Suspension Of Microorganisms Research Articles

331 微生物の濃厚溶液におけるメゾスケール流動構造(OS1-2:生物流体とバイオミメティクス,オーガナイズドセッション1:生物流体とバイオミメティクス)

331 微生物の濃厚溶液におけるメゾスケール流動構造(OS1-2:生物流体とバイオミメティクス,オーガナイズドセッション1:生物流体とバイオミメティクス)

Numerical investigation of thermo-bioconvection in a suspension of gravitactic microorganisms

This paper investigates the effect of heating or cooling from below on the development of gravitactic bioconvection in a square enclosure with stress free sidewalls. The governing equations are the Navier–Stokes equations with the Boussinesq approximation, the diffusion equation for the motile microorganism and the energy equation for the temperature. The control volume method is used to solve numerically the complete set of governing equations. It was found that the suspension is destabilized by heating from below and stabilized by cooling from below. A transition from a subcritical bifurcation to a supercritical bifurcation was observed in the case of heating from below when the thermal Rayleigh number was increased.

Hydrodynamic interaction of two swimming model micro-organisms

In order to understand the rheological and transport properties of a suspension of swimming micro-organisms, it is necessary to analyse the fluid-dynamical interaction of pairs of such swimming cells. In this paper, a swimming micro-organism is modelled as a squirming sphere with prescribed tangential surface velocity, referred to as a squirmer. The centre of mass of the sphere may be displaced from the geometric centre (bottom-heaviness). The effects of inertia and Brownian motion are neglected, because real micro-organisms swim at very low Reynolds numbers but are too large for Brownian effects to be important. The interaction of two squirmers is calculated analytically for the limits of small and large separations and is also calculated numerically using a boundary-element method. The analytical and the numerical results for the translational–rotational velocities and for the stresslet of two squirmers correspond very well. We sought to generate a database for an interacting pair of squirmers from which one can easily predict the motion of a collection of squirmers. The behaviour of two interacting squirmers is discussed phenomenologically, too. The results for the trajectories of two squirmers show that first the squirmers attract each other, then they change their orientation dramatically when they are in near contact and finally they separate from each other. The effect of bottom-heaviness is considerable. Restricting the trajectories to two dimensions is shown to give misleading results. Some movies of interacting squirmers are available with the online version of the paper.

Velocity profiles and discontinuities propagation in a pipe flow of suspension of motile microorganisms

Suspension of motile gravitactic unicellular algae flowing down in a vertical pipe concentrates near its axis in the form of a thin thread. Such a thread is unstable relative to the travelling nodule-like structures. We study the dynamics of nodules experimentally and describe them in terms of a hydrodynamic model.

Clinical and laboratory testing of a silver-impregnated lens case

Purpose Lens case contamination is a well-documented occurrence for contact lens wearers despite the efficacy of current lens disinfectants. Several microorganisms have a propensity to attach to surfaces and may become more tolerant of disinfection upon attachment. Non-compliance with disinfection regimens occasionally occurs wherein patients store their lenses in saline or in tap water. A silver-impregnated lens case was developed in an attempt to decrease case contamination. These studies examine the performance of the case both in vitro and in vivo. Methods In vitro, lens cases were challenged with 10 3 microorganism suspensions of bacteria. After 24 h incubation at room temperature, aliquots of inocula were removed and spread plated onto appropriate growth media. Surviving colonies were counted and microorganism log drop values from initial challenge inocula were determined. Two 40-subject 1-month contralateral clinical studies were conducted with SOLO-care Aqua ® solution using one bowl of a silver-impregnated case and one bowl of a standard lens case for lens storage. Lens cases were collected and cultured for aerobic bacteria. Results In vitro efficacy data show significantly lower numbers of recovered microbes from silver-impregnated cases than from control cases. In both clinical studies, silver-impregnated cases had a statistically significantly lower proportion of bacterial contamination than control cases. The majority of microorganisms isolated from silver-impregnated cases were members of the normal skin flora. Conclusion The performance of the silver-impregnated case in vitro and the observed lower proportion of contaminated silver-impregnated lens cases in a clinical setting demonstrate the case's ability to decrease bacterial contamination.

The Onset of Convection in a Suspension of Gyrotactic Microorganisms in Superimposed Fluid and Porous Layers: Effect of Vertical Throughflow

The purpose of this paper is to investigate the effect of vertical throughflow on the onset of bioconvection in a suspension of gyrotactic microorganisms. A dilute suspension of gyrotactic microorganisms in a shallow system that consists of superimposed fluid and porous layers is considered. A linear instability analysis of this problem is performed and the Galerkin method is utilized to solve the eigenvalue problem. The analysis leads to an equation for the critical Rayleigh number. It is shown that the vertical throughflow stabilizes the system.

