Dynamic Growth Conditions Research Articles

The Challenge of Treating Oral Infections Caused by Biofilms

In natural systems, the harsh environments, nutrient/respiration needs, and sheer flow, make a community lifestyle preferable or inevitable for microorganisms. Furthermore, the bacteria take advantage of the communities’ organization to protect them from eradication by conventional antimicrobial therapy. A biofilm community is a microorganism aggregate characterized by cells that are attached to a substratum or interface or to each other; are embedded in a matrix of extracellular polymeric substances (EPS) that they have produced; and exhibit an altered phenotype with respect to growth rate and gene transcription [1]. The oral cavity is an example of a challenging environment for the long-term persistence of bacteria and fungi. Fluctuations in nutrient supply, temperature, pH, and the shear force of saliva flow have selected for a biofilm community adapted to high cell density, species diversity, and dynamic growth conditions [2, 3]. The microorganism production of EPS matrix is also very important for their interaction with the environment [4,5]. The EPS provides a physical barrier that inhibits attachment to macrophages and phagocytes, while the reduced microorganisms’ metabolic activity precludes the use of antibiotics that act on them during growth periods [6-9]. Those are some of the challenges encountered when there is a need to treat or eradicate a disease-causing biofilm. Beyond conventional treatments, which employ a variety of antimicrobial agents, the actual disruption of biofilms currently entails mechanical procedures such as scouring. In order to inactivate the encased microbial cells, antimicrobial molecules must diffuse throughout the biofilm matrix; but the EPS constituting this matrix present a diffusional barrier for these molecules by influencing either their rate of transport to the biofilm interior or by the reaction of the antimicrobial with the matrix material [1]. The viscoelastic properties of the polysaccharides in the EPS are also attributed to the difficulty in disrupting the mature biofilm [10]. Among well-documented

Multi-walled carbon nanotube-induced inflammatory response and oxidative stress in a dynamic cell growth environment

BackgroundRapid increase in multi-walled carbon nanotube (MWCNT) production for their industrial and biomedical applications has led to concerns over the effects of MWCNTs on human health and the environment. Both animal and in vitro studies have provided important findings about MWCNT-induced effects on the lung cells or tissues. In vitro studies have provided a considerable amount of fundamental information on MWCNT-induced effects on the specific lung cells. However, the cell culture systems used in those studies were limited by the absence of dynamic nature of lung tissues. We hypothesized that MWCNT-induced cellular responses such as proliferation, inflammation, and oxidative stress under dynamic cell growth environment may differ from those under static cell growth environment.ResultsIn this study, we used a dynamic cell growth condition to mimic mechanically dynamic environment of the lung and characterized interleukin 8 (IL-8), reactive oxygen species (ROS), glutathione (GSH), and cell proliferation for three days following exposure of MWCNTs at different concentrations (5, 10, and 20 μg/ml) to A549 cell monolayer under both static and dynamic cell growth conditions. Our results demonstrated the distinct differences in the levels of inflammatory response and oxidative stress between static and dynamic cell growth conditions.ConclusionsIn conclusion, the dynamic cell growth system used in this study provided important changes in cellular responses that were not found in the static cell growth system and were similar to animal studies. The dynamic cell growth system can be considered as a viable alternative to in vivo test system in combination with existing in vitro static cell growth systems to evaluate the effect of MWCNTs on cellular responses in the respiratory system.

Modeling the Growth of Listeria monocytogenes in Soft Blue-White Cheese

The aim of this study was to develop a predictive model simulating growth over time of the pathogenic bacterium Listeria monocytogenes in a soft blue-white cheese. The physicochemical properties in a matrix such as cheese are essential controlling factors influencing the growth of L. monocytogenes. We developed a predictive tertiary model of the bacterial growth of L. monocytogenes as a function of temperature, pH, NaCl, and lactic acid. We measured the variations over time of the physicochemical properties in the cheese. Our predictive model was developed based on broth data produced in previous studies. New growth data sets were produced to independently calibrate and validate the developed model. A characteristic of this tertiary model is that it handles dynamic growth conditions described in time series of temperature, pH, NaCl, and lactic acid. Supplying the model with realistic production and retail conditions showed that the number of L. monocytogenes cells increases 3 to 3.5 log within the shelf life of the cheese.

