A comparison of airborne bacterial fallout between orthopaedic and vascular surgery.

INTRODUCTION The objective of the study was to compare bacterial fallout during vascular prosthesis insertion and orthopaedic major joint replacement performed in conventional and laminar flow ventilation, respectively. MATERIALS AND METHODS A prospective single-centre case control study of 21 consecutive elective vascular procedures involving prosthetic graft insertion and 24 consecutive elective orthopaedic major joint replacements were tested for degree of bacterial fallout using agar settle plates. Preparation time, waiting time and total procedure duration were collected at the time of surgery, and bacterial colony counts on the agar settle plates from airborne bacterial fallout were counted after an incubation period. RESULTS Bacterial fallout count in vascular prosthetic graft insertion was 15-fold greater than in orthopaedic prosthetic joint insertion (15, (IQR 15) vs 1, (IQR 3) respectively, P < 0.0001, Wilcoxon). Waiting time and patient transfer did not significantly increase bacterial fallout counts during the procedure (P = 0.9). CONCLUSIONS Vascular surgical theatres have significantly higher bacterial fallout compared with orthopaedic theatres. This may be partly explained by orthopaedic surgery being routinely performed in laminar flow ventilation, a practice which has not been widely adopted for vascular surgery, in which prosthetic infection may also result in significant mortality and morbidity.

Automated line scan analysis to quantify biosensor activity at the cell edge.

Biosensors are valuable tools used to image the subcellular localization and kinetics of protein activity in living cells. Signaling at the edge of motile cells that regulates cell protrusion and retraction is important in many aspects of cell physiology, and frequently studied using biosensors. However, quantitation and interpretation is limited by the heterogeneity of this signaling behavior; automated analytical approaches are required to systematically extract large data sets from biosensor studies for statistical analysis. Here we describe an automated analysis to relate the velocity at specific points along the cell edge with biosensor activity in adjoining regions. Time series of biosensor images are processed to interpolate a smooth edge of the cell at each time point. Profiles of biosensor activity ('line scans') are then calculated along lines perpendicular to the cell edge. An energy minimization method is used to calculate a velocity associated with each line scan. Sorting line scans by the proximal velocity has generated novel biological insights, as exemplified by analysis of the Src merobody biosensor. With the large data sets that can be generated automatically by this program, conclusions can be drawn that are not apparent from qualitative or 'manual' quantitative techniques. Our 'LineScan' software includes a graphical user interface (GUI) to facilitate application in other studies. It is available at hahnlab.com and is exemplified here in a study using the RhoC FLARE biosensor.

Systems biology analysis of G protein and MAP kinase signaling in yeast.

Approximately a third of all drugs act by binding directly to cell surface receptors coupled to G proteins. Other drugs act indirectly on these same pathways, for example, by inhibiting neurotransmitter reuptake or by blocking the inactivation of intracellular second messengers. These drugs have revolutionized the treatment of human disease. However, the complexity of G protein signaling mechanisms has significantly hampered our ability to identify additional new drug targets. Moreover, today's molecular pharmacologists are accustomed to working on narrowly focused problems centered on a single protein or enzymatic process. Here we describe emerging efforts in yeast aimed at identifying proteins and processes that modulate the function of receptors, G proteins and MAP kinase effectors. The scope of these efforts is far more systematic, comprehensive and quantitative than anything attempted previously, and includes integrated approaches in genetics, proteomics and computational biology.

The triad of bilateral retinoblastoma, dysplastic naevus syndrome and multiple cutaneous malignant melanomas: a case report and review of the literature.

We report a case of a patient with the triad of retinoblastoma, dysplastic naevus syndrome (DNS) and multiple cutaneous melanomas. The combination of retinoblastoma and DNS is a significant risk factor for the development of cutaneous melanoma. This risk extends to family members. We recommend that survivors of (inherited) retinoblastoma and their relatives are closely screened for the presence of dysplastic naevi.

Stochasticity in transcriptional regulation: origins, consequences, and mathematical representations.