Stability analysis of thermo-bioconvection in suspensions of gravitactic microorganisms in a fluid layer

In this paper, we investigate the effect of heating or cooling from below on the stability of a suspension of motile gravitactic microorganisms in a shallow fluid layer. The linear perturbation theory is used to obtain the stability diagram and the critical conditions for the onset of convection. It is found that the thermo-effects may either stabilize or destabilize the suspension, and decrease or increase the wavelength of the bioconvective pattern.

Antimicrobial effect, in vitro, of gutta-percha points containing root canal medications against yeasts and Enterococcus faecalis

The objective of this study was to determine the in vitro susceptibility of Enterococcus faecalis and the most prevalent Candida species as therapy-resistant microorganisms to gutta-percha points containing root canal medications. Gutta-percha points containing calcium hydroxide (Calcium Hydroxide Plus Points), chlorhexidine diacetate (Activ Points), or calcium hydroxide-chlorhexidine combinations (CHX/Ca Combi Points) were tested for their ability to inhibit growth of pure cultures of Candida albicans, Candida glabrata, Candida parapsilosis, Candida krusei, Candida tropicalis, Saccharomyces cerevisiae, and Enterococcus faecalis. Approximately 2 x 10(7) microorganisms per assay were suspended in diluted human serum and co-incubated with the gutta-percha points placed in Eppendorf tubes in an incubator for up to 2 weeks. A tube was removed at 1, 2, 3, 4, 7, and 14 days, and then opened and microorganism suspensions were serially diluted in a sterile 0.9% NaCl solution. Aliquots of the dilution steps were streaked onto solid medium. After incubating the plates in an incubator at 37 +/- 1 degrees C for 48 hours, CFU numbers per milliliter of suspension were calculated. Calcium Hydroxide Plus Points or Activ Points did not exhibit sufficient antimicrobial or anticandidal activity for Enterococcus faecalis, Candida albicans, C. glabrata, C. parapsilosis, C. krusei, or C. tropicalis within 14 days. Only Saccharomyces cerevisiae was susceptible to the calcium hydroxide or chlorhexidine diacetate containing gutta percha points. CHX/Ca Combi Points killed C. albicans, C. glabrata, C. krusei, C. tropicalis, and S. cerevisiae completely. However, E. faecalis and C. parapsilosis were resistant to CHX/Ca Combi points within 14 days. The results show the gutta percha points containing a mixture of calcium hydroxide and chlorhexidine diacetate have efficacies superior to calcium hydroxide or chlorhexidine diacetate alone against some microorganisms except E. faecalis and C. parapsilosis.

Investigation of the onset of bioconvection in a suspension of oxytactic microorganisms subjected to high-frequency vertical vibration

This paper investigates the effect of vertical vibration on the stability of a dilute suspension of oxytactic microorganisms in a shallow horizontal fluid layer. For the case of high-frequency vibration, an averaging method is utilized to derive the equations describing the mean flow by decomposing the solutions of governing equations into two components: one that varies slowly with time, and a second that varies rapidly with time. Linear stability analysis is used to investigate the stability of the obtained averaged equations. It is predicted that high-frequency, low-amplitude vertical vibration has a stabilizing effect on a suspension of oxytactic microorganisms confined in a shallow horizontal layer.

The onset of bio-thermal convection in a suspension of gyrotactic microorganisms in a fluid layer: Oscillatory convection

A linear stability analysis is applied to investigate the onset of bioconvection in a horizontal layer of fluid containing a suspension of motile microorganisms with heating or cooling from below. With cooling from below the stabilizing effect of the thermal stratification is opposed to the destabilizing effect resulting from the congregation of the microorganisms, and oscillatory convection is possible in certain circumstances. The stability criterion is found in terms of a thermal Rayleigh number, a bioconvection Rayleigh number, a bioconvection Péclet number, a gyrotactic number, and a measure of the cell eccentricity, together with (in the case of oscillatory convection) a Prandtl number and a Lewis number.