Length-dependent effect of single-walled carbon nanotube exposure in a dynamic cell growth environment of human alveolar epithelial cells

Despite the great use of nanomaterials for engineering and medical applications, nanomaterials may have adverse consequences by accidental exposure, because of their nanoscale size, composition and shape. Like many nanomaterials, carbon nanotubes (CNTs) have been used for many proven applications, but the size of the CNTs makes them more readily become airborne and can therefore create the risk of being inhaled by a worker. In this study, we evaluated single-walled CNT (SWCNT)-induced effects on cellular responses such as cell proliferation, inflammatory response and oxidative stress in dynamic cell growth condition. A dynamic cell growth environment was established to mimic the dynamic changes in the amount of circumferential and longitudinal expansion and contraction occurred during normal breathing movement in the lung. Two different length (short: outer diameter (OD) 1-2 nm, length 0.5-2 μm; long: OD 1-2 nm, length 5-30 μm) of SWCNTs were used at different exposure concentrations (5, 10 and 20 μg/ml) during the different exposure duration (24, 48 and 72 h). Dynamic environment facilitated altered interaction between SWCNTs and A549 monolayer. Cellular responses in dynamic condition were significantly different from those in static condition. Moreover, cellular responses were dependent on the length of SWCNTs both in static and dynamic cell growth conditions.

Influence of Co-Cr Particles and Co-Cr Ions on the Growth of Staphylococcal Biofilms

In the last decades, hip prostheses with a metal-on-metal (MOM) bearing have been implanted by orthopedic surgeons worldwide. However, concerns are now raised towards the metal particles and degradation products released by MOM-bearings into surrounding tissue, although effects of Co-Cr wear on infection are also unknown. Therefore, we here determine the viable volumes of staphylococcal biofilms formed on polystyrene in the absence and presence of Co-Cr particles and Co-Cr ions. Three clinically derived and two commercially available staphylococcal strains were grown in the presence of 2 mg/mL Co-Cr particles or 1000/500 µg/L Co-Cr ions derived from Co-Cr salts or from particle supernatant, under static and dynamic growth conditions. A dynamic model simulates the conditions that apply for biofilm formation in the human body, as synovial fluid in mobile patients with hip prostheses is in constant motion with accompanying shear rates. Images of 24 h old biofilms were made with confocal laser scanning microscopy and analyzed with the mathematical computer program COMSTAT, yielding the biovolume of a biofilm. X-ray photoelectron spectroscopy was performed on the particles to study their elemental surface composition. Most isolates showed a tendency of reduced biofilm growth in the presence of Co-Cr particles compared to growth during exposure to metal ions, but this was only significant in one strain under the dynamic growth condition (Staphylococcus aureus 7388). Characterization of the outer surface of the particles revealed a Co-Cr oxide layer enriched by Mo relative to the bulk concentration. MOM bearings produce metal particles which were found to possess antibacterial characteristics under dynamic growth conditions. Further research is needed towards the clinical relevance of this finding.

Effect of exposure conditions on SWCNT-induced inflammatory response in human alveolar epithelial cells

There has been an increasing interest in the development and applications of carbon nanotubes (CNTs) due to their huge potential in industrial and medical applications, but the toxicological properties of these materials have not been well characterized, especially the effects of nanoparticle exposure under different conditions on cellular responses. Nano-structured particles are potentially hazardous when they deposit in the respiratory system. In this study, we characterized the effects of single walled CNT (SWCNT) exposure on interleukin-8 (IL-8) expression in human alveolar epithelial cells (A549) under various exposure conditions. We measured the level of IL-8 expression in the presence and absence of serum following exposure of SWCNTs. The results demonstrated that IL-8 expression was enhanced in the presence of serum. When A549 cells were exposed to low concentrations of SWCNTs, IL-8 expression kept increasing, even after removal of SWCNTs from the media. In addition, SWCNT exposure under dynamic cell growth condition induced changes in IL-8 expression.

