal disease and systemic disorders such as heart disease and diabetes. METHODS AND RESULTS: Using a microplate-based approach, a bio-inspired small molecule library was screened for anti-biofilm activity against the oral species Streptococcus mutans UA159, Streptococcus sanguis 10556 and Actinomyces oris MG1. To complement the static screen, a flow-based BioFlux microfluidic system screen was also performed under conditions representative of the human oral cavity. Several compounds were found to display biofilm inhibitory activity in all three of the oral bacteria tested. These compounds were also shown to inhibit bioluminescence by Vibrio harveyi and were thus inferred to be quorum sensing (QS) inhibitors. CONCLUSION: Due to the structural similarity of these compounds to each other, and to key molecules in AI-2 biosynthetic pathways, we propose that these molecules potentially reduce biofilm formation via antagonism of QS or QS-related pathways. SIGNIFICANCE AND IMPACT OF THE STUDY: This study highlights the potential for a non-antimicrobial-based strategy, focused on AI-2 cell-cell signalling, to control the development of dental plaque. Considering that many bacterial species use AI-2 cell-cell signalling, as well as the increased concern of the use of antimicrobials in healthcare products, such an anti-biofilm approach could also be used to control biofilms in environments beyond the human oral cavity.

Mini-review: Microbial coaggregation: ubiquity and implications for biofilm development.

Coaggregation is the specific recognition and adherence of genetically distinct microorganisms. Because most biofilms are polymicrobial communities, there is potential for coaggregation to play an integral role in spatiotemporal biofilm development and the moderation of biofilm community composition. However, understanding of the mechanisms contributing to coaggregation and the relevance of coaggregation to biofilm ecology is at a very early stage. The purpose of this review is to highlight recent advances in the understanding of microbial coaggregation within different environments and to describe the possible ecological ramifications of such interactions. Bacteria that coaggregate with many partner species within different environments will be highlighted, including oral streptococci and oral bridging organisms such as fusobacteria, as well as the freshwater sphingomonads and acinetobacters. Irrespective of environment, it is proposed that coaggregation is essential for the orchestrated development of multi-species biofilms.

Salt or sugar for your injured brain? A meta-analysis of randomised controlled trials of mannitol versus hypertonic sodium solutions to manage raised intracranial pressure in traumatic brain injury.

BACKGROUND: Rising intracranial pressure (ICP) is a poor prognostic indicator in traumatic brain injury (TBI). Both mannitol and hypertonic sodium solutions are used to treat raised ICP in patients with TBI. OBJECTIVE: This meta-analysis compares the use of mannitol versus hypertonic sodium solutions for ICP control in patients with TBI. DATA SOURCES AND STUDY ELIGIBILITY: Randomised clinical trials in adults with TBI and evidence of raised ICP, which compare the effect on ICP of hypertonic sodium solutions and mannitol. METHODS: The primary outcome measure is the pooled mean reduction in ICP. Studies were combined using a Forest plot. RESULTS: Six studies were included, comprising 171 patients (599 episodes of raised ICP). The weighted mean difference in ICP reduction, using hypertonic sodium solutions compared with mannitol, was 1.39 mm Hg (95% CI -0.74 to 3.53). LIMITATIONS: Methodological differences between studies limit the conclusions of this meta-analysis. CONCLUSIONS: The evidence shows that both agents effectively lower ICP. There is a trend favouring the use of hypertonic sodium solutions in patients with TBI.

Circulating 25-hydroxyvitamin D concentration and the risk of type 2 diabetes: results from the European Prospective Investigation into Cancer (EPIC)-Norfolk cohort and updated meta-analysis of prospective studies.

AIMS/HYPOTHESIS: Epidemiological evidence is suggestive, but limited, for an association between circulating 25-hydroxyvitamin D (25[OH]D) and risk of type 2 diabetes. We conducted a systematic review and meta-analysis that included new data from previously unpublished studies. METHODS: Using a nested case-cohort design in the European Prospective Investigation into Cancer (EPIC)-Norfolk study, we identified a random subcohort and incident type 2 diabetes cases occurring between baseline (1993-1997) and 2006. In the Ely prospective study we identified incident type 2 diabetes cases between 1990 and 2003. We conducted a systematic review of prospective studies on 25(OH)D and type 2 diabetes published in MEDLINE or EMBASE until 31 January 2012, and performed a random-effects meta-analysis combining available evidence with results from the EPIC-Norfolk and Ely studies. RESULTS: In EPIC-Norfolk, baseline 25(OH)D was lower among incident type 2 diabetes cases (mean [SD] 61.6 [22.4] nmol/l; n=621) vs non-case subcohort participants (mean 65.3 [23.9] nmol/l; n=826). There was an inverse association between baseline 25(OH)D and incident type 2 diabetes in multivariable-adjusted analyses: HR (95% CI) 0.66 (0.45, 0.97), 0.53 (0.34, 0.82), 0.50 (0.32, 0.76), p trend <0.001, comparing consecutive increasing 25(OH)D quartiles with the lowest. In Ely, 37 incident type 2 diabetes cases were identified among 777 participants. In meta-analysis, the combined RR of type 2 diabetes comparing the highest with lowest quartile of 25(OH)D was 0.59 (0.52, 0.67), with little heterogeneity (I (2) =2.7%, p=0.42) between the 11 studies included (3,612 cases and 55,713 non-cases). CONCLUSIONS/INTERPRETATION: These findings demonstrate an inverse association between circulating 25(OH)D and incident type 2 diabetes. However, causal inference should be addressed through adequately dosed randomised trials of vitamin D supplementation or genetic Mendelian randomisation experiments.

