Senescence can explain microbial persistence

It has been known for many years that small fractions of persister cells resist killing in many bacterial colony-antimicrobial confrontations. These persisters are not believed to be mutants. Rather it has been hypothesized that they are phenotypic variants. Current models allow cells to switch in and out of the persister phenotype. Here, a different explanation is suggested for persistence, namely senescence. Using a mathematical model including age structure, it is shown that senescence provides a natural explanation for persistence-related phenomena, including the observations that the persister fraction depends on growth phase in batch culture and dilution rate in continuous culture.

Role of cohesion in the material description of biofilms

Biofilm structure plays an important role in biofilm function and control. It is thus important to determine the extent to which mechanics may determine structure in biofilms. We consider a generic qualitative constitutive description of biofilm incorporating as assumptions a small number of fundamental physical properties of biofilm viscoelasticity and cohesion. Implications of cohesive energy on biofilm structure are then explored. Steady solutions and energy minima are studied and it is demonstrated that cohesion energy leads naturally to a free surface film state. It is found that in many circumstances, biofilms could be subject to heterogeneity formation via spinodal decomposition. Such material heterogeneity may have important implications for structural stability in biofilms both on short and long time scales.

Traveling wave solutions of a reaction diffusion model for competing pioneer and climax species

Presented is a reaction-diffusion model for the interaction of pioneer and climax species. For certain parameters the system exhibits bistability and traveling wave solutions. Specifically, we show that when the climax species diffuses at a slow rate there are traveling wave solutions which correspond to extinction waves of either the pioneer or climax species. A leading order analysis is used in the one-dimensional spatial case to estimate the wave speed sign that determines which species becomes extinct. Results of these analyses are then compared to numerical simulations of wave front propagation for the model on one and two-dimensional spatial domains. A simple mechanism for harvesting is also introduced.

Modelling production of extracellular polymeric substances in a Pseudomonas aeruginosa chemostat culture

Formation of extracellular polymeric substances (EPSs) by mucoid Pseudomonas aeruginosa was investigated using literature data from chemostat cultures. The data were used to calibrate a product formation regime allowing substrate sufficient and endogenous EPS formation. Yield coefficients for both formation conditions were elucidated based on metabolic pathway analysis. Growth and non-growth related specific formation rates of 0.18 g CEPS/g Ccell/h and 0.03 1/h were estimated, respectively. The exogenous and endogenous EPS yield was found to be 0.77 g CEPS/g Cglu and 0.79 g CEPS/g Ccell, respectively. Being structurally equivalent to comprehensive maintenance models, this model allows for non-growth related product formation, showing the same quality of fit as previous models restricted to exogenous EPS precursors.

Hemodialysis access graft stenosis: US detection

PURPOSE

To prospectively evaluate the sensitivity of ultrasonography (US) in diagnosing stenosis of hemodialysis access grafts and their drainage veins in patients clinically suspected of having graft dysfunction.

MATERIALS AND METHODS

Thirty-eight patients in whom dysfunction of their hemodialysis access grafts was suspected underwent both Doppler US and angiography. Gray-scale and color US were combined with spectral analysis of the graft, anastomoses, and venous outflow. Flow velocity at anastomoses and suspected stenotic areas was measured. The volume of flow in the graft was also measured. The prospective US criterion for diagnosis of stenosis was a focal twofold or higher elevation of peak systolic velocity (PSV) compared with the PSV immediately upstream. A blinded angiographic evaluation of the graft and drainage veins followed US. Angiographic diagnosis of stenosis required at least 50% narrowing in luminal diameter. US and angiographic results were then compared.

RESULTS

Angiography allowed diagnosis of 43 stenoses in 34 patients. US depicted 92% (37 of 40) of these stenoses, with a 94% positive predictive value for any individual patient. Focal 2- to 2.9-times PSV elevation was associated with 75% or greater stenosis. Graft flow volume and resistive index change did not correlate with stenosis.

CONCLUSION

US reliably depicts stenoses of hemodialysis access grafts and drainage veins in a clinically selected population when PSV criteria are used.

C3: information science in uniform

This contribution explores an aspect of information science, which is little treated in the literature, but on which enormous sums of money are spent annually. This is the subject of information and the prosecution of war. What follows may be considered as a kind of tutorial on this huge, but poorly understood realm of information science applications. My objective at the workshop was to acquaint the participants with an overview of how information has been woven into the fabric of conflict. At present, information is so tightly woven with combat that the term information warfare has been coined. It may come as a surprise to think in these terms about information science.

Defining systems based on information exchange: structure from dynamics

We take the occasion of the workshop to examine a proposition that systems may be better defined in terms of interactions based on information exchange rather than on atomic elements. Although speculative, the paper is in the spirit of exploration within a workshop atmosphere. It is enough for us that the interactions be perceived to exist. On this basis, components become interactors, which signal each other through the exchange of information mediated by some interaction mechanism. At a minimum, interactions need only be imputed. Consequences for the appropriate definition of a system parameter based on our position are examined. Possible mathematical avenues are introduced. In the process, a connection with belief systems is explored.

An autologous blood program coordinated by a regional blood center: a 5-year experience

The Southern Arizona Regional Red Cross blood program offers preoperative autologous blood deposit to all patients and intraoperative autotransfusion services to all hospitals in the region. During a 5-year period, the amount of preoperatively deposited autologous blood and intraoperatively salvaged red cells available increased from 0.3 to 19.6 percent of the community's total collections. Further increases in the availability and use of autologous blood may be achieved by community-wide integration of services.

Specific 125I-radioimmunoassay for cholyglycine, a bile acid, in serum

The concentration of the conjugated bile acid, cholylglycine, in serum is a sensitive and specific indicator of hepatic function. We describe a convenient, specific, and precise radioimmunoassay for cholylglycine, in which 125I-labeled cholylglycyltyrosine is used as tracer. In addition, a blocking agent in the buffer system eliminates binding of bile acids to serum albumin. Therefore no extraction is required. We found no interference by (a) abnormal concentrations of albumin or gamma-globulin, (b) lipemic sera, (c) hemolyzed sera, (d) anticoagulants, or (e) various commonly used drugs. The reference interval for fasting subjects is estimated to be 0.0 to 0.6 mg/L. Our clinical studies show that serum cholylglycine concentrations are usually abnormal in most hepatobiliary diseases, such as viral hepatitis, alcoholic liver disease, cirrhosis, and pediatric liver diseases.

Specific 125I-radioimmunoassay for cholyglycine, a bile acid, in serum

The concentration of the conjugated bile acid, cholylglycine, in serum is a sensitive and specific indicator of hepatic function. We describe a convenient, specific, and precise radioimmunoassay for cholylglycine, in which 125I-labeled cholylglycyltyrosine is used as tracer. In addition, a blocking agent in the buffer system eliminates binding of bile acids to serum albumin. Therefore no extraction is required. We found no interference by (a) abnormal concentrations of albumin or gamma-globulin, (b) lipemic sera, (c) hemolyzed sera, (d) anticoagulants, or (e) various commonly used drugs. The reference interval for fasting subjects is estimated to be 0.0 to 0.6 mg/L. Our clinical studies show that serum cholylglycine concentrations are usually abnormal in most hepatobiliary diseases, such as viral hepatitis, alcoholic liver disease, cirrhosis, and pediatric liver diseases.