Effects of diesel particulate matters on inflammatory responses in static and dynamic culture of human alveolar epithelial cells

Diesel particulate matter (DPM 1 1 Diesel particulate matter. ) possesses the potential to induce acute and chronic health issues upon occupational and daily exposure. Many recent studies have focused on understanding molecular mechanisms to depict DPM's side effects inside the lung using static in vitro cell culture models. These studies have provided abundant fundamental information on DPM's adverse effects on cellular responses, but these systems were limited by the absence of dynamic nature to access relevant cellular responses and functionality. We hypothesized that the exposure of DPM under dynamic environment may affect the levels of cellular inflammation and reactive oxygen species, which may be different from those under static environments. In this study, we used the dynamic cell growth condition to mimic mechanically dynamic environment similar to the normal breathing in vivo. We also used high (20, 10, and 5 ppm) and low (3, 1, 0.1, and 0.01 ppm) ranges of DPM exposure to mimic different levels of exposure, respectively. Following 24-, 48-, and 72-h exposure of DPM, Interleukin-8 (IL-8 2 2 Interleukin-8. ), C-reactive protein (CRP 3 3 C-reactive protein. ), reactive oxygen species (ROS 4 4 Reactive oxygen species. ), and total amount of protein were analyzed. Our results demonstrated the distinct differences in the profiles of inflammatory mediators (IL-8, CRP, and ROS) between the static and dynamic cell growth conditions.

The adaptive response of anaerobically grownSaccharomyces cerevisiaeto hydrogen peroxide is mediated by the Yap1 and Skn7 transcription factors

The molecular mechanisms involved in the ability of cells to adapt and respond to differing oxygen tensions are of great interest to the pharmaceutical, medical and fermentation industries. The transcriptional profiles reported in previous studies of cells grown under anaerobic, aerobic and dynamic growth conditions have shown significantly altered responses including induction of genes regulated by the oxidative stress transcription factor Yap1p when oxygen was present. The present study investigated the phenotypic changes that occur in cells when shifted from anaerobic to aerobic growth conditions and it was found through mutant analyses that the elevated activity of Yap1p during the shift was mediated by the phospholipid hydroperoxide-sensing protein encoded by GPX3. Cell viability and growth rate were unaffected even though anaerobically grown cells were found to be hypersensitive to low doses of the oxidative stress-inducing compound hydrogen peroxide (H(2)O(2)). Adaptation to H(2)O(2) treatment was demonstrated to occur when anaerobically grown wild-type cells were aerated for a short time that was reliant on the Yap1p and Skn7p transcription factors.

Growth of functional single crystals of complex compounds on the basis of the solubility phase diagrams of ternary systems

The validity of solubility phase diagrams of ternary systems for determining the optimal (concentration and temperature) dynamic growth conditions for single crystals of congruently and incongruently dissolving solid phases is shown. It is found that the optimal composition of the mother liquor for growing solid-phase single crystals corresponds to the solution in the solid-phase solubility curve that is located at the maximum distance from the points of invariant equilibria. More than 40 ternary systems have been used and more than 60 new and known large functional single crystals of stoichiometric composition and optical quality that belong to different chemical classes have been grown on their basis under dynamic conditions.

Antibacterial Activity of Soil‐Bound Antibiotics

There is some concern that antibiotic residues in land-applied manure may promote the emergence of antibiotic resistant bacteria in the environment. The goal of this study was to determine whether or not soil bound antibiotics are still active against bacteria. The procedure involved sorbing various amounts of tetracycline or tylosin on two different textured soils (Webster clay loam [fine-loamy, mixed, superactive, mesic Typic Endoaquolls] and Hubbard loamy sand [sandy, mixed, frigid Entic Hapludolls]), incubating these soils with three different bacterial cultures (an antibiotic resistant strain of Salmonella sp. [Salmonella(R)], an antibiotic sensitive strain of Salmonella sp. [Salmonella(S)], and Escherichia coli ATCC 25922), and then enumerating the number of colony forming units relative to the control. Incubation was done under both static and dynamic conditions. Soil-adsorbed antibiotics were found to retain their antimicrobial properties since both antibiotics inhibited the growth of all three bacterial species. Averaged over all other factors, soil adsorbed antimicrobial activity was higher for Hubbard loamy sand than Webster clay loam, most likely due to higher affinity (higher clay content) of the Webster soil for antibiotics. Similarly, there was a greater decline in bacterial growth with tetracycline than tylsoin, likely due to greater amounts of soil-adsorbed tetracycline and also due to lower minimum inhibitory concentration of most bacteria for tetracycline than tylosin. The antimicrobial effect of tetracycline was also greater under dynamic than static growth conditions, possibly because agitation under dynamic growth conditions helped increase tetracycline desorption and/or increase contact between soil adsorbed tetracycline and bacteria. We conclude that even though antibiotics are tightly adsorbed by clay particles, they are still biologically active and may influence the selection of antibiotic resistant bacteria in the terrestrial environment.