Production of cell-cell signalling molecules by bacteria isolated from human chronic wounds.

AIM: To (i) identify chronic wound bacteria and to test their ability to produce acyl-homoserine-lactones (AHLs) and autoinducer-2 (AI-2) cell-cell signalling molecules and (ii) determine whether chronic wound debridement samples might contain these molecules. METHODS AND RESULTS: Partial 16S rRNA gene sequencing revealed the identity of 46 chronic wound strains belonging to nine genera. Using bio-reporter assays, 69.6% of the chronic wound strains were inferred to produce AI-2, while 19.6% were inferred to produce AHL molecules. At least one strain from every genus, except those belonging to the genera Acinetobacter and Pseudomonas, were indicated to produce AI-2. Production of AI-2 in batch cultures was growth-phase dependent. Cross-feeding assays demonstrated that AHLs were produced by Acinetobacter spp., Pseudomonas aeruginosa and Serratia marcescens. Independent from studies of the bacterial species isolated from wounds, AHL and/or AI-2 signalling molecules were detected in 21 of 30 debridement samples of unknown microbial composition. CONCLUSION: Chronic wound bacteria produce cell-cell signalling molecules. Based on our findings, we hypothesize that resident species generally produce AI-2 molecules, and aggressive transient species associated with chronic wounds typically produce AHLs. Both these classes of cell-cell signals are indicated to be present in human chronic wounds. SIGNIFICANCE AND IMPACT OF THE STUDY: Interbacterial cell-cell signalling may be an important factor influencing wound development and if this is the case, the presence of AHLs and AI-2 could be used as a predictor of wound severity. Manipulation of cell-cell signalling may provide a novel strategy for improving wound healing.

Physicochemical parameters influencing coaggregation between the freshwater bacteria Sphingomonas natatoria 2.1 and Micrococcus luteus 2.13.

The aim of this study was to explore the physicochemical parameters that influence coaggregation between the freshwater bacteria Sphingomonas natatoria 2.1 and Micrococcus luteus 2.13. Using visual coaggregation assays, the effect of different buffers, solutions of differing ionic strength, pH, temperature, and viscosity on the degree of coaggregation was assessed. Coaggregation occurred maximally in distilled water but was inhibited when coaggregates were suspended in a commonly-used oral bacterial coaggregation buffer, saline solutions, and Tris-Cl buffers. Coaggregation was weakly expressed in standard laboratory buffers. The ionic strength of inorganic salt solutions required to inhibit coaggregation depended upon the inorganic salt being tested. Coaggregation occurred at a pH of 3-10, between 5 and 80°C and was inhibited in solutions with a viscosity of 22.5 centipoises at 20°C. Inhibition of coaggregation with NaCl impaired biofilm development. When developing buffers to test for coaggregation, the natural liquid environment should be considered. Coaggregation between S. natatoria 2.1 and M. luteus 2.13 is only affected by physicochemical conditions beyond those typically found in natural freshwater ecosystems. Such a robust ability to coaggregate may enhance the ability of S. natatoria 2.1 and M. luteus 2.13 to develop a niche in freshwater biofilms.

Coaggregation by the freshwater bacterium Sphingomonas natatoria alters dual-species biofilm formation.

Coaggregation is hypothesized to enhance freshwater biofilm development. To investigate this hypothesis, the ability of the coaggregating bacterium Sphingomonas natatoria to form single- and dual-species biofilms was studied and compared to that of a naturally occurring spontaneous coaggregation-deficient variant. Attachment assays using metabolically inactive cells were performed using epifluorescence and confocal laser scanning microscopy. Under static and flowing conditions, coaggregating S. natatoria 2.1gfp cells adhered to glass surfaces to form diaphanous single-species biofilms. When glass surfaces were precoated with coaggregation partner Micrococcus luteus 2.13 cells, S. natatoria 2.1gfp cells formed densely packed dual-species biofilms. The addition of 80 mM galactosamine, which reverses coaggregation, mildly reduced adhesion to glass but inhibited the interaction and attachment to glass-surface-attached M. luteus 2.13 cells. As opposed to wild-type coaggregating cells, coaggregation-deficient S. natatoria 2.1COGgfp variant cells were retarded in colonizing glass and did not interact with glass-surface-attached M. luteus 2.13 cells. To determine if coaggregation enhances biofilm growth and expansion, viable coaggregating S. natatoria 2.1gfp cells or the coaggregation-deficient variant S. natatoria 2.1COGgfp cells were coinoculated in flow cells with viable M. luteus 2.13 cells and allowed to grow together for 96 h. Coaggregating S. natatoria 2.1gfp cells outcompeted M. luteus 2.13 cells, and 96-h biofilms were composed predominantly of S. natatoria 2.1gfp cells. Conversely, when coaggregation-deficient S. natatoria 2.1COGgfp cells were coinoculated with M. luteus 2.13 cells, the 96-h biofilm contained few coaggregation-deficient S. natatoria 2.1 cells. Thus, coaggregation promotes biofilm integration by facilitating attachment to partner species and likely contributes to the expansion of coaggregating S. natatoria 2.1 populations in dual-species biofilms through competitive interactions.

