A method to investigate sterilization processes and the bacterial inactivation resolved in time and space.

In this study, a Computational Fluid Dynamics (CFD) model was developed to predict all relevant phenomena occurring during a moist heat sterilization process at a high level of temporal and spatial resolution. The developed CFD model was used to simulate the distribution of, e.g., pressure, temperature and residual air within a large-scale industrial steam autoclave (multiphase flow models) which was not published until now. Moreover, the thermodynamic behavior and distribution of fluids and temperatures inside the sterilization load was simulated which were verified with measurements. Based on the obtained sterilization temperature profiles in connection with the sterilization environment (e.g., NCGs, natural convection), the bacterial inactivation could be simulated. A complete moist heat sterilization process was simulated, including all relevant phenomena inside an autoclave chamber and a Peritoneal Dialysis Bag System (PDBS), which represents a complex sterilization item. To verify the simulation results, simulated pressures and temperatures were compared with measurement data for both the autoclave chamber and the PDBS. The results show that the simulated and measured values were in excellent accordance. By using the novel CFD model, the distribution of steam and residual air inside the autoclave chamber, as well as the natural convection inside the sterilization load, could be precisely predicted. To predict the inactivation of Geobacillus stearothermophilus inside different moist heat environments, the CFD model was extended with bacterial inactivation kinetics based on measurement data. The simulation results clearly indicate that our developed CFD model can be used to predict the inactivation kinetics of bacteria, depending on the sterilization temperature profile of the sterilization process as well as the moist heat sterilization environment, and to resolve the kinetics in time and space. Therefore, the developed CFD model represents a powerful tool that might be used in the future to predict, e.g., ″worst case″ locations for any given autoclave and sterilization load or any other relevant process parameter, enabling the operator to develop an effective sterilization process.

IgCAMs redundantly control axon navigation in Caenorhabditis elegans.

BACKGROUND: Cell adhesion molecules of the immunoglobulin superfamily (IgCAMs) form one of the largest and most diverse families of adhesion molecules and receptors in the nervous system. Many members of this family mediate contact and communication among neurons during development. The Caenorhabditis elegans genome contains a comparatively small number of IgCAMs, most of which are evolutionarily conserved and found across all animal phyla. Only some of these have been functionally characterized so far. RESULTS: We systematically analyzed previously uncharacterized IgCAMs in C. elegans. Green fluorescent protein reporter constructs of 12 IgCAMs revealed that expression generally is not confined to a single tissue and that all tissues express at least one of the IgCAMs. Most IgCAMs were expressed in neurons. Within the nervous system significant overlap in expression was found in central components of the motor circuit, in particular the command interneurons, ventral cord motoneurons as well as motoneurons innervating head muscles. Sensory neurons are underrepresented among the cells expressing these IgCAMs. We isolated mutations for eight of the genes showing neuronal expression. Phenotypic analysis of single mutants revealed limited neuronal defects, in particular axon navigation defects in some of the mutants. Systematic genetic interaction studies uncovered two cases of functional overlap among three and four genes, respectively. A strain combining mutations in all eight genes is viable and shows no additional defects in the neurons that were analyzed, suggesting that genetic interactions among those genes are limited. CONCLUSION: Genetic interactions involving multiple IgCAMs affecting axon outgrowth demonstrate functional overlap among IgCAMs during nervous system development.

The C. elegans L1CAM homologue LAD-2 functions as a coreceptor in MAB-20/Sema2 mediated axon guidance.

The L1 cell adhesion molecule (L1CAM) participates in neuronal development. Mutations in the human L1 gene can cause the neurological disorder CRASH (corpus callosum hypoplasia, retardation, adducted thumbs, spastic paraplegia, and hydrocephalus). This study presents genetic data that shows that L1-like adhesion gene 2 (LAD-2), a Caenorhabditis elegans L1CAM, functions in axon pathfinding. In the SDQL neuron, LAD-2 mediates dorsal axon guidance via the secreted MAB-20/Sema2 and PLX-2 plexin receptor, the functions of which have largely been characterized in epidermal morphogenesis. We use targeted misexpression experiments to provide in vivo evidence that MAB-20/Sema2 acts as a repellent to SDQL. Coimmunoprecipitation assays reveal that MAB-20 weakly interacts with PLX-2; this interaction is increased in the presence of LAD-2, which can interact independently with MAB-20 and PLX-2. These results suggest that LAD-2 functions as a MAB-20 coreceptor to secure MAB-20 coupling to PLX-2. In vertebrates, L1 binds neuropilin1, the obligate receptor to the secreted Sema3A. However, invertebrates lack neuropilins. LAD-2 may thus function in the semaphorin complex by combining the roles of neuropilins and L1CAMs.

AST-1, a novel ETS-box transcription factor, controls axon guidance and pharynx development in C. elegans.

Neurons send out axons and dendrites over large distances into target areas where they eventually form synapses with selected target cells. Axonal navigation is controlled by a variety of extracellular signals and neurons express receptors only for that subset of signals they need to navigate to their own target area. How the expression of axon guidance receptors is regulated is not understood. In genetic screens for mutants with axon guidance defects, we identified an ETS-domain transcription factor, AST-1, specifically required for axon navigation in certain classes of interneurons. In addition, ast-1 has a role in the differentiation of the ventral cord pioneer neuron AVG. Outside the nervous system, ast-1 is essential for morphogenesis of the pharynx. Ast-1 is transiently expressed in several classes of neurons (including AVG) during neuronal differentiation with a peak expression during late stages of neuronal differentiation and axon outgrowth. Ast-1 genetically interacts with other transcription factors controlling neuronal differentiation like lin-11 and zag-1 as well as components of the netrin pathway suggesting that ast-1 might control the expression of components of the netrin signal transduction machinery.

zag-1, a Zn-finger homeodomain transcription factor controlling neuronal differentiation and axon outgrowth in C. elegans.

The nervous system consists of diverse subtypes of neurons, whose identities must be specified during development. One important aspect of the differentiation program of neurons is the expression of the appropriate set of genes controlling axon pathway selection. We have identified a novel Znfinger/homeodomain containing transcription factor, zag-1, required for particular aspects of axonal pathfinding. In zag-1 mutants, motorneuron commissures either branch prematurely or fail to branch at the correct point. Ventral cord interneurons show defects in the guidance towards the ventral cord and also in the ventral cord. Several neurons misexpress differentiation markers, including glutamate receptor subunits and chemosensory receptors. zag-1 is expressed transiently in embryonic and postembryonic neurons during differentiation as well as in some mesodermal tissues. Null mutants of zag-1 are unable to swallow food and die as L1 larvae with a starved appearance, indicating that zag-1 has an additional role in pharynx development. The vertebrate homolog, deltaEF1, is highly conserved and known to act as transcriptional repressor in various tissues. Our data indicate that zag-1 also acts as transcriptional repressor controlling important aspects of terminal differentiation of neurons.