Representation of culture transition states inA.suboxydans

The kinetics of the biotransformation of D-sorbitol to L-sorbose by Acetobacter suboxydans (NRRL B-72) features both substrate and product inhibition. Model-based reactor operating strategies can eliminate the inhibitions and improve the yield and productivity of the fermentation. Unstructured models are usually unable to acknowledge complex intracellular physiological changes and therefore their application to dynamic growth conditions is limited. By considering RNA as a bottleneck growth limiting compound a structured mathematical model was developed to describe the transient growth of Acetobacter suboxydans. The model parameters were determined by a non-linear regression technique which minimized the deviation between the model prediction and the experimental (extracellular and intracellular) continuous culture data. The model was used to simulate the transient culture behaviour during the step-down in the dilution rates (from 0·1 h−1 to 0·05 h−1) in the continuous culture experiments. The experimental results and the model simulation results showed reasonable agreement. © 1998 Society of Chemical Industry

Representation of culture transition states in A. suboxydans

The kinetics of the biotransformation of D-sorbitol to L-sorbose by Acetobacter suboxydans (NRRL B-72) features both substrate and product inhibition. Model-based reactor operating strategies can eliminate the inhibitions and improve the yield and productivity of the fermentation. Unstructured models are usually unable to acknowledge complex intracellular physiological changes and therefore their application to dynamic growth conditions is limited. By considering RNA as a bottleneck growth limiting compound a structured mathematical model was developed to describe the transient growth of Acetobacter suboxydans. The model parameters were determined by a non-linear regression technique which minimized the deviation between the model prediction and the experimental (extracellular and intracellular) continuous culture data. The model was used to simulate the transient culture behaviour during the step-down in the dilution rates (from 0·1 h−1 to 0·05 h−1) in the continuous culture experiments. The experimental results and the model simulation results showed reasonable agreement. © 1998 Society of Chemical Industry

Dynamic delamination growth in laminated composite structures

The dynamic growth of a thin strip delamination in a thick base laminate under in-plane loadings has been analysed. A variational principle, coupled with a Griffith-type fracture criterion, is used to formulate the delamination growth problem. Two approximate solutions, including one mode and two modes, respectively, are calculated in this paper. The resulting equations of motion and the dynamic local growth condition at the crack tip turn out to be two and three coupled ordinary differential equations for one-mode and two-mode solutions. A fourth-order Runge-Kutta method is then used to obtain the numerical solutions. The results show that delamination growth will approach a state of arrest for materials with high fracture toughness, and continue all the way without a limit for low fracture toughness materials. The inertial effect is important and should not be ignored in calculation of the arrested delamination length for high fracture toughness materials. For materials with low fracture toughness, the inertial effect is significant and high admissible modes are noticeable. A comparison between the present results and the previously known quasi-dynamic solution is also given.

Dynamic analysis of delamination growth

T dynamic problem of the growth of a thin homogeneous strip delamination in a thick base plate under axial loading has been studied with a Griffith-type fracture criterion adopted. The variational equation of motion and the dynamic local growth condition at the crack tip are derived. The resulting nonlinear free boundary problem is solved by a numerical technique that combines both the finite element method and the Newton-Raphson iterative method/The local growth condition at the delamination front is examined at each time step of the integration process. It is found that the ratio of the applied compressive strain to the bifurcation strain of the delaminated layer is an important parameter in determining the delamination growth behavior. The results of the present analysis are compared with those of the quasidynamic analysis.