Development and evaluation of an edible antimicrobial film based on yam starch and chitosan

Edible antimicrobial films are an innovation within the biodegradable active packaging concept. They have been developed in order to reduce and/or inhibit the growth of microorganisms on the surface of foods. This study developed an edible antimicrobial film based on yam starch (Dioscorea alata) and chitosan and investigated its antimicrobial efficiency on Salmonella enteritidis. A solution of yam starch (4%) and glycerol (2%) was gelatinized in a viscoamilograph and chitosan added at concentrations of 1%, 3% and 5%. Films with and without chitosan were produced by the cast method. To evaluate the antimicrobial activity of the films, two suspensions of S. enteritidis were used in BHI medium, corresponding to counts of 2 × 108 and 1.1 × 106 CFU/ml. The suspensions (50 ml) were poured into flasks. The films were cut into 5 × 5 and 5 × 10 cm rectangles to be used at ratios of 1 : 1 (1 cm2/ml microorganism suspension) and 2 : 1 (2 cm2/ml). The film 30 µm thick on average. As a control, pure chitosan at an amount corresponding to that contained in the 3% and 5% films (5 × 10 cm) was added to flasks containing the microorganism suspension. Also, flasks containing only a suspension of S. enteritidis were used as control. The suspensions, in flasks, were kept at 37°C in a waterbath with agitation. Suspension aliquots were removed every hour for reading the optic density (OD595) and plating onto PCA medium. The results showed that chitosan has a bactericidal effect upon S. enteritidis. Films treated with chitosan at different concentrations showed similar antimicrobial efficiency, in addition to being dependent on diffusion. The chitosan-treated films caused a reduction of one to two log cycles in the number of microorganisms, whereas the pure chitosan presented a reduction of four to six log cycles compared with the control and starch film. The films showed good flexibility. Copyright © 2005 John Wiley & Sons, Ltd.

115 微生物の準希薄溶液のレオロジー(OS5-3,オーガナイズドセッション5:マイクロ・ナノバイオメカニクス,学術講演)

115 微生物の準希薄溶液のレオロジー(OS5-3,オーガナイズドセッション5:マイクロ・ナノバイオメカニクス,学術講演)

The onset of thermo-bioconvection in a shallow fluid saturated porous layer heated from below in a suspension of oxytactic microorganisms

The aim of this paper is to present a continuum model for thermo-bioconvection of oxytactic bacteria in a porous medium and investigate the combined effects of microorganisms' upswimming and heating from below on the stability of bioconvection in a horizontal layer filled with a fluid saturated porous medium. Different from traditional bioconvection, thermo-bioconvection has two destabilizing mechanisms that contribute to creating the unstable density stratification. This problem may be relevant to a number of geophysical applications, such as the investigation of the dynamics of oxytactic species of thermophiles (heat loving microorganisms) living in hot springs, microbial-enhanced oil recovery, and modeling oil- and gas-bearing sedimentary basins. The utilization of the Galerkin method to solve a linear stability problem leads to a correlation between the critical value of the bioconvection Rayleigh number and the traditional “thermal” Rayleigh number.

Investigation of the onset of thermo-bioconvection in a suspension of oxytactic microorganisms in a shallow fluid layer heated from below

This paper investigates the combined effect of density stratification due to oxytactic upswimming and heating from below on the stability of a suspension of motile oxytactic microorganisms in a shallow fluid layer. Different from traditional bioconvection, thermo-bioconvection has two destabilizing mechanisms that contribute to creating the unstable density stratification. This problem may be relevant to a number of geophysical applications, such as the investigation of the dynamics of some species of thermophiles (heat loving microorganisms) living in hot springs. By performing a linear stability analysis, we obtained a correlation between the critical value of the bioconvection Rayleigh number and the traditional, “thermal” Rayleigh number. It is established that heating from below makes the system more unstable and helps the development of bioconvection.

Design and performance of a single-pass bubbling bioaerosol generator

We describe and analyze a new particle generator that utilizes a bursting bubble principle and eliminates carrier fluid reuse. In this Liquid Sparging Aerosolizer (LSA), a suspension of particles or microorganisms is pumped at a flow rate of 0.2–2 mL min−1 to the top surface of a porous stainless-steel disk where it forms a thin suspension film. Filtered air is then sparged through the disk into the film causing it to break into bubbles that subsequently burst, releasing particles into the air. The released particles are then captured by the sparging air stream and are carried away. Particles that impinge the glass vessel and liquid droplets not captured by the air stream drain to the bottom of the vessel and play no further role in the aerosolization process. We tested the LSA with disks of different pore sizes (0.2, 0.5, 2.0 and 10.0 μm) and different air flows (2–30 L min−1) through the porous disks while generating polydisperse and monodisperse particles. Our tests showed that the use of 0.5 and 2.0 μm porosity disks resulted in the highest output of PSL particles in the desired size range, i.e., comparable to bacterial size. Each pore size seemed to have an optimal air flow rate; the produced aerosol concentration increased with increasing suspension delivery rate. The LSA also demonstrated stability of output concentration when aerosolizing particles over extended periods of time. In addition, the size distribution of injury-sensitive Pseudomonas fluorescens bacteria virtually did not change during 90 min of continuous aerosolization by the LSA. In fact, there was no (0%) viability loss, whereas the bacterial spectrum produced by a Collison nebulizer changed significantly over 90 min and there was a 50% loss in viability. The results indicate that the new instrument could be used to generate particles for the evaluation of pathogen collection methods, inhalation and other studies where extended delivery of stable and undamaged biological aerosols is required.

