Relations between macroscopic and microscopic adhesion of Streptococcus mitis strains to surfaces

Application of physico-chemical models to describe bacterial adhesion to surfaces has hitherto only been partly successful due to the structural and chemical heterogeneities of bacterial surfaces, which remain largely unaccounted for in macroscopic physico-chemical characterizations of the cell surfaces. In this study, the authors attempted to correlate microscopic adhesion of a collection of nine Streptococcus mitis strains to the negatively charged, hydrophilic silicon nitride tip of an atomic force microscope (AFM) with macroscopic adhesion of the strains to a negatively charged, hydrophilic glass in a parallel-plate flow chamber. The repulsive force probed by AFM upon approach of the tip to a bacterial cell surface ranged from 1·7 to 7·7 nN depending on the strain considered and was found to correspond to an activation barrier, governing initial, macroscopic adhesion of the organisms to the glass surface. Moreover, maximum distances at which attractive forces were probed by the AFM upon retraction of the tip (120 to 1186 nm) were related to the area blocked by an adhering bacterium, i.e. the distance kept between adhering bacteria. Bacterial desorption could not be related to adhesive forces as probed by the AFM, possibly due to the distinct nature of the desorption process occurring in the parallel-plate flow chamber and the forced detachment in AFM

Mechanistic framework to link root growth models with weather and soil physical properties, including example applications to soybean growth in Brazil

Background and aimsRoot elongation is generally limited by a combination of mechanical impedance and water stress in most arable soils. However, dynamic changes of soil penetration resistance with soil water content are rarely included in models for predicting root growth. Better modelling frameworks are needed to understand root growth interactions between plant genotype, soil management, and climate. Aim of paper is to describe a new model of root elongation in relation to soil physical characteristics like penetration resistance, matric potential, and hypoxia.MethodsA new diagrammatic framework is proposed to illustrate the interaction between root elongation, soil management, and climatic conditions. The new model was written in Matlab®, using the root architecture model RootBox and a model that solves the 1D Richards equations for water flux in soil. Inputs: root architectural parameters for Soybean; soil hydraulic properties; root water uptake function in relation to matric flux potential; root elongation rate as a function of soil physical characteristics. Simulation scenarios: (a) compact soil layer at 16 to 20 cm; (b) test against a field experiment in Brazil during contrasting drought and normal rainfall seasons.Results(a) Soil compaction substantially slowed root growth into and below the compact layer. (b) Simulated root length density was very similar to field measurements, which was influenced greatly by drought. The main factor slowing root elongation in the simulations was evaluated using a stress reduction function.ConclusionThe proposed framework offers a way to explore the interaction between soil physical properties, weather and root growth. It may be applied to most root elongation models, and offers the potential to evaluate likely factors limiting root growth in different soils and tillage regimes

The oral microbiome – an update for oral healthcare professionals

For millions of years, our resident microbes have coevolved and coexisted with us in a mostly harmonious symbiotic relationship. We are not distinct entities from our microbiome, but together we form a 'superorganism' or holobiont, with the microbiome playing a significant role in our physiology and health. The mouth houses the second most diverse microbial community in the body, harbouring over 700 species of bacteria that colonise the hard surfaces of teeth and the soft tissues of the oral mucosa. Through recent advances in technology, we have started to unravel the complexities of the oral microbiome and gained new insights into its role during both health and disease. Perturbations of the oral microbiome through modern-day lifestyles can have detrimental consequences for our general and oral health. In dysbiosis, the finely-tuned equilibrium of the oral ecosystem is disrupted, allowing disease-promoting bacteria to manifest and cause conditions such as caries, gingivitis and periodontitis. For practitioners and patients alike, promoting a balanced microbiome is therefore important to effectively maintain or restore oral health. This article aims to give an update on our current knowledge of the oral microbiome in health and disease and to discuss implications for modern-day oral healthcare

Antibacterial activity and mode of action of selected glucosinolate hydrolysis products against bacterial pathogens

Plants contain numerous components that are important sources of new bioactive molecules with antimicrobial properties. Isothiocyanates (ITCs) are plant secondary metabolites found in cruciferous vegetables that are arising as promising antimicrobial agents in food industry. The aim of this study was to assess the antibacterial activity of two isothiocyanates (ITCs), allylisothiocyanate (AITC) and 2-phenylethylisothiocyanate (PEITC) against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Listeria monocytogenes. The antibacterial mode of action was also characterized by the assessment of different physiological indices: membrane integrity, intracellular potassium release, physicochemical surface properties and surface charge. The minimum inhibitory concentration (MIC) of AITC and PEITC was 100 g/mL for all bacteria. The minimum bactericidal concentration (MBC) of the ITCs was at least 10 times higher than the MIC. Both AITC and PEITC changed the membrane properties of the bacteria decreasing their surface charge and compromising the integrity of the cytoplasmatic membrane with consequent potassium leakage and propidium iodide uptake. The surface hydrophobicity was also non-specifically altered (E. coli and L. monocytogenes become less hydrophilic; P. aeruginosa and S. aureus become more hydrophilic). This study shows that AITC and PEITC have strong antimicrobial potential against the bacteria tested, through the disruption of the bacterial cell membranes. Moreover, phytochemicals are highlighted as a valuable sustainable source of new bioactive products.This work was supported by the Operational Programme for Competitiveness Factors - COMPETE and by the Portuguese Foundation for Science and Technology through Project Phytodisinfectants - PTDC/DTP-SAP/1078/2012 (COMPETE: FCOMP-01-0124-FEDER-028765), the PhD grant awarded to Ana Abreu (SFRH/BD/84393/2012), and the post-doctoral grants awarded to Anabela Borges (SFRH/BPD/98684/2013) and Lucia C. Simoes (SFRH/BPD/81982/2011). Also, this work was undertaken as part of the European Research Project SUSCLEAN (Contract no FP7-KBBE-2011-5, project number: 287514) and the COST Action FA1202. The authors are solely responsible for this work. It does not represent the opinion of the European Community, and the Community is not responsible for any use that might be made of data appearing herein