Transcriptional regulation is an inherently noisy process. The origins of this stochastic behavior can be traced to the random transitions among the discrete chemical states of operators that control the transcription rate and to finite number fluctuations in the biochemical reactions for the synthesis and degradation of transcripts. We develop stochastic models to which these random reactions are intrinsic and a series of simpler models derived explicitly from the first as approximations in different parameter regimes. This innate stochasticity can have both a quantitative and qualitative impact on the behavior of gene-regulatory networks. We introduce a natural generalization of deterministic bifurcations for classification of stochastic systems and show that simple noisy genetic switches have rich bifurcation structures; among them, bifurcations driven solely by changing the rate of operator fluctuations even as the underlying deterministic system remains unchanged. We find stochastic bistability where the deterministic equations predict monostability and vice-versa. We derive and solve equations for the mean waiting times for spontaneous transitions between quasistable states in these switches.

A macroscopic description of biomolecular transport.

We present a general algorithm for computing the effective diffusion coefficient of a general class of biomolecular transport processes. The method can be applied to spatially discrete and continuous processes and takes into account the effects of thermal diffusion and chemical kinetics. To provide an illustration of the algorithm, the problem of protein translocation is considered.

Models of post-translational protein translocation.

Organellar Hsp-70 is required for post-translational translocation into the endoplasmic reticulum and mitochondria. The functional role played by Hsp-70 is unknown. However, two operating principles have been suggested. The power stroke model proposes that Hsp-70 undergoes a conformational change, which pulls the precursor protein through the translocation pore, whereas, in the Brownian ratchet model, the role of Hsp-70 is simply to block backsliding through the pore. A mathematical analysis of both mechanisms is presented and reveals that qualitative differences between the models occur in the behavior of the mean velocity and effective diffusion coefficient as a function of Hsp-70 concentration. An experimental method is proposed for measuring these two quantities that only relies on current experimental techniques.

Force generation in RNA polymerase.

RNA polymerase (RNAP) is a processive molecular motor capable of generating forces of 25-30 pN, far in excess of any other known ATPase. This force derives from the hydrolysis free energy of nucleotides as they are incorporated into the growing RNA chain. The velocity of procession is limited by the rate of pyrophosphate release. Here we demonstrate how nucleotide triphosphate binding free energy can rectify the diffusion of RNAP, and show that this is sufficient to account for the quantitative features of the measured load-velocity curve. Predictions are made for the effect of changing pyrophosphate and nucleotide concentrations and for the statistical behavior of the system.

Energy transduction in ATP synthase.

Mitochondria, bacteria and chloroplasts use the free energy stored in transmembrane ion gradients to manufacture ATP by the action of ATP synthase. This enzyme consists of two principal domains. The asymmetric membrane-spanning F0 portion contains the proton channel, and the soluble F1 portion contains three catalytic sites which cooperate in the synthetic reactions. The flow of protons through F0 is thought to generate a torque which is transmitted to F1 by an asymmetric shaft, the coiled-coil gamma-subunit. This acts as a rotating 'cam' within F1, sequentially releasing ATPs from the three active sites. The free-energy difference across the inner membrane of mitochondria and bacteria is sufficient to produce three ATPs per twelve protons passing through the motor. It has been suggested that this proton motive force biases the rotor's diffusion so that F0 constitutes a rotary motor turning the gamma shaft. Here we show that biased diffusion, augmented by electrostatic forces, does indeed generate sufficient torque to account for ATP production. Moreover, the motor's reversibility-supplying torque from ATP hydrolysis in F1 converts the motor into an efficient proton pump-can also be explained by our model.

A cisternal maturation mechanism can explain the asymmetry of the Golgi stack.

Morphological data suggest that Golgi cisternae form at the cis-face of the stack and then progressively mature into trans-cisternae. However, other studies indicate that COPI vesicles transport material between Golgi cisternae. These two observations can be reconciled by assuming that cisternae carry secretory cargo through the stack in the anterograde direction, while COPI vesicles transport Golgi enzymes in the retrograde direction. This model provides a mechanism for cisternal maturation. If Golgi enzymes compete with one another for packaging into COPI vesicles, we can account for the asymmetric distribution of enzymes across the stack.

Protein turbines. I: The bacterial flagellar motor.