Autoinducer-2 is produced in saliva-fed flow conditions relevant to natural oral biofilms.

AIMS: We evaluated the ability of a dual-species community of oral bacteria to produce the universal signalling molecule, autoinducer-2 (AI-2), in saliva-fed biofilms. METHODS AND RESULTS: Streptococcus oralis 34, S. oralis 34 luxS mutant and Actinomyces naeslundii T14V were grown as single- and dual-species biofilms within sorbarods fed with 25% human saliva. AI-2 concentration in biofilm effluents was determined by the Vibrio harveyi BB170 bioluminescence assay. After homogenizing the sorbarods to release biofilm cells, cell numbers were determined by fluorometric analysis of fluorescent antibody-labelled cells. After 48 h, dual-species biofilm communities of interdigitated S. oralis 34 and A. naeslundii T14V contained 3.2 x 10(9) cells: fivefold more than single-species biofilms. However, these 48-h dual-species biofilms exhibited the lowest concentration ratio of AI-2 to cell density. CONCLUSIONS: Oral bacteria produce AI-2 in saliva-fed biofilms. The decrease of more than 10-fold in concentration ratio seen between 1 and 48 h in S. oralis 34-A. naeslundii T14V biofilms suggests that peak production of AI-2 occurs early and is followed by a very low steady-state level. SIGNIFICANCE AND IMPACT OF THE STUDY: High oral bacterial biofilm densities may be achieved by inter-species AI-2 signalling. We propose that low concentrations of AI-2 contribute to the establishment of oral commensal biofilm communities.

Change in religious beliefs, parental pressure, and attitudes of college students toward higher education as related to religious fundamentalism.

Men (n = 55) and women (n = 99) college students (M age = 22.3 yr., SD = 6.1, range 18 to 58 years), from a moderate-sized midwestern university reported attitudes toward the goals and purposes of higher education, perceptions of parental pressure and support, and change in religious beliefs. The Religious Fundamentalist Scale, the Quest Scale, Faith-keeping, and Obedience to Parents Scales were also administered. Students classified as religious fundamentalists had more negative attitudes toward the goals and purposes of higher education goals and toward faculty. An interaction of Sex x Fundamentalist Classification indicated that nonfundamentalist college men reported greater change in their religious beliefs, relative to other groups. Perceptions of parental pressure or support were unrelated to scores on fundamentalism. The implications of students' religious backgrounds in relation to academic success were discussed.

ArcR modulates biofilm formation in the dental plaque colonizer Streptococcus gordonii.

Biofilm formation and cell-cell sensing by the pioneer dental plaque colonizer Streptococcus gordonii are dependent upon arginine. This study aimed to identify genetic factors linking arginine-dependent responses and biofilm formation in S. gordonii. Isogenic mutants disrupted in genes required for the biosynthesis or catabolism of arginine, or for arginine-dependent gene regulation, were screened for their ability to form biofilms in a static culture model. Biofilm formation by a knockout mutant of arcR, encoding an arginine-dependent regulator of transcription, was reduced to < 50% that of the wild-type whereas other strains were unaffected. Complementation of S. gordonii ∆arcR with a plasmid-borne copy of arcR restored the ability to develop biofilms. By DNA microarray analysis, 25 genes were differentially regulated in S. gordonii ∆arcR compared with wild-type under arginine-replete conditions including eight genes encoding components of phosphotransferase systems for sugar uptake. By contrast, disruption of argR or ahrC genes, which encode paralogous arginine-dependent regulators, each resulted in significant changes in the expression of more than 100 genes. Disruption of a gene encoding a putative extracellular protein that was strongly regulated in S. gordonii ∆arcR had a minor impact on biofilm formation. We hypothesize that genes regulated by ArcR form a critical pathway linking arginine sensing to biofilm formation in S. gordonii. Further elucidation of this pathway may provide new targets for the control of dental plaque formation by inhibiting biofilm formation by a key pioneer colonizer of tooth surfaces.