Bioconvection

Bioconvection patterns are usually observed in the laboratory in shallow suspensions of randomly, but on average upwardly, swimming micro-organisms which are a little denser than water, but have also been found in situ in micropatches of zooplankton [ Kils (1993), 1993. Bull. Mar. Sci. 53, 160–169]. The mechanism of upswimming differs between bottom-heavy algae and oxytactic bacteria. Rational continuum models have been formulated and analysed in each of these cases for low cell volume fraction. These will be described, as will new theoretical and experimental developments, including nonlinear analysis of the patterns, dispersion in shear flows, measurements of algal cell swimming behaviour, and new attempts to set up a model for more concentrated suspensions. The paper will review all work in this area since 1992, the year of the publication of the article “Hydrodynamic phenomena in suspensions of swimming micro-organisms” by Pedley and Kessler [1992b. Annu. Rev. Fluid Mech. 24, 313–358].

A novel procedure for the measurement of the kinetics of styrene biodegradation in a biofilter

AbstractA novel procedure for the study of the biodegradation kinetics of styrene is proposed in this paper. Microbial growth tests in the presence of styrene were performed using suspensions of microorganisms prepared from samples of filter bed material. This material had been directly withdrawn previously from an operating biofilter employed for the removal of styrene vapours from air. The kinetics tests were initiated immediately after transfer of filter bed samples from the active styrene filter bed to sealed flasks containing a mineral‐based medium, and were performed in such a manner that no enrichment technique or lag phase treatment was necessary to activate the desired biodegradation of styrene. The complete biodegradation of freshly introduced styrene was observed within a few hours of the filter bed's initial contact with the active microbial suspension. A novel theoretical development, as proposed in this study, has provided us with the means for estimating the yield coefficient of the biomass with respect to the styrene consumed and the kinetic coefficients of the growth rate without having to perform any analyses of the liquid phase after start‐up of the growth tests. Only monitoring of the styrene and carbon dioxide concentrations in the liquid and gas phases in the test flasks was necessary. The Haldane model, with inhibition expected at high styrene concentrations, was found to be the best to represent the biodegradation kinetics of styrene in this environment. Copyright © 2005 Society of Chemical Industry

The onset of bioconvection in a suspension of gyrotactic microorganisms in a fluid layer of finite depth heated from below

The aim of this paper is to investigate the effect of heating from below on the stability of a suspension of motile gyrotactic microorganisms in a fluid layer of finite depth. This problem is relevant to a number of geophysical applications, such as investigation of the dynamics of some species of thermophiles (heat-loving microorganisms) living in hot springs. It is established that heating from below makes the system more unstable and helps the development of bioconvection. By performing a linear stability analysis, a correlation for the critical bioconvection Rayleigh number is obtained.

Effect of Fouling on Stability of Bioconvection of Gyrotactic Microorganisms in a Porous Medium

The main objective of this article is to investigate the effect of fouling on the stability of a uniform suspension of gyrotactic motile microorganisms in a fluid-saturated porous medium. Fouling occurs because of the deposition of microorganisms on a porous matrix. This deposition decreases porosity and permeability of the porous medium. Stability analysis carried out in this article reveals that there is a critical porosity of the porous medium. If the porous medium utilized for this process has a smaller porosity than critical, the uniform suspension of gyrotactic microorganisms is stable and bioconvection does not develop. If the porous medium has larger porosity than critical, the uniform suspension is unstable and bioconvection develops. In this article, a combination of analytical and numerical methods is utilized to solve this problem. First, a linear stability analysis is carried out analytically. Then, at the final stage of the research, numerical methods are utilized to compute the critical Darcy number.

Stability of a suspension of gyrotactic microorganisms in superimposed fluid and porous layers

The aim of this paper is to investigate the stability of a suspension of motile gyrotactic microorganisms in a system that consists of superimposed fluid and porous layers. This is relevant to many biological applications, such as growing motile microorganisms in Petri dishes. By performing a linear stability analysis a correlation for the critical Rayleigh number is obtained.