NADH fluorescence in a fed batch fermentation by C.acetobutylicum

The existing process kinetics model of the acetone-butanol fermentation was adjusted and adapted for the fed-batch mode of operation. The optimal sugar feeding strategy for maximum solvent production was determined from the model and implemented in an experiment where the fluorescent features of the culture were also determined. While the model predictions agreed with experimentally observed trends, the actual data did not compare well. The characterisation of the culture physiological state under dynamic growth conditions was attempted by utilizing on-line fluorescence measurements and the concept of stoichiometric metabolic pathway rates. This methodology served well in assessing the NADH related culture metabolic activity and the substrate consumption rate in the solventogenic phase. Le modèle de cinétique des procédés existant pour la fermentation acétone-butanol a été adapté pour une alimentation discontinue. On a déterminé la stratégie d'alimentation en sucre optimale pour une production de solvant maximum à partir du modèle et on l'a appliquée dans une expérience, pour laquelle les caractéristiques de fluorescence de la culture ont également été déterminées. Tandis que les prédictions du modèle concordent bien avec les tendances observées expérimentalement, les données réelles se comparent mal. On a tenté de caractériser l'état physiologique de la culture dans des conditions de croissance dynamiques en utilisant des mesures de fluorescence directes et le concept des vitesses des trajectoires métaboliques stoechiométriques. Cette méthodologie est utile pour l'évaluation de l'activité métabolique des cultures associées au NADH et de la vitesse de consommation du substrat dans la phase solvantogène.

Characterization of Transient Cultures of Clostridium acetobutylicum

AbstractThe inability of unstructured mathematical models to acknowledge complex intracellular physiological changes limits their applicability for dynamic culture growth conditions. By considering RNA as a bottleneck growth‐limiting compound, a structured model was developed to describe the transient and steady‐state growth of Clostridium acetobutylicum. The linear relationship between the on‐line NADH fluorescence and the sugar utilization specific rates was incorporated in the mathematical model to facilitate in situ assessment of the culture metabolic activity. The improved performance of the proposed structured model was demonstrated. It simulated the transient culture metabolism better than the unstructured Monod model. However, it still failed to simulate the metabolic switchover between acidogenic and solventogenic Clostridium culture behavior.

Relationship Between the Growth Phase of Pseudomonas fragi and Its Attachment to Stainless Steel.

ABSTRACTAttachment of Pseudomonas fragi ATCC 4973 to a sterile stainless steel surface was followed under stationary and dynamic growth conditions at 25°C and 4°C using scanning electron microscopy techniques. The organism was grown in 10% reconstituted nonfat dry milk for 28 hr at 25°C and 9 days at 4°C. Attachment was ob served in both the stationary and dynamic environments at 1/2 hr at 25°C and at 2 hr at 4°C. There appeared to be no difference in the development of attachment fibrils on the organisms in the two environments or at the two temperatures. The extent of attachment increased as the microbial population increased over the growth cycle under both environments at both temperatures.

Dynamics in prestressed media with moving phase boundaries: a continuum theory of failure in solids

Spontaneous failure in a solid medium is described as a localized transition of the material from one physical state to another, characterized in part by contrasting rheological properties and density. Such a process is viewed as a local disordering of the relatively ordered structure of the solid due to any variety of causes, such as massive microfracturing or shear melting, and can be confined to a very thin zone, but nevertheless of finite volume such that a volumetric transition energy can be defined. This leads to the description of failure as a generalized phase transition in a prestressed continuum, with instability and transition zone growth being driven by the energy contributions from the relaxation of stress in the surrounding medium. Direct application of mass, momentum and energy conservation to such a generalized phase transition leads to ‘jump’ conditions specified on the growing boundary surface of the transition zone, that relate the rupture growth to discontinuous changes in the dynamic field variables across the failure zone boundary. These field discontinuities are, in turn, related to the localized changes in physical properties induced by failure. Dynamical conditions for rapid spontaneous failure growth in a stressed medium are investigated in some detail, and we find that the failure boundary growth can be simply expressed in terms of energy ‘failure condition’ and a dynamic growth condition specifying the rupture velocity. These results imply that the integral energy change associated with earthquakes is in the range 10^4−10^6 erg/g. Further the failure growth rate is shown to be expressible in terms of the rheological properties of the material before and after failure. For shear melting resulting in a low viscosity fluid, for example, the rupture velocity will be near the shear velocity of the original material. A general Green's function solution for the radiation due to stress relaxation in the medium surrounding the growing failure zone is given and provides the basis for detailed computations of the strain or displacement field changes due to spontaneous failure processes. In particular, it is shown that the jump conditions for the growing transition zone boundary appear naturally as surface integral terms over the boundary. Since these boundary conditions contain the failure rate explicitly, then these terms include effects that have not been represented in previous integral representations of the radiation field resulting from failure. Further, we show that the formal Green's integral representation for the dynamical wave field can be used with known, simple Green's functions to generate approximate solutions for complex failure processes occurring in media with inhomogeneous material properties and prestress.