Modeling the response of a biofilm to silver-based antimicrobial.

Biofilms are found within the lungs of patients with chronic pulmonary infections, in particular patients with cystic fibrosis, and are the major cause of morbidity and mortality for these patients. The work presented here is part of a large interdisciplinary effort to develop an effective drug delivery system and treatment strategy to kill biofilms growing in the lung. The treatment strategy exploits silver-based antimicrobials, in particular, silver carbene complexes (SCC). This manuscript presents a mathematical model describing the growth of a biofilm and predicts the response of a biofilm to several basic treatment strategies. The continuum model is composed of a set of reaction-diffusion equations for the transport of soluble components (nutrient and antimicrobial), coupled to a set of reaction-advection equations for the particulate components (living, inert, and persister bacteria, extracellular polymeric substance, and void). We explore the efficacy of delivering SCC both in an aqueous solution and in biodegradable polymer nanoparticles. Minimum bactericidal concentration (MBC) levels of antimicrobial in both free and nanoparticle-encapsulated forms are estimated. Antimicrobial treatment demonstrates a biphasic killing phenomenon, where the active bacterial population is killed quickly followed by a slower killing rate, which indicates the presence of a persister population. Finally, our results suggest that a biofilm with a ready supply of nutrient throughout its depth has fewer persister bacteria and hence may be easier to treat than one with less nutrient.

Nanoparticle deposition onto biofilms.

We develop a mathematical model of nanoparticles depositing onto and penetrating into a biofilm grown in a parallel-plate flow cell. We carry out deposition experiments in a flow cell to support the modeling. The modeling and the experiments are motivated by the potential use of polymer nanoparticles as part of a treatment strategy for killing biofilms infecting the deep passages in the lungs. In the experiments and model, a fluid carrying polymer nanoparticles is injected into a parallel-plate flow cell in which a biofilm has grown over the bottom plate. The model consists of a system of transport equations describing the deposition and diffusion of nanoparticles. Standard asymptotic techniques that exploit the aspect ratio of the flow cell are applied to reduce the model to two coupled partial differential equations. We perform numerical simulations using the reduced model. We compare the experimental observations with the simulation results to estimate the nanoparticle sticking coefficient and the diffusion coefficient of the nanoparticles in the biofilm. The distributions of nanoparticles through the thickness of the biofilm are consistent with diffusive transport, and uniform distributions through the thickness are achieved in about four hours. Nanoparticle deposition does not appear to be strongly influenced by the flow rate in the cell for the low flow rates considered.

Measuring and modeling thermal fluctuations at nanometer length scales.

The size of mechanical, electrical, and optical devices continues to be reduced. As the length scales of such devices decrease, coupling to the external environment greatly increases. Thermal fluctuations due to momentum exchange between air molecules and micron scale devices under ambient conditions can effect the dynamics of a system. To illustrate this we use an atomic force microscope cantilever and detection system to measure background noise and thermal fluctuations of a micron size beam. The beam is modeled by a Langevin-type equation that is externally forced by a white-noise spectrum having an analytic as opposed to a statistical form. This model is compared with experimental data. It is found that at higher frequencies, a white-noise spectrum is not sufficient to model such a system. We modify the forcing spectrum so that it decays at higher frequencies and subsequently achieve closer agreement between the model and the experimental observations.

A single-pool inositol 1,4,5-trisphosphate-receptor-based model for agonist-stimulated oscillations in Ca2+ concentration.

Relying on quantitative measurements of Ca2+ activation and inhibition of the inositol 1,4,5-trisphosphate (IP3) receptor in the endoplasmic reticulum, we construct a simplified kinetic model to describe the properties of this channel. Selecting rate constants to fit key kinetic and equilibrium data, we find that the model reproduces a variety of in vivo and in vitro experiments. In combination with Ca(2+)-ATPase activity for Ca2+ uptake into the endoplasmic reticulum, the model leads to cytoplasmic oscillations in Ca2+ concentration at fixed IP3 concentration and only a single pool of releasable Ca2+, the endoplasmic reticulum. Incorporation of a positive-feedback mechanism of Ca2+ on IP3 production by phospholipase C enriches the properties of the oscillations and leads to oscillations in Ca2+ concentration accompanied by oscillations in IP3 concentration. We discuss the possible significance of these results for the interpretation of experiments.

Two roles of Ca2+ in agonist stimulated Ca2+ oscillations.

We propose a mechanism for agonist-stimulated Ca2+ oscillations that involves two roles for cytosolic Ca2+: (a) inhibition of inositol-1,4,5-trisphosphate (IP3) stimulated Ca2+ release from the endoplasmic reticulum (ER) and (b) stimulation of the production of IP3 through its action on phospholipase C (PLC), via a Gq protein related mechanism. Relying on quantitative experiments by Parker, I., and I. Ivorra (1990. Proc. Natl. Acad. Sci. USA. 87:260-264) on the inhibition of Ca2+ release from the ER using caged-IP3, we develop a kinetic model of inhibition that allows us to simulate closely their experiments. The model assumes that the ER IP3 receptor is a tetramer of independent subunits that can bind both Ca2+ and IP3. Upon incorporation of the action of Ca2+ on PLC that leads to production of IP3, we observe in-phase-oscillations of Ca2+ and IP3 at intermediate values of agonist stimulation. The oscillations occur on a time scale of 10-20 s, which is comparable to the time scale for inhibition in Xenopus oocytes. Analysis of the mechanism shows that Ca(2+)-inhibition of IP3-stimulated Ca2+ release from the ER is an essential step in the mechanism. We also find that the effect of Ca2+ on PLC can lead to an indirect increase of cytosolic Ca2+, superficially resembling "Ca(2+)-induced Ca(2+)-release." The mechanism that we propose appears to be consistent with recent experiments on REF52 cells by Harootunian, A. T., J. P. Y. Kao, S. Paranjape, and R. Y. Tsien. (1991. Science [Wash. DC]. 251:75-78.) and we propose additional experiments to help test its underlying assumptions.