The bacterial flagellar motor is driven by a flux of ions between the cytoplasm and the periplasmic lumen. Here we show how an electrostatic mechanism can convert this ion flux into a rotary torque. We demonstrate that, with reasonable parameters, the model can reproduce many of the experimental measurements.

First passage statistics of periodically driven models for neural dynamics.

The dynamics of two simple neuron models subjected to periodic stimuli is studied at the level of the first passage time probability density. The results from analytic treatments of these models are presented, and a discussion of the important properties displayed by these models is given. Specifically, both models possess resonans phenomena in the first passage probability distribution, arising from of the interplay of characteristic time-scales in the system.

Fulminant hepatic failure associated with oral administration of diazepam in 11 cats.

Acute fulminant hepatic necrosis was associated with repeated oral administration of diazepam (1.25 to 2 mg, PO, q 24 or 12 h), prescribed for behavioral modification or to facilitate urination. Five of 11 cats became lethargic, atactic, and anorectic within 96 hours of initial treatment. All cats became jaundiced during the first 11 days of illness. Serum biochemical analysis revealed profoundly high alanine transaminase and aspartate transaminase activities. Results of coagulation tests in 3 cats revealed marked abnormalities. Ten cats died or were euthanatized within 15 days of initial drug administration, and only 1 cat survived. Histologic evaluation of hepatic tissue specimens from each cat revealed florid centrilobular hepatic necrosis, profound biliary ductule proliferation and hyperplasia, and suppurative intraductal inflammation. Idiosyncratic hepatotoxicosis was suspected because of the rarity of this condition. Prior sensitization to diazepam was possible in only 1 cat, and consistent risk factors that could explain susceptibility to drug toxicosis were not identified. On the basis of the presumption that diazepam was hepatotoxic in these cats, an increase in serum transaminase activity within 5 days of treatment initiation indicates a need to suspend drug administration and to provide supportive care.

Enhanced quantum fluctuations in a chaotic single mode ammonia laser.

A detailed study of the effects of quantum fluctuations in a chaotic single mode laser is presented. It has been well established that the linear noise approximation eventually becomes invalid for the case of chaotic dynamics. A more accurate description of the laser is achieved through use of nonlinear Langevin equations. Simple expressions for the time evolution of the phases of the electric field and polarization are derived. These expressions predict that chaotic dynamics will greatly enhance phase diffusion. This prediction is verified through numerical simulations. A quantitative method, for determining the amount of amplification of quantum noise by chaos is discussed. This method makes use of a metric introduced in symbolic dynamics. The fluctuations are shown to have been amplified by over two orders of magnitude, making them macroscopically visible.

Antiendothelial cell antibodies in lupus: correlations with renal injury and circulating markers of endothelial damage.

Systemic lupus erythematosus is characterized by the production of a broad spectrum of autoantibodies. Autoantibodies directed against endothelial cells (AECA) have been particularly well documented. We investigated associations between such antibodies, double-stranded DNA (dsDNAb), phospholipid (cardiolipin, ACA), and indices of activity and chronicity scored on renal biopsy specimens from 22 patients with acute lupus. AECA were present in 73% of these patients, and both the percentage of patients with AECA and the mean antibody titre fell significantly as patients entered remission. When patients already on immunosuppressive therapy were excluded from analysis (n = 7), only levels of AECA and DNAb (p = 0.02) correlated with histological evidence of active lesions and the presence of glomerular epithelial cell crescents; no correlation was found with chronic changes in the renal biopsies. Serum von Willebrand factor (vWf) and serum total protein S levels, two parameters reflecting endothelial cell function, were also measured during acute disease and remission. vWf concentrations were elevated during acute disease (m = 1.9 IU/ml, p = 0.02), but the values did not correlate with AECA titres. In contrast, total protein S levels were reduced (0.81 IU/ml vs. 0.97 IU/ml, p = 0.01) during active disease, but remained within the normal range (0.56-1.16 IU/ml). Furthermore, protein S levels were inversely related to levels of AECA (r = -0.4, p = 0.01). AECA were therefore present in most patients with acute lupus nephritis and were associated with histological evidence of active renal injury and serological evidence of endothelial cell dysfunction. These data provide indirect support for a pathogenic role for AECA in lupus nephritis.