Kanamycin sulfate was replaced by gentamicin sulfate in an effort to control an outbreak of nosocomial infections caused by enteric organisms with R-factor-mediated kanamycin resistance in an intensive care nursery. Within a month the kanamycin-resistant organisms were essentially eliminated from the nursery, indicating that the selective pressure provided by the extensive use of kanamycin was a major factor in causing and propagating the outbreak. Over a period of observation of 15 months, a significant increase in the gentamicin resistance of the Gram-negative intestinal flora of the infants occurred, but no clinical infections due to gentamicin-resistant enteric organisms were observed.

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As the diagnostic utility of lymphocyte subset analysis has been recognized in the clinical research laboratory, a wide variety of reagents and cell preparation, staining and analysis methods have also been described. Methods that are perfectly suitable for analysis of smaller sample numbers in the biological or clinical research setting are not always appropriate and/or applicable in the setting of a high volume clinical reference laboratory. We describe here some of the specific considerations involved in choosing a method for flow cytometric analysis which minimizes sample preparation and data analysis time while maximizing sample stability, viability, and reproducibility. Monoclonal T- and B-cell reagents from three manufacturers were found to give equivalent results for a reference population of healthy individuals. This was true whether direct or indirect immunofluorescence staining was used and whether cells were prepared by Ficoll-Hypaque fractionation (FH) or by lysis of whole blood. When B cells were enumerated using a polyclonal anti-immunoglobulin reagent, less cytophilic immunoglobulin staining was present after lysis than after FH preparation. However, both preparation methods required additional incubation at 37 degrees C to obtain results concordant with monoclonal B-cell reagents. Standard reagents were chosen on the basis of maximum positive/negative separation and the availability of appropriate negative controls. The effects of collection medium and storage conditions on sample stability and reproducibility of subset analysis were also assessed. Specimens collected in heparin and stored at room temperature in buffered medium gave reproducible results for 3 days after specimen collection, using either FH or lysis as the preparation method. General strategies for instrument optimization, quality control, and biohazard containment are also discussed.

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A design approach for the quasi-static balancing of four-bar linkages with torsion springs is proposed. Such approach is useful on the design of statically balanced fully compliant mechanisms by setting the stiffness of the Pseudo-Rigid-Body-Model. Here the positive stiffness exhibited by torsion springs at the R-joints is compensated by a negative stiffness function. The negative stiffness is created by a non-zero-free-length linear spring connected between the coupler link and the ground, and where both connecting points trace a line directed to the coupler link's instant center of rotation. An full example of the static balancing of two compliant Burmester's linkage for straight path generation are developed, where actuation energy on the compliant designs is reduced in 66% and 54%.