Education exchange. Perceptions: one's view.

The purpose of this article is to stimulate a response between technologists and educators. The concept behind the "Education Exchange" was to provide a linkage, ie, communications, between our members. The information presented here is not intended to offend an individual(s), group(s), or organization(s). The intention, from the viewpoint of an educator, is to help individuals (students) to become technologists and to help technologists become better technologists.

Health care coalitions: continuity and change.

The purpose of this study has been to investigate how coalitions have changed during 1983-1986, to describe the current characteristics of coalitions, and to speculate about their future roles and likely evolution. Several insights emerge from the empirical findings of this study. First, the number of operational health care coalitions has greatly expanded over the last several years to the point where almost every state and metropolitan area of the country has at least one. Second, the service area of most coalitions is generally county-wide, although there has been significant growth in the number of coalitions that serve states. Third, coalitions are expanding their membership composition and including not only business members but also hospitals, physicians, insurance companies, and labor organizations. Fourth, coalitions are becoming more financially secure; most have annual cash budgets, and most rely on dues. Fifth, coalitions are increasingly hiring and using paid professional staff. Last, coalitions are expanding their agendas beyond investigating direct health care costs to examine some of the underlying issues (such as hospital and medical professional liability issues, the financing of uncompensated care, and ethical issues) and are developing programs to address them. For the near future, the extension of recent trends suggests how coalitions will look and function. Further down the road, health care coalitions may evolve into health care public/private policy forums or associations of health benefits managers and/or associations for managed care purchasers. In conclusion, the trends we documented and the projections of the future of coalitions appear to be in keeping with the summary perspective of John T. Dunlop (1987) who indicates: Coalitions provide a continuing forum in which parties become more interested and informed about health care costs, utilization and the problems and operations of the other participants. The discourse encourages a more extensive and informed development and sharing of data. Coalitions reflect and need to recognize the inevitable internal conflicts and interests of the constituent organizations. While some coalitions tend to flounder on internal conflicts and capacity to generate effective leadership; many are fruitfully addressing the hard issues of health care in a community, such as managed care, capitation payments, excess beds and capital requirements, and access to health care by the uninsured. As coalitions mature, beyond discourse and data, they are likely to concentrate on a few of the distinctive problems of their communities and the interaction within the health care environment to address these problems.

The efficacy of a leptospirosis vaccine in preventing leptospiruria in pigs.

A commercially manufactured leptospirosis vaccine containing serovars pomona and hardjo and licensed for use in cattle and sheep was investigated to determine if it would prevent leptospiruria in pigs exposed to serovar pomona. Twenty piglets were each vaccinated twice at an interval of three weeks. Twenty other piglets were unvaccinated and served as controls. Three weeks after the second dose of vaccine all animals were exposed for 64 to 89 days to a natural infection with pomona. During the investigation blood samples were examined serologically and urine samples were examined by dark ground microscopy and cultured for the presence of leptospirae. Attempts were made to culture leptospirae from kidneys at slaughter. Kidneys were also examined histologically for evidence of leptospira infection. One vaccinated animal developed a respiratory disease. It was treated with antibiotics and removed from the trial. Leptosphuria was demonstrated in six of the remaining 19 vaccinated pigs and leptospirae were found in nine of 578 (1.5%) urine samples examined from these animals during the period of exposure. In contrast leptospiruria occurred in 19 of 20 unvaccinated pigs and leptospirae were found in 253 of 642 (39.4%) urine samples examined from these animals. Histopathological lesions consistent with leptospirosis were found in kidneys examined from two of 16 vaccinates and 17 of 18 non-vaccinates. Antibodies to serovar pomona were detected in 12 of 19 vaccinated pigs examined three weeks after the second dose of vaccine and before exposure to infection, and in all of 18 unvaccinated pigs examined after exposure to infection. It was concluded that use of this vaccine in pigs resulted in a significant degree of protection against leptospiruria.

Prevalence and in-vitro antimicrobial sensitivity of Bordetella bronchiseptica in the nasal cavity of pigs.

The prevalence of Bordetella bronchiseptica in the nasal cavity of pigs and the in-vitro sensitivity of isolates to a variety of antimicrobial agents was investigated. B. Bronchiseptica was recovered from 372 nasal swabs collected from 1000 (37.2%) pigs slaughtered at 20-30 weeks old at an abattoir. The swabs were collected from groups of 5-206 pigs derived from 25 herds. All isolates tested against bacitracin, clindamycin, furazolidone, penicillin, spectinomycin, streptomycin and tylosin were found to be resistant. Of the 372 isolates tested against ampicillin and erythromycin 22 (6%) were sensitive to the former and 365 (98%) were moderately sensitive to the latter, the remainder were resistant. All isolates tested against neomycin and tetracycline were sensitive and with few exceptions, (2%), they were also sensitive to chloramphenicol. Overall, 259 of the 372 (70%) isolates were sensitive to sulphonamides, identical results being obtained with sulphadiazine, sulphafurazole and a trimethoprim-sulphamethoxazole combination. An association between in-vitro resistance to sulphanomides and extensive use of this group of drugs was demonstrated on three of eight